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                                A Facial Color Transition Model to
                                   Express Character Emotion
                                          Kyu Ho Park, Seung-Ho Shin, KyuSik Chang and Tae Yong Kim1
                               GSAIM, Chung-Ang University, 221 Heukseok-Dong, Dongjak-Gu, Seoul, Republic of Korea


         ABSTRACT
             High quality graphics for game characters has been continuously improving, spurred by the astonishing growth of
             the graphics technology. Despite such improvements, the current expression of emotion has limited representation
             because it is difficult to implement it in real-time and a large amount of storage is required to store sprites for various
             feelings. Since users are demanding a more expressive character to reflect emotion, such restrictions can prevent
             the users from getting fully indulged in a game. To address this, we propose a facial color transition model, which
             is a combination of the emotional colors based on the theory of emotion, the emotion–color association, and the
             emotional transition with personal traits. The model is implemented by using the homeostatic value, the accumulated
             stimulus, and nonlinear transition functions, which support diverse changes according to the character’s personality
             with low computational cost. The reflection of the game character’s emotion on its facial color will not only make
             users immerse into the game, but also enrich their fantasy in games.

             Keywords:
             Color transition model, Emotional colors, Emotion expression, Emotion–color association, Facial color, Game character.



      1. 	 INTRODUCTION                                                         facial expression is manually coded and decomposed
                                                                                into the specific Action Units which are contraction
      As the game industry and technology rapidly grow, users                   or relaxation of one or more muscles. Muscle actions
      demand better computer performance, higher quality                        to express emotions are simulated by displacing or
      graphics, and more advanced artificial intelligence for                   changing the control points inside the geometry of
      games. Such demands spur the production of games                          a face [5]. Limitation of these methods includes that
      loaded with sophisticated graphics comparable to                          only selected muscles have been considered and their
      real photos. Earlier, games used to have characters                       interrelation is hard to simulate various emotional states
      composed of limited number of polygons and had to                         [6,7]. Even in the simple case for fast implementation by
      be supported by low-performance computers. While                          moving major facial parts [8], such as eyebrows, eyes,
      nowadays game characters appear more natural, there                       cheeks, and mouth, the emotional states are expressed
      are still difficulties in expressing characters’ emotions                 exaggeratively and unnaturally.
      in detail because computing resources should be shared
      with other functions such as physics calculation, scene                   In this work, after comparing and analyzing 60
      graph management, and applying artificial intelligence.                   animations, we suggest a novel Facial Color Transition
                                                                                Model (FCTM) that expresses varying skin colors
      Though many facial color studies were able to suggest                     according to the strength of external stimuli. The
      the facial color models [1-3] based on actual human blood                 model is implemented by using the homeostatic value,
      flow, pulse, or skin temperature, which expressed facial                  the accumulated stimulus, and nonlinear transition
      colors with increasing redness for a certain emotion, in                  functions, which support diverse changes according to
      real games and animations, these methods of varying                       the character’s traits, as opposed to previous methods
      redness proved to be inefficient in expressing wide range                 that expressed emotion through blood flow, skin
      of facial colors of emotional states within a restricted                  temperature, or interrelation of facial muscles with
      time for games.                                                           complicated mathematical models, which require much
                                                                                calculation time to simulate feelings accurately.
      Other works that investigated facial changes associated
      with emotional expression focused on the measurement                      This paper is organized as follows. In Section 2, we
      of muscle activity. The Facial Action Coding System                       explain Robert Plutchik’s psychoevolutionary theory
      (FACS) [4] is a comprehensive and widely used method                      of emotion [9], colors and emotions [10], and Eysenck’s
      of objectively describing facial activity. Using FACS, a                  dimensions of personality theory [11]. In Section 3,


      156                                                                           IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
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                                                           Park KH: A Facial Color Transition Model


      the FCTM based on the theory of color personality                          of survival. For example, when an attack or an escape
      is proposed. FCTM consists of an emotion–color                             has been accomplished, the relationship between an
      association and an emotional transition model based on                     individual and environment changes; since the goal has
      the human personality theory for the emotional stability                   been achieved, the emotional reaction also ceases [13].
      and the transition speed. In Section 4, the simulation                     Although it is not certain whether emotional state comes
      results of FCTM according to the reaction of emotion–                      first or physiological awakening comes first, it is often
      color association are evaluated. Finally, conclusions and                  said that an impulsive reaction occurs after an emotional
      future works are discussed in Section 5.                                   state [12,14]. Moreover, such impulsive reaction
                                                                                 is expressed in the form of tensing muscles, facial
      2. 	 EMOTION AND PERSONALITY THEORIES                                      expression, making fists, running away, or attacking, and
                                                                                 it tends to recover the previous emotional state, which
      Although the definition of “emotion” may vary on the                       is called the behavioral homeostatic feedback system
      fields of study, the term is defined as “a sequence of                     [9]. This reaction can be applied to the emotional relief
      events that starts with the occurrence of an arousing                      against stimulus.
      stimulus and ends with a passionate feeling” [9].
      Physiological psychologist Neil R. Carlson also said,                      2.2 	 Colors’ Association with Emotions
      “emotion is a passive or active feeling aroused by a
      specific situation” [12]. Since the action and reaction                    Color, along with action and language, is a crucial
      situation is common in games, the emotion of a character                   element in expressing emotion. The symbol of colors and
      needs to be expressed to describe the current situation.                   how emotion is affected are examined in order to verify
                                                                                 the influence of colors.
      In this section, we introduce the theories of emotion,
      colors, and personality, which are the bases of our                        Color association and symbolism: Color association
      transition model.                                                          is the association of a specific person, an event, or an
                                                                                 experience to a color, and symbolism is to express an
      2.1 	 Robert Plutchik’s Psychoevolutionary Theory of                       abstract notion or feelings. Thus, if a common image is
            Emotion                                                              symbolized among many people and it gains a public
                                                                                 acknowledgment, then it is called the symbol of a
      The theory of psychological evolution consists of three                    color [10]. Colors corresponding to psychological
      distinct models: the structural model, the sequential                      emotions are matched by combining their metaphorical
      model, and the derivative model [9]. Each model has                        notion with associated representation.
      fundamentally different views and our study will focus
      on the structural model and the sequential model.                          Perception of color and emotional effect: Colors have
      The derivative model, which explains certain human                         many emotional impacts, namely, temperature, strong
      behaviors that are seen in lower animals, is not directly                  and weak, hard and soft, and active and calm. For
      related to the human feelings and it is not used in this
      paper.

      The practical use of the psychoevolutionary theory allows
      the categorization of emotions expressible in characters,
      and the relationship of emotions corresponding to
      representative colors will be composed.

      Structural model (primary emotion and secondary
      emotion): Similar to the three primary colors, Robert
      Plutchik stated that human emotions consist of eight
      primary emotions (Joy, Trust, Fear, Surprise, Sadness,
      Disgust, Anger, and Anticipation) and other emotions
      can be combined by these eight primary emotions. The
      emotions outside the circle represent combinations of
      two adjacent primary emotions that are called secondary
      emotions, as shown in Figure 1. Each primary emotion
      shows a medium level of intensity.

      Sequential model (system of active equilibrium
      feedback): Emotion provides a feedback of one’s reaction                   Figure 1: Cross-section of multi-dimensional emotion
      to an event and also operates to increase the chance                       model [8].


      IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011                                                                                157
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                                                           Park KH: A Facial Color Transition Model


      hardness and softness, brightness and low saturation                        depending on the character’s traits.
      create a soft feeling, whereas dimness and high
      saturation create a hard feeling. Also, weaker contrast                     3. 	 FACIAL COLOR TRANSITION MODEL
      and saturation convey calmness as opposed to stronger
      contrast and saturation, which convey activeness [10].                      The FCTM is a combination of the facial color association
                                                                                  obtained by analysis of 60 animations and an emotional
      These color association and emotional effects of colors                     model based on the human personality theory about the
      are used as properties to express emotions for the FCTM.                    emotional stability and reaction speed.

      2.3 	 Dimensions of Personality Theory                                      3.1 	 Derivation of Representative Color from Animation
                                                                                        Characters
      The theory of four temperaments was improved by
      Immanuel Kant and Wilhelm Wundt. Kant and Wundt                             The emotional and psychological effects of colors
      claimed that the conventional four temperaments varied                      on each individual have received contributions both
      according to the two major dimensions of emotions:                          from personal experiences and the culture. Each color
      speed (introverted or extraverted) and intensity                            represents distinctive emotions attached to it. Red
      (stable or unstable) [11]. They claimed that in terms of                    embodies excitement and passion, both positively and
      emotional reaction speed, melancholic and phlegmatic                        negatively. Blue is described as dependable and cool, and
      temperaments have slower reaction speed compared                            the emotional meaning of blue shows devotion, piety and
      to choleric and sanguine temperaments, and in terms                         sincerity. The emotional meaning associated with green
      of emotional intensity, melancholic and choleric                            is guilt, envy, and jealousy.
      temperaments are unstable compared to phlegmatic
      and sanguine temperaments [15], as shown in Figure 2.                       Emotion–color association as shown in Table 1 is drawn
                                                                                  based on the Theory of Emotion, such as color symbolism
      The Dimensions of Personality Theory states that human                      and association for the primary and secondary emotions
      emotional reaction depends on personality and trait.                        [9]. Its representative colors are deduced from the
      By applying this theory, when a character’s emotion is                      conventional associations in novels, design textbooks,
      altered by an external factor, its results can be diversely                 and classical literature in Korea. Even if other nations or
      expressed in terms of skin colors. If the emotional change                  cultures can have different mappings, the representative
      were to be linear, it would not have been suitable for                      colors for emotions are derived by analyzing actual
      expressing a variety of emotions because all characters                     animation or game contents as described below.
      would respond to an external factor in the same
      manner. So, the FCTM utilizes Eysenck’s Dimensions                          Since we do not have the numerical values for the
      of Personality Theory to produce various responses                          representative emotional colors, we analyze the
                                                                                  character’s facial colors of emotions that are painted by
                                                                                  artists in popular animations. During the analysis of
                                                                                  animation sequences, the emotion–color relationship
                                                                                  can be detected by observing the changes of facial colors.
                                                                                  Figure 3 shows the sequences of images that represent
                                                                                  the changes in facial colors of two different emotional
                                                                                  transition situations.

                                                                                  The facial colors of characters in the source animations
                                                                                  are measured to find each representative color given in
                                                                                  Table 1. The measure is calculated by comparing the
                                                                                  character’s excited state with normal state. Natural skin
                                                                                  color image, excluding hair, eyebrows, eyes, teeth, lips,
                                                                                  and shadow, are extracted for comparison. There are
                                                                                  many works to detect facial area automatically using
                                                                                  color information, which can be a challenging task since
                                                                                  the facial color is affected by various factors such as
                                                                                  illumination, background, and ethnicity [16]. Especially,
                                                                                  many of the existing methods are not effective when face
                                                                                  color varies frequently with emotions or it is exaggerated
                                                                                  to depict emotions. Thus, since we focus on the color
                                                                                  difference between the normal state and one of excited
      Figure 2: Personality and individual differences [10].                      emotional states, we manually select a facial point and


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                                                           Park KH: A Facial Color Transition Model


      set ranges of red, green, and blue values of facial colors                           1
      from various characters in animations. When Color (Pf) is                  ∆Req =                 ∑ {Re q(x , y ) − Rnq(x , y )} 		
                                                                                           N ( x , y )∈Facial Re gion
                                                                                                                                                                 (1)
      the color of a manually picked pixel (Pf) that is included
      in facial area, FacialRegion is a set of pixels in a face with                      1 L
      {P(x,y) | Color(Pf) −d< Color(P) < Color(Pf) +d for each                    ∆Re =     ∑ (∆Req )
                                                                                          L q=1
                                                                                                                                                                 (2)
      color channel, and P is connected with Pf }, where d is a                                           	
      small constant value.
                                                                                 In the above equations, N is the number of pixels in
      With this selected facial region, the procedure to get the                 the FacialRegion and ∆Req is the red channel average
      differences of facial colors is as follows:                                difference between a normal emotion and an expressed
      Step 1: A facial image is selected when an emotional state                 emotion for one animation (q). L is the number of
      of a character reaches its maximum.                                        animations in the set Q, and ∆Re is the red channel
      Step 2: Each R, G, B value is added for the facial region                  average for one emotion (e) from all animations (green
      and the averages of color channels are obtained by                         and blue differences are calculated the same way as red).
      dividing the number of pixels in the face.                                 By Equations (1) and (2) and a set of animations, we
      Step 3: Color difference between a normal state and an                     can construct the emotion–color association as shown
      emotional state is averaged for all 60 animations.                         in Table 2.

      We denote the set of animations as Q = {1(Akira),                          Table 2 shows the representative emotion–color
      2(Alradin), q, …, 60(PrincessMonnoke)} and the set of                      association by differences of red, green, and blue color
      emotions as E = {n(Normal), a(Anger), e, …, w(Awe)},                       values with changes of contrast and brightness. Colors
      where q or e is an instance of animation or emotion,                       with an asterisk (*) represent the emotions with very
      respectively.                                                              small changes from their initial state to the emotional




      Figure 3: Facial colors with emotional transition; normal to anger transition (top sequence) and acceptance to aggressiveness
      transition (bottom sequence).
                                                                                 Table 2: Representative emotion–color association values
                                                                                 Emotion                   Color          C/B        ∆R          ∆G         ∆B
      Table 1: Emotion–color association in literature
                                                                                 Joy                       *              –/+
      Emotion                                                 Color
                                                                                 Acceptance                Green                   −27         40          −12
      Joy                                                     Red
                                                                                 Fear                      Blue                    −114        −55         −9
      Acceptance                                              Green
                                                                                 Surprise                  *             +/+
      Fear                                                    Blue
                                                                                 Sadness                   *             –/–
      Surprise                                                Yellow
                                                                                 Disgust                   Khaki                    −81        −19         −5
      Sadness                                                 Black/blue
                                                                                 Anger                     Red                       11        −48         −43
      Disgust                                                 Khaki
                                                                                 Anticipation              *             +/+
      Anger                                                   Red
                                                                                 Love                      Pink                     −26        −62         −47
      Anticipation                                            Blue
                                                                                 Submission                *              –/–
      Love                                                    Pink
                                                                                 Awe                       Purple                   −27         18          98
      Submission                                              Gray
                                                                                 Disappointment            *              –/–
      Awe                                                     Purple
                                                                                 Remorse                   *              –/–
      Disappointment                                          Blue
                                                                                 Contempt                  Navy                     −16        10           92
      Remorse                                                 Gray
                                                                                 Aggressiveness            Red                       80        −18         −45
      Contempt                                                Navy
                                                                                 Optimism                  *             +/+
      Aggressiveness                                          Red
      Optimism                                                Green              C/B means contrast/brightness. Plus sign, minus sign, and asterisk represent
                                                                                 increasing, decreasing, and meaningless variation, respectively



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                                                           Park KH: A Facial Color Transition Model


      one. It indicates how many values have to be changed                        where Ii is current input stimulus, Hi is homeostatic value
      from the normal state to a certain emotion given in                         at i time, and w is an emotional intensity weight.
      Table 1.
                                                                                  Figure 4 illustrates the steps to calculate the accumulated
      Though in the facial muscle expression there are                            stimulus. Figure 4(a) shows input stimuli with times and
      unique, highly recognizable, and pan-cultural facial                        Figure 4(b) depicts homeostatic values with or without
      emotions [17], colors and emotions do not have one-to-                      inputs. In Figure 4(c), accumulated stimuli are calculated
      one mapping because of racial or cultural differences.                      by inputs and homeostatic values.
      There are also dual mappings that become hard to
      interpret. For example, red cheeks could mean shame                         Emotional intensity weight: According to Dimensions
      or love, but a fully red face could mean anger or                           of Personality Theory [11], melancholic and choleric
      aggressiveness. In this work, however, we find some                         temperaments are unstable compared to phlegmatic
                                                                                  and sanguine temperaments. In other words, with the
      salient mappings that are commonly described and
                                                                                  same stimulus, the melancholic and choleric traits show
      understood within bounded nations (Korea and Japan)
                                                                                  much more changes in emotion compared to the other
      by analyzing animations, and use the mapped colors
                                                                                  two traits. The emotionally unstable type has a relatively
      as features for emotions presented on the entire face.
                                                                                  large value for w in Equation (3) and for the stable type
      For other nations or cultures, different mappings with                      w is set to a small value.
      Table 2 can be investigated and used for the emotional
      color representation.                                                       Emotional transition function (F I for introverted
                                                                                  temperament and FE for extraverted temperament):
      3.2 	 Modelling of Emotional Transition with Personality                    The transition speed responds obtusely to introverted
            Dimension                                                             types while responding sensitively to extraverted types.
                                                                                  Melancholic and phlegmatic temperaments have slower
      Diverse changes in emotion would not be apparent if
                                                                                  transition speed compared to choleric and sanguine
      the change of emotion is to be linear. Thus, we design
                                                                                  temperaments. Such responses can be best described by
      an emotion-reaction function that supports such diverse
                                                                                  two functions: an exponential function and a logarithmic
      changes according to the character’s personality and trait.
                                                                                  function. Figure 5(a) shows a slow change in emotion
                                                                                  due to low sensitivity; on the other hand, with high
      The model of emotional changes according to personality
                                                                                  sensitivity, Figure 5(b) shows a rapid change with values
      consists of four parts: homeostatic value, calculation of
                                                                                  of Si using Equations (4) and (5):
      accumulated stimulus, emotionally intensity weights
      for stable and unstable traits, and emotional transition
      functions for introverted and extraverted traits. These                     FI(Si ) = e( Si /p ) 		                                         (4)
      are based on Eysenck’s study of four major features of
      traits, which are related to reaction speed and transition                  FE(Si ) = log e (Sip ) 				                                     (5)
      intensit Homeostatic value: Homeostasis is a trait that
                                                                                  where p is a regulation value and it is assigned 21, which
      wants to maintain equilibrium, which means that an                          shows natural and symmetric emotional transition
      emotional state tends to return normal state after the                      within the range of possible variation.
      relaxation of excitement. If a character is affected by a
      certain stimulus Ii and no additional stimulation occurs,                   The value of red for an emotional state (Rei) at i-th time
      homeostatic value H is subtracted from Ii repeatedly                        with an input (Ii) can be calculated by adding the normal
      until the state reaches the normal state. Though H can be
      varied according to circumstances, we use H as a constant
      value for the purpose of simulation.

           0, if there is a stimulus at time i
      Hi = 
           h , otherwise

      Calculation of accumulated stimulus: If a character is
      excited with Ii, accumulated stimulus (Si) is computed
      by adding previous Si-1 with the difference between Ii                                  (a)                  (b)                   (c)
      and Hi as shown in Equation (3)
                                                                                  Figure 4: Calculation of accumulated stimulus in FCTM:
                                                                                  (a) input stimulus, (b) homeostatic value, (c) accumulated
       Si ← max{0 , Si − 1 + ( Ii − Hi ) × w} 			                       (3)       stimulus.


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                                                           Park KH: A Facial Color Transition Model


      red value (Rn) to the difference ( ∆Re ) in Table 2 with the               for the color variation and the reaction speed. In the
                           
      portion of changes F(Si ) in Equation (6).                                 experiments d for FacialRegion is 10, and w in Equation
                                                                                 (3) is set by 1 for the stable trait and 2 for the unstable
                       
      Rei = Rn + ∆Re × F(Si ),    if 0 < Rei < 255 		                   (6)      trait. Though some emotional colors can be expressed
                                                                                 in facial regions instead of the entire face, since the size
      The transition function F(Si) is normalized to have                        of a game character’s face is small, a specified color is
      a value in [0, 1], which is denoted by F(Si ). The                        used for the entire face and we calculate representative
      normalized transition function can be FI  (Si ) in the case               colors from entire faces as we consider the entire face of
                                                                                a character as the target to express emotions.
      of an introvert type and FE (Si ) when it is an extravert
      type. Green and blue channels are calculated in the
                                                                                 Figure 6 shows the facial color transition images for a
      same way as red.
                                                                                 melancholic trait character. After inputting sequence
                                                                                 of stimuli, the acceptance emotion is expressed by the
      4. 	 VERIFYING THE FACIAL COLOR TRANSITION                                 FCTM. Eventually, as time progresses without any
           MODEL                                                                 stimuli, the facial color reverts to its normal state.
      In this work, we derived the emotion–color association
                                                                                 Figure 7 shows examples of a 3D character’s face
      and suggest the FCTM based on the Dimensions
                                                                                 processed by the FCTM. The expression of an emotion is
      of Personality Theory about four temperaments
                                                                                 achieved by simply changing the colors of pixels on the
      (melancholic, phlegmatic, choleric, and sanguine), which
                                                                                 texture image according to the stimulated time. So, the
      is modeled by the emotional transition functions for the
                                                                                 method is easy and fast to apply to real-time applications.
      reaction speed (introverted or extraverted) and by the
      emotional intensity weight for the emotional stability                     4.1 	 Emotional Color Evaluation
      (unstable or stable). Four temperaments can be simulated
      differently by adjusting the properties of the emotional                   Usually, the emotional change of a character is rarely
      reaction functions and the emotional intensity weights.                    presented in a game. On the contrary, in animation, most
                                                                                 of the character’s emotions are signaled by changes in
      In this section, we evaluate the effectiveness of the model                facial color, which are designed by artists. We evaluate




                                          (a)                                                                        (b)

      Figure 5: Emotional transition functions: (a) function for introverted types and (b) function for extraverted types.




      Figure 6: A 2D example of FCTM for melancholic trait and acceptance emotion.


      IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011                                                                                161
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                                                           Park KH: A Facial Color Transition Model


      the effectiveness of the FCTM by comparing the                              by one or several stimuli from the environment and its
      emotional colors of FCTM with those of characters from                      transition of facial color is simulated by FCTM (Fx) or
      popular animations.                                                         animated by an artist (Ax), absolute color values from
                                                                                  the simulation may be different from the corresponding
      Tables 3 and 4 show facial colors for eight emotions                        animation, but the percentage of color channels is very
      with the corresponding animation contents and FCTM                          similar in both cases, which means that facial colors are
      simulations, respectively. The number of stimuli in                         different in brightness but they are similar enough to
      Table 3 is counted manually for each emotion from the                       present emotions in hue. In the cases of “A6” and “F6”
      emotional circumstances in animation contents. The                          (the blue color portion of “A6” is significantly larger than
      strength of stimulus in Table 4 presents the number of                      that of “F6” to present the emotion of “awe”), since three
      inputs with the estimated strength to accomplish the final                  inputs are stimulated and the blue color of normal state
      excitement. In the case of “F4”, there are three stimulus                   in the animation is originally set by a lower value, the
      inputs with strength of 50, 72, and 86 to mimic emotional                   distribution of colors is somewhat different. Except some
      circumstances as given in Table 3.                                          cases, FCTM can simulate emotional colors relatively
                                                                                  similar to the created colors in animations.
      Final facial colors for the emotions in both tables are
      different because the FCTM uses the average difference                      4.2 	 Transition Speed Evaluation
      between one of exited states and the normal state, while                    We compare changes in RGB values between an original
      the colors of normal states in each animation are varied.                   animation sequence and an FCTM sequence. After
      However, the ratios of red, green, and blue channels                        detecting the region of a face by the skin color range,
      for every emotion are very similar in both the tables as                    we compute the average colors in each channel from the
      shown in Figure 8.                                                          extracted face, and then we depict the average values of
                                                                                  red, green, and blue channels according to frames for the
      Figure 8 shows the comparison of colors between                             original animation sequence and for the FCTM sequence.
      animation contents and the simulations of FCTM by                           Finally, we compute the difference between the colors of
      color percentage. The label “Ax” represents the color                       transitions in each sequence as shown in Figure 9.
      ratio of an emotion from animation contents and “Fx”
      means the color ratio of a simulation from FCTM. When                       Table 3: Facial color expression in animation contents
      a character with melancholic temperament is excited                         No. Animation         Emotion         Main      Number of Facial color
                                                                                      contents                          color      stimuli    (R,G,B)
                                                                                  A1 Macross zero       Acceptance      Green         1      145, 182,
                                                                                                                                                131
                                                                                  A2 Beauty and the     Fear            Blue          1     54, 57, 72
                                                                                     beast
                                                                                  A3 Akira              Disgust         Khaki         1       56, 55, 46
                                                                                  A4 Akira              Anger           Red           3      135, 65, 35
                                                                                  A5 Only yesterday     Love            Pink          3       184, 141,
                                                                                                                                                 134
                                                                                  A6 The prince of  Awe          Purple               3       39, 42, 71
                                                                                     Egypt
      Figure 7: Examples of FCTM 3D Character: (a) anger, (b)                     A7 Jubei Ninpucho Contempt     Navy                 1      96, 93, 143
      acceptance, (c) awe, and (d) normal emotional states.                          Ninja
                                                                                  A8 Macross zero Aggressiveness Red                  3       238, 154,
                                                                                                                                                113


                                                                                  Table 4: Facial color expression by FCTM for melancholic
                                                                                  traits
                                                                                  No.       Strength of      Emotion           Number of     Facial color
                                                                                             stimulus                           stimuli        (R,G,B)
                                                                                  F1           (100)         Acceptance            1       124, 164, 108
                                                                                  F2           (100)         Fear                  1          67, 70, 88
                                                                                  F3           (100)         Disgust               1        100, 100, 81
                                                                                  F4      (50), (72), (86)   Anger                 3         132, 53, 22
                                                                                  F5      (50), (72), (86)   Love                  3       178, 132, 124
                                                                                  F6      (50), (72), (86)   Awe                   3       153, 122, 144
                                                                                  F7           (100)         Contempt              1         84, 78, 135
      Figure 8: Color ratios of animation contents and FCTM for
                                                                                  F8      (50), (72), (86)   Aggressiveness        3        233, 107, 76
      eight emotions.


      162                                                                               IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
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journal
                                                           Park KH: A Facial Color Transition Model




                            (a)                                                       (b)
      Figure 9: Color changes by anger emotion: (a) melancholic temperament with error and (b) choleric temperament with
      error.

      Figure 9 shows the comparison between two                                  Furthermore, the application of the FCTM to 2D textures
      temperaments: (a) melancholic and (b) choleric                             of 3D model proves that it can directly be used for
      temperaments for FCTM sequences. The standard                              real-time applications. The FCTM can provide more
      deviation of error for melancholic temperament is 3.88                     improved reality and immersion to games by expressing
      and for choleric temperament it is 9.13. Results show that                 the character’s emotion and the FCTM can be used not
      the melancholic temperament is more similar than the                       only in the game industry, but also other fields requiring
      choleric temperament to the animation character, and the                   the expression of emotions as well.
      FCTM can simulate the transition speed of the original
      animation by altering the trait property with little error.                Future studies will focus on an emotional method to
                                                                                 represent regional changes in a face for larger characters,
      5. 	 CONCLUSION                                                            and we modify FCTM for commercial applications.

      Despite improved graphics and smarter intelligence,                        6. 	 ACKNOWLEDGMENT
      emotions of game character are still expressed
      insufficiently. Moreover, the currently used physiological                 This study was supported by the MKE under the HNRC-
      variance of redness is too limited to express a wide range                 ITRC support program supervised by the NIPA (NIPA-
      of emotions in games and animations. To address this                       2010-C1090-1011-0010) and Basic Science Research Program
      limitation, we suggest the FCTM that consists of the                       through the National Research Foundation of Korea (NRF)
                                                                                 funded by the Ministry of Education, Science and Technology
      emotion–color association obtained by the analysis of
                                                                                 (2010-0021892).
      60 animations and the emotional transition model based
      on the emotional stability and the transition speed. The
      experimental results support the usability of colors to
                                                                                 REFERENCES
      express emotions and demonstrate the effectiveness                         1.	    T Yamada and T Watanabe, “Effects of facial color on virtual facial
      of emotional transitions for various temperaments.                                image synthesis for dynamic facial color and expression under



      IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011                                                                                      163
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journal
                                                                Park KH: A Facial Color Transition Model


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      4.	    P Ekman, and W Friesen, “Facial Action Coding System: A Technique                  Transaction Publishers, pp. 34-5, 2006.
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      AUTHORS
                           Kyu Ho Park received his M.S. degree in Advanced                                   KyuSik Chang received his M.S. degree in Computer
                           Imaging Engineering at Chung-Ang University, Seoul,                                Engineering at SangMyung University, Seoul, Korea.
                           Korea. Currently, he is working toward the Ph.D.                                   Currently, he is working toward the Ph.D. degree in
                           degree in Advanced Imaging Engineering at Chung-Ang                                Advanced Imaging Engineering at Chung-Ang University.
                           University. His research interests include in Computer                             His research interests include in Computer Music, Sound
                           Game, Image Processing, and Human-computer                                         Processing, and Sound Synthesing.
                           Interaction.
                                                                                                              E-mail: multimidi@multimidi.co.kr
      E-mail: oracle1027@wm.cau.ac.kr
                                                                                                           Tae Yong Kim (Corresponding Author) received his B.S.
                          Seung-Ho Shin received his B.S. degree from In-Ha                                degree in Electrical Engineering and M.S. degree in
                          University, M.S degree in Media Tech. from Sogang                                Communication Engineering from Han-Yang University,
                          University, and Ph.D. in Advanced Imaging Science                                Seoul, Korea, in 1986 and 1988, respectively, and Ph.D.
                          at Chung-Ang University, Seoul, Korea. Currently, he                             in Computer Science and Engineering from Pohang
                          is a technical manager for mobile DTV in SK Telecom                              University of Science & Technology, Korea, in 1998.
                          Corporation, Seoul, Korea. His research interests include                        Currently, he is a professor at the Graduate School of
                          AV Codec techniques (H.264/AVC, MPEG-2 and 4), 3DTV,         Advanced Imaging Science, Multimedia and Film, Chung-Ang University,
      Computer Vision, and Digital Image Processing.                                   Seoul, Korea from 2003. His research interests include in Computer Vision,
                                                                                       Image Processing, and A.I.
      E-mail: shin5693@hanmail.net
                                                                                       E-mail: kimty@cau.ac.kr

                                          DOI: 10.4103/0377-2063.81746; Paper No. JR 525_09; Copyright © 2011 by the IETE




      164                                                                                     IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011

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Facial color transition model to express char emotion

  • 1. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal A Facial Color Transition Model to Express Character Emotion Kyu Ho Park, Seung-Ho Shin, KyuSik Chang and Tae Yong Kim1 GSAIM, Chung-Ang University, 221 Heukseok-Dong, Dongjak-Gu, Seoul, Republic of Korea ABSTRACT High quality graphics for game characters has been continuously improving, spurred by the astonishing growth of the graphics technology. Despite such improvements, the current expression of emotion has limited representation because it is difficult to implement it in real-time and a large amount of storage is required to store sprites for various feelings. Since users are demanding a more expressive character to reflect emotion, such restrictions can prevent the users from getting fully indulged in a game. To address this, we propose a facial color transition model, which is a combination of the emotional colors based on the theory of emotion, the emotion–color association, and the emotional transition with personal traits. The model is implemented by using the homeostatic value, the accumulated stimulus, and nonlinear transition functions, which support diverse changes according to the character’s personality with low computational cost. The reflection of the game character’s emotion on its facial color will not only make users immerse into the game, but also enrich their fantasy in games. Keywords: Color transition model, Emotional colors, Emotion expression, Emotion–color association, Facial color, Game character. 1. INTRODUCTION facial expression is manually coded and decomposed into the specific Action Units which are contraction As the game industry and technology rapidly grow, users or relaxation of one or more muscles. Muscle actions demand better computer performance, higher quality to express emotions are simulated by displacing or graphics, and more advanced artificial intelligence for changing the control points inside the geometry of games. Such demands spur the production of games a face [5]. Limitation of these methods includes that loaded with sophisticated graphics comparable to only selected muscles have been considered and their real photos. Earlier, games used to have characters interrelation is hard to simulate various emotional states composed of limited number of polygons and had to [6,7]. Even in the simple case for fast implementation by be supported by low-performance computers. While moving major facial parts [8], such as eyebrows, eyes, nowadays game characters appear more natural, there cheeks, and mouth, the emotional states are expressed are still difficulties in expressing characters’ emotions exaggeratively and unnaturally. in detail because computing resources should be shared with other functions such as physics calculation, scene In this work, after comparing and analyzing 60 graph management, and applying artificial intelligence. animations, we suggest a novel Facial Color Transition Model (FCTM) that expresses varying skin colors Though many facial color studies were able to suggest according to the strength of external stimuli. The the facial color models [1-3] based on actual human blood model is implemented by using the homeostatic value, flow, pulse, or skin temperature, which expressed facial the accumulated stimulus, and nonlinear transition colors with increasing redness for a certain emotion, in functions, which support diverse changes according to real games and animations, these methods of varying the character’s traits, as opposed to previous methods redness proved to be inefficient in expressing wide range that expressed emotion through blood flow, skin of facial colors of emotional states within a restricted temperature, or interrelation of facial muscles with time for games. complicated mathematical models, which require much calculation time to simulate feelings accurately. Other works that investigated facial changes associated with emotional expression focused on the measurement This paper is organized as follows. In Section 2, we of muscle activity. The Facial Action Coding System explain Robert Plutchik’s psychoevolutionary theory (FACS) [4] is a comprehensive and widely used method of emotion [9], colors and emotions [10], and Eysenck’s of objectively describing facial activity. Using FACS, a dimensions of personality theory [11]. In Section 3, 156 IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
  • 2. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model the FCTM based on the theory of color personality of survival. For example, when an attack or an escape is proposed. FCTM consists of an emotion–color has been accomplished, the relationship between an association and an emotional transition model based on individual and environment changes; since the goal has the human personality theory for the emotional stability been achieved, the emotional reaction also ceases [13]. and the transition speed. In Section 4, the simulation Although it is not certain whether emotional state comes results of FCTM according to the reaction of emotion– first or physiological awakening comes first, it is often color association are evaluated. Finally, conclusions and said that an impulsive reaction occurs after an emotional future works are discussed in Section 5. state [12,14]. Moreover, such impulsive reaction is expressed in the form of tensing muscles, facial 2. EMOTION AND PERSONALITY THEORIES expression, making fists, running away, or attacking, and it tends to recover the previous emotional state, which Although the definition of “emotion” may vary on the is called the behavioral homeostatic feedback system fields of study, the term is defined as “a sequence of [9]. This reaction can be applied to the emotional relief events that starts with the occurrence of an arousing against stimulus. stimulus and ends with a passionate feeling” [9]. Physiological psychologist Neil R. Carlson also said, 2.2 Colors’ Association with Emotions “emotion is a passive or active feeling aroused by a specific situation” [12]. Since the action and reaction Color, along with action and language, is a crucial situation is common in games, the emotion of a character element in expressing emotion. The symbol of colors and needs to be expressed to describe the current situation. how emotion is affected are examined in order to verify the influence of colors. In this section, we introduce the theories of emotion, colors, and personality, which are the bases of our Color association and symbolism: Color association transition model. is the association of a specific person, an event, or an experience to a color, and symbolism is to express an 2.1 Robert Plutchik’s Psychoevolutionary Theory of abstract notion or feelings. Thus, if a common image is Emotion symbolized among many people and it gains a public acknowledgment, then it is called the symbol of a The theory of psychological evolution consists of three color [10]. Colors corresponding to psychological distinct models: the structural model, the sequential emotions are matched by combining their metaphorical model, and the derivative model [9]. Each model has notion with associated representation. fundamentally different views and our study will focus on the structural model and the sequential model. Perception of color and emotional effect: Colors have The derivative model, which explains certain human many emotional impacts, namely, temperature, strong behaviors that are seen in lower animals, is not directly and weak, hard and soft, and active and calm. For related to the human feelings and it is not used in this paper. The practical use of the psychoevolutionary theory allows the categorization of emotions expressible in characters, and the relationship of emotions corresponding to representative colors will be composed. Structural model (primary emotion and secondary emotion): Similar to the three primary colors, Robert Plutchik stated that human emotions consist of eight primary emotions (Joy, Trust, Fear, Surprise, Sadness, Disgust, Anger, and Anticipation) and other emotions can be combined by these eight primary emotions. The emotions outside the circle represent combinations of two adjacent primary emotions that are called secondary emotions, as shown in Figure 1. Each primary emotion shows a medium level of intensity. Sequential model (system of active equilibrium feedback): Emotion provides a feedback of one’s reaction Figure 1: Cross-section of multi-dimensional emotion to an event and also operates to increase the chance model [8]. IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011 157
  • 3. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model hardness and softness, brightness and low saturation depending on the character’s traits. create a soft feeling, whereas dimness and high saturation create a hard feeling. Also, weaker contrast 3. FACIAL COLOR TRANSITION MODEL and saturation convey calmness as opposed to stronger contrast and saturation, which convey activeness [10]. The FCTM is a combination of the facial color association obtained by analysis of 60 animations and an emotional These color association and emotional effects of colors model based on the human personality theory about the are used as properties to express emotions for the FCTM. emotional stability and reaction speed. 2.3 Dimensions of Personality Theory 3.1 Derivation of Representative Color from Animation Characters The theory of four temperaments was improved by Immanuel Kant and Wilhelm Wundt. Kant and Wundt The emotional and psychological effects of colors claimed that the conventional four temperaments varied on each individual have received contributions both according to the two major dimensions of emotions: from personal experiences and the culture. Each color speed (introverted or extraverted) and intensity represents distinctive emotions attached to it. Red (stable or unstable) [11]. They claimed that in terms of embodies excitement and passion, both positively and emotional reaction speed, melancholic and phlegmatic negatively. Blue is described as dependable and cool, and temperaments have slower reaction speed compared the emotional meaning of blue shows devotion, piety and to choleric and sanguine temperaments, and in terms sincerity. The emotional meaning associated with green of emotional intensity, melancholic and choleric is guilt, envy, and jealousy. temperaments are unstable compared to phlegmatic and sanguine temperaments [15], as shown in Figure 2. Emotion–color association as shown in Table 1 is drawn based on the Theory of Emotion, such as color symbolism The Dimensions of Personality Theory states that human and association for the primary and secondary emotions emotional reaction depends on personality and trait. [9]. Its representative colors are deduced from the By applying this theory, when a character’s emotion is conventional associations in novels, design textbooks, altered by an external factor, its results can be diversely and classical literature in Korea. Even if other nations or expressed in terms of skin colors. If the emotional change cultures can have different mappings, the representative were to be linear, it would not have been suitable for colors for emotions are derived by analyzing actual expressing a variety of emotions because all characters animation or game contents as described below. would respond to an external factor in the same manner. So, the FCTM utilizes Eysenck’s Dimensions Since we do not have the numerical values for the of Personality Theory to produce various responses representative emotional colors, we analyze the character’s facial colors of emotions that are painted by artists in popular animations. During the analysis of animation sequences, the emotion–color relationship can be detected by observing the changes of facial colors. Figure 3 shows the sequences of images that represent the changes in facial colors of two different emotional transition situations. The facial colors of characters in the source animations are measured to find each representative color given in Table 1. The measure is calculated by comparing the character’s excited state with normal state. Natural skin color image, excluding hair, eyebrows, eyes, teeth, lips, and shadow, are extracted for comparison. There are many works to detect facial area automatically using color information, which can be a challenging task since the facial color is affected by various factors such as illumination, background, and ethnicity [16]. Especially, many of the existing methods are not effective when face color varies frequently with emotions or it is exaggerated to depict emotions. Thus, since we focus on the color difference between the normal state and one of excited Figure 2: Personality and individual differences [10]. emotional states, we manually select a facial point and 158 IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
  • 4. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model set ranges of red, green, and blue values of facial colors 1 from various characters in animations. When Color (Pf) is ∆Req = ∑ {Re q(x , y ) − Rnq(x , y )} N ( x , y )∈Facial Re gion (1) the color of a manually picked pixel (Pf) that is included in facial area, FacialRegion is a set of pixels in a face with 1 L {P(x,y) | Color(Pf) −d< Color(P) < Color(Pf) +d for each ∆Re = ∑ (∆Req ) L q=1 (2) color channel, and P is connected with Pf }, where d is a small constant value. In the above equations, N is the number of pixels in With this selected facial region, the procedure to get the the FacialRegion and ∆Req is the red channel average differences of facial colors is as follows: difference between a normal emotion and an expressed Step 1: A facial image is selected when an emotional state emotion for one animation (q). L is the number of of a character reaches its maximum. animations in the set Q, and ∆Re is the red channel Step 2: Each R, G, B value is added for the facial region average for one emotion (e) from all animations (green and the averages of color channels are obtained by and blue differences are calculated the same way as red). dividing the number of pixels in the face. By Equations (1) and (2) and a set of animations, we Step 3: Color difference between a normal state and an can construct the emotion–color association as shown emotional state is averaged for all 60 animations. in Table 2. We denote the set of animations as Q = {1(Akira), Table 2 shows the representative emotion–color 2(Alradin), q, …, 60(PrincessMonnoke)} and the set of association by differences of red, green, and blue color emotions as E = {n(Normal), a(Anger), e, …, w(Awe)}, values with changes of contrast and brightness. Colors where q or e is an instance of animation or emotion, with an asterisk (*) represent the emotions with very respectively. small changes from their initial state to the emotional Figure 3: Facial colors with emotional transition; normal to anger transition (top sequence) and acceptance to aggressiveness transition (bottom sequence). Table 2: Representative emotion–color association values Emotion Color C/B ∆R ∆G ∆B Table 1: Emotion–color association in literature Joy * –/+ Emotion Color Acceptance Green −27 40 −12 Joy Red Fear Blue −114 −55 −9 Acceptance Green Surprise * +/+ Fear Blue Sadness * –/– Surprise Yellow Disgust Khaki −81 −19 −5 Sadness Black/blue Anger Red 11 −48 −43 Disgust Khaki Anticipation * +/+ Anger Red Love Pink −26 −62 −47 Anticipation Blue Submission * –/– Love Pink Awe Purple −27 18 98 Submission Gray Disappointment * –/– Awe Purple Remorse * –/– Disappointment Blue Contempt Navy −16 10 92 Remorse Gray Aggressiveness Red 80 −18 −45 Contempt Navy Optimism * +/+ Aggressiveness Red Optimism Green C/B means contrast/brightness. Plus sign, minus sign, and asterisk represent increasing, decreasing, and meaningless variation, respectively IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011 159
  • 5. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model one. It indicates how many values have to be changed where Ii is current input stimulus, Hi is homeostatic value from the normal state to a certain emotion given in at i time, and w is an emotional intensity weight. Table 1. Figure 4 illustrates the steps to calculate the accumulated Though in the facial muscle expression there are stimulus. Figure 4(a) shows input stimuli with times and unique, highly recognizable, and pan-cultural facial Figure 4(b) depicts homeostatic values with or without emotions [17], colors and emotions do not have one-to- inputs. In Figure 4(c), accumulated stimuli are calculated one mapping because of racial or cultural differences. by inputs and homeostatic values. There are also dual mappings that become hard to interpret. For example, red cheeks could mean shame Emotional intensity weight: According to Dimensions or love, but a fully red face could mean anger or of Personality Theory [11], melancholic and choleric aggressiveness. In this work, however, we find some temperaments are unstable compared to phlegmatic and sanguine temperaments. In other words, with the salient mappings that are commonly described and same stimulus, the melancholic and choleric traits show understood within bounded nations (Korea and Japan) much more changes in emotion compared to the other by analyzing animations, and use the mapped colors two traits. The emotionally unstable type has a relatively as features for emotions presented on the entire face. large value for w in Equation (3) and for the stable type For other nations or cultures, different mappings with w is set to a small value. Table 2 can be investigated and used for the emotional color representation. Emotional transition function (F I for introverted temperament and FE for extraverted temperament): 3.2 Modelling of Emotional Transition with Personality The transition speed responds obtusely to introverted Dimension types while responding sensitively to extraverted types. Melancholic and phlegmatic temperaments have slower Diverse changes in emotion would not be apparent if transition speed compared to choleric and sanguine the change of emotion is to be linear. Thus, we design temperaments. Such responses can be best described by an emotion-reaction function that supports such diverse two functions: an exponential function and a logarithmic changes according to the character’s personality and trait. function. Figure 5(a) shows a slow change in emotion due to low sensitivity; on the other hand, with high The model of emotional changes according to personality sensitivity, Figure 5(b) shows a rapid change with values consists of four parts: homeostatic value, calculation of of Si using Equations (4) and (5): accumulated stimulus, emotionally intensity weights for stable and unstable traits, and emotional transition functions for introverted and extraverted traits. These FI(Si ) = e( Si /p ) (4) are based on Eysenck’s study of four major features of traits, which are related to reaction speed and transition FE(Si ) = log e (Sip ) (5) intensit Homeostatic value: Homeostasis is a trait that where p is a regulation value and it is assigned 21, which wants to maintain equilibrium, which means that an shows natural and symmetric emotional transition emotional state tends to return normal state after the within the range of possible variation. relaxation of excitement. If a character is affected by a certain stimulus Ii and no additional stimulation occurs, The value of red for an emotional state (Rei) at i-th time homeostatic value H is subtracted from Ii repeatedly with an input (Ii) can be calculated by adding the normal until the state reaches the normal state. Though H can be varied according to circumstances, we use H as a constant value for the purpose of simulation. 0, if there is a stimulus at time i Hi =  h , otherwise Calculation of accumulated stimulus: If a character is excited with Ii, accumulated stimulus (Si) is computed by adding previous Si-1 with the difference between Ii (a) (b) (c) and Hi as shown in Equation (3) Figure 4: Calculation of accumulated stimulus in FCTM: (a) input stimulus, (b) homeostatic value, (c) accumulated Si ← max{0 , Si − 1 + ( Ii − Hi ) × w} (3) stimulus. 160 IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
  • 6. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model red value (Rn) to the difference ( ∆Re ) in Table 2 with the for the color variation and the reaction speed. In the  portion of changes F(Si ) in Equation (6). experiments d for FacialRegion is 10, and w in Equation (3) is set by 1 for the stable trait and 2 for the unstable  Rei = Rn + ∆Re × F(Si ), if 0 < Rei < 255 (6) trait. Though some emotional colors can be expressed in facial regions instead of the entire face, since the size The transition function F(Si) is normalized to have of a game character’s face is small, a specified color is a value in [0, 1], which is denoted by F(Si ). The used for the entire face and we calculate representative normalized transition function can be FI  (Si ) in the case colors from entire faces as we consider the entire face of  a character as the target to express emotions. of an introvert type and FE (Si ) when it is an extravert type. Green and blue channels are calculated in the Figure 6 shows the facial color transition images for a same way as red. melancholic trait character. After inputting sequence of stimuli, the acceptance emotion is expressed by the 4. VERIFYING THE FACIAL COLOR TRANSITION FCTM. Eventually, as time progresses without any MODEL stimuli, the facial color reverts to its normal state. In this work, we derived the emotion–color association Figure 7 shows examples of a 3D character’s face and suggest the FCTM based on the Dimensions processed by the FCTM. The expression of an emotion is of Personality Theory about four temperaments achieved by simply changing the colors of pixels on the (melancholic, phlegmatic, choleric, and sanguine), which texture image according to the stimulated time. So, the is modeled by the emotional transition functions for the method is easy and fast to apply to real-time applications. reaction speed (introverted or extraverted) and by the emotional intensity weight for the emotional stability 4.1 Emotional Color Evaluation (unstable or stable). Four temperaments can be simulated differently by adjusting the properties of the emotional Usually, the emotional change of a character is rarely reaction functions and the emotional intensity weights. presented in a game. On the contrary, in animation, most of the character’s emotions are signaled by changes in In this section, we evaluate the effectiveness of the model facial color, which are designed by artists. We evaluate (a) (b) Figure 5: Emotional transition functions: (a) function for introverted types and (b) function for extraverted types. Figure 6: A 2D example of FCTM for melancholic trait and acceptance emotion. IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011 161
  • 7. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model the effectiveness of the FCTM by comparing the by one or several stimuli from the environment and its emotional colors of FCTM with those of characters from transition of facial color is simulated by FCTM (Fx) or popular animations. animated by an artist (Ax), absolute color values from the simulation may be different from the corresponding Tables 3 and 4 show facial colors for eight emotions animation, but the percentage of color channels is very with the corresponding animation contents and FCTM similar in both cases, which means that facial colors are simulations, respectively. The number of stimuli in different in brightness but they are similar enough to Table 3 is counted manually for each emotion from the present emotions in hue. In the cases of “A6” and “F6” emotional circumstances in animation contents. The (the blue color portion of “A6” is significantly larger than strength of stimulus in Table 4 presents the number of that of “F6” to present the emotion of “awe”), since three inputs with the estimated strength to accomplish the final inputs are stimulated and the blue color of normal state excitement. In the case of “F4”, there are three stimulus in the animation is originally set by a lower value, the inputs with strength of 50, 72, and 86 to mimic emotional distribution of colors is somewhat different. Except some circumstances as given in Table 3. cases, FCTM can simulate emotional colors relatively similar to the created colors in animations. Final facial colors for the emotions in both tables are different because the FCTM uses the average difference 4.2 Transition Speed Evaluation between one of exited states and the normal state, while We compare changes in RGB values between an original the colors of normal states in each animation are varied. animation sequence and an FCTM sequence. After However, the ratios of red, green, and blue channels detecting the region of a face by the skin color range, for every emotion are very similar in both the tables as we compute the average colors in each channel from the shown in Figure 8. extracted face, and then we depict the average values of red, green, and blue channels according to frames for the Figure 8 shows the comparison of colors between original animation sequence and for the FCTM sequence. animation contents and the simulations of FCTM by Finally, we compute the difference between the colors of color percentage. The label “Ax” represents the color transitions in each sequence as shown in Figure 9. ratio of an emotion from animation contents and “Fx” means the color ratio of a simulation from FCTM. When Table 3: Facial color expression in animation contents a character with melancholic temperament is excited No. Animation Emotion Main Number of Facial color contents color stimuli (R,G,B) A1 Macross zero Acceptance Green 1 145, 182, 131 A2 Beauty and the Fear Blue 1 54, 57, 72 beast A3 Akira Disgust Khaki 1 56, 55, 46 A4 Akira Anger Red 3 135, 65, 35 A5 Only yesterday Love Pink 3 184, 141, 134 A6 The prince of Awe Purple 3 39, 42, 71 Egypt Figure 7: Examples of FCTM 3D Character: (a) anger, (b) A7 Jubei Ninpucho Contempt Navy 1 96, 93, 143 acceptance, (c) awe, and (d) normal emotional states. Ninja A8 Macross zero Aggressiveness Red 3 238, 154, 113 Table 4: Facial color expression by FCTM for melancholic traits No. Strength of Emotion Number of Facial color stimulus stimuli (R,G,B) F1 (100) Acceptance 1 124, 164, 108 F2 (100) Fear 1 67, 70, 88 F3 (100) Disgust 1 100, 100, 81 F4 (50), (72), (86) Anger 3 132, 53, 22 F5 (50), (72), (86) Love 3 178, 132, 124 F6 (50), (72), (86) Awe 3 153, 122, 144 F7 (100) Contempt 1 84, 78, 135 Figure 8: Color ratios of animation contents and FCTM for F8 (50), (72), (86) Aggressiveness 3 233, 107, 76 eight emotions. 162 IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011
  • 8. [Downloaded free from http://www.jr.ietejournals.org on Monday, December 31, 2012, IP: 203.153.32.66]  ||  Click here to download free Android application for this journal Park KH: A Facial Color Transition Model (a) (b) Figure 9: Color changes by anger emotion: (a) melancholic temperament with error and (b) choleric temperament with error. Figure 9 shows the comparison between two Furthermore, the application of the FCTM to 2D textures temperaments: (a) melancholic and (b) choleric of 3D model proves that it can directly be used for temperaments for FCTM sequences. The standard real-time applications. The FCTM can provide more deviation of error for melancholic temperament is 3.88 improved reality and immersion to games by expressing and for choleric temperament it is 9.13. Results show that the character’s emotion and the FCTM can be used not the melancholic temperament is more similar than the only in the game industry, but also other fields requiring choleric temperament to the animation character, and the the expression of emotions as well. FCTM can simulate the transition speed of the original animation by altering the trait property with little error. Future studies will focus on an emotional method to represent regional changes in a face for larger characters, 5. CONCLUSION and we modify FCTM for commercial applications. Despite improved graphics and smarter intelligence, 6. ACKNOWLEDGMENT emotions of game character are still expressed insufficiently. Moreover, the currently used physiological This study was supported by the MKE under the HNRC- variance of redness is too limited to express a wide range ITRC support program supervised by the NIPA (NIPA- of emotions in games and animations. To address this 2010-C1090-1011-0010) and Basic Science Research Program limitation, we suggest the FCTM that consists of the through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology emotion–color association obtained by the analysis of (2010-0021892). 60 animations and the emotional transition model based on the emotional stability and the transition speed. The experimental results support the usability of colors to REFERENCES express emotions and demonstrate the effectiveness 1. T Yamada and T Watanabe, “Effects of facial color on virtual facial of emotional transitions for various temperaments. image synthesis for dynamic facial color and expression under IETE JOURNAL OF RESEARCH | VOL 57 | ISSUE 2 | MAR-APR 2011 163
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