2. What is color?
Color is the characteristic of
human visual
perception described through
color categories, with names
such as Red, Orange, Yallow,
Green, Blue and Purple.
3. Specfing Color.
Colors perception usually involves three qualities.
Hue : Distinguishes between colors like Red, Green, Blue etc.
Saturation : Color saturation refers to the intensity of color in an image.
Lightness : The percived intensity of reflecting .
Sometimes lightness is called brightness. If the object is emitting light instead of
reflecting it.
In order to use colors precisely in computer graphics, we need to be able to
specify and measure colors.
4. Combining colors in images.
Additive (RGB) shining colord lightes
on a white ball.
Subtracting (CMYK) mixing paint colors and illuminating
with white light.
5. Additive & Subtractive Color
Additive color is a method to create color by mixing a number of
ddifferent light colors, with shades of red, green, and blue being
the most common primary colors used in additive color system.
In four-color printing process the CMYK colors (Cyan,
Magenta, Yellow, and blacK) which are overlapped in various
combinations and proportions to produce all other colors. The
visible color is the reflected (and not the retained) color, and
is called ‘subtractive’.
6. HSV colors space.
HSV is named as such for three values: hue, saturation, and value.
This color space describes colors (hue or tint) in terms of their shade (saturation or
amount of gray) and their brightness value.
Tint: The color we use ( Red, Green, Blue).
Saturation : Color saturation refers to the intensity of color in an image.
Luminance: How bright is the color.
8. Precise Colors Specifications.
Pigment Colors subjective … depands on human observer surrounding colors, light
of environment etc.
We need to objective specification light is electromagnetic energy in the 400 to
700 nm wave length range.
Dominant wavelength : is the wavelength of colors we see.
Excitation purity: is the proportional of pure colored to white light.
Brightness: is the amount of light.
11. Color Model in vedios
Largely derive from older analog methods of coding color for TV.
Luminance is separated from color information.
For example, a matrix transform method called YIQ is used to transmit TV signals in
North America and Japan.
In Europe, a matrix transform called YUV is used.
Finally, digital video mostly uses a matrix transform called YcbCr that is closely
related to YUV.
12. How well do we see colors?
What color do we see the best?
Yallow-Green at 550 nm.
What color do we see the worst?
Blue at 440 nm.
Can perceive color difference of 10nm at extreme (volet and red) and 2nm
between blue and red.
Metamers – different energy radiation look like the same colors perception also
effected by surrounding light and edaptation.
13. Color Space.
Three types of cones suggests colors is a 3D quality. How define 3D color suggests.?
Idea:
Shine given wave length on a screen.
Users must control three leasers producing three wavelength (say R700nm, G546nm
and B436nm).
14. CIE Colors Space.
The CIE (comission International of Eclairage) define three hypothetical light X, Y
and Z with these spectra.
Idea: Any wavelength can be matched perptually by positive combination of X, Y
and Z.
15. CIE chromaticity Diagram.
For simplicity we often Project
to the 20 plane.
X+y+z=1
X= X / (x+y+z)
Y= Y/(x+y+z)
Z= 1-X-Y
