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Color theory .

23. May 2021
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Color theory .

1. Color Theory Additive and subtractive synthesis of color MAAZ UL HAQ C.L GUPTA EYE INSTITUTE
2. Introduction of Color • wavelengths of light have different colors. – For example, red light has λ ≈ 650nm, blue light has λ ≈ 480nm and purple light has λ ≈ 420nm. – But there is much more to color than pure monochromatic light • For example, why does mixing red paint and blue paint make purple paint? – Surely monochromatic plane waves can’t suddenly change wavelength, so what is go ing on when we mix colors? Also, there are colors (like cyan or brown) which do not appear in the rainbow – What wavelengths do they have? – As we will see, the wavelength of monochromatic light is only the starting point for t hinking about color. • What we think of as a color depends on the way our brains and our visual sys tem processes the light coming into our eyes.
3. History of Color • The earliest studies of color were done by Newton. – He understood that white light was a combination of lots of wavelengths. – He performed some ingenious experiments to show this, des cribed in his book Optiks (1704). – In his classic Optiks, Newton compared the colors going in a circle making a whell. His color wheel was • The next big advance came in 1853 by the mathematicia n Hermann Grassmann. – Grassmann was intrigued by the idea that two colors could mix to produce a different color, such as red+blue=purple. He showed that when you have an equation like this, you can add any color to either side, and it will still be a match, for example, red+blue+yellow=purple+yellow. This is known as Grassmann’s law
4. History of Color – He did a cool demonstration where he took black and white photos of the sa me colorful object using red, green and blue filters. Then when he projected those photos back again, through the same filters, the original multicolored object could be seen Another great contributor to our understanding of color was James Clerk Maxwell. • The amazing thing was that it wasn’t just the red, blue and green colors that showed up, but the oranges and yellows and purples as well – all the colors • How is that possible? If the filters just let through pure red, blue, and green wavelengths, then none of the orange wavelengths would pass through. So how could they be reproduced? To understand this, we need to understand the perception of color.
5. The EYE & Color Perception Color cannot be understood without understanding more of how we humans process it with our cognitive system. The important part of the eye relevant to color perception are: 1. Rods 2. Cones • Rods and cones are the photoreceptors in the eye. • There are many more rods (∼120 million) than cones (∼6 million) in the eye. • The Rods are scattered all retina, except in the fovea, which is the central part of the macula, which is the central part of the retina. • The fovea is all Cones. There are a few cones outside of the fovea, but none towards the edges of the retina.
6. The Cone cells • There are 3 kinds of Cones, called: 1. Short (blue) 2. Medium (green) and 3. Long (red) • which correspond to different sensitivities in wavelength. • The reason we have a 3-dimensional space of color perception ( we are trichromats) is because we have three cones. • Note that the “red” cone, is closer to having it’s maximal sensitivity in ye llow than in red. • Since the cones are in the central part of the eye, we have the best color perception in the center of our field of view. • Most animals, such as dogs, only have 2 cones and are dichromats. It’s n ot that dogs are color blind – they can distinguish all the colors of the rai nbow, all the hues.
7. The Rod cells • There are 20 times as many rods as cones in the eye. – Rods have greater sensitivity to low light conditions and for seeing motion. Since the rods are mostly scattered a round the periphery of the retina, we have better motio n perception at the edge of our field of view. – This makes sense evolutionarily – we want to see predat ors coming in from the side. When we are looking right at something, we want to know more details, like its col or. – Since the rods are also in different places in the eye tha n cones, and since there are so many more of them, our rods do not just act like another cone with blueish sensit ivity – Basically, rods are used to interpret intensity, not color
8. rods do not see red. This is why darkrooms are red. Note that the “red” cone, is closer to having it’s maximal sensitivity in yellow than in red
9. Basics terminology of colors theory 1. The Color Wheel 2. Hue 3. Value 4. Saturation 5. Tint 6. Shades 7. Neutral 8. Color temperature
10. The color wheel • The color wheel is a chart representing the relationships between colors. Based on a cir cle showing the colors of the spectrum origi nally fashioned by Sir Isaac Newton in 1666. • The color wheel is the basis of color theory, because it shows the relationship between colors. • There are two types of color wheel. – The RYB or red, yellow, blue color wheel is typica lly used by artists, as it helps with combining pai nt colors. – Then there is the RGB, or red, green and blue col or wheel, which is designed for online use, as it r efers to mixing light – like on a computer or TV s creen.
11. Color combinations There are 12 main colors on the color wheel, divided into primary, second ary and tertiary colors. 1. Primary colors : are the colors that, added together, create pure white light in RGB. 1. In RGB These colors are red, green and blue. 2. In the CMY color wheel, primary colors are colors that can’t be mixed from o ther colors. There are three primary colors: red, yellow, and blue. 2. Secondary colors are colors that result from mixing two primary colors . There are three secondary colors. 3. Tertiary colors are colors made by combining a secondary color with a primary color. There are six tertiary colors.
12. Colour Triangle • A colour triangle is an arrangement of colors within a triangle, based on the additive combination of three primary colors at its corners. • It’s a method to draw/remember color wheel
13. Hue, Saturation and Luminance Hue • A hue is basically any color on the c olor wheel. • We can adjust the saturation and lu minance of a hue.
14. Saturation: • Saturation is the intensi ty or purity of the color.
15. Luminance of a color Luminance is the amount of brightness or light in a color.
16. Shade, Tints & Tones of Color We can create shades, tints and tones of a color by adding bla ck, grey and white to a base hue. Shade • A shade is created by adding black to a base hue, darkening the color. • This creates a deeper, richer color.
17. Tint • A tint is created by adding white to a base hue, lightening the col or. • This can make a color less intense, and is useful when balancing more vivid color combinations.
18. Tones • A tone is created by combining grey—with a base hue. • Like tints, tones are subtler versions of the original color.
19. Modern Color Theory: 1. Additive Color Theory 2. Subtractive Color Theory • To understand how color management works, we need a basic knowledge of the additive and subtractive systems of color reproduction. • Both use a small number of primary colors that combine to produce a large number of colors, but the way they do that is quite different.
20. Additive Color Theory: • By mixing red, green and blue (the additive pri maries - RGB) in different combinations and at varying levels of intensity, we can simulate the f ull range of colors in nature. • If the reflected light contains a mix of pure red, green, and blue light, the eye perceives white. • When no light is present, the eye perceives blac k. – Combining two pure additive primaries produces a sub tractive primary. – Televisions, mobile phones, tablets and computer moni tors use the additive color system because they are emi ssive devices. – They start with darkness and add red, green, and blue li ght to create the spectrum of colors.
21. Subtractive Color Theory • When multiple pigments (paint colors) are combined, they subtract a gr eater number of light waves and create a new color. We call this subtra ctive color theory. • Subtractive color theory starts with white as base color. White objects have no pigments that subtract light waves. • As we add paints or dyes with specific pigments, we reduce the kind of l ight waves that re reflected and the colors get darker. • Eventually if we block enough light waves that not enough reflected to give a color perception and as a result the objects appear black. – The three Primary colors of Subtractive theory is CMY (Cyan, magenta & Blue ). – Printing processes use cyan, magenta, and yellow inks to control the amount of red, green, and blue light that is reflected from white paper.
22. Subtractive Primaries
23. This diagram shows how the subtractive primaries remove their additive counterpart from light to produce the appearance of a color.
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