ANALYSIS OF COLOR

1. ANALYSIS OF COLOR

2. What is color? The subject of color is complex because it includes many factors. Color is the physics of light. Color is the chemistry and physics of the materials that light "colors."

3. What is color? Color is the human response to light Color is the human judgment of the color response.

4. What is color? In themselves each of the components are made up of a complicated series of factors.Together they create the human sensation we call color.

5. Instrumental Measurement of Color To create a computerized device that will measure and describe color like we see and judge color; we need to simulate the system that creates the human color response: Color instruments need a controlled light source that we can define mathematically

6. Instrumental Measurements The colored materials to be measured must be presented to the instrument in a uniform way. Devices are created in the instrument that senses the light in the human visual range that is reflected or transmitted from the materials to be measured.

7. What is a Color Computer Computer programs relate the data from the color instrument to the human response to color using mathematical simulations of light, human vision and judgment. Thus you can see that the color computer is as complex as the human color response

8. Color begins with light. What do we know about light and color? Light travels at the rate 300,000 Km/s in the vacuum of space and slows as the material it passes through becomes denser. Light can pass through clear gasses, liquids, solids and a vacuum. When you change the density of the media, you slow the speed and bend the light waves in a predictable manner. This is called the refractive index of a material. To give you an idea how fast light travels, light would go around the earth more than seven times in one second.To give you an idea how fast light travels, light would go around the earth more than seven times in one second.

9. Light can be measured in wavelengths in the spectrum of electromagnetic radiant energy  Wavelengths of light between 400nm and 700nm are the range of light energy where 99% of human color response occurs (called the visual range) and is commonly referred to as the visual spectrum. Light can be selectively scattered and absorbed by some materials in gasses, liquids and solids. As a group, these materials are called colorants.

10. HOW ARE COLORS CREATED BY LIGHT? Each wavelength area in the visual spectrum creates one pure color sensation. The individual wavelengths in the visual range are called monochromatic light. Objects illuminated with monochromatic light can only exhibit that single color.

11. For example, red, orange, yellow, green, blue, violet are primary, monochromatic light colors.

12. When all wavelengths of light in the visual spectrum, between 400-700nm, are mixed at equal energy, we see the "perfect" white light.

13. When all wavelengths in the visual spectrum between 400-700nm are not present, we have the "perfect" black. 

14.  If you have only one wavelength of light in the visual spectrum, you will only see one color. Adding other wavelengths changes the color as the light mixes. Light sources, that is "real" lights, such as sunlight, incandescent, tungsten, and fluorescent, have different balances of wavelengths of light.

15.  The eye is the window to the color experience. Whether the light comes directly from a light source and is subject to additive light mixing or is reflected by or transmitted through a material, it is the brightness and balance of the light energy that creates the color stimulus

16.  Light enters the eye, passing through the cornea, aqueous humor, the lens, through the vitreous humor, and falls on the light-sensitive retina. Three types of cone cells in the retina respond to the color balance of the light stimulus. There are red cone cell responders, green cone cell responders and blue cone cell responders.

17.  Since there are more than 7 million cone cells in the retina, we can see many different colors in one scene at the same time. Rod cells relate to the brightness of light (white to black). There are over 17 million rod cells

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19.  Experiments were done in the 1920's using observers working with devices that allowed the observer to mix red, green, and blue filtered light to match target colors created by another filtered light.

20.  Based on the data, calculations were developed to simulate the average color matching characteristics of people having normal vision. (The R, G, B data was previously discussed as the retinal response.) The retinal response data is transformed to X,Y,Z as shown in the next section.

21.  If we are interested in how a color of an object looks, we need to know what type of lighting with which we will be looking at the object. In the color computer, we have stored the illuminant mathematical tables for the light sources in which we are interested.

22.  We now measure the object color in which we are interested with a color instrument. The data is then used in the color calculation.

23.  These curves are the tristimulus values X, Y, Z. This is the basis for the mathematics in the color computer that tells us how a color will look based on a color measurement.

24.  The vision sensations that are sent to the brain create the three dimensions of color judgment response that is often referred to as three-dimensional color space. The dimensions are light to dark (L); reddish to greenish (a); yellowish to bluish (b).

25.  brightness: the attribute of a visual sensation according to which a sample appears to exhibit more or less lightness. hue: the color of a sample relating to primary colors such as red, yellow, green, blue or its absolute color. This becomes hard to define in terms of complex mixtures of color such as browns or purple. In terms of color difference, any color can change in hue and be defined in these terms.

26.  Chroma: the colorfulness of a sample relating the saturation relative of the range from a pure hue to a neutral color having no hue (lying along the gray scale from white to black.

27.  Experiments were done that were set up to test how an observer would judge just barely visual color differences

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29. Color Space

30. We express this data in the three dimensions of human color response. The mathematics is expressed as L, a, b factors defined as either Hunter L,a,b or CIE L,a,b: 

31. a = +a redness to greenness -a b = +b yellowness to blueness -b (greener or less red the "a" factor becomes smaller) (redder or less green the "a" factor is larger) (yellower or less blue, the "b" factor is larger) bluer or less yellow, the "b" factor becomes smaller

32. LAB Color Space Common Systems 1. CIE XYZ 2. CIE L*, a*, b* 3. L a b Hunter L= lightness (black=0, white= 100) a= (+) red, (-) green b= (+) yellow, (-) blue

33. How do Lab values describe color? LIGHTNESS: Bright colors, dark colors L= lightness (black=0, white= 100) CHROMA: Saturation of a particular color, vivid to dull Chroma*= ?a*2 + b*2 HUE: (angle). Color or predominant wavelength (true reading). Numeric description of the color Red, yellow, blue. Hue*= tan-1 (b*/a*)

34. Example of a Calculation CARROT BABY FOOD: L*= 45.81 a*= 33.99 b*=58.55 Hue*= tan-1 (58.55/33.99) = 59.86 Chroma = ?(33.99)2 + (58.55)2= 67.70

35. COLOR WHEEL

36. CORRECTION FOR QUADRANT HUE (angle ?) a>0 y b=0 therefore, Hue= ? a<0 y b>=0 therefore, Hue= 180 +? a<0 y b<0 therefore, Hue= 180 +? a>0 y b<0 therefore, Hue= 360 +?

37. ORANGES Green-yellow L*= 76 a*=-2.0 b*=56 Hue?? 92 vivid orange-yellow L*= 74 a*=2.0 b*=56 Hue?? 88 Chroma?? 56 dull orange yellow L*= 63 a*=1.2 b*=34 Hue?? 88 Chroma?? 34