Digital Color Theory: Creating & Displaying Digital Color

1. Chapter II, Digital Color Theory: Lesson II Creating / Displaying Digital Color http://www.kodak.com/country/US/en/digital/dlc/book3/chapter2/digColorM2_1.shtml

2. For thousands of years, people have used natural dyes and pigments to produce color

3. Artists have produced masterful mixtures of color. Of course, each painting was a unique one of a kind.

4. The printing press allowed reproduction of color. Block printing in multiple colors dates back to the 15th century.

5. Color photography was the breakthrough that allowed direct reproduction of the colors in nature. The first color photograph was taken by James Clerk Maxwell to illustrate the principle of additive color. Three separate black-and-white film exposures were made and projected using filters

6. Today's color film integrates three micro-thin layers of colorants on a clear base. The colorants are cyan, magenta, and yellow dyes.

7. Color photography captures gradations of color and tone that are smooth and natural to the eye. It's called a "continuous tone" medium.

8. Development of the halftone screen in the 1880's was the breakthrough that allowed process color printing of color images. The screen creates small halftone dots, which can simulate subtle gradations of color and tone.

9. In effect, this process mimics the first color photograph. Filters separate color into black-and-white images. These separated images are recombined on a press with dots of color ink.

10. Today, four process color inks are normally used: cyan, magenta, yellow, and black. Black was once called the "key" and is represented by a "K."

11. Television was another notable advance in color reproduction. Red, green, and blue phosphors create the colors we see on a TV monitor. Video began as an analog technology.

12. Computer monitors display colors recorded digitally. Digital imaging is not revolutionizing color reproduction. The purpose of most digital imaging is to produce a full color print.

13. Colorants in desktop digital printers vary. Some combinations of cyan, magenta, yellow, and black dyes, inks or toners can be used. Understanding how color is produced can help you create high-quality digital images.

14. Additive and subtractive color mixing are the two primary methods for reproducing a range of colors.

15. The additive system combines light to produce a range of colors. Red, green, and blue are the primary additive colors. Equal amounts of all three produce white light.

16. When two equal amounts of primary additive colors are mixed, complementary colors are created.

17. Example1

20. Television is the most familiar application of additive color mixing. A close look at the screen image shows clusters of red, green and blue dots or stripes, which are phosphors.

21. These phosphors emit colored light when struck by electrons. Red, green and blue light is emitted in mixtures that simulate a wide range of colors.

22. Filters offer another method for controlling the color of light. They play an important role in digital scanners and cameras. Filters control the colors recorded by passing some colors and blocking others.

23. For example, if we shine white light through a green filter, only the green light passes. Red and blue are absorbed. Remember that combining red and blue light produces magenta. So you can think of the green filter as absorbing magenta. A filter passes its own color and absorbs or blocks its complement.

24. Red filters pass red light and absorb cyan. Cyan is a combination of green and blue.

25. Blue filters pass blue light and absorb yellow light. A blue filter subtracts red and green from white light. Filters produce color by subtracting wavelengths of light.

26. Unlike additive color mixing, the subtractive system works by taking color away from white light. When all color has been removed from light, what's left is black. The subtractive system uses colored pigments and dyes that filter light. Its primary colors are cyan, magenta and yellow.

27. There is a relationship between primary additive and subtractive colors. You can see this by placing the colors in a triangle. Additive primaries are placed at points around the triangle. Subtractive primaries are placed between the two additive primaries that combine to produce them.

28. Subtractive colors subtract the color across from them, their complement, from white light.

29. Here you see the effect magenta paint has on white light, which is composed of equal amounts of red, green and blue. Green light is subtracted by the magenta paint. Only red and blue are reflected. Red and blue combine to form magenta, which is the color you see.

30. When cyan is mixed with magenta paint, the cyan subtracts its complement red from the remaining light. That leaves only blue ... which is what you see.

31. If the third subtractive primary yellow is added to the mix, all light is blocked. Combining equal amounts of cyan, magenta and yellow subtracts all light and produces black.

32. A full range of intermediate colors is produced by controlling the amount of each primary in the subtractive color mixture.

33. The three-color process is at the heart of color reproduction on any type of paper.

34. Whether the colorants are dyes, inks, or toners, they act as filters. They block complementary colors and reflect their own color from the white surface of the paper.

35. The three color process produces a wide range of color hues by varying the strength of subtractive primaries that are overprinted. Let's consider why red, green and blue primaries are not used in the three-layer process.

36. Let's begin with the red layer. It will pass its own color red. It will filter out green and blue, which create its complement, cyan. Now suppose you need to make yellow from red, green and blue layers. To make yellow, you need to combine green and red. When you overprint green on top of red, you find that all color is blocked. The green layer blocks its complement magenta which includes red. There is no color left to be reflected from the paper

37. Additive colors cannot be used because they block two of the primary additive colors. Subtractive colors block only one. This is why layers of cyan, magenta and yellow are used in many color systems, including photography and printing.

38. This chart compares the color gamut of additive and subtractive systems. They are quite different. Each can create some colors the other system can't produce. This makes precise matching difficult.

39. In general, additive systems such as computer monitors can create more light colors than a subtractive system, which conversely, can create more dark colors. Each excels at producing its own primaries.

40. Successful color reproduction is the art and science of mixing and matching colors to the client's satisfaction.

41. Digital systems capture, display, process and print color images.

42. At each stage, color is represented in digit code as a series of ones and zeros.

43. Each imaging device must convert that numeric code into a color image.

44. The pixel is the basic building block of all digital images. The term stands for "picture element." It is the smallest unit of an image

45. A pixel can be compared to a stitch in a needle point image. Each represents the smallest unit of the image. When you see the entire image, the stitches blend together to form a recognizable picture. The needle point picture is a uniform grid of stitches. Every stitch is located very precisely within the grid. It has the same properties as a pixel.

46. A single stitch displays only one color, and all stitches are the same shape and size. Your computer image is also made up of individual "stitches" or pixels. Pixels are very small. On a monitor, there may be 72 pixels per inch. Laser printers produce 300 or more per inch. Like a stitch in a needle point image, every pixel resides within a uniform grid, called a "bit map," that cannot be varied.

47. A digital device must be capable of representing three properties of a pixel: its color, location, and size.

48. Pixels cannot overlap, so their size is determined by the resolution of the grid or "bit map."

49. The resolution of output devices is typically much higher than the 72 pixels per inch that you see on your computer monitor, so pixels are smaller.

50. Location of a pixel is assigned a numeric value, based on the horizontal and vertical pixel-count on the grid.