Photography 1 ch 5
Additive, , Subtractive
All colors can be created with three primary colors. The visual sensation of any color in the spectrum can be matched with the right mix of primary colors because our eyes sense color with three different "cone" cells, each of which has a peak sensitivity to a different wavelength. three-color systems are in use. the additive (red, green, and blue) and the subtractive (cyan, magenta, and yellow) primaries. An additive process was used only briefly in early color photography, but additive color is used in today's digital sensors, television sets, and computer monitors. A subtractive process is used in color films and in all printing—from desktop digital printers to the giant offset presses that print magazines and books. _____ color (right. center) mixes red, green, and blue light in varying proportions to produce any color. Mixed at full strength, the three primaries together produce white light. Additive color requires three separate light sources. A CRT television or computer monitor, for example, reproduces a full range of colors by using three separate electron beams that each illuminates one of the three sets of colored phosphors coated on the inside of the screen. An LCD or LED monitor or television has a screen, lit with white light from behind, that uses liquid crystals and millions of transistors to regulate how much light is allowed to pass through tiny red, blue, and green filters. ________ color (right, bottom) mixes the subtractive primary colors, cyan (a bluish green), magenta (a purplish pink), and yellow. These colors absorb (in turn) red, green, and blue wavelengths, thus subtracting them from white light. These subtractive primaries are the complementary colors of the three additive primaries, red, green, and blue (see color wheel, right, top). Mixed all together at full strength, the subtractive primaries absorb all colors of light, producing black. But, mixed in varying proportions, they can produce any color in the spectrum. A color slide, for example, has three layers of dye images superimposed on a transparent support. The colors on the slide—and in the photographic image on that slide—change as the proportion of dyes in each area changes. Many primary-school art teachers contuse red with magenta and blue with cyan, so most of us grew up thinking—in error—that red, yellow, and blue are the primary colors. The photographic color wheel. The color primaries for the subtractive process are cyan, magenta. and yellow (CMY). The additive primaries are their complementary colors (those opposite on the color wheel), red. green. and blue (RGB). Removing quantities of these colors (in the subtractive process) or adding them (in the additive process) can create all other colors. Cyan is sometimes confused with blue and red with magenta, especially in the way they influence mixed colors; learning to tell them apart will make it easier to identity the color that needs to be changed when you are adjusting colors in an image. In the additive system, separate colored lights combine to produce other colors. The three additive primary colors are red, green, and blue. Although it is difficult to imagine. green and red light mix to produce yellow. Easier to believe is that red and blue light mix to produce magenta, and green and blue mix to produce cyan. When equal parts of all three primary-colored beams of light overlap, the mixture appears white to the eye. CRT, LCD, and LED televisions all produce color by the additive system. A picture tube is covered with green, red, and blue phosphors or liquid crystals that can be mixed in various combinations to produce any color, including white. Computer monitors, electronic viewfinders, and digital camera viewing screens work the same way; the image you see has been created by a mix of illumination in the additive primaries. In the subtractive process, colors are produced when a or pigment absorbs some wavelengths and so passes on or reflects only part of the spectrum. White light is a mixture of all wavelengths. Here. the three subtractive primaries—yellow. cyan. and magenta—have been placed over a source of white light. Where yellow and cyan (which absorb blue and red, respectively) overlap, they pass green; where cyan and magenta (which absorbs green) overlap, they pass blue; where magenta and yellow overlap, they pass red. Where all three overlap, all wavelengths are blocked and we see no color—black. All modern photographic and printing materials utilize the subtractive process.
Hue, Value, Saturation,
COLOR CHARACTERISTICS Photographic color can't duplicate colors in a scene, it can only fool the eye. Light reflected from an object usually contains all the wavelengths of the visible spectrum in varying quantities. The daylight that illuminates a green apple contains all wavelengths in more-or-less equal quantities. The apple reflects a high percentage of the green wavelengths and very little (absorbing the remainder) of the red and blue ones, so we see green. To reproduce that sensation of seeing the green of an apple, photographs are limited to using three very specific primary colors that do not necessarily contain all the wavelengths of the spectrum. Photographic color can look accurate because of the way our eyes identify color. But the colors in a photograph are not actually the same as those of its subject, in the same way that the photograph itself is not actually the same as its subject. Color systems divide all colors into three measurements—hue, value, and saturation. _____ is the most intuitive of these; it is what we normally name the color of an object—a blue car, a green hat. ______ (sometimes called lightness or luminance) is a measure of the brightness or darkness of the color, or of the gray that would be left if a color's hue were removed, as in a black-and-white photograph. You can imagine a blue car and a green hat that might have the same luminance. _______ (or chroma) is a description of a color's purity. You could have a tomato and a brick that might be the same red hue (neither one more blue or yellow than the other). The difference is that a tomato is a more pure—or saturated—red than a brick. Various factors can affect saturation (see box below). The way photographs are made gives you control over some important characteristics of their color. Remember that the colors in a photograph only reference, they don't duplicate, those of a subject; it is up to you, the photographer, to control that difference for your own ends. You may want your viewer to believe strongly in the accuracy of your photographs, or it may be more important that your viewer have a specific emotional response to them. The way you treat color has a strong effect on the interpretation of your pictures; experiment to find out how to make the best use of these important controls.
Grayscale, gamut
COLOR MODES AND GAMUTS Photographs reproduce all the colors in a scene by using only the three primary colors: red, green, and blue (see page 94 and the diagram, right top). Digital photographs are captured, or color film is scanned, in the form of pixels, each of which represents specific brightnesses of red, green, and blue light. Each color's brightness—from dark to light— is commonly represented by a number from 0 to 255 (see the box on page 109). So the color of one pixel might be written as 68, 122, 213, a mix of a dark red, medium green, and light blue. This is called the RGB Color Mode. The publishing and printing industries use the CMYK mode, which adds black (abbreviated K to avoid confusion with blue) to the subtractive primary colors, cyan, magenta, and yellow. Colors in the CM Y K mode are described by four numbers, usually from one to 100%, which refer to ink coverage. Black-and-white has its own color mode called ______. Each tone between black and white is represented by a single number. A ______ is the entire range of colors that can be seen, captured. described, or reproduced by a given device. Our eyes perceive a greater gamut (many more colors) than any film, digital camera, or scanner can record, and more than any computer monitor can display. In turn, these devices usually have a larger gamut than any printer/ or printing press. And each individual device operates within a different gamut. The gamut of a printer, for example, depends on the paper and ink used, as well as the specific kind of printer. Accurate color reproduction is made complicated because you can see colors your camera can't capture, and it captures colors your printer can't print. If that weren't bad enough, the same spot on the same colored object will be recorded as a slightly different set of RGB numbers by each different digital camera or scanner. And given the same set of RGB numbers, different monitors and printers will produce different colors. We all really need help; it's called color management. Digital photography uses primarily an RGB (red, green, blue) color mode. All scanners, digital cameras, monitors, film recorders, and television sets are called RGB devices because separate amounts of these three primary colors of light—red, green, and blue—combine to create other colors. Green and red light mix to produce yellow; red and blue light produce magenta; green and blue produce cyan. Black is the absence of any of the colors, white is the simultaneous maximum brightness of all three together, and neutral grays are made up of equal amounts of each. Digital imaging gives great control of color and how it is rendered. Such control has not always been available. Angelmaier's series Pflanzen und Tiere, that includes this image, is a direct comment on the nature of color management. She lays out twelve art historical tomes that reproduce Albrecht Dürer's 1502 watercolor of a young hare. Our perceptions of a work of art, she suggests, are controlled by variations in the process of reproduction. Most of us will never see the original (in a Vienna palace) and will have instead an "original" experience with one of these.
electromagnetic spectrum
Color photography was at one time a special and unusual process. Now, we think of black-and-white photographs as regular pictures with the color turned off. In this chapter. you'll find what you need to know about the way photography can reproduce and match any color we can see in the spectrum (left) by using different amounts of only three specific hues. And in chapter 7 you'll see how various photographic systems and software applications let you address and alter each of those colors Independently, and you'll understand why you would want to. Color is a quality of your subject, of the light falling on it, and of the image you make from it. To make the best use of color's expressive possibilities, you need to understand some of the science of color and some of its psychology. along with how to measure, name, translate, and control the full spectrum. Light is part of the ______ _____, a continuum of wavelike energy from gamma waves through visible light to radio waves. The waves can be measured; the wavelength or distance from crest to crest ranges from 0.000000001 millimeter for some gamma rays to six kilometers for some radio waves. The human eye—and most digital sensors and films—will respond to smaller spectrum within this larger one. of wavelengths from about 400 nanometers (billionths of a meter) to 700 nanometers.
