Chuck Gardner's Photography Class
Part Seven - Color Management
by Chuck Gardner
What is Color Management?

Color management is the practical application of the science of color perception and reproduction to make it possible to predict and previsualize how colors will be reproduced using differing mediums such as fabric and photographic dyes, CRT and LCD computer screens, and various types of printing.

Human perception of color is highly subjective and changes depending on the viewing conditions. Color management quantifies color using a device called a photospectrometer, which can record the intensity of each wavelength (i.e., color) of light. Using this tool color scientists have create a "roadmap" for color which can be used as a tool for standardization and communication of color information between devices.

Imagine for a moment you are the marketing department of a clothing line which is launching a new line of clothes featuring this season's popular color, pastel purple. You'd want the customer to see that color accurately regardless of whether they viewed the product on television, the Internet, a glossy magazine, or a newspaper. How can this possibly be accomplished? By knowing in advance how each reproduction method wlll alter the appearance of the color, and then altering the color values in the file to compensate for the differences.

Throughout the reproduction process an image may pass through many hands and be viewed on many computer screens and proofs. If a photographer "tweeks" the photo so it looks good on his monitor, then sends it to a designer who changes it to suit his different viewing conditions, then sends it to a printing company who alter it yet again to compensate for dot gain and other things that occurs on press, there may be so much manipulation of the image data that the original color information and image detail is lost.

Why does a digital photographer need to know about it?

The CCD sensors in a consumer level (8 bit-per-color) digital camera can only record 256 levels each of red, green, and blue (RGB) luminance. These values are the same when the file is opened on any computer, but the photograph will look different depending on the intensity and constast of the monitor it is viewed on.

Take the color "white" for example. In a camera file pure white is recorded as the maximum values (255) of red, green, and blue (i.e. 255/255/255). On a computer screen the intensity of the red, green, and blue phosphors can be adjusted individually o make this "pure" white value of the appear almost any color. Color management tools now included with all computer systems allow the user to calibrate the "white point" of the monitor, measured in degrees Kelvin, and contrast, measured as "gamma" to one of several industry standards. This will ensure that the appearance of a file edited on the photographer's computer will be the same on other computers when the file is downloaded via the Internet or viewed from a disk.

When digital camera files are printed, with the RGB data values used by the camera and monitor are converted to the Cyan, Yellow, Magenta, and Black (CYMK) colors of printing inks. How the image will look after this color conversion process takes place depends on the purity of the inks, the color of the paper, and most significantly the light under which the printed image is viewed. A print viewed under tungten light will differ from one viewed under natual light, and how it appears under natural sunlight will vary depending on the time of day.

When color management is used the translation RGB color data to CYMK is done via conversion tables called ICC profiles. Tables for monitor and printer/ink/paper combinations are created by displaying a standard color target with known color values and measuring how it is reproduced. It now possible to "soft proof" a color subject in PhotoShop version 6.0 by viewing an on-screen simulation of how it will print created from the printer ICC profile.

Understanding color management and how PhotoShop uses it will give a digital photographer more creative control over the medium. It will help ensure the colors and contrast edited by the photographer on his screen appear the same on others. If the photos are printed it will ensure the color and contrast on the printed page is as close to the screen image as possible.

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