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Adjusting Color & Exposure
In Adobe Photoshop
Solving Color and White Balance Problems
The information in this module is perhaps the most important. These days, the ability to make precise color corrections has become a vital skill for anyone who attempts to make their own prints.
Color balance is a tricky issue. Often in printing, scanning, and in digital photography, you will have an image that has color problems. Okay, I'll rephrase that you will almost always have this problem to one degree or another.
Color Balance is a general term refering to the fine balancing of the colors in visible light, read below for more information on how light and color work.
White Balance refers specifically to the way the Color Balance is adjusted so white objects will appear white under any lighting conditions. The human eye is well adapted, in connection with our brains, to adjust the color information it receives so that objects we know to be white, appear white.
If this did not happen, and we processed light as it is, "white" objects would look yellow under tungsten light, green under flourescents, etc.
Digital Cameras have a series of built in White Balance profiles that correct for the color shift under various lighting conditions. However, unless you make a custom White Balance setting for every specific location, the image will be off to one deggree or another.
The techniques in this module will cover how to correct color shifts. These tools are useful to correct problems that occurred when the image was taken, scanned, or printed.
The following are the sections of this module:
How Light and Color Work
In order to efficiently and effectively work with color correction, one must gain a basic understanding of how color works, and be able to truly see color (or the lack of certain colors) in prints. Without this understanding, you will not be able to make the color adjustment judgement calls.
Most of this understanding comes with repeated exposure, trial and error, and sheer experience. However, there are some basic concepts that will help you begin to see the give and take of color. All digital files must be in RGB because all profiles are based on this color sceme.
RED, GREEN, and BLUE (RGB) are the basic compontents of visible light. This is an additive color scheme. CYAN, MAGENTA, YELLOW, and BLACK (CMYK), is the subtractive color scheme.
As demonstrated in the image on the left, different combinations of Red, Green, and Blue will produce either Cyan, Magenta, Yellow, or White (all of them combined). The lack of them all will result in Black.
The term "subtractive color scheme" comes from the fact that the color we see in objects and prints, and made by CMYK printing, is reflected light minus any degree of Red Green and Blue. If a print absorbs green and blue light, only to reflect red, we see a red print. If the print only absorbs red light, it will reflect blue and green and the result will be Cyan.
Thus, if you subtract various wavelengths of light through absorption, you can produce any shade of color you want.
In color management, you will be printing test prints and evaluating how closely the print matches either your monitor, or what you desire regardless of what your monitor displays. You will need to decide if the print has too much Red, Green, Blue, Cyan, Yellow, Or Magenta in it.
Realize that each of these colors has a direct or indirect efect upon one another. If one area of your print is too Green, and you pull it out, the entire print will become more Magenta (Green's counterpart). This is good if the entire image has too much of a green cast, the correction serves to balance out the color.
However, the print may have the correct density of Magenta, except in one area (such as a face). If you do a global color correction in order to correct for the skin tones of the face, you may make the background too Maganta.
The problem of one color being too dense in only one area of the print is called crosssover. With crossover, you must utilize more advanced color correction in order to get the desired effect.
For a quick reference on the give and take of color (what happens when you add or subtract a color), look at the Color Balance control window (available in Image: Adjustments: Color Balance - or "ctrl B" / "command B")
As you can see, taking Yellow out of a print will increase the amount of Blue, and visa versa.
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