Before we can move on to the practical steps for applying color management to your system, there is one other somewhat abstract concept we need to cover.
As I mentioned above, computers interpret visual colors as numbers that they can manipulate to produce the effects we see on monitors and digital prints. To define and visualize the range of colors that different monitors and printers can render, color scientists devised a system that models these different spectrums of colors as if they existed as three-dimensional rainbows called Color Spaces.
Color spaces come in different sizes that depend on what they are designed to represent. For example, the Lab color space is extremely large because it represents all of the colors possible for the human eye to see. The sRGB is relatively small because it represents only the colors that can be rendered in a typical web browser. There are even color spaces that represent the colors that can be printed on a given paper with a given set of inks.
Understanding color spaces is useful because one key decision digital photographers have to make is the color space they will use as the "Working Space" for their computer systems. You can think of this as the arena or "gamut" within which all of your digital image editing takes place. Any colors that fit inside a given color space are said to be within that space's gamut; any colors that don't are said to be "out of gamut."
Problems can arise when there is a mismatch between the color space you have chosen to work in and the color space of the image you are working on. If your working space is too small for the image you're editing, colors that were present in the image will simply be compressed until they fit within the gamut of your working color space. You'll notice this as a loss of subtlety and saturation in your image.
On the other hand, if your working color space is much bigger than the images you're working on, the image's colors will be spread out when you try to edit the image creating gaps called color-banding and posterization.
For this reason it makes sense to choose a color space large enough to encompass the colors of your work, but not so large that it creates its own problems.
One nice feature of color spaces is that they can be modeled in three dimensions with software like Color Think from Chromix and even be combined to see how they compare with each other.
In Figure 133 the sRGB color space is shown embedded in the Adobe RGB 1998 color space and, as you can see, the Adobe color space (shown as a wire frame) is much larger because, in general, it is designed to account for the colors of images intended for ink jet printers.
Current, high-quality ink jet printers are designed to print colors that are even beyond the range of Adobe's RGB 1998 color space. Figure 134 is a comparison of Adobe's color space and a custom profile I had made for my Epson printer.
Notice that although the Adobe color space is generally very large, there are intense yellow colors that are beyond its gamut. If you were to bring an image that had these colors into an Adobe RGB 1998 working space they would be "clipped" or converted to less saturated numbers.
Digital editing software can be set up to warn you when colors are unprintable or out of gamut.
An alternative would be to use a larger color space like ProPhoto as your standard working Color Space and then use the Epson profile when you print. The later sections Choosing your Color Space and Choosing your Printer Profile explains how to do this.
Once you define a given color space as your working standard, that information is tagged on to every image you edit and save. If you send that file to someone whose computer is set to a different working color space, Photoshop will alert you there is a color space mismatch and offer you choices for conversion.
Color spaces are known by initials like "CIE LAB" or "LUV," but for digital photographers the following is what you need to know about the most widely used color spaces:
• sRGB is a relatively small color space designed to provide a convenient standard for consumer digital cameras and Web designers. In general, sRGB is too small a color space for digital photography intended for fine ink jet prints.
• ColorMatch RGB is a standardized monitor color space that is often used as a default when more specific color spaces aren't available. It has a wider gamut than sRGB but a smaller one than Adobe RGB 1998.
• ProPhoto RGB is an extremely wide color space preferred by many digital photographers who work with high-quality images intended for reproduction on photo-quality ink jet printers or recording on photographic film.
• Adobe RGB 1998 is a wide gamut color space that is currently preferred by most digital photographers making fine ink jet prints.
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