Device-Independent ColorBasically, the problem with HSB, RGB, and CMY (and even CMYK) is that they don't describe how a color looks; they only describe the color's ingredients. You've probably walked into a television store and seen about a hundred televisions on the wall, each of them receiving the same color information. But none of them displays the colors in the same way.
Figure 4-4. Device-dependent color and color gamuts[View full size image] Lab ColorFortunately, there's CIE Lab, which appears on the Mode menu simply as Lab. Lab is designed to describe what colors look like, regardless of the device they're displayed on, so we call it device independent.Whereas in HSB the hues are represented as lying around a wheel, Lab color uses a more accurate but significantly less intuitive arrangement. In Lab, the third axis (which lies perpendicular to the page and is roughly equivalent to brightness in HSB) is the luminance axisit represents how bright the color appears to the human eye. But unlike brightness in HSB, it takes into account the fact that we see green as brighter than blue.Whole books have been written on Lab color (we've even read some of them), and while they may be of great interest to color scientists, they're unlikely to help you get great-looking images on a deadline. For now, there are really only three things you need to know about Lab color.While HSB, HSL, and LCH are based on the way we think about color, and RGB and CMYK are based on the ways devices such as monitors and printers produce color, Lab is based on the way humans actually see color. A Lab specification describes the color that most people will see when they look at an object under specified lighting conditions.Photoshop uses Lab as a reference when it does mode changes. For instance, when you switch from RGB mode to CMYK mode, Photoshop uses Lab to decide what color is being specified by each device-dependent RGB value, and then comes up with the right device-dependent CMYK equivalent. You'll see why this is so important in the next chapter, Color Settings.Finally, you shouldn't feel dumb if you find it hard to get your head around Lab color. It is difficult to visualize, because it's an abstract mathematical constructit isn't based on amounts of things we can understand readily, like RGB or HSB. It uses differing amounts of three primaries to specify colors, but those primaries don't really correspond to anything we can actually experience. |