Joe’s How-To
A Practical Guide to Color Space
is in terms of subtlety. A color space whose color values range from 0 to 255 is capable of much greater subtlety than a color space whose values range from 0 to 9. A shade that can be displayed in a color space is considered “in-gamut,” and shades that cannot be displayed are “out-of-gamut.”
Joe Doherty August 2021 Focal Points Magazine
You’ve probably come across the terms sRGB, Adobe RGB, and ProPhoto RGB. One or more of these are listed as options in your camera menus and editing software. They influence what you see on your monitor, how your images appear on the web, and how you print your photographs. But what are they, and what are the practical implications of choosing one over another?
The color spaces sRGB, Adobe RGB, and ProPhoto RGB each have a progressively larget gamut. sRGB has 16.8 million shades of color. Adobe RGB has about 1 billion. ProPhoto has . . . I don’t know how many shades it has, but that isn’t a problem. ProPhoto is the color space that Lightroom assigns to your raw file when you import it from your camera. But there is a hitch. There are no monitors capable of displaying the ProPhoto gamut. The type of monitors used by photographers display sRGB or Adobe RGB, so for practical purposes ProPhoto doesn’t matter.
sRGB, Adobe RGB, and ProPhoto RGB are color spaces. They define the shades of Red, Green, and Blue (RGB) that can be output by your camera, that can be displayed on your device, and that can be printed. If you are familiar with The Zone System, popularized by Ansel Adams, you’re familiar with the idea of a scale that progresses from pure black to pure white, with eight or more shades of gray in between. Color spaces are similar. Each color (R, G, or B) has a value. If all values are zero (0,0,0), then the “color” is black. If all of the values are at their maximum (255,255,255 for sRGB), then the “color” is white. Combinations of these values produce the shades we can see and use.
What are the practical implications of using sRGB or Adobe RGB? It depends on what you want to do with your images. I’m going to assume that you are familiar with raw files from your camera. Raw files have no color space, and they have no white balance, so the software you use will ultimately determine the color space.
Those shades are the “gamut” of a color space. There are two ways to think about gamut. The first is to think of each color space as a triangle anchored at the corners by values of red, green, and blue. Some color spaces are simply bigger. They can render deeper shades of those colors than others. The second way to think about gamut 12
If your goal is to share your images on the web and upload images to make prints (at Costco or Shutterfly, for example), then sRGB is probably fine. Web browsers can only display sRGB, and many processes for making prints (traditional wet prints, prints on aluminum, custom greeting cards, etc.) utilize the sRGB color space. Most computer moni12
