Today’s Question: You’ve talked about choosing a color space for editing our photos, but why do we need to choose a color space in the first place? Couldn’t we all just use a single space that includes all colors?
Tim’s Quick Answer: Because the number of colors available in an image is limited by the bit depth of the image, it can be advantageous to choose a color space that is well-suited to how an image will ultimately be shared.
More Detail: A color space defines the range of colors that will be available in an image. It would therefore be reasonable to assume we could just use a color space that includes the entire range of the visible spectrum, so that any color capable of being seen with normal human vision would be available for our images.
However, images are limited in the total number of colors they can contain, based on the bit depth of the image. For example, 8-bit per channel images can contain almost 16.8 million colors, and 16-bit per channel images can contain more than 281 trillion colors. So, particularly for 8-bit per channel images, it can be important to choose a color space carefully, especially if strong adjustments might be applied to an image.
Because of these issues, color spaces have been created with specific purposes in mind. For example, the sRGB color space was created to encompass the range of colors that could be displayed on a typical monitor based on the available hardware at the time. However, for various types of print output a different color space makes sense because of the different colors that can be reproduced with different types of printers and print media.
It is also important to keep in mind that simply choosing the largest available color space is often not a good idea. For example, the ProPhoto RGB color space is huge, going beyond the visible spectrum, which makes it sound like a great choice. However, with such a large color space it is very easy to create posterization (the loss of smooth gradations) in an image with strong adjustments on an 8-bit per channel image.
If you’re working with 16-bit per channel images, it is relatively safe to always work in a very large color space such as ProPhoto RGB. However, for 8-bit per channel images I recommend opting for a smaller color space such as sRGB or Adobe RGB.
