Raw and Colour Space

Almost all dSLRs (except some of the really, really old dSLRs from the early 2000) provide two colour spaces, the ubiquitous sRGB (standard RGB)¹ and aRGB (adobe RGB)². aRGB was developed by Adobe as a colour space that would cover the full CMYK colour space used by printing presses like magazines…

A raw file has a much larger colour space than either sRGB or aRGB. The raw file has a colour space than is even larger than ProPhoto (the widest colour space that is commonly used). So there are 5 questions (warning there is some geek speak):

1. Why is there no camera setting with the ProPhoto³ colour space? Neither Canon, nor Nikon… provide a ProPhoto colour space on their camera.

   Historical reasons. It’s only in the last 2 years that some CMOS sensors have been able record the colours of the ProPhoto colour space.

   Technical reasons. There is no guarantee that absolutely all the colours of the ProPhoto colour space are included in the raw file. Each camera manufacturer tweaks their CMOS sensor for the Canon look or the Nikon look or the Sony look…

2. Why set a colour space in the camera, since (almost) all raw images are the equivalent of ProPhoto. Even today, a lot of photographers, including professional photographers, set their cameras to JPEG (like almost all sports photographers) and even a few of them set their cameras to raw + jpeg. Here’s another example of “we’ve always done it that way!”

3. What about JPEG with aRGB colour space. It’s kind of an oxymoron. The standard JPEG images are 8 bit files⁴. aRGB needs 12 bit files⁵. There are 12bit JPEGs, but they are pretty much used only in medical applications, not the photo world.

4. What about my Lightroom/Photoshop/DarkTable…? Almost all current image processing software use the ProPhoto 16 bit colour space for all their internal processing to keep things as accurate as possible, so don’t worry.

5. What setting should I use in the camera? If you have using JPEG photos, then use the sRGB. If you have using only RAW it doesn’t really matter since Lightroom/Photoshop do all their work in ProPhoto and use the selected colour space only during the output. There is no commercial monitor or printer that support the ProPhoto colour space.