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In talking to a colleague of mine yesterday, we got onto the subject of color spaces in digital photography. He's a Nikon buff, I use Canon (specifically, an EOS 50D); I don't know if that is relevant to my question or not, but mention it for completeness.

I shoot RAW essentially 100% of the time, and have the in-camera color space setting at AdobeRGB (sRGB is also offered). The raw converter in turn is set to produce sRGB output files. As I understand the process, the general flow is for raw shooting: raw sensor data readout (including A/D conversion), compression, write to a raw file, then in post-processing rather than in-camera apply color space/color temperature/etc; for JPEG shooting: raw sensor data readout, apply color space/color temperature/etc, JPEG compression, write to memory card (in camera).

Hence, when he said that I should leave the camera set to sRGB for best/consistent results despite using the camera's raw format, it didn't really make much sense to me. I have mulled it over for a while now and it still doesn't really make any sense.

One of the answers to What is RAW, technically? seems to support my view of the differences in the data recorded in RAW and JPEG modes, respectively.

I did find What's the difference between Adobe RGB and sRGB and which should I set in my camera?, but the answers there seem to focus more on the difference between AdobeRGB and sRGB. My question is, when shooting RAW, does it ever matter (except for the image preview) whether the camera is set to sRGB or AdobeRGB? If it does, then why, and in what situations? Is my understanding of the "raw" format processing chain flawed?

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3 Answers 3

up vote 14 down vote accepted

The answer is basically the same as this one on white balance and raw. You're right, it doesn't matter at all in how the image is recorded or stored.

As you note, the selected color space applies to the preview image and to the histogram. The camera also may make metering decisions intended to avoid clipping (overexposing to the full saturation point) in particular channels, and that may be affected by choice of color space in-camera. I think this is less likely to be a real problem than having the white balance far off might be, though.

But I'd also take a careful look at the preview image in both modes. The rear LCD screen isn't something you can calibrate on most cameras. I think it's more likely that sRGB is correctly represented, and the screen might not cover the Adobe RGB gamut very well. (And really, I'd not be surprised if many cameras don't really handle preview display of Adobe RGB correctly at all — that's a lot more complicated than simply having the mechanism to save in that space.) I'd do some test shots and see which looks most like what your final printed output does, and then use that — that'll make the review screen more useful. It may very well turn out that an accurate display of sRGB is more like your final results than a bad rendition of Adobe RGB (even if you ultimately do use Adobe RGB in the end).

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This makes sense, assuming that my understanding of the raw processing chain is correct. :) In practice, I rarely use the LCD preview for much of anything beyond getting a general idea of how the picture turned out (I do tend to check the histogram, though) and instead spend some time working with color temperature, curves etc in post, so color rendition accuracy in camera preview is not particularly important to me. That said, I will try to take the same scene with the same light and exposure, with the camera set to both, and compare the results. –  Michael Kjörling May 10 '12 at 12:27
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Yeah, as I understand your understanding, it is correct. :) –  mattdm May 10 '12 at 12:51
    
Another possibility is that the camera saves the preview JPEG, which is what the screen on the camera displays, in sRGB color space regardless of whether you have selected Adobe RGB or sRGB as your output color space. It is my understanding that even when your output is JPEG, the preview is a separate thumbnail version sized to fit the resolution of the screen on the camera. –  Michael Clark Feb 8 '13 at 14:27

Actually, to get the full benefit of shooting RAW, the output of the RAW converter should be set to a wide gamut format for transfer into Photoshop. If you're using Adobe Camera Raw, you can set it to 16 bit Pro Photo RGB; if you're using Canon's own Digital Photo Professional, you can set its Default Working color space to Wide Gamut RGB which is also 16 bit. sRGB is 8 bit and restricts you to the color range that JPEGs can handle.

You can see what Pro Photo RGB and Wide Gamut RGB's gamuts look like in their respective Wikipedia articles. After a little careful sliding of one or the other's scrollbar up and down to line up the two graphs vertically in adjacent tabs, you can toggle between them to see the differences. Pro Photo has a bit more in the saturated greens, while Wide Gamut has a bit more in the deep red-violet area - but they're each much wider than even Adobe RGB.

I've discovered that opening a CR2 in DPP and having it transfer the picture to Photoshop gives richer colors than using ACR or even Lightroom as my pipleline into Photoshop - and going through the DNG Converter is in last place in my estimation of color quality.

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While all this may be true, it doesn't seem to have any bearing as to whether you should select Adobe RGB or sRGB in camera. –  Philip Kendall Feb 8 at 21:46
    
There is nothing about sRGB that makes it 8-bit. –  James Snell Feb 9 at 12:44

It does not matter what you set in camera as RAW. RAW is RAW, it is not modified until post. Most monitors will not display aRGB and many printers do not print aRGB. I select aRGB as the assigned profile and my printer tells me much is out of gamut. I am forced to work in sRGB as that is where my color gamut is for my monitor and printer.

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