Digital Photos; Post-Process sRGB=>Adobe RGB or Not?

I use a Canon Digital EOS 350D (oldie, but goodie) with L-series lens and post-process in Photoshop before sending them for printing. Post processing normally consists of correcting the levels via Histogram and/or a bit of contrast tweaking with Curves. However, it sometimes involves 'clean-up, as well

For various reasons (i.e. carelessness!), I have only just noticed that, for the last few months, my camera has been set to use the sRGB colour space rather than Adobe RGB. This has now been fixed but the question remains as to what I should do with my photos which have been taken using that sRGB profile?
Photoshop is set to use Adobe RGB and now(!) warns me when I open a photo with an sRGB colour profile. So should I accept the option to convert the photo to use Adobe RGB colours, or the option to ignore conversion and use the embedded sRGB colours, instead?

I am well aware of the advantages of using the Adobe RGB colour space when printing is required, but have no knowledge of the implications or impacts of converting an sRGB photo into Adobe RGB, via post-processing. So, all advice or comments gratefully received

There's a lot of codswallop talked about the benefits of Adobe RGB versus other colour spaces. By all means use Adobe RGB if you want to. There's nothing wrong with it. However, the extended colour range that it supports cannot be displayed by computer monitors or reproduced by most printers (and certainly not lab printers).

If you are using a properly calibrated colour work-flow, it doesn't really matter what colour space you use. If you are just relying on manufacturers' standard colour profiles, stick with whatever colour space gives you the best results.

One thing you should avoid is switching images back and forth between one colour space and another. You can get away with doing it a few times but if you do it a lot (i.e. if it's part of your work-flow) this may introduce cumulative errors that can degrade your images. It's always best to stay in the same workspace as much as possible.

Edited by micksharpe (Sat 08-Mar-14 16:58:13)

Hi Mick

Thanks for the reply. Totally understand your points about not switching colour spaces multiple times and the fact that my monitor only supports (according to spec) 75% of the Adobe RGB gamut. However, I'm a bit confused about your comment that commercial printers don't use it. Is this really the case? I'm quite happy to believe that 'home printer' set-ups probably wouldn't support/be able to use Adobe RGB but I would have that this shouldn't be a problem for commercial printing set-ups

In reply to a post by SimpleSimon1:

I'm a bit confused about your comment that commercial printers don't use it. Is this really the case?

Commercial print shops will certainly accept images that use Adobe RGB. However, they all use 4-colour (CMYK) printers and the colour gamut that these printers can achieve is no better than any bog-standard consumer printer (since the same dyes are used). Anyway, it is possible that they will convert images to sRGB before printing.

Edited by micksharpe (Mon 10-Mar-14 17:06:44)

In reply to a post by SimpleSimon1:

Photoshop is set to use Adobe RGB and now(!) warns me when I open a photo with an sRGB colour profile. So should I accept the option to convert the photo to use Adobe RGB colours, or the option to ignore conversion and use the embedded sRGB colours, instead?

I am well aware of the advantages of using the Adobe RGB colour space when printing is required

Photoshop doesn't need to be set to use Adobe RGB when working with photos. By default, it opens, edits and saves images in the embedded profile. The "Working space" option really would be better renamed "Default editing space". If you changed it to Adobe RGB - this makes no difference when it comes to working with photos from your camera, unless you also choose to always convert other profiles, or you choose to be asked each time and then opt to convert. You may choose to convert for workflow reasons and/or because you want to make use of the larger gamut in your grading. The dithered conversion from sRGB to Adobe RGB is relatively harmless and mostly imperceptible on almost all material, but we always must use our eyes as the final arbiter.

Display technologies are the most capable of rendering Adobe RGB gamut. Offset and inkjet printers can go some way outside of sRGB, esp in green and cyan, lab C-types only go very slightly out in yellows and high luminance.

I have to admit that I have been a bit sloppy with my digital work flow recently, mainly because I take snapshots these days with my Pentax K10D and I no longer use a complete colour-managed work-flow even though I have the kit to do it.

Orginally, when I was using the K10D to photograph textiles, I set it for raw mode output only with an Adobe RGB colour space. Fine. No problemo. The camera spat out 48-bit DNG images and Photoshop yummed them up.

Now, however, I've switched to JPEG output since I don't need to be so fussy about image quality and JPEGs take up far less room, but I've left the colour space set to Adobe RGB instead of switching it to sRGB. No problemo? Maybe not.

The CMOS sensors in my K10D and your 350D both produce 12-bit values for each colour (red, green and blue) in an image but these values must be manipulated before they can be stored in an image file using the required colour space. My K10D produces 48-bit (3 x 16-bit) DNG images in RAW mode and/or 24-bit (3 x 8-bit) JPEG images in compressed mode, and I can select sRGB or Adobe RGB colour space for either image format.

Now Adobe RGB provides a larger colour space than sRGB and so more bits per pixel are required to provide the same level of colour gradation. If, on my K10D, I select RAW mode with Adobe RGB there is no problem since the 12-bit colour values can easily be up-scaled to 16-bits with plenty of head-room for the extended colour space.

However, if I select JPEG mode with Adobe RGB, then I may have problems since the 12-bit colour values must be down-sampled to 8 bits and then down-sampled some more to provide the head-room that Adobe RGB needs. I would be much better off switching to sRGB with JPEG output to avoid this extra compression and inevitable loss of image quality. Of course, if the K10D produced 16-bit JPEG images, there would be little to worry about.

I'm not sure if the K10D can capture colour values outside the sRGB colour space. I'll have to find out. If it can, then it makes sense to use Adobe RGB with RAW mode. If not, then I might as well stay with sRGB. Since I shoot mainly in JPEG mode these days and the K10D only produces 8-bit JPEG images, I should definitely be using sRGB. You should probably do the same.

There are plenty of useful articles about colour spaces on the web written by people with a lot more experience that I have. Try this one.

Keep the originals - untouched so that if you do mess it up through conversion you always have te fallback.

Where to start?

In reply to a post by micksharpe:

Orginally, when I was using the K10D to photograph textiles, I set it for raw mode output only with an Adobe RGB colour space.

No, you didn't. The whole point of RAW and DNG is that the data is not converted to a colour space and other aspects of an ICC profile. The setting you refer to is nothing more than a metadata tag, usually used in-camera if the file is further processed or analyzed, and usually ignored out-camera.

In reply to a post by micksharpe:

Now Adobe RGB provides a larger colour space than sRGB and so more bits per pixel are required to provide the same level of colour gradation. If, on my K10D, I select RAW mode with Adobe RGB there is no problem since the 12-bit colour values can easily be up-scaled to 16-bits with plenty of head-room for the extended colour space.

Leaving aside the fact the setting, as you now know, has no effect on the RAW or DNG file, the bit-depth increase is just zero-padded not interpolated by a magic eye. So even if you did have a 12-bit Adobe RGB image the camera is not improving or giving headroom for the image compared to a 12-bit sRGB file.

In reply to a post by micksharpe:

However, if I select JPEG mode with Adobe RGB, then I may have problems since the 12-bit colour values must be down-sampled to 8 bits

The camera sensor data is significantly more "linear" than the gamma-referred profiles which are more perceptually efficient, so you can't compare 12 to 8 like that.

In reply to a post by micksharpe:

I'm not sure if the K10D can capture colour values outside the sRGB colour space. I'll have to find out. If it can, then it makes sense to use Adobe RGB with RAW mode.

You know what I'm gonna say by now.

In reply to a post by micksharpe:

If not, then I might as well stay with sRGB. Since I shoot mainly in JPEG mode these days and the K10D only produces 8-bit JPEG images, I should definitely be using sRGB. You should probably do the same.

Due to the power of appropriate dithering, the perceptible difference is really tiny and usually nil and swamped by display or print inaccuracies. The "banding" argument is not a sensible reason to opt for a smaller colour space. The photographer should be free to choose whatever he wishes based on other considerations, though I agree with your sentiment that there is a lot of twaddle banded about that sRGB is not suitable for "serious" photographers.