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10-28-2017, 04:04 PM - 2 Likes   #1
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Fun and confusion with colour spaces - RAW vs. output JPEGs (yellows especially!)

Subject to further testing, I'm more-or-less in the process of moving to Linux Mint 18.2 as my operating system. At the same time - as a result of Adobe's new licensing model - I'm moving to Darktable for my RAW development, and GIMP for image editing. The rationale behind all of this is to free myself from the forced-payment license structure of operating systems and applications (though I do intend to donate voluntarily to those collectives and individuals who develop the software - on my terms, when I can).

As part of my testing with Darktable (v2.2.5), I've re-discovered a problem I believe I've had previously when exporting images from Lightroom - and that is, certain highly saturated colours (especially rich, bright yellows) appear to lose their intensity in JPEG exports. I initially believed this was due to a difference between the internally-used colour gamut in my RAW development software versus the sRGB-based colour gamut in 8-bit JPEG output.

Based on some helpful replies from an earlier thread I started, and further research on the web, I've solved most of my problems in this area now - though I'm left with some uncertainty around Darktable's soft-proofing and gamut warning functionality (which, for now, I put down to my lack of understanding, given that I'm new to the software and operating system!).

I'll start by saying that I've colour-profiled my desktop using the open-source DisplayCAL utility and an X-Rite ColorMunki Display tool, and I've confirmed that this profile is active.

The problem I experienced was as follows:

I would load a DNG RAW file (one with rich, bright yellows) into Darktable, make my adjustments, then export to an 8-bit JPEG using the "sRGB (web-safe)" colour profile. I would then view the photo using the Linux "Image Viewer" tool, and the photo would look less-saturated - especially the yellows.

Darktable has both soft-proofing and gamut warning tools, which allow the output colour-space to be selected. With soft-proofing set to "sRGB (web-safe)", the colours looked identical to the JPEG export viewed in Image Viewer (ie. under-saturated, especially the yellows). This led me to think (falsely, I believe) that the problem was gamut-related, and the exported file was limited to that colour reproduction.

What I've found - as a result of the replies from my previous thread (thanks to those who replied!), and further research - is that the Image Viewer tool isn't using my calibrated colour profile... Nor, for that matter - by default - was my Firefox browser.

By going into Firefox's "about:config" settings area and adjusting the colour management settings to enable colour management and use my calibrated display profile, its display of my exported JPEG image was extremely close to the live-edited image in Darktable (with any minor differences attributable, I believe, to 8-bit compression). This confirmed that the output image wasn't missing any significant colour information from the adjusted RAW.

The good news is that I can now adjust an image in Darktable, export it as JPEG using the sRGB colour space, and view it with Firefox such that it looks (almost) identical to the live-edited image in Darktable. It follows that the same exported file (whether in JPEG, or TIFF) should be usable for printing via a colour-calibrated professional printing service accepting sRGB images

My confusion / lack of understanding remains around Darktable's soft-proofing facility, which appears to show the image as it would be in a non-colour-profiled viewer. Perhaps that's how it's supposed to work? I'm not sure just now, but I'll look into this, as it requires more learning...

The big take-away from all this, for me at least, is that the exported JPEGs were always OK... but the viewing tool wasn't colour-profiled, hence I didn't see all the colours that were stored within that image. Furthermore, since this is the first time I've (knowingly) configured my browser to display images using my calibrated display profile, it makes me think that I've been viewing everyone else's images inaccurately, and most people will see my images inaccurately too. Not a huge issue, but something to think on

If you've read this far, I'd make a request and recommendation: In order to appreciate your own and other people's images at their best within your browser, please ensure it's configured to use colour management! I believe that some (perhaps all?) don't use it by default, and it can make a huge difference to the colour rendering!

With thanks to all of those who replied to my previous thread...


Last edited by BigMackCam; 10-28-2017 at 05:23 PM.
10-28-2017, 04:17 PM - 1 Like   #2
pjv
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Great research done Mike. This will be very helpful to many, I believe.
10-28-2017, 04:24 PM - 1 Like   #3
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Mike - Check out the discussion of this bug report on colour profile management in darktable. The input of the dt developer here is useful, methinks.

Bug #9596: Soft proofing seems not to work as expected - darktable - darktable - photography workflow application

Jack
10-28-2017, 05:04 PM   #4
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QuoteOriginally posted by pjv Quote
Great research done Mike. This will be very helpful to many, I believe.
Thanks, Pete I suspect my findings may already be well-known to many, but it's is certainly new to me, so hopefully one or two others may find this useful

QuoteOriginally posted by jbinpg Quote
Mike - Check out the discussion of this bug report on colour profile management in darktable. The input of the dt developer here is useful, methinks.

Bug #9596: Soft proofing seems not to work as expected - darktable - darktable - photography workflow application

Jack
Thanks, Jack I read through that series of posts. I believe my (perceived) problem is different, unless I've understood those posts incorrectly. What I see in my live, non-soft-proofed editing in Darktable, and what I now see in my colour-managed JPEG viewer (in my case, Firefox), match very well - with very minor differences attributable, I suspect, to 8-bit compression. They're almost identical, perceptually. However, the soft-proofed view in Darktable shows colour reproduction that is exactly what I see in the non-colour-managed Linux "Image Viewer" (or in Firefox prior to enabling colour management). Furthermore, the gamut warning tool shows the exact areas that are de-saturated. My immediate conclusion - though one I believe to be too simplistic, due to limited or mis-understanding - is that the soft-proofing and gamut-checking views are based on non-colour-managed output. I find that difficult to believe, but that's how it seems to me for now, until I do more research...


Last edited by BigMackCam; 10-28-2017 at 05:35 PM.
10-28-2017, 06:26 PM   #5
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What does running "darktable-cmctest" show you?
10-28-2017, 10:25 PM   #6
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Curious.
I've been using darktable with Fedora for years, and never seen any issues similar to those described with exported jpg and the Linux image-viewer. Lucky I guess.

Cheers,
Terry
10-29-2017, 02:27 AM   #7
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QuoteOriginally posted by jbinpg Quote
What does running "darktable-cmctest" show you?
darktable-cmstest returns the following:

darktable-cmstest version 2.2.5
this executable was built with colord support enabled
darktable itself was built with colord support enabled

primary CRTC is at CRTC 0
CRTC for screen 0 CRTC 1 has no mode or no output, skipping
CRTC for screen 0 CRTC 2 has no mode or no output, skipping
CRTC for screen 0 CRTC 3 has no mode or no output, skipping

eDP1 the X atom and colord returned the same profile
X atom: _ICC_PROFILE (20840 bytes)
description: 8605 2017-10-25 sRGB S 3xCurve+MTX
colord: "/home/mike/.local/share/icc/8605 2017-10-25 sRGB S 3xCurve+MTX.icc"
description: 8605 2017-10-25 sRGB S 3xCurve+MTX

Your system seems to be correctly configured

"/home/mike/.local/share/icc/8605 2017-10-25 sRGB S 3xCurve+MTX.icc" is the most recent profile I created with DisplayCAL and my ColorMunki Display, so all looks good
10-29-2017, 12:06 PM - 1 Like   #8
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QuoteOriginally posted by BigMackCam Quote
The big take-away from all this, for me at least, is that the exported JPEGs were always OK... but the viewing tool wasn't colour-profiled, hence I didn't see all the colours that were stored within that image. Furthermore, since this is the first time I've (knowingly) configured my browser to display images using my calibrated display profile, it makes me think that I've been viewing everyone else's images inaccurately, and most people will see my images inaccurately too. Not a huge issue, but something to think on
Yes. This is one reason why I still use a printed portfolio most of the time. I can't tell you how many timed I have had someone who was looking at images on some TN display that they got at office max telling me my colors were off.

10-29-2017, 10:28 PM - 1 Like   #9
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Mike - I assume you have read the Section 3.2.10. on color management in the dt docs (link below):

3.2.10.Color management | user manual | darktable

Note that you only get some of the rendering options if you toggle on the “always use LittleCMS 2 to apply output color profile” option in the core options.

Jack
10-31-2017, 04:43 PM   #10
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QuoteOriginally posted by jbinpg Quote
Mike - I assume you have read the Section 3.2.10. on color management in the dt docs (link below):

3.2.10.Color management | user manual | darktable

Note that you only get some of the rendering options if you toggle on the “always use LittleCMS 2 to apply output color profile” option in the core options.
Many thanks, Jack I had read that section... but, I'm in my early stages with Darktable, so there's a difference between me reading and fully digesting I'm happy, for now, knowing that my JPEG files do use the sRGB colour gamut (8-bit compression accepted, of course). I just need to understand - I think - the operation (and any limitations) of Darktable's soft-proofing and gamut warning functions a bit better!
10-31-2017, 08:35 PM - 1 Like   #11
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Anybody going down the rabbit hole of colour management with their digital photography should have this link bookmarked:

Color Management: Color Space Conversion

And here is another link with some intelligent discussion on the matter:

https://discuss.pixls.us/t/how-to-cope-with-colours-going-out-of-gamut/3320/9

It is not as straight forward as one would wish.

Jack
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