Questions regarding the Darktable theme

[anon41087856]

Krita and dt.

[Jose_Figueres (jofial)]

DT of course, I didn’t know Krita.

Thanks

[Beau (Beau R)]

I’m brand new to darktable. I read about rendering method in the manual, optimizing (darktable’s internal method) makes complete sense, but I concluded that soft proofs and final output whether to file or printer were run through a CMS and profile that corresponded to the target. Can someone explain what Aurelien’s statement really means? Taken at face value it would seem to completely negate any efforts to process an image if there is no way to control the final output. Thx

[paperdigits (Mica)]

@Beau

Can someone explain what Aurelien’s statement really means?

Which statement? Aurelien makes a lot of statements.

@Beau

Taken at face value it would seem to completely negate any efforts to process an image if there is no way to control the final output

I don’t understand what you’re trying to get across with this statement.

[Beau (Beau R)]

I somehow thought the “reply” would have the context. Take two, with context, the question is is in response to the following by Aurelien.

Also, it baffles me that LittleCMS2 at darktable’s output actually never worked (there is no gamut mapping in there, it’s actually useless) and nobody seems bothered, but somehow borders and shadows in the UI make people talk for weeks.

I’m brand new to darktable. I read about rendering method in the manual, optimizing (darktable’s internal method) makes complete sense, but I concluded that soft proofs and final output whether to file or printer were run through a CMS and profile that corresponded to the target. Can someone explain what Aurelien’s statement really means? Taken at face value it would seem to completely negate any efforts to process an image if there is no way to control the final output. Thx

[priort (Todd Prior)]

@Beau

Also, it baffles me that LittleCMS2 at darktable’s output actually never worked (there is no gamut mapping in there, it’s actually useless) and nobody seems bothered, but somehow borders and shadows in the UI make people talk for weeks.

I think it is fair to be confused. I sort of ignored this statement back when AP made it. It was my understanding at some point that gamut mapping although offered at export was only actually performed ie using the settings for relative perceptual etc if LittleCMS was enabled in preferences…but this comment could lead one to believe that it doesn’t work even then??

My images are close enough for what I do so I have not tried to dig any further…

[paperdigits (Mica)]

@Beau

I somehow thought the “reply” would have the context. Take two, with context, the question is is in response to the following by Aurelien

I try and quote things (highlight some text and a menu will pop up, then select “quote”) so that is crystal clear who I’m replying to and the context that I’m working with. Not enough people here use the quote feature

@Beau

it baffles me that LittleCMS2 at darktable’s output actually never worked (there is no gamut mapping in there, it’s actually useless)

I’d say it is not useless nor baffling and the user manual says exactly what LCMS does: darktable 3.8 user manual - processing

I don’t really understand where gamut mapping comes into it, but a quote would solve that.

[Beau (Beau R)]

@anon41087856

Also, it baffles me that LittleCMS2 at darktable’s output actually never worked (there is no gamut mapping in there, it’s actually useless) and nobody seems bothered, but somehow borders and shadows in the UI make people talk for weeks.

I mean, seriously, we are making an EXIF reader here ?

I think lack of my forum quoting skill, is causing AP’s statement to be attributed to me?

I am brand new to darktable, but have read the manual, watched AP’s videos, and processed a few images (scene-referred).

• I do understand that one can choose to manage color using littleCMS or the (internal method) which is much faster.
• But if the target ICC profile contains a LUT the option is overridden to use littleCMS regardless.

Based on AP’s comment quoted above, I am guessing that for the scene-referred pipeline that LittleCMS is not invoked for things like printing or exporting to a sRGB file? But this seems surprising to me given the great deal of attention AP has given to technically correct processing (WRT physics and psychophysics) done up to this point? So I have no idea what the quote really means, but hoping someone can share their insights. Thx

[paperdigits (Mica)]

@Beau

I think lack of my forum quoting skill, is causing AP’s statement to be attributed to me?

Ah, yes.

@Beau

I am guessing that for the scene-referred pipeline that LittleCMS is not invoked for things like printing or exporting to a sRGB file?

If you export a file (printing included) and have the LCMS option enabled or your ICC forces darktable to use LCMS, then it is invoked.

@Beau

So I have no idea what the quote really means, but hoping someone can share their insights

I read it as “we could do gamut mapping using LCMS but for some reason I don’t understand, we don’t to gamut mapping and that seems like a mistake to me.”

[RawConvert (Andrew)]

@Beau

So I have no idea what the quote really means, but hoping someone can share their insights.

I’m a bit baffled too, but LittleCMS is something I’ve looked at before. Two years ago I started this thread

I can't get rendering intent to work, any ideas please? -Progress **

I was playing with the indigo bunting and soon realised much of my image was out of sRGB gamut, so I thought I’d try perceptual intent. I haven’t used the intents in dt previously and soon realised I need littleCMS on, so did that and re-launched dt for good measure. I output 2 jpegs, one perceptual, one relative colorimetric, but I couldn’t see any difference flicking between them. There was loads of cyan on pressing the gamut button. Then I tried different display intents by right-clicking…

which showed LittleCMS did in fact deliver a difference between perceptual and colorimetric output intents. At the time I reckoned it was therefore doing a decent perceptual rendering, which was what I wanted, providing I used the sRGB_v4_ICC_preference profile, and not the default sRGB websafe. I’ve been using the former ever since. What baffled me was that its perceptual intent looked the same as sRGBwebsafe with any intent, so I wondered if that had somehow been made perceptual.
Anyway I just re-tested with 4.0 and there’s still that difference between perceptual and abs.colorimetric using LittleCMS and the preference profile.
Are “gamut mapping” (as per Aurelien Filmic 6) and “traditional” perceptual intent two ways to achieve the same goal i.e. reducing gamut for your output step?
It was only a few months ago when I read that apparently LittleCMS does not work properly.

Edit: before “What baffled me was that it looked the same as sRGBwebsafe with any intent”
after “What baffled me was that its perceptual intent looked the same as sRGBwebsafe with any intent”

[age]

@RawConvert

Anyway I just re-tested with 4.0 and there’s still that difference between perceptual and abs.colorimetric using LittleCMS and the preference profile.

Perceptual rendering intent doesn’t work with srgb, it 's not a bug.

ICC Profile Conversion Intents

" Furthermore, the sRGB color space profile is a matrix profile, so there’s no perceptual intent table in the first place. Without a perceptual intent table in the sRGB profile, you simply can’t do a perceptual intent conversion to sRGB (but see the gray box below).

Why image editing software defaults to “perceptual intent” when converting an image to the sRGB and other matrix profiles is anyone’s guess"

There are old discussion in this forum too

[RawConvert (Andrew)]

@age

Perceptual rendering intent doesn’t work with srgb

Isn’t it more correct to say it doesn’t work with a matrix-only profile, and sRGBwebsafe is matrix-only.
The color.org sRGB preference profile has a LUT I believe, which presumably explains why results vary by selected intent. But I’m not claiming that profile + LittleCMS + specifying perceptual intent truly delivers perceptual. It just looked quite believable to me.