On 23.09.12 at 09:28 a.m. ndummy001@yahoo.co.jp wrote:

GIMP(win) has some color management features on settings dialog. But it's not enough( e.g. black point calibration )

I agree with you, that color management is a very important part to make GIMP a high-end photo manipulation application as written in the product vision. Many users and developers share that opinion. You could for instance read the postings of Elle Stone and yvind Kols a.k.a. pippin to see the ongoing efforts on this topic. As you can see, the GIMP team takes this topic seriously.

The settings dialog is not the only part where you find color management in GIMP. Have you already looked at the Image/Mode/Assign Color Profile... and Image/Mode/Convert to Color Profile... menu items? Particularly the latter contains the desired black point compensation. Also check View/Display Filters..., move there the 'Color proof' filter to the right list and click it. It give you a proof view of the image and its options also contain Black point compensation.

Developers must implement these if you all truly thinking that GIMP is important.

I think it's a mistake to judge from one part to the whole. At least 16K users only at Google+ don't share your opinion (to say it with Alexandre ;-) and not all GIMP users are on G+.

Kind regards,

Sven

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On 9/23/12, ndummy001@yahoo.co.jp wrote:

GIMP(win) has some color management features on settings dialog. But it's not enough( e.g. black point calibration ) Developers must implement these if you all truly thinking that GIMP is important.

I agree with what you say about the color management settings dialog. Neither the Gimp Display settings nor the Softproof settings provide the user with the very important choice of whether to use or not to use black point compensation.

Also, Gimp display rendering intent (and probably the softproof rendering intent, but I haven't checked) gives different results for "relative colorimetric" and "perceptual", even when the destination profile is a matrix profile (the more usual case for monitor profiles).

The problem is, matrix profiles don't support perceptual intent: perceptual intent requires a lookup table and matrix profiles don't have lookup tables. As matrix profiles don't support perceptual intent, having "perceptual intent" and "relative colorimetric" give different results means a coding decision was made at some point in the past.

In the lcms.c code, I found the following lines:

if (config) intent = config->display_intent; else
intent = GIMP_COLOR_RENDERING_INTENT_PERCEPTUAL;

bpc = (intent == GIMP_COLOR_RENDERING_INTENT_RELATIVE_COLORIMETRIC);

which means that in Gimp, for your display profile, "relative colorimetric intent" is hard-coded to give you "relative colorimetric intent with black point compensation," and "perceptual intent" gives you "without black point compensation".

Which gives you a partial workaround for the missing user option of being able to choose "with or without black point compensation". If you are using a matrix profile as your monitor profile, you really can choose whether or not to use black point compensation, albeit in a totally non-intuitive way. But if you are using a lut display profile with a perceptual intent table and a relative colorimetric intent table, you are stuck with "without black point compensation" if you choose "perceptual intent" and you are stuck with "with black point compensation" if you choose "relative colorimetric intent".

(As an aside, if you are using the V2 sRGB matrix profile as your monitor profile, along with any standard RGB working space (sRGB, BetaRGB, ClayRGB, Widegamut, etc), you won't see any difference between "relative" (which in Gimp is with black point compensation) and "perceptual" (which in Gimp is without black point compensation), because sRGB and all the other standard working spaces all have zero black points.)

Fixing the missing black point compensation option involves editing "lcms.c", "preferences-dialog.c" and probably a few other files. I would cheerfully attempt the task myself, but I think the "gui" portion is beyond my coding skills, so I would need help from someone more versed in the Gimp code.

On 9/23/12, scl wrote:

On 23.09.12 at 09:28 a.m. ndummy001@yahoo.co.jp wrote:

The settings dialog is not the only part where you find color management in GIMP. Have you already looked at the Image/Mode/Assign Color Profile... and Image/Mode/Convert to Color Profile... menu items? Particularly the latter contains the desired black point compensation.

The Image/Mode/Convert menu items does offer the option of using or not using black point compensation. But proper color management requires that the same options be available for the monitor profile and for softproofing.

Also check View/Display Filters..., move there the 'Color proof' filter to the right list and click it. It give you a proof view of the image and its options also contain Black point compensation.

The Gimp Color Proof Display Filter seems to offer everything anyone would want in the way of softproofing and display options. Unfortunately, as far as I can tell from comparing the results to other image editors (Cinepaint, Krita), the Gimp Color Proof Display Filter doesn't work properly.

Kind regards, Elle Stone

El 23/09/12 19:11, Elle Stone escribi:

The Gimp Color Proof Display Filter seems to offer everything anyone would want in the way of softproofing and display options. Unfortunately, as far as I can tell from comparing the results to other image editors (Cinepaint, Krita), the Gimp Color Proof Display Filter doesn't work properly. Kind regards, Elle Stone

I've used this one in 2.6 for print softproofing: Gives better results than the print preview settings in GIMP and seems to be more consistent with what I get from CMYKtool, which has a very reliable preview (at least in my experience).

I'd love to have something like this in GIMP in the future.

Gez.

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On Mon, Sep 24, 2012 at 2:28 AM, Guillermo Espertino (Gez) wrote:

I've used this one in 2.6 for print softproofing: Gives better results than the print preview settings in GIMP and seems to be more consistent with what I get from CMYKtool, which has a very reliable preview (at least in my experience).

Did you mean to link to http://registry.gimp.org/node/24944 ? :)

Alexandre Prokoudine http://libregraphicsworld.org

El 23/09/12 19:33, Alexandre Prokoudine escribi:

On Mon, Sep 24, 2012 at 2:28 AM, Guillermo Espertino (Gez) wrote:

I've used this one in 2.6 for print softproofing: Gives better results than the print preview settings in GIMP and seems to be more consistent with what I get from CMYKtool, which has a very reliable preview (at least in my experience).

Did you mean to link to http://registry.gimp.org/node/24944 ? :)

I was asking myself where I put the link and YOU HAD IT! Next time don't take my things without asking first. Thank you.

:-p

Gez.

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