I've been reading through the various sections of the online GIMP
documentation that relate to color management, which prompted me to take
a closer look at the Display Filters.
Most of the observations below are related to the Color Management and
Color Proof ("Soft Proof") Display filters. As background for people who
haven't used soft proofing, soft proofing isn't just for preparing an
image to be printed on paper. Rather it's useful any time an image is
destined for display on a device other than the one on which it was
created (eg a digital photo frame on a wall). It's also useful when an
image is to be converted from one ICC profile to another (eg when
converting from ProPhoto or a camera or scanner input profile to sRGB).
"Edit/Preferences/Color Management" settings are global, affecting all
open images. Choices made in "View/Color Display Filters" are applied on
a per image basis. At present "View/Color Display Filters" and
"Edit/Preferences/Color Management" interact in sometimes very
unexpected ways, especially when the user sends multiple copies of the
various Display filters over to the Active filter list. Some expected
and unexpected results of using the Display Filters are:
a. If "Edit/Preferences/Color Management" is set to "Color managed
display" and "View/Color Display Filters" has the Color Management
Filter active (which it is by default), then unchecking the Color
Management Display filter disables color management for the image for
which the "View/Color Display Filters" dialog was opened. This makes
sense and is an example of using the per image Display Filters to
override the Color Management Settings global settings.
b. If "Edit/Preferences/Color Management" is set to "No color
management" and "View/Color Display Filters" has the Color Management
Filter active, then "View/Color Display Filters" Active Color Management
filter doesn't override the "No color management" choice made in the
Preference/Color Management dialog. In this case the per image choice
doesn't override the global choice.
c. The Color Proof Display Filter works when color management is
disabled. This provides accurate results if (and only if) the monitor is
calibrated to exactly match sRGB - not too likely given today's LCD
monitors, but still theoretically possible.
d. The Color Proof Display Filter doesn't provide the option to enable
and disable marking out of gamut colors.
e. If the "Mode of operation" is set to "Print simulation" in the
globally applied "Edit/Preferences/Color Management" settings dialog,
and if the user also chooses to activate the per image "Color Proof"
display filter, then the global choices made in the Color Management
settings are applied on top of the per image choices made in the Color
Proof Display filter, and the results are wrong.
f. Multiple active copies of the Color Proof Display Filter in turn
apply each copy's soft proofing choices, with increasingly wrong results.
g. One active copy of the Color Management display filter acts as
expected. But multiple active copies of the Color Management display
filter each in turn apply the conversion from the image ICC profile to
the monitor ICC profile. If the monitor ICC profile is "none" or is
sRGB, the multiple active Color Management filters make no difference.
But when using an actual monitor profile (sRGB doesn't adequately
describe LCD monitors), successively applying multiple copies of the
Color Management filter results in increasingly noticeable and wrong
color and tonality changes.
h. Multiple active copies of the Contrast and Gamma filters also are
applied successively. This seems unlikely to be useful.
i. Multiple active copies of the Color Deficient Vision filter also add
one to the other, but only if different Color deficiency types are
chosen. Once one each of insensitivity to red, green, and blue are
chosen, additional active Color Deficient Vision filters make no
difference in what's shown on the screen (for example, removing green
twice doesn't make magenta).
I don't know how difficult it would be to change the way the per image
Display Filters currently interact with the global Color Management
settings, but I put together some suggestions in hope of starting a
discussion:
1. In the Display Filters dialog, the user should only be able to send
one copy of the Available Filters over to the Active Filters panel. To
compensate, the Active Color Deficient Vision filter should have a list
with check boxes rather than a drop-down menu, so the user could check
one, two, or all three types at the same time.
2. The Color Management and Color Proof display filters should both be
in the Active Filter list by default, with Color Management checked by
default and Color Proofing unchecked by default.
3. If the user has already chosen to be in "Print Simulation Mode of
operation" in the "Preferences/Color Management" dialog, then that
choice affects all open images. But for those images for which the user
has also activated the Color Proof display filter, choices made in the
display filter should completely override choices made in the Color
Management Preferences dialog. This includes not only the proofing
profile but also the rendering intent and whether or not to use black
point compensation. In no case should a choice made in the display
filter "add to" the effect of a choice made in the "Preferences/Color
Management" dialog.
4. The Color Proof display filter should include the option to enable
and disable marking out of gamut colors, overriding any choice made in
"Preferences/Color Management".
5. Currently the Active Color Proof display filter opens with no choices
having been preselected. Instead the Color Proof display filter settings
should default to showing the soft proofing choices that were already
made in the global Color Management Preferences. That way, if the user
wants to change all of the global settings for just the one image, the
same number of clicks are required, but if the user only wants to change
one or two settings, fewer clicks are required.
6. The "Color Proof" display filter should be labelled "Soft Proof" to
be consistent with terminology used in the global Color Management
Settings. And the Color Management Settings "Print simulation" Mode of
operation should read "Device/Profile simulation", to provide a hint to
the user that soft proofing covers more than just preparing an image for
printing.
7. Users who have color management disabled in "Preferences/Color
Management" should have the option to enable color management on a per
image basis using the Color Management display filter dialog, parallel
to the current option to use the display filters to disable color
management on a per image basis.
8. At present, when Color Management is activated, which rendering
intent to use and whether or not to use black point compensation are
only controllable via the "Preferences/Color Management" dialog, which
affects all open images. These same options should also be available in
the Active Color Management display filter (defaulting to the same
choices that were made in the Preferences/Color Management dialog), so
they can be changed on a per image basis.
9. Some people have more than one monitor profile, for example a matrix
profile for image editing and one or more LUT profiles for soft
proofing. So it would be useful to be able to use the Active Color
Management display filter to override the globally set monitor profile
on a per image basis.
10. Because the Display Filters apply on a per image basis, the user
needs to be able to tell at a glance which open image is affected by
which Display Filter dialog. Perhaps the Display Filter title bar could
display the image file name so the user knows exactly which image which
be affected by a change in an open Display Filter dialog. Or perhaps
clicking on an image could also highlight the corresponding Display
Filter dialog. Or perhaps the Display Filter dialog really should be in
an Image drop-down menu rather than a separately opened, stand-alone
dialog box.
11. I'm not clear on the intended use cases for the Contrast, Gamma, and
Color deficiency Display Filters (emulation? compensation?). But if
there are users who need these Filters applied routinely for all images,
then these Filters should also be in the global Preferences/Color
Management Settings dialog.
Cheers,
Elle
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