[Gimp-developer] Gimp color picker's displayed colors

[Elle Stone <l elle stone gmail com>]

For some silly reason I assumed that the Gimp color picker's displayed
colors are accurately displayed if one is working on an sRGB image.
But that isn't true because the Gimp color picker isn't color-managed.
Instead the color picker RGB values are sent straight to the screen
without having first been converted from the image's working color
space to the monitor profile.

What this means in practice is the only time the color picker's color
patches are displayed accurately is if the monitor has been calibrated
to match the working color space that the image itself is actually in.

The only working color space to which most monitors traditionally have
been calibrated is sRGB (ColorMatchRGB and AppleRGB being two notable
exceptions).

So unless your monitor has been calibrated to sRGB *and* your image
likewise is an sRGB image, the Gimp color picker won't show you
accurate colors. The color picker RGB *numbers* are accurate but the
displayed *color* is not. The farther your monitor's actual
calibration+profile is from sRGB, the farther off the displayed colors
will be from what they ought to look like.

The only practical solution to the problem of un-color-managed and
hence inaccurately displayed color picker colors is that you calibrate
your monitor to match sRGB and then only work on sRGB images.

One problem with this practical solution is that you *can't* calibrate
most LCD monitors to 100% match sRGB. If you try, you inevitably
reduce the color gamut of your LCD monitor, there's a good chance that
you'll introduce banding, and you still won't get a completely
accurate display of the colors that you've color-picked. See: sRGB,
the Universal Monitor Profile — Not So Good for LCD Monitors
(http://ninedegreesbelow.com/photography/srgb-bad-monitor-profile.html)

Another problem with this practical solution is that most of today's
LCD monitors, even wide-gamut LCD monitors, *can't* display all sRGB
colors. Wide-gamut monitors have color gamuts that are larger than the
sRGB color gamut, but almost none of them entirely encompass sRGB.
According to a monitor profile for a recent $2500 wide-gamut monitor,
even this very pricey monitor can't display *all* sRGB colors, being
weak in blues compared to sRGB. The monitor profile for a recent $450
consumer-grade monitor indicates that it could only display 88% of all
sRGB colors. See: sRGB: good working space for CRTs, not so good for
LCDs (http://ninedegreesbelow.com/photography/srgb-bad-working-space-profile.html)

If you use sRGB as your monitor profile for your uncalibrated monitor
(or if you disable color management) and you work on an sRGB image,
the color picker's displayed colors *will* match the colors that you
color-pick from your image. But it's a virtual certainty that the
colors you see are very far from accurate.

Best regards,
Elle