Hi All,

It would be really nice to be able to click a button or have a view module option that would indicate clipped colors by coloring them in some way (perhaps black for shadows, white for highlights), with an option to make these pixels blink.

UFRaw, darktable, RawTherapee, PhotoFlow all provide this functionality via buttons on a bar below the image. In GIMP, maybe the status bar would be a good location.

This topic was briefly mentioned on the gimp dev list back in April 2015. There are two open bug reports. Also the question came up today on the pixls.us forum:

https://discuss.pixls.us/t/clipped-pixels/5394

https://bugzilla.gnome.org/show_bug.cgi?id=316355

https://bugzilla.gnome.org/show_bug.cgi?id=316356

http://gimp.1065349.n5.nabble.com/GIMP-2-9-useability-out-of-gamut-and-HDR-channel-values-td45195.html#a45198 - there was a suggestion that this functionality already exists, but if it does, I can't find it :) .

Best, Elle

On 10/20/2017 09:18 AM, Alexandre Prokoudine wrote:

On Fri, Oct 20, 2017 at 4:03 PM, Elle Stone wrote:

http://gimp.1065349.n5.nabble.com/GIMP-2-9-useability-out-of-gamut-and-HDR-channel-values-td45195.html#a45198

- there was a suggestion that this functionality already exists, but if it does, I can't find it :) .

Color managements prefs

Alex

Hi Alex,

Do you mean the "Mark out of gamut colors" option under soft proofing? That would only work if the following were true:

1. The user picked the current editing color space as the color space for soft proofing.

2. LCMS soft proofing would need to show out of gamut colors when the source and destination color space have the same bounded color gamut, which currently is not the case. Leastways right now I'm looking at an image with hugely out of gamut channel values, with the appropriate soft proofing settings in Preferences. Not a single pixel is marked as out of gamut.

3. For cases where the user has chosen linear precision, LCMS soft proofing would need to work properly for linear RGB, which currently is not the case. As an aside, for using LCMS for soft proofing and gamut checks, it would be better if the RGB values sent to LCMS were at "perceptual precision", regardless of what precision the user has chosen.

Even if LCMS soft proofing changed in the future, the gamut check doesn't differentiate between clipped/oog shadow colors and clipped/oog highlight colors.

Using LCMS to check for out of gamut colors does slow down the speed at which GIMP can display changes in the image made while editing.

Also going into Preferences is a bit cumbersome for something the user might not want to leave permanently activated. Buttons/checkboxes similar to what the raw processors use would be very much more convenient.

Elle

On 11/02/2017 04:21 PM, Ell via gimp-developer-list wrote:

On Fri, 20 Oct 2017 09:03:01 -0400 Elle Stone wrote:

Hi All,

It would be really nice to be able to click a button or have a view module option that would indicate clipped colors by coloring them in some way (perhaps black for shadows, white for highlights), with an option to make these pixels blink.

master has a clip-warning display filter now (commit 5b118a260b), which does that. No blinking, though :)

Hi Ell, and thank you! That clip warning display filter is really nice!

Regarding the blinking, personally I don't much like blinking pixels - probably the only advantage of blinking is to draw attention to very small areas that have out of display range colors. Seeing these areas probably requires zooming in to 100% for just about all image editing softwares, so the blinking per se doesn't seem all that useful.

Yesterday when I compiled GIMP the new filter was there, but nothing was happening on the image - not sure why. But today I updated GIMP again, and recompiled, and made an image that was a gradient from -1.0f to +2.0f. The gradient ran from the upper left to the lower right corner. The Clip Warning shows diagonal parallel red and black bars for the highlights, and diagonal parallel blue and black bars for the shadows.

Are there supposed to be diagonal bars instead of solid blotches of the user-chosen warning colors? If so, how would this work with images with just speckles and very small areas of out of display range colors? I'll try to do some more experimenting later on today.

The option to choose the clipping warning colors is really nice, allows to choose different default colors, and also to change the warning colors for images that actually have a lot of in-gamut colors that are displayed close to the preset colors.

Best, and again thank you! The new clip warning was such a nice surprise! Elle

On 11/03/2017 10:45 AM, Ell via gimp-developer-list wrote:

Yes, the diagonal stripes are basically a static substitute for blinking: it's possible that your image has areas with similar color to the warning color, but it's much less likely that these areas also have a stripe pattern, making the warning more distinguishable.

I'm not sure why this would be specifically problematic with small our-of-range areas (though obviously less useful in these cases.) Note that the size of the stripe pattern is independent of the area size, or the zoom level, so, in particular, when you zoom in you can see the pattern over individual pixels.

Hi Ell,

I just tried the clip warning with an image that I knew had small patches of out of gamut colors - works like a charm! Even for small sprinkles of out of gamut colors - using the tool I found a few pixels in my test image that I didn't already know were out of gamut, but sure enough they were.

Best,
Elle

OK, now I'm very puzzled. The Clip Warning shows the exact same pixels as out of gamut, regardless of what RGB color space the image is actually in.

Experimenting, it looks like perhaps the clip warning is always determining "out of gamut" with respect to GIMP's built-in sRGB color space, even if the image is in a larger color space and none of the pixels are out of gamut in the larger color space.

For example, for a Rec.2020 image opened with default GIMP, none of the colors are out of gamut wrt Rec.2020. But quite a few colors in the highlights (bright saturated yellow-greens - leaves backlit by the sun) have out of gamut colors after converting the image to GIMP's built-in sRGB color space.

Is this the case? The clip warning always and only shows colors that are out of gamut wrt to GIMP's built-in sRGB color space?

Best, a very puzzled Elle