DT color not accurrate when zoomed

Hi All,

I stumbled on a strange color discrepancy when zooming in/out in DT.

When zoomed out (fit) - the color is almost black and the measurements are also displaying the same.

When zoomed in (100%) - the colors are purple but the eye dropper still reads almost black.

When the image is actually exported the purple color is visible not the black - regardless of the resolution.

Has anybody seen such behavior? Is it known or I should submit an issue?
(I can observe this only on certain images)

DT 4.6.1 - flatpak on PopOS 20.04

Are you sure its not the second swatch…

I double checked it and I am adding the corresponding RAW and .xmp
I think it is caused by diffuse and sharpen - specifically 4rth order.
Still I don’t think this is good.

20240316_154550_06174.ARW.xmp (14.7 KB)
20240316_154550_06174.ARW (36.3 MB)

What version of DT are you using…can you use the new HQ processing preview….

I think the HQ is in the next version.

I get the following if I have the picker set to use sRGB ie via the histogram profile…

62 25 105


10, 4 32 if I leave it where I normally do on Linear Rec 2020…

Seems about right…

Can you check the top right of the letter “B” in Bookstore please?
Even on your screenshot the frame around the sign gets quite dark. The Cafe - specifically “fe” gets noticeably darker.

My take and it could be wrong…if you take your image out of the gate not much in the way of editing and lighten it…then you see the right lettering is darker… Your edits play with this and esp your tone eq instances.

When you zoom the impact of the tone eq is not visually the same…Zoomed in you can’t really notice it but when you zoom out it almost creates a vignette or shadow effect…

I guess others can comment on what they see

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It might be totally unrelated, but I submitted a bug 3 years ago about incorrect color picker readings when zoomed in: Global color picker values inconsistent with what's visible - Windows, maybe related to negadoctor · Issue #9920 · darktable-org/darktable · GitHub

The Github issue is still open. It might be worth checking to see if this is related.

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So I opened your image with the xmp file you supplied. I took a snapshot and then zoomed to 100%. The colors were visibly identical and swiping the snapshot across the image caused no change. I then took a color picker reading of the large letter C and regardless of zoom I got identical readings. I can not replicate your problem on Windows DT4.7 +780.

I chose not to read the letter B as the color was very uneven it this might impact the accuracy of measurements between zooms.

Thank you for testing!
Did you try zoom out like this? And specifically the letter “B” from Bookstore.

When you zoom out in the darkroom, the image is processed using a downscaled copy of the raw file (say, 1080p rather than 30MPx). If you are using modules that process a given pixel based on the properties of the pixels around it (e.g. diffuse or sharpen) then those modules will give a different output when given more pixels to work with (i.e. when zoomed in). For example, sharpening that is very strong when zoomed out will become much more subtle when zoomed in (and much closer to the final processed image). It wouldn’t surprise me if this affected picked colour values as well (I haven’t done any testing to verify).

In the next feature release of darktable it will be possible to turn on high quality processing in the darkroom. This will make processing take longer (at least initially) because it is processing the entire raw file (as if you were exporting) instead of just a downscaled version, but it will also mean that the chances of differences between zoom levels are decreased.

N.B. If you work on your images in pixelpipe order (applying modules lower in the pixelpipe first) some of those speed issues with HQ processing will hopefully be mitigated by caching of the lower order modules’ output. Don’t quote me on that though – I haven’t played with it much yet.

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Thank you @elstoc
This explains a lot. I can see that in lighttable zooming in/out progressively lightens or darkens the image.
It is one more reason to reach towards the bigger screen - while it is not immune to the behavior it is going to be less pronounced than the 2k screen.

I did open Color display not accurate when zoomed (out) · Issue #16494 · darktable-org/darktable · GitHub
If nothing else - at least it would provide a link between the 2 systems (github and pixls.us)

I had it set to fit the screen on a 43 inch monitor and 100%. There was no change. The letter B has patchy colors and I thought this may affect the reading a lot if the size of the reading patch shifted between zooms, so I used the letter C which had areas of smoother color. My numbers did not shift when I did readings and visually there was no change.

I had it set to fit the screen on a 43 inch monitor and 100%. There was no change. The letter B has patchy colors and I thought this may affect the reading a lot if the size of the reading patch shifted between zooms, so I used the letter C which had areas of smoother color. My numbers did not shift when I did readings and visually there was no change.

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I think this may have something to do with it.
I have access to 2 monitors - the main one is 27" 2k and the second 27" 4k
The 2k monitor exhibits the issue much easier than the 4k. To some extend - it is possible to resize DT to not use the full screen but a portion - say 1/4 then maneuver within it. Or change to lighttable view and maneuver the icons (or thumbnails) - between very small and very big. This of course would be just for testing purposes.

If that is not it - then likely your version already has high quality processing - what @elstoc and @priort are pointing to. If this is the case - then I will patiently wait for the next release.

I think it more about how it looks visually than the color. Same for me the color picker values don’t change. I’m not sure scaling the preview has the potential to change them…I also always draw a box and don’t make point measurements so maybe that helps but for sure you are going to see what Chris described. The raw image is several times the resolution of the monitor and that scaling esp say in the case of the very dark blue hues near black already will appear to darken when you zoom out. also zooming on the letters surrounds them with a light back ground and this to me creates a perceptually different environment to the zoomed out view where there are two instances of the tone eq altering brightness. Finally I looked at the image with no editing. Only brighten it up a bit and actually adding either filmic or sigmoid exaggerated the difference in the letters The C would seem darker if you left them off… So the zooming along with some tonal tweaks could increase the perceptual difference even if the color isn’t really changing

I have this option but I did not activate that option when doing the test. I just can not reproduce your issue.

This led to something good actually!
4.7.0+785~g241bf89f7e does not show the issue

I am too late to learn but to my pleasant surprise the development version is available in appimage

This gives me much more flexibility to test.
Thank you all!


Take a backup of your db and turn off xmp writing for the Dev version if you plan on going back.

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