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Color Balance Adjustment Layer "escapes" its mask when parameters are extreme
Closed, ResolvedPublicBUG


System Information
Operating system: Mac OS X 10.13.6 (17G10021)
Graphics card: Intel Iris Graphics 6100
Blender Version
Broken: First encountered in 2.82, also tested in "Version 2.82a (2.82a 2020-03-12)", also tested in a nightly, the download page called it "Blender 2.83 Alpha, April 04, 23:21:36 - 505a19ed75b2, macOS 64 bit, 193.81MB". Bug reproduced the same in all 3.

Short description of error

I have a Color Balance Adjustment Layer on my video. The adjustment layer has a Mask confining it to a small rectangle in the center. However if I turn the amount of color balance up to be "too extreme", the adjustment escapes the mask. Most of the image is unaffected when this happens, but a narrow range of colors in the entire image (including outside the mask) *is* affected by the extreme color balance. It looks as if a "magic wand" tool were applied.

  • Reproduce using example file **

Download and run this example file. It should have a single frozen image packed into the file, some text captions, and then about 27 seconds in an adjustment layer is added masked to a small rectangle in the center of the screen.

Open this and start playing. You will see the effect about 27 seconds in and it will look like this:

The rectangle in the center which is bright black and green is exactly as expected. The purple bleeding all over the rest of the screen is a bug.

My EXPECTED BEHAVIOR is when a mask is applied to a color adjustment, the image outside the mask does not change.

AN INTERESTING OBSERVATION: If you click Adjustment 1, then look in the Modifiers tab, then scroll down to Gamma, if you change the Gamma you will find that as you drag it around the bug changes in interesting ways. The bug does not express at all if the Gamma is at anything less than maximum intensity. If you change the hue of the gamma, the purple areas flicker and change to cyan or other colors.

  • My original steps to reproduce **

I made a video file based on File->New->Video Editing and imported audio and video. I applied an Adjustment Layer to the video in my file. There were some dim LED lights visible in the video and I wanted them to pop, so I added a Color Balance adjustment layer to ramp the contrast up as far as it goes. However this made other objects in the scene appear weird, so I limited the adjustment layer to a mask using the instructions in this video : I Render Imaged one frame, drew the rectangle I wanted, gave that rectangle a mask name, then applied the mask by name back in the Color Balance Adjustment Layer pane. I immediately found that this was breaking colors outside the mask, turning parts of my hand purple.

Afterward I discovered that I could replace the Color Balance adjustment layer with a Curves adjustment layer and I did NOT reproduce the problem using Curves. So I am not blocked on this bug (because in my real project I am using curves now), but it is a bug.

The example file is a copy of my WIP video file but I took out the video and audio and replaced it with a still image so it would be easier to download.

Event Timeline

Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.Apr 12 2020, 6:25 PM
Richard Antalik (ISS) changed the subtype of this task from "Report" to "Bug".

@Richard Antalik (ISS), since you've got patch, considering you've picked up the task to work on.

P.S. See the feedback in the patch, it should be simple to finalize it and commit! :)