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Video Editing (outline on the border)
Confirmed, NormalPublicKNOWN ISSUE

Description

System Information
Operating system: Windows-10 64 Bits
Graphics card: GeForce GTX 750 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.89

Blender Version
Broken: version: 2.93.0 Alpha, branch: master, commit date: 2021-03-22 17:02, hash: rB62987a6f9845
Worked: (newest version of Blender that worked as expected)

Short description of error
Some images with an alpha channel have grey outline when scaled up and different bicubic or bilinear interpolation is used.

Exact steps for others to reproduce the error
Issue is visible immediately after opening .blend file

Event Timeline

Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Needs Information from Developers.Tue, Apr 6, 3:49 PM

@Richard Antalik (ISS): is this expected behavior?

Problem here is that pixels that are out of white opaque area are transparent and black. You can check RGB channels with color sampler tool.
So when black and white pixels are interpolated during render, they are slightly grey and slightly transparent.
So technically this issue described is not a bug.

The only way to "fix" this would be to provide user control over interpolation so it can be set to none(nearest). Not sure whether this would be good solution (breaks philosophy of "should just work"). I would like to check with @Sergey Sharybin (sergey) what he thinks about this first.

The assumption regarding bicubic interpolation, is not correct. With transform effect strip the effect is the similar. Strip untitled.001 produces no image in your sample file. Path to image is incorrect.
During preview no interpolation(nearest) is used on transformed strips and during render bilinear interpolation is used.

Another issue is with text strip. Pixels are output as 8-bit associated alpha and VSE can't blend this format properly. It is definitely possible to improve this instance, but it has been working like this for ages so this isn't regression. But I would be fine with confirming that issue as bug and solving it when there is time to do so

@Sergey (SergeyA) can you please report issue with text strip separately and update this report so it focuses on one issue only?

I have updated description so it describes only one issue and created better example file.

Richard Antalik (ISS) changed the task status from Needs Information from Developers to Confirmed.Thu, Apr 8, 5:08 PM
Richard Antalik (ISS) changed the subtype of this task from "Report" to "Known Issue".

Classifying this as known issue as there is no easy solution that could be done as bugfix.

@Sergey (SergeyA), as workaround you can use Convert to Float option in Color panel on image strip, that will convert image to associated alpha, where this issue doesn't happen. This will reduce performance of the strip however.

Sergey (SergeyA) added a comment.EditedFri, Apr 9, 1:59 PM

A separate report has been generated for the problem with the outline around the white text strip https://developer.blender.org/T87337