"Swipe" feature on PNG diff seems to show differences in partially-transparent pixels #17735
Description
The problem
When viewing a change in a PNG file in Github for Desktop and using the Swipe tab, partially-transparent pixels sometimes "stack", resulting in darker opacity on one side of the swipe. This can confuse users as it appears as if portions of the image have changed when they really haven't.
Release version
3.3.5 (x64)
Operating system
Windows 10 Home 22H2 build 19045.3570
Steps to reproduce the behavior
- Create a repository
- Commit a PNG (included here)
- Make a change to a portion of the PNG
- Commit the change
- View the diff
- Select the Swipe tab
- Swipe left/right
- Look closely at some of the edges of the art
Observe: Portions of the partially-transparent art "stack", increasing opacity even though no changes have been made
Expected: Portions of the PNG which have not changed should not show any differences on the left/right side of the swipe.
Log files
No response
Screenshots
It is subtle, but observe the portion of the top part of the gun with the blue coloring. I recommend opening this PNG in a separate browser window, and zooming in.
To make it easier to see, I have also created a zoomed-in screenshot of the problem. The dotted line shows where the Swipe boundary is located. Both the top and bottom gun show the problem, but I only included the dotted line across the top gun so that you can see the boundary clearly on the bottom gun (where the arrow points).
Additional context
No response