Artifact in Rotation Transformation
Environment/Versions
- GIMP version:
- Package: 2.10.24, official release (from gimp.org)
- tested on bf1b405a with similar results
- Operating System: Windows 10 21H1
Description of the bug
After rotation transformation, there will be a lot of artifact (or noise) that make the boarder between two colors appear very jagged
Reproduction
The easiest way to see it is to do it on a picture with high contrast (e.g. black on white), and with a lot of straight/smooth curves, such as geometry shapes.
Now, this is with the base color rotation (e.g. without different-color anti-aliasing). It may be more difficult to observe when Gimp does anti-aliasing upon finishing transformation. To remove the anti-aliasing, you can fill the background (white areas) with the color of the anti-alias filler (typically some sort of grey. color pick them) and then fill them back to white when done.
Reproduction steps:
- Load a picture with high contrast (b&w for illustration purposes work best)
- Rotate The picture in Gimp
- zoom in
On a colored picture where similar colors meet it might be very hard to notice. But on a picture meant for illustration purposes, where clean lines are very important, this "problem" is very easily seen and is quite hard to correct (unless sacrificing sharpness by blurring the picture)
Additional information
If you insert a "right triangle" (or a line 30 degrees from vertical) in MS paint, save the picture in 16 color bmp format (so the anti-aliasing is easier to spot), open it in gimp and rotate it -15 degrees (so it form a -45 line), there are regions where there are extra pixels (of both erase and fill). Also, if you look at the line that were drawn at 60 degrees, there are also extra pixels along the way.