Rotate tool in 2.10 blurring layers

[rich2005]

Quote:..Again, new to this, so I have no idea if there are any other details needed to understand the situation.

Anti-aliasing (AA) Bitmap (raster) graphic editing applications use rectangular pixels to form the image. For non vertical / horizontal or curves semi-transparent pixels are used to give an impression of smoothness. When you use scaling or rotation then AA is introduced according to the operation. Most noticeable when there are horizontal or vertical lines which initially do not require AA.
(Edit: Also small graphics such as small text in a larger image, the graphic tends to get 'swamped' by the anti aliasing. The best way is make the text a path, rotate the path, and put the path back to a graphic. )

Quote: Each time I rotate a layer it becomes more blurred. The amount I rotate does not seem to affect how much it blurs.

Each rotation can introduce more AA but if you complete the adjustment before closing the tool , rotate or unified-transform that limits the interpolation to one operation. For scaling and rotating try and use the unified-transform tool for an all-in-one operation.

The applicable interpolation for rotating a large image, none or not much scaling are cubic or no-halo. I can not see much difference, I prefer no-halo but my choice. This a short comparison between the two finishing off with interpolation none, showing why you need AA. https://i.imgur.com/qzDuemy.mp4

[makeitwork101]

I understand that this an old thread, but I too noticed the blurring/degradation of sharp edges when using the rotate tool in GIMP 2, which wasn't an issue in prior versions when rotating a layer by 90° or 180°.

I've just started using GIMP 3, and was hoping that the issue would be resolved, but it hasn't.

Although it makes sense that, due to interpolation, degradation of square pixels is to be expected when rotating by angles other than 90° or 180°, it doesn't make sense that an older version of GIMP would be better at rotating squares than a newer version. To my knowledge GIMP has yet to provide a satisfactory solution, but if all you want is a simple 90° or 180° rotation, I have a clunky workaround.

It's been a while since I've used Windows but, like Linux, I'm sure it has a basic "Image Viewer" and I'm sure that viewer has a rotate option. When I want to rotate an image by 90° or 180°, I open it with system's viewer, rotate it and close the viewer. The viewer then asks me if I want to "save changes to image" and I select "save."

The image is then saved, at the new angle, and I see zero degradation of the sharp edges made of square pixels... see attached images.

It's far from perfect, and again, it only works when rotating by 90° or 180°, but I hope it helps.

           

[CmykStudent_]

makeitwork101: My guess is that we use to special-case 90 and 180 degree rotations, and now they all use the same transform process.

The current work is to create "less destructive" transforms, where we don't immediately apply the transform but use the matrix for rendering (until you do a destructive change like painting on the layer). This will allow you to re-rotate/scale/etc without losing quality. It's based off 3.2's link layer work, and a new contributor has already applied it to text transforms: Non-destructive geometric transforms for text layers (!2943) · Merge requests · GNOME / GIMP · GitLab