High-quality arbitrary-angle rotation

[stephan_g]

Currently XnView supports two quality modes of rotation by arbitrary (custom) angles:
1. Crappy - nearest-neighbor interpolation.
2. OK - with "smoothing" checkbox enabled, does bilinear interpolation or somesuch.

What about a really high-quality option that uses e.g. the excellent Lanczos algorithm already employed for resizing? The "Smoothing" checkbox may need to mutate into a 3-state quality (vs. speed) slider, but other than that the necessary code should basically already be there.

[XnTriq]

This is a very good idea, no doubt.
For resizing photographic images I never use any other programs.

[Troken]

I agree, the quality of the arbitary rotate could be better. If Lanczos could be an option it would be splendid.

[Troken]

Any news on this matter? I stongly belive this should be a feature soon. Rotation quality should be much better, since XnView otherwise is such a competent piece of software.

[DOS386]

stephan_g wrote (almost 1 year ago):

Currently XnView supports two quality modes of rotation by arbitrary (custom) angles:
1. Crappy - nearest-neighbor interpolation.

Actually it's a nearest-neighbor pick, no interpolation at all.

2. OK - with "smoothing" checkbox enabled, does bilinear interpolation or somesuch.
What about a really high-quality option that uses e.g. the excellent Lanczos algorithm already employed for resizing?

Troken wrote:

Any news on this matter? I stongly belive this should be a feature soon. Rotation quality should be much better, since XnView otherwise is such a competent piece

I highly support this.

Also I did test ( download results - 150 KiB ) :

- Bilinear zoom is only marginally worse than Lanczos (at least in this test)
- Rotate "smooth" is very ugly compared to Bilinear zoom, and I have no idea why
- Zoom bilinear vs zoom Lanczos results in a diagonal drift ... seems to be a bug
- The "smooth" thingie does not work at all in NCONVERT:



- "rotate_flag smooth" is "recognized" but ignored ... ROT0.PNG and ROT1.PNG are identical and both use NN pick

- "rotate_flag smiley" complains about bad resize flag

- Still visible OS/2-bug, DOS/32A junk not visible because I had patched it off

Thus the IMHO only possible solution:

- Make all sampling algos available for rotate also (GFL + NC + XN)
- Delete the "rotate_flag smooth" completely
- Rename "rtype" into "samp" and use it for both resize and rotate
- Update the help: quick=NN ???

Code: Select all

  -rtype            : Type of resampling

Code: Select all

  -samp             : Sampling algorithm for resize and rotate
              quick (nearest neighbor pick)
              linear (bi-linear)
              hermite  
              gaussian
              bell     
              bspline  
              mitchell 
              lanczos (Lanczos 3) 

[xnview]

Use -rotate 1 -rotate_flag smooth

[DOS386]

Use -rotate 1 -rotate_flag smooth

COOL ... it helps, thanks so my "does not work at all in NCONVERT" was wrong, OTOH most of the points of my post and this thread are still valid, however , most notably the syntax inconsistence and availability of Lanczos sampling algo for rotating. Also, I have some further ideas about possible improvements of NCONVERT syntax - should I post them ?

[dandv]

+1 for high-quality rotation, and please make "smooth" checked by default in the Rotation dialog box. The first time I used Rotation in XnView, I thought "OK, this is probably be as good as in Irfan", and after saving the image, I noticed the jigsaw effect

[Troken]

... and please make "smooth" checked by default in the Rotation dialog box. ...

Good idea! I support this suggestion.