Rotation changes the bit depth from 1bit to 8bit

[dma_k]

I have noticed that when I apply the rotation (Image → Rotate → Custom) to the 1bit (binary) image, it is converted to 8bit. That is unexpected. Is rotation not possible for binary data? It should be even more simpler

[DOS386]

I have noticed that when I apply the rotation (Image → Rotate → Custom) to the 1bit (binary) image, it is converted to 8bit.

Right, 8 bit greyscale.

That is unexpected. Is rotation not possible for binary data? It should be even more simpler

Rotation of binary pixels is possible, but not interpolation ("Smooth"). If interpolation is desired, the image must be "upgraded". There is still a flaw BTW, the image should be upgraded to 16 bit linear greyscale ... note that 8 bit linear greyscale is not feasible, and doing linear interpolation on 8 bit non-linear brightness is incorrect and causes unnecessary quality and brightness loss.

See http://newsgroup.xnview.com/viewtopic.php?t=19897 why

[dma_k]

Rotation of binary pixels is possible, but not interpolation ("Smooth"). If interpolation is desired, the image must be "upgraded". There is still a flaw BTW, the image should be upgraded to 16 bit linear greyscale ... note that 8 bit linear greyscale is not feasible, and doing linear interpolation on 8 bit non-linear brightness is incorrect and causes unnecessary quality and brightness loss.

See http://newsgroup.xnview.com/viewtopic.php?t=19897 why

I am not sure, what you actually mean for interpolation ("smoothing") during the rotation... Could you be more verbose?

In any case, the image can be automatically converted back to binary after the rotation, right? So what do you think: the current behaviour is OK, or it can/should be improved?

[DOS386]

not sure, what you actually mean for interpolation ("smoothing") during the rotation... Could you be more verbose?

Try to rotate (by 30 deg maybe) with and without "Smooth" ... check the results.

In any case, the image can be automatically converted back to binary after the rotation, right?

Sure, but this is a lossy conversion and might be usually a bad idea, so it's OFF for now ...

So what do you think: the current behaviour is OK, or it can/should be improved?

The point where I see an urgent need for improvement is to auto convert to 16bppc (thus 64 bpp total for RGBA) linear whenever necessary to do things right (zoom (except NN)), blur, rotate (except NN AKA "non-smooth"), trapez/barrel corrections (not implemented yet), ...). I see no point to keep 1 bpp binary on rotate (except 90 deg).

[XnTriq]

I am not sure, what you actually mean for interpolation ("smoothing") during the rotation... Could you be more verbose?

• Photography.com: Aliasing & Antialiasing
• Martin Vogel: Antialiasing
• Webopedia: antialiasing
• Wikipedia: Anti-aliasing

• Shawn Hargreaves: Texture aliasing

Could you post an example, dma_k?

[dma_k]

Try to rotate (by 30 deg maybe) with and without "Smooth" ... check the results.

I have made a try for this image. I personally see no results for rotation without and with smoothing:

In any case, the image can be automatically converted back to binary after the rotation, right?

Sure, but this is a lossy conversion and might be usually a bad idea, so it's OFF for now ...

Perhaps that could be a preference option ([x] Stay in the same color depth with rotating / zooming the image) or automatically stay in binary when smoothing is OFF?

XnTriq, thank you for links. I understand the principle of anliasing, but for me it makes sense only for non-binary images.

[xnview]

Yes, to be able to make smooth rotation

[DOS386]

I have made a try for http://dead???files.com/files/7wot0u1d2 this image. I personally see no results for rotation without and with smoothing

Link is dead but rotate works for me, I do get results and they are different. Look better or count colours

[XnTriq]

I personally see no results for rotation without and with smoothing:

That's because smoothing is only applied to the preview thumbnail, even if Apply to image is activated
You have to confirm with OK to see the difference.

• 
  [ z00m ]

XnTriq, thank you for links. I understand the principle of anliasing, but for me it makes sense only for non-binary images.

Not all binary images are created equal
Please make a few experiments with vision3d05.gif (from Vision3D User Manual).

Perhaps that could be a preference option ([x] Stay in the same color depth with rotating / zooming the image) or automatically stay in binary when smoothing is OFF?

In my tests (30° clockwise w/o smoothing) the color depth of Scan001.TIF was't increased

[dma_k]

In my tests (30° clockwise w/o smoothing) the color depth of Scan001.TIF was't increased

Thank you! I have overlooked that if smoothing is off, then the color depth is not changing.

SOLVED

[Jaff]

Not quite on topic: preview with smoth checked on non 90 degrees rotation show in preview (applied to image) 1 bit image but only when is pressed [OK] button is converted to 8 bit and show real rotated and smoothed image