Blur in compositor produces artifacts #39307

Closed
opened 2014-03-21 00:38:49 +01:00 by Filip Sauer · 14 comments

System Information
Operating system and graphics card
Win 7 64bit, ATI Radeon HD 5700 series

Blender Version
Broken: official 2.70, but was present in older builds too

Short description of error
Certain values of blur produce artifacts.

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
Just render the attached file and see the borders of the blurred area where it gets sharply cropped. This only happens with some values of blur. Also visible on attached image.
blurBUG.jpg

blurBUG.blend

**System Information** Operating system and graphics card Win 7 64bit, ATI Radeon HD 5700 series **Blender Version** Broken: official 2.70, but was present in older builds too **Short description of error** Certain values of blur produce artifacts. **Exact steps for others to reproduce the error** Based on a (as simple as possible) attached .blend file with minimum amount of steps Just render the attached file and see the borders of the blurred area where it gets sharply cropped. This only happens with some values of blur. Also visible on attached image. ![blurBUG.jpg](https://archive.blender.org/developer/F82010/blurBUG.jpg) [blurBUG.blend](https://archive.blender.org/developer/F82009/blurBUG.blend)
Author

Changed status to: 'Open'

Changed status to: 'Open'
Author

Added subscriber: @cdog

Added subscriber: @cdog
Lukas Tönne was assigned by Sergey Sharybin 2014-03-21 09:47:08 +01:00

Added subscribers: @LukasTonne, @Sergey

Added subscribers: @LukasTonne, @Sergey

@LukasTonne, mind looking into this report? :)

@LukasTonne, mind looking into this report? :)
Lukas Tönne removed their assignment 2014-03-21 10:19:33 +01:00
Jeroen Bakker was assigned by Lukas Tönne 2014-03-21 10:19:33 +01:00
Member

Added subscriber: @Jeroen-Bakker

Added subscriber: @Jeroen-Bakker
Member

@Jeroen-Bakker assigning to you, seems to be combination of opencl and maybe area-of-interested once more ...

NOTE: You may have to bump up the brightness on this image, i couldn't see the error at first.

@Jeroen-Bakker assigning to you, seems to be combination of opencl and maybe area-of-interested once more ... NOTE: You may have to bump up the brightness on this image, i couldn't see the error at first.

Added subscriber: @ignatz

Added subscriber: @ignatz

I believe that the artifacts that cdog is referring to are more clearly seen in the attached rework of his image.

I bumped the gamma from 1.00 up to something like 1.85 and there is clearly some 'garbage' on the edges of the blurred cube.

blurBUG-2.png

I believe that the artifacts that cdog is referring to are more clearly seen in the attached rework of his image. I bumped the gamma from 1.00 up to something like 1.85 and there is clearly some 'garbage' on the edges of the blurred cube. ![blurBUG-2.png](https://archive.blender.org/developer/F82060/blurBUG-2.png)
Author

Yes, that's it. Sorry - I guess my screen is too bright, so I could see it well :)
I wonder, though, if the part where it gets narrower should be there at all (when blurring in X direction only). I would expect the correct result to look like this.
expected.jpg

Yes, that's it. Sorry - I guess my screen is too bright, so I could see it well :) I wonder, though, if the part where it gets narrower should be there at all (when blurring in X direction only). I would expect the correct result to look like this. ![expected.jpg](https://archive.blender.org/developer/F82065/expected.jpg)

Added subscriber: @sebastian_k

Added subscriber: @sebastian_k

Yeah, confirmed as well. Interestingly it only happens with 256x256. If I set chunks to anything else. for example 32x32, it looks fine.

Yeah, confirmed as well. Interestingly it only happens with 256x256. If I set chunks to anything else. for example 32x32, it looks fine.
Member

The issue also happens when the chunks are on different size:
for chunks 64x64 the bug happens when the X is set lower than 64
etc.
so will check the tile dependacy of the fast gaussian blur

The issue also happens when the chunks are on different size: for chunks 64x64 the bug happens when the X is set lower than 64 etc. so will check the tile dependacy of the fast gaussian blur
Member

Changed status from 'Open' to: 'Resolved'

Changed status from 'Open' to: 'Resolved'
Member

Fixed in d9557d01bd

"The fast gaussian blur is not an accurate formula. When deciding
which tiles are selected for input there was always a constant for correcting

  the accuracy.
  
  It seems that the constant was not enough and has been adjusted. (2 => 3)."

Strange enough this was issue was not been raised before. There might be other 'settings' that this issue still happens. If so we need to increase the value again.

Fixed in d9557d01bd2f724bc8995c916f91d66ef85d2faa "The fast gaussian blur is not an accurate formula. When deciding which tiles are selected for input there was always a constant for correcting ``` the accuracy. It seems that the constant was not enough and has been adjusted. (2 => 3)." ``` Strange enough this was issue was not been raised before. There might be other 'settings' that this issue still happens. If so we need to increase the value again.
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Reference: blender/blender#39307
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