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Gaussian Blur Mistreats Alpha


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#1 pyrochild

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Posted 05 April 2010 - 07:15 AM

Repro 1:
  • Create a new image
  • Fill the image with half-transparent white
  • Run Gaussian Blur at default radius; the whole image should noticeably darken
  • The image is noticeably darker. Check the color channels; they're definitely not white anymore
Before|After
Posted ImagePosted Image

Repro 2:
  • Create a new image
  • Delete a section in the middle of the image
  • Run Gaussian Blur at default radius
  • Repeat with Ctrl+F until you see edges darkening; should be noticeable on the 5th time, and painful on the 6th
Before|After
Posted ImagePosted Image

Repro 3:
  • Open an image
  • Use a transparency gradient across the whole image
  • Run Gaussian Blur at default radius
  • There should now be noticeable banding across the gradient.
Before|After
Posted ImagePosted Image
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#2 Rick Brewster

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Posted 05 April 2010 - 07:31 AM

Do you have a version of the 'before' image with alpha channel?
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#3 pyrochild

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Posted 05 April 2010 - 07:42 AM

Do you have a version of the 'before' image with alpha channel?


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#4 Rick Brewster

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Posted 05 April 2010 - 08:03 AM

Ok I've filed a bug targeted for v4.0.
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#5 Rick Brewster

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Posted 30 March 2012 - 01:49 AM

This is fixed for 4.0, thanks to Ed Harvey.
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#6 pyrochild

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Posted 01 April 2012 - 12:56 AM

Awesome, I had almost forgotten about this :P
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#7 barbieq25

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Posted 01 April 2012 - 09:20 AM

Pyro, I had no idea this was in fact a bug. I knew the outcome would be bad if I tried it, so I knew that I could not run GB with certain things. Thanks for pointing this out & for Ed Harvey & Rick fixing it.
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