Gradient masks - any recent changes?

[gnidam]

Hi all,

until version (Linux)

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Version: ImageMagick 6.8.9-10 Q16 x86_64 2015-03-03 
Features: DPC Modules OpenMP

using a gradient mask this way:

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convert -depth 16 -size 1x4096 gradient: -flip -write mpr:gradient \
    \( mpr:gradient -sigmoidal-contrast 8x50% \) \( mpr:gradient \) \
    -composite imtest.tif

worked just fine, leading to (graph from gradient):

With later versions

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Version: ImageMagick 6.9.1-0 Q16 x86_64 2015-03-29 
Features: DPC Modules OpenMP

however, i just get (again the graph):

So the gradient mask seems not to be applied.
I couldn't find anything in the changelog why that happens... so have I been doing this wrong all along or is it a bug?

Thx,
Martin

[fmw42]

I would have to agree. Assuming you are using a 3 image composite and the last is the mask, then all three of these show the same results for me on IM 6.9.1.0 Q16 Mac OSX, which is identical to just the sigmoidal-contrast image.

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convert -size 1x256 gradient: -rotate 90 -write mpr:gradient \
\( mpr:gradient -sigmoidal-contrast 8x50% \) \( mpr:gradient \) \
-compose over -composite miff:- | profile -f 1 - show:

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convert -size 1x256 gradient: -rotate 90 \
\( -clone 0 -sigmoidal-contrast 8x50% \) \( -clone 0 \) \
-compose over -composite miff:- | profile -f 1 - show:

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convert -size 1x256 gradient: -rotate 90 -sigmoidal-contrast 8x50% miff:- | profile -f 1 - show:

whereas swapping the first two images leads to a linear profile

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[code]convert -size 1x256 gradient: -rotate 90 -write mpr:gradient \
\( mpr:gradient -sigmoidal-contrast 8x50% \) +swap \( mpr:gradient \) \
-compose over -composite miff:- | profile -f 1 - show:

[/code]


That would indicate to me that the masked composite is not working correctly.

[gnidam]

Btw, thresholding the composite mask works as expected:

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convert -size 1x265 gradient: -flip \
    \( -clone 0 -sigmoidal-contrast 8x50% \) \
    \( -clone 0 -threshold 50% \) \
    -composite imtest3.tif

...so midtones in the mask don't have any effect, just maxval give full opacity?

[snibgo]

I agree there is a bug. It is a weird one. Comparing v6.9.0-0 with 6.9.1-0, Windows BAT syntax:

These give the same correct outputs:

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%IMG690%convert ^
  -size 1x4096 ^
  xc:black ^
  ( xc:white ) ^
  ( gradient:black-white ) ^
  -compose Over -composite imtest4.tif

%IMG691%convert ^
  -size 1x4096 ^
  xc:black ^
  ( xc:white ) ^
  ( gradient:black-white ) ^
  -compose Over -composite imtest4a.tif

If we change "xc:black" to "gradient:black-black" ...

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%IMG690%convert ^
  -size 1x4096 ^
  gradient:black-black ^
  ( xc:white ) ^
  ( gradient:black-white ) ^
  -compose Over -composite imtest5.tif

%IMG691%convert ^
  -size 1x4096 ^
  gradient:black-black ^
  ( xc:white ) ^
  ( gradient:black-white ) ^
  -compose Over -composite imtest5a.tif

... the 691 output is entirely white.

[magick]

We can reproduce the problem you posted and have a patch in ImageMagick 6.9.1-1 Beta within the next few days. Thanks.