Add border of 'cmyk(0,0,0,255)' is about 5 times slower than

[futuramedium]

Adding border of 'cmyk(0,0,0,255)' is about 5 times slower than 'cmyk(255,0,0,0)'

I process CMYK images appr. 5600x3600, and try to add black border with

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convert  -colorspace CMYK -depth 8 -density 150 -compress Zip -border 5 -bordercolor 'cmyk(0,0,0,255)' -debug 'All' -monitor 1.tif 2.tif

It takes 75 sec on my machine. Then I try

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convert  -colorspace CMYK -depth 8 -density 150 -compress Zip -border 5 -bordercolor 'cmyk(255,0,0,0)' -debug 'All' -monitor 1.tif 2.tif

and it finishes in only 15 seconds! Why?

The same difference (depending on border color) is when I add border with

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montage -colorspace CMYK -depth 8 -density 150 -compress Zip -geometry +5+5 -background 'cmyk(0,0,0,255)' -debug 'All' -monitor 1.tif 2.tif

and

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montage -colorspace CMYK -depth 8 -density 150 -compress Zip -geometry +5+5 -background 'cmyk(255,0,0,0)' -debug 'All' -monitor 1.tif 2.tif

version is 6.3.5.6

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xpress@computer:~$ convert -version
Version: ImageMagick 6.3.5 08/15/07 Q8 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2007 ImageMagick Studio LLC

[futuramedium]

well, i found that changing 'cmyk(0,0,0,255)' to 'cmyk(0,0,0,254)' restores speed to normal

'254' suites my purpouses and problem may be considered solved. But bug (isn't it a bug?) still exists, beware

[magick]

Use this command to get fast proper results:

• convert 1.tif -colorspace CMYK -bordercolor 'cmyk(0,0,0,225)' -border 5 -depth 8 -density 150 -compress Zip 2.tif

[futuramedium]

i see
thank you!