Bug 691462 - Image much darker after icc_work merge - part deux
Summary: Image much darker after icc_work merge - part deux
Status: RESOLVED FIXED
Alias: None
Product: Ghostscript
Classification: Unclassified
Component: Color (show other bugs)
Version: master
Hardware: PC All
: P4 normal
Assignee: Michael Vrhel
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2010-07-15 15:59 UTC by Marcos H. Woehrmann
Modified: 2011-08-15 02:43 UTC (History)
1 user (show)

See Also:
Customer:
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Attachments
screenshot.png (64.80 KB, image/png)
2010-07-15 15:59 UTC, Marcos H. Woehrmann
Details
screenshot2.png (63.80 KB, image/png)
2010-07-15 16:10 UTC, Marcos H. Woehrmann
Details

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Description Marcos H. Woehrmann 2010-07-15 15:59:02 UTC
Converting the file gray-to-cmyk-with-transfer.ps (which can be found in tests_private/compare_files) with head (r11508) to a 1 bit cmyk format (pkmraw) results in a very dark image; r11305 and earlier versions produe a much lighter image.  Converting to a continuous tone format (ppmraw) with either r11305 or r11508 results in an image which is close in appearance to r11305.  See the attached screenshot.

This does not appear to be the same issue as Bug 691444, since that issue was fixed in r11505 and this issues continues to occur in r11508. 

Example command line:

  bin/gs -sDEVICE=pkmraw -o test.pkm -r72 ./gray-to-cmyk-with-transfer.ps
Comment 1 Marcos H. Woehrmann 2010-07-15 15:59:37 UTC
Created attachment 6489 [details]
screenshot.png
Comment 2 Marcos H. Woehrmann 2010-07-15 16:10:31 UTC
Created attachment 6490 [details]
screenshot2.png

As a further test that the r11305 pkmraw image is closer to the ppmraw image than the head pkmraw image I generated 600 DPI pkmraw images for both versions and then scaled them down to 200 x 200 pixels by using linear interpolation, see attached.
Comment 3 Michael Vrhel 2010-07-30 16:46:41 UTC
A look at going to tiff32nc and it also occurs there.  Apparently I must not be using the transfer function when we are going to CMYK.  This should be easy to track down.
Comment 4 Michael Vrhel 2010-07-30 17:49:29 UTC
OK.  So the transfer curves ARE getting applied.  This is what is creating the negative of the image.  The issue is that we are doing a different color conversion from the gray image to a cmyk output color space due to our default ICC profiles. Prior to the ICC merge the code used the default BG/UCR curves and a 1-X type model for this mapping.  Running with -dUseCIEColor in 8.71 you will see something even darker than what is created with the ICC code.  What I probably need to do is to create a set of ICC profiles that give similar mappings to what the old PS rendering gave without -dUseCIEColor.   If someone desired this type of mapping they could swap in those profiles.