blurred CMYK JPEGs when using color management

[axelrose]

Hello all,

I observe some unwanted blurring when I convert an image from RGB JPEG to CMYK JPEG.

This can be seen in screenshot taken from Photoshop, input upper left,
output lower left:

If I leave out color management or if I convert from one RGB profile
to another or if the image input is smaller all runs fine.
It doesn't make a difference whether I use QuantumDepth 16 or 32
of if I use littlecms or littlecms2

Code: Select all

 > convert -version
Version: ImageMagick 6.6.9-4 2011-04-14 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP OpenCL  

> otool -L `which convert`
/Users/ar/bin/convert:
	/tools/ImageMagick-6.6.9-4/lib/libMagickCore.4.dylib (compatibility version 5.0.0, current version 5.1.0)
	/tools/ImageMagick-6.6.9-4/lib/libMagickWand.4.dylib (compatibility version 5.0.0, current version 5.1.0)
	/tools/ImageMagick-6.6.9-4/lib/liblcms2.2.dylib (compatibility version 3.0.0, current version 3.1.0)
	/tools/ImageMagick-6.6.9-4/lib/libtiff.3.dylib (compatibility version 13.0.0, current version 13.4.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 125.2.1)
	/tools/ImageMagick-6.6.9-4/lib/libfreetype.6.dylib (compatibility version 13.0.0, current version 13.2.0)
	/tools/ImageMagick-6.6.9-4/lib/libjasper.1.dylib (compatibility version 2.0.0, current version 2.0.0)
	/tools/ImageMagick-6.6.9-4/lib/libjpeg.8.dylib (compatibility version 12.0.0, current version 12.0.0)
	/tools/ImageMagick-6.6.9-4/lib/libpng15.15.dylib (compatibility version 18.0.0, current version 18.0.0)
	/usr/lib/libbz2.1.0.dylib (compatibility version 1.0.0, current version 1.0.5)
	/tools/ImageMagick-6.6.9-4/lib/libxml2.2.dylib (compatibility version 10.0.0, current version 10.8.0)
	/tools/ImageMagick-6.6.9-4/lib/libiconv.2.dylib (compatibility version 8.0.0, current version 8.0.0)
	/tools/ImageMagick-6.6.9-4/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.5)
	/System/Library/Frameworks/OpenCL.framework/Versions/A/Libraries/libclparser.dylib (compatibility version 1.0.0, current version 1.0.0)

This is the script I used for testing:

Code: Select all

IN=sample.jpg
test -r $IN || (echo "not readable: '$IN'"; exit 1)

PROFPATH=/Users/me/iccprofiles
test -d $PROFPATH || (echo "not a dir: '$PROFPATH'"; exit 1)
RGBICC=$PROFPATH/AdobeRGB1998.icc
test -r $RGBICC || (echo "not readable: '$RGBICC'"; exit 1)
RGBICC2=$PROFPATH/eciRGB_v2.icc
test -r $RGBICC2 || (echo "not readable: '$RGBICC2'"; exit 1)

CMYKICC=$PROFPATH/SWOP2006_Coated5v2.icc
test -r $CMYKICC || (echo "not readable: '$CMYKICC'"; exit 1)
OUT1=$IN-no-icc.jpg
OUT2=$IN-cmyk-icc.jpg
OUT3=$IN-rgb-icc.jpg

rm -f $OUT1 $OUT2 $OUT3

# not using any color management
/tools/ImageMagick-6.6.9-4/bin/convert jpg:$IN -quality 100 -depth 8 $OUT1

# using ICC profiles to match from RGB to CMYK
/tools/ImageMagick-6.6.9-4/bin/convert jpg:$IN -quality 100  \
-profile $RGBICC -profile $CMYKICC -depth 8 $OUT2

# using ICC profiles to match from one RGB to another RGB

/tools/ImageMagick-6.6.9-4/bin/convert jpg:$IN -quality 100  \
-profile $RGBICC -profile $RGBICC2 -depth 8 $OUT3

file $OUT1 $OUT2 $OUT3

The input file "sample.jpg" is http://dl.dropbox.com/u/84530/IM/sample.jpg

Can anybody confirm if this is a bug?

Thanks, Axel.

[blueklein76]

I'm seeing the same thing when applying an ICC profile. When outputting as a JPEG the images turn crazy blurry, but if you save as a different file format they are fine. I guess this must be a bug.

[axelrose]

A cumbersome but possible workaround is to go from RGB JPEG to CMYK TIFF and from there to CMYK JPEG.

No blurring anymore.

[ccampbell]

Use identify to check the jpeg:subsampling-factor property. Subsampling values other than 1x1 are not valid for CMYK JPEGs and can result in this sort of blurring.

I would think ImageMagick should reset this when you convert an RGB JPEG to CMYK, but it doesn't seem to (at least in v.6.6..

[blueklein76]

This issue seems to have been resolved at version 6.8.2-4 with the change log entry listed as:

2013-02-02 6.8.2-4 Cristy - Do not subsample raw CMYK JPEG images (reference viewtopic.php?f=3&t=22731).