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Problem Converting RGB jpg to CMYK

https://imagemagick.com/discourse-server/viewtopic.php?t=12639

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Problem Converting RGB jpg to CMYK

Posted: 2008-12-06T21:55:30-07:00
by jamesls77
Hello,

I'm having a problem sRGB jpgs to CMYK colorspace for printing. The resulting images end up with some very weird things happening to resolution and quality.

Here's the command I've been trying:

Code: Select all

mogrify -format jpg -profile sRGB.icm -profile CMYKProfile.icc c:\images\*.jpg
The really strange thing is that when I run the same command and create a new tiff instead of a jpeg, everything looks great:

Code: Select all

mogrify -format tif -profile sRGB.icm -profile CMYKProfile.icc c:\images\*.jpg
Now what's really strange is when I convert that resulting tif from the second example to jpg, the problem shows up again.

Any suggestions?

Re: Problem Converting RGB jpg to CMYK

Posted: 2008-12-06T22:49:05-07:00
by magick
Convert one image and identify it:
  • identify -verbose image.jpg
Verify its in the CMYK colorspace. Also verify that the compression quality is reasonable-- 75 or above. Finally take a look at the JPEG sampling factor. It should be something reasonable like 1x1 or 2x2.

Re: Problem Converting RGB jpg to CMYK

Posted: 2008-12-06T23:25:26-07:00
by jamesls77
An addendum... I've managed to successfully convert to the CMYK colourspace in IM. I've verified this in Photoshop and now in IM... just the result is funny.

Here's a snip from the identify operation:

Geometry: 3645x3525+0+0
Resolution: 600x600
Print size: 6.075x5.875
Units: PixelsPerInch
Type: ColorSeparation
Endianess: Undefined
Colorspace: CMYK

Compression: JPEG
Quality: 85
Orientation: Undefined
Properties:
create-date: 2008-12-06T03:36:09-05:00
jpeg:colorspace: 4
jpeg:sampling-factor: 2x2,1x1,1x1,1x1
modify-date: 2008-12-06T23:23:48-05:00
signature: 48cba2a5557e59e8904444dc9a41085063db368a76c258b19d579780ae66e20e
Profiles:
Profile-icc: 1657032 bytes
Indigo 250 Ink v2.0 - Hewlett-Packard

It is in CMYK color space with the correct profile attached and only one profile is attached. JPEG quality is 85 and it's at the proper resolution. I'm not sure what the sampling factor means.
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