Wrong colors when generate a CMYK PDF from CMYK Jpeg.

[SergioO]

Hi. I'm using IM command line version 6.3.3 on a RedHat Linux server. My target is to produce a PDF file to send to the printer company. The printer company just take two channels of this File, the cyan and the black channel, so, they disregard any other color information present in the PDF.

I created a CMYK jpeg file with information in the two channels I'm interested (C and K) I can check that the colors are ok using the identify -verbose command.

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Image: ./Page_2C.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Class: DirectClass
  Geometry: 2549x3300+0+0
  Type: ColorSeparation
  Endianess: Undefined
  Colorspace: CMYK
  Channel depth:
    Cyan: 8-bit
    Magenta: 1-bit
    Yellow: 1-bit
    Black: 8-bit
  Channel statistics:
    Cyan:
      Min: 0 (0)
      Max: 255 (1)
      Mean: 12.7423 (0.0499698)
      Standard deviation: 48.7892 (0.19133)
    Magenta:
      Min: 0 (0)
      Max: 0 (0)
      Mean: 0 (0)
      Standard deviation: 0 (0)
    Yellow:
      Min: 0 (0)
      Max: 0 (0)
      Mean: 0 (0)
      Standard deviation: 0 (0)
    Black:
      Min: 0 (0)
      Max: 255 (1)
      Mean: 64.6772 (0.253636)
      Standard deviation: 84.3338 (0.330721)
  Total ink density: 176%

Then I want to use this file to create the CMYK PDF to send to the printer company, so I run this command:

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convert -density 300 CMYK.jpg -colorspace CMYK CMYK.pdf

The problem is that the Black channel information on the jpeg doesn't get reproduced on the PDF, look at the response of the identify command of the PDF file:

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Format: PDF (Portable Document Format)
  Class: DirectClass
  Geometry: 2549x3300+0+0
  Type: ColorSeparation
  Endianess: Undefined
  Colorspace: CMYK
  Channel depth:
    Cyan: 8-bit
    Magenta: 8-bit
    Yellow: 8-bit
    Black: 1-bit
  Channel statistics:
    Cyan:
      Min: 0 (0)
      Max: 255 (1)
      Mean: 3.95436 (0.0155073)
      Standard deviation: 25.931 (0.10169)
    Magenta:
      Min: 0 (0)
      Max: 255 (1)
      Mean: 3.53907 (0.0138787)
      Standard deviation: 23.3805 (0.0916883)
    Yellow:
      Min: 0 (0)
      Max: 255 (1)
      Mean: 3.45841 (0.0135624)
      Standard deviation: 23.1124 (0.0906369)
    Black:
      Min: 0 (0)
      Max: 0 (0)
      Mean: 0 (0)
      Standard deviation: 0 (0)
  Total ink density: 300%

The Black channel of the PDF file now is empty and, for some reason, I have information on the Magenta and Yellow channels, although the appearance of the pictures remains similar, I cannot use this file for the printer company because they don't use the magenta and yellow channels.

I want to convert the CMYK JPG to the CMYK PDF keeping the colors in the same channels. What can be done to solve that?

Thank you.

[magick]

We tried your command with the latest ImageMagick release 6.3.4-10 and it produces the desired result (i.e. a reasonable black channel).

[SergioO]

That's right, I downloaded and compiled the 6.3.4 version. The resulting PDF seems OK. I'll submit the file to the printer company and check their answer. I'll post again if any problem. Thank you very much for your help.

[SergioO]

The printer company processed the file just fine. Thank you again.