0 Replies Latest reply on Mar 5, 2009 4:56 AM by Gernot Hoffmann

    CMYK encoding for printer targets

    Gernot Hoffmann Level 3
      For instance the target ECI2002CMYKi1(A3)_1_2.tif
      contains - according to the reference file - CMYK
      numbers by steps of 10, some values by steps of 5
      and some single values 3 and 7. The maximum is 100.
      All tests by CS2.

      Let's consider for a patch with one value 70.0 the
      indicated numbers:
      Photoshop 8bpc: 70%
      Photoshop 16bpc: 70%
      Photoshop 32bpc: 0.698
      Illustrator: 0.698

      0.70*255 = 178.5
      Wrong rounding 178
      178/255 = 0.698

      Aha, it's a problem of mapping 0..100 to 0..255
      and eventually of wrong rounding.
      This leads to the conclusion, that CMYK values
      in the TIFF should be defined as integer numbers
      0..255 and that the reference file should contain
      decimal numbers with sufficient accuracy in this
      format: ###.## .

      It's perhaps not really essential for the accuracy
      of a calibration, but why should everything be based
      on a wrong concept ?

      By the way:
      I think I've solved the problem, how to modify targets
      for a guaranteed inklimit, if this should be still
      interesting.

      Best regards --Gernot Hoffmann