gimp and ICC color working spaces

Discussion in 'Darkroom Developing and Printing' started by Dale, Nov 14, 2012.

  1. Dale

    Dale Guest

    gimp has 2 use cases

    1) monitor proofing
    2) print proofing

    yet it only has RGB and CMYK choices for working spaces

    I don't know if Photoshop or other software has a CIE colorimetric
    choice for working space, but in order to measure and track color it
    would be a lot easier to have one

    I know there are issues like gamut differences and rendering intents

    but if you want to measure the colorimetry of the monitor or proof and
    match it to the print, you need to start with CIE, not RGB or CMYK,
    ideally CIECAM but ICC has not gone there yet as far as I know
    Dale, Nov 14, 2012
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  2. Am 14.11.2012 05:56, schrieb Dale:
    The gimp bug report and feature request list is here:"GIMP"
    Thomas Richter, Nov 14, 2012
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  3. There is no bug though.

    The "RGB" and "CMYK" labels are just that, labels for
    two selectable workspaces that the user can easily
    switch between.

    But the workspace assigned to either of those two labels
    can be
    1) virtually anything the system administrator
    has installed and made available, or
    2) anything the user chooses to install privately.

    Any user that wants to use a different workspace merely
    needs to download whatever it is and install it. In
    GIMP, select the Edit->Preferences->Color Management
    menu. Both the "RGB" and "CMYK" profile options have a
    selection box, and the last option in either box is to
    "Select color profile from disk". Once a profile has
    been selected it will then show up as one of the
    available options and choosing it will not require
    locating it again.

    Sources for such profiles include LCMS, Argyll, and others.
    Floyd L. Davidson, Nov 14, 2012
  4. Dale

    Dale Guest

    you are right, my post was not a bug report, I was trying to prompt a
    feature discussion

    RGB aand CMYK are sensitometric and densitrometric spaces respectively,
    and are linear withh with respect to light

    I was suggesting a colorimetric working space like CIELAB or CIELUV
    because delta E* is linear with just noticeable differences of the eye
    and can be measured with a colorimeter or spectrophotometer or
    Dale, Nov 15, 2012
  5. Dale

    Dale Guest

    CIECAM would be better, of course you have to pick a standard CAM
    (appearance) for the profile connection space to convert between CAMs

    the current ICC perceptual connection space uses an ideal print for the
    CAM, this is not ideal for transparent and translucent display materials
    or additive systems, they have a larger gamut than a print and you have
    to make up information when you render from the standard CAM (the print)
    to these gamuts, maybe you can have choices for the standard CAM
    Dale, Nov 15, 2012
  6. Dale

    Dale Guest

    did you say before that gimp's CMM was 8bit?

    8bit encompasses the visual range of colors, but processing, to meet
    Nyquist would be 16bit or higher

    I used to make color profiles and know that few have precision of 1 delta E*

    I also know there is little difference between good enough color and
    perfect color, and that some things are better off left to editing than
    Dale, Nov 15, 2012
  7. Am 15.11.2012 02:57, schrieb Dale:
    First, this is a *PROFILE* connection space. It is unrelated to
    *PERCEPTUAL* rendering. Once more!

    Second, it is *UNRELATED* to ideal printing. The PCS has nothing to do
    with printing, rendering intent, the material you print on or its

    Third, the PCS doesn't have a "gamut". XYZ is able to represent all
    colors, if you like to.
    Thomas Richter, Nov 15, 2012
  8. Am 15.11.2012 04:18, schrieb Dale:
    Yes, it's to my very knowledge .
    That's not a frequency, so it's not related to *Nyquist*. But yes,
    depending on the steep of the tone mapping curves, you might get banding
    (quantization artifacts) due to the limitation of the resolution.
    Thomas Richter, Nov 15, 2012
  9. Dale

    Dale Guest

    you are confusing the PCS with the CMM, the PCS does have rendering
    choices that you make on input and output profiles
    Dale, Nov 16, 2012
  10. Am 16.11.2012 01:59, schrieb Dale:
    *Sigh*, no I'm not confusing this. I've already written CMMs, if you
    care. The PCS does not have rendering choices in the same sense that the
    R^3 does not have vector choices. It is the CMM that can implement
    various rendering intents.
    Thomas Richter, Nov 16, 2012
  11. Dale

    Martin Leese Guest

    Dale is just a troll. Please stop feeding
    the trolls.
    Martin Leese, Nov 16, 2012
  12. Dale

    Dale Guest

    we kind of got off my original post, can gimp or do other osftwares have
    colorimetric working spaces like CIELAB, CIEXYZ, etc., as opposed to
    spaces like RGB and CMYK?
    Dale, Nov 17, 2012
  13. Dale

    Dale Guest

    a profile can be populated with 4 intents, perceptual relative to a
    print, maintain saturation, colorimetric and absolute colorimetric

    the PCS is instantiated to represent the intents and conversion spaces
    chosen or specified
    Dale, Nov 17, 2012
  14. Dale

    Dale Guest

    go to alt.usenet.kooks and recommend me for a kook award

    I haven't had one in years
    Dale, Nov 17, 2012
  15. Dale

    Dale Guest

    there IS a cabal
    Dale, Nov 17, 2012
  16. No, it's not, for the last time! An *ICC profile* includes a rendering
    intent. It *also* defines a profile connection space, but the profile
    connection space has no rendering intent.

    How often do I need to explain you that the PCS is just a common
    coordinate space to express colors both of the input and the display (or
    output) device?

    The ICC profile contains enough information to convert from the device
    color space to the PCS and back. It defines the type of the PCS, it also
    defines the rendering intent which, again, defines the peculiarities in
    how to interpret the coordinate transformation (or how or where to find
    it). But the PCS is nothing but the coordinate frame in which colors are
    expressed. It doesn't have an intent. If coordinate transformations
    could be done in infinite precision, and if we wouldn't care about
    practical implementation limits, the PCS would not even matter. We could
    pick XYZ for everything and express coordinates always in XYZ.

    The CMM is the piece of software that implements the coordinate
    transformation to and from the PCS. It implements the rendering, and by
    that also defines how to realize the rendering intent - it has some freedom.

    But why the heck don't you just download the specs from and
    read them yourselves?
    Thomas Richter, Nov 17, 2012
  17. Dale

    Dale Guest

    the profile intent choices define the PCS and instantiate it in the CMM
    Dale, Nov 18, 2012
  18. Am 18.11.2012 04:42, schrieb Dale:
    No, it doesn't.
    Thomas Richter, Nov 18, 2012
  19. Dale

    Dale Guest

    then how does the CMM connect intent choice on both the input and output
    Dale, Nov 20, 2012
  20. Why don't you just download the ICC specs from and study it?

    The ICC profile defines how to map the device colorspace to the PCS by
    including tables and/or parameters for the transformation.

    The PCS is constant, but depending on the ICC profile, more than one
    table/parameters exists how to implement the mapping. The CMM checks the
    rendering intent, and then picks table A, B or C that transforms the
    device colors to the PCS coordinates. The PCS stays always the same,
    typically XYZ. Despite this explicit dependency, the CMM may also
    (implicitly) make rendering-intent specific algorithmic choices, for
    example how to handle out-of-gammut colors or how to implement an
    adaption on the illumination source.

    Thomas Richter, Nov 21, 2012
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