color reference conversions and use cases

Discussion in 'Darkroom Developing and Printing' started by Dale, Mar 4, 2014.

  1. Dale

    Dale Guest

    ICC (International Color Consortium) has four color reference appearance
    assumptions
    RIMM, Reference Input Medium Metric, dealing with dynamic range and wide
    gamut
    ERIMM, Extended Reference Input Medium Metric, dealing with exposure
    latitude
    ROMM, Reference Output Medium Metric,, dealing with dynamic range and
    wide gamut
    PRM(G), Perceptual Rendering Medium (Gamut), an ideal print and environment

    http://www.color.org/index.xalter
    http://www.color.org/search.xalter?q=rimm&go.x=0&go.y=0
    http://www.color.org/search.xalter?q=erimm&go.x=0&go.y=0
    http://www.color.org/search.xalter?q=romm&go.x=0&go.y=0
    http://www.color.org/search.xalter?q=prm&go.x=0&go.y=0

    RIMM, ERIMM and ROMM are constructed from ProPhoto RGB
    http://en.wikipedia.org/wiki/ProPhoto_RGB

    RIMM and ERIMM have use case considerations where scene reproduction is
    preferred, and the use case is soft display or projection accuracy of scene

    ROMM and PRM(G) have use case considerations where output approval is
    preferred, and the use cases are soft proof or hard proofs

    you could use a soft proof use case for soft display or projection, by
    appropriate reference choice, working space choice and output choice,,
    but this interface is kludgey

    when a particular use case is developed as such in a vertical workflow
    there is little problem

    when workflows intersect, such as purposing a RIMM encoded image to a
    ROMM designed workflow, there must be a conversion Reference Appearance

    pre-ICC Kodak R&D used PRM(G) integrated into the PCS (Profile
    Connection Space) as such a Reference Appearance, and I think this was
    implemented in early ICC specifications too, the problem was it did not
    address wider gamuts like transparencies, translucencies and
    projections, but worked very well in print output

    as long as RIMM,, ERIMM and ROMM are all based on ProPhoto RGB this
    issue is mute in all considerations of systems investment, except when a
    RIMM or ERIMM image is repurposed to a PRM(G) workflow

    if digital capture exceeds the dynamic range and gamut and exposure
    latitude of the film assumptions in ProPhoto RGB, this leaves a
    different output for ROMM since the camera will not be an output device,
    and the need for a Reference Appearance like PRM(G) arises again

    certainly this will not be PRM(G) for considerations listed above, which
    I learned the hard way

    PRM(G) could be a ROMM choice, in fact leaving all ROMM as a workflow
    choices, could be a practical solution, but not an elegant one

    eventually ICC will have to address appearance matching along with color
    matching once and for all, color matching is a use case in purely
    measurement workflows but not in viewing use cases

    a reference gamut for such a PCS Reference Appearance could be the eye
    (CIE 1931, 1976) with some viewing assumptions, and even some image
    dependent considerations such as light source (D50, D65, D40, D90, etc.)
    http://en.wikipedia.org/wiki/CIECAM
     
    Dale, Mar 4, 2014
    #1
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