UPD Mail Archive: UPD> Color handling

UPD> Color handling

From: Norbert Schade (norbertschade@comcast.net)
Date: Fri Feb 20 2004 - 16:16:05 EST

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    Today we had a chance to discuss color handling in a small group (Mark Hamzy, Jim Sommer, Jody from the Gnome organization and me) to check the UPDF design and compare to the needs in the FSG.

    We agreed that at the first glance it looks like UPDF would provide all tags needed to describe the way the device is expecting color data.

    1. The UPDF Color feature
    Multiple color records can be created, e.g. for monochrome and color.
    A color record offers RGBColor elements, which tell about the colors the device supports, e.g. CMYK, which would mean the definition of four RGBColor elements.
    The bit depth can be set per color. if the complete bit depth can be supported by the device, no additional halftoning is required.
    The color records also tell, whether the color info should be provided per pixel, per band or per scanline.

    2. The UPDF PhotoHalftoning feature
    There are halftoning feature for vector and text as well. But we can concentrate on raster (= photo), as that's the only place where halftoning patterns are likely used on the host (we consciously are ignoring the download of patterns).
    Let's say a device only supports two of the eight bits a driver has to deal with. Then the remaining six bits are supposed to be resolved by halftoning.

    We are facing a XML limitation here. There are no two-dimensional arrays in XML. So we have to split the matrix up into lines. By default the remaining six bits may be resolved by a 6x6 matrix. This would result in six of the OneHorizontalLineOfTheHalftoningMatrix elements, each with six comma separated values.
    That's the best flexibility we can get in XML for that definition.

    3. The UPDF RasterObject object
    This is the specification of the way raster graphic is handled.
    This moment we can concentrate on the Band element.
    If no Band element is specified, the device can deal with the whole page as a band.
    Otherwise you would see the maximum size defined here.

    That's the high level explanation of how it's done in UPDF.
    There are no LUT. However one can add ICC Profiles to the device configuration and LUT can be taken from there.

    I'm going to put the current files out on the web tonight.
    you can find it under ftp://ftp.pwg.org/pub/pwg/upd/wd/
    schemas are located in subdirectory 'schemas'.

    Norbert Schade

    Norbert Schade
    69 Prescott Drive
    North Chelmsford
    MA 01863
    phone: 1-978-251-1017
    email: norbertschade@comcast.net

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