Arcane Question on Color Tables

Discussion in 'Photoshop' started by Jim, Sep 30, 2004.

  1. Jim

    Jim Guest

    Hi All,

    Any ideas on the following using Windows and PS7.

    1) Open an image

    2) Image > Mode > Indexed Color

    3) Image > Mode > Color Table: Save the table as test.act

    4) Alt-PrintScreen to capture the Color Table menu.

    5) File > New and paste in the clipboard so that now the Color Table
    menu is an image file.

    6) With a binary file editor, open the file test.act and read off the
    first few values.

    7) Using the Info Palette, put your mouse cursor over the table cells
    that correspond to the cells read from the previous step and note that

    Here is what I got.

    Color Table RGB Value RGB value in Info palette
    5,254,255 8, 255, 255 and 0,247,255
    22,251,255 24,247,255 and 16,247,255
    19.248,255 16,247,255
    8,248,255 8,247,255

    Now my question is why the discrepancy between the RGB values in the
    color table and the values as picked up in the screen capture of the
    color table graphic?

    Any ideas?


    Best Regards, Jim Plaxco
    National Space Society
    Jim, Sep 30, 2004
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  2. Jim

    Mike Russell Guest

    Photoshop uses your monitor's display profile to convert RGB values from
    your working space to your monitor space. If you set your working space to
    your monitor profile, the numbers will match.

    If you like this kind of puzzle, here'a another one. Create two images, and
    assign one of the image's profile to Wide Gamut RGB. Now use the paint
    brush to paint any of the pure RGB colors (red, yellow, green, etc) in the
    Swatches palette. Use the info palette to verify that these colors are
    painted as advertised.

    Now pick a color from the second or third rows of the Swatches, for example
    the Pastel Red which is leftmost in the third row. When you paint that
    color, notice that the RGB values are now different in the two images.

    Can you explain why the colors are different for Pastel Red, but not the
    colors from the top row?
    Mike Russell, Sep 30, 2004
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  3. Jim

    Jim Guest

    Hi Mike,

    That never occurred to me. Thank you for this insight. Alas, with
    Photoshop it seems that there is always something new to learn.

    Actually, no! I don't even know what possessed me to go through the
    above procedure. This all came about because I was investigating
    creating my own color tables programmatically.

    Not a chance. Perhaps it has something to do with the wishy-washy
    nature of pastels,

    Thanks again Mike.

    Best Regards, Jim Plaxco
    National Space Society
    Jim, Oct 1, 2004
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