Re: Which scanners REALLY provide 36 bit output? HP?

From: Stephen Williams (
Date: Wed Dec 13 2000 - 17:05:29 PST

  • Next message: Steve Underwood: "Re: Which scanners REALLY provide 36 bit output? HP?" said:
    > When you try color metrics (measuring differences between colors),
    > things get even more scary. Colorimetrisis found out that the human
    > chromacity space IS 3D, but its metrics are non-euclidean.... said:
    > Do you still dare to scan? :-)


    My company has built several color CCD-based cameras, and the customer's
    are universally weird about the expectations:-) And I can't say I blame
    them. Whereas a gray scale image of a gray document can be deemed "good"
    or "bad" by engineering measurements, color vision is largely a psychological
    phenomenon and the judgment of good vs bad is mostly aesthetic and/or
    application specific.

    We found that when an observer is asked to judge the best from a set of
    images, the "accurate" (in an engineering/colorimetry sense) image is almost
    *never* chosen. An observer usually prefers excessively bright and slightly
    saturated color images over crisp, precise images. And the scanners that you
    buy (and televisions too, it seems) are optimized accordingly.

    And from that perspective, the colors chosen in animated cartoons make
    a lot more sense. (Purple hair?-)

    And none of this is good news to someone who wants to create archival
    images of precious documents. We've been there, too, and the conclusion
    is that for all but the most extreme cases, good ol' 12bit JPEG (and an
    environmentally controlled vault) are about as good as is worth the
    effort. If some hot new image processing technique comes to light, you
    are just going to have to accept the reality that you will need to open
    the vault and rescan the document with the lighting/sensors required
    of the technique.

    Steve Williams                "The woods are lovely, dark and deep.              But I have promises to keep,            and lines to code before I sleep,       And lines to code before I sleep."

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