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

From: Steve Underwood (steveu@coppice.org)
Date: Fri Dec 08 2000 - 06:16:20 PST

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  Bob Washburne wrote:

  > The store where I purchased the HP 5370C also sells the 6300C. This
  > appears to be better supported (supports SCL under the HP backend and I
  > have a SCSI I/F for it). But is it pulling the same marketing crap of
  > claiming 36 bpp while only delivering 24? I only mention HP because I
  > can get them locally. If there is a better scanner out there I wouldn't
  > mind getting it mail order.

  The 42 and 48 bit scanner blurbs are generally speaking with forked tongue,
  but suprisingly 36 bit ones are not. They put 36 bits into the gamma
  corrector within the scanner, and get a 24 bit clean output. If you start
  with less that 36 bits you don't even get a meaningful 24 bits out of the
  scanner. A 24 bit scanner gives crap results. A 30 bit one isn't too bad. A
  36 bit one gives about 24 bits of real meaningful output. Beyond that the
  noise from the CCD makes the extra bits highly dubious.

  When looking at colour depths you need to check carefully whether they are
  pre- or post-gamma correction. It makes a huge difference.

  Regards,
  Steve

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