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

From: Nick Lamb (njl98r@ecs.soton.ac.uk)
Date: Thu Dec 07 2000 - 21:45:45 PST

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  On Fri, Dec 08, 2000 at 12:17:17AM -0500, Bob Washburne wrote:
  > Scan a small image with bit depth set to 12 and save it as a png file.
  > Then look at that file with gimp and examine its properties. I believe
  > gimp will tell you what the color depth is. That should pretty much
  > confirm what is happening.

  Nope. "Consumer-grade" Gimp is an 8 bit per channel app, through to
  the core. You can load a 16-bit PNG image, but the color accuracy
  will be silently truncated. No ordinary releases of Gimp will include
  higher color accuracy for some time yet, mostly because so few people
  need it.

  If you want to do image processing of very accurate, very high res.
  images you should probably check out VIPS instead of, or as well as
  Gimp.

  Using file(1) should enable you to detect if a PNG image is 8-bit or
  16-bit per sample. Note that not all SANE frontends can output more
  than 8-bits per sample anyway, I think XSane can.

  Both PNG and SANE only transport 8 bit or 16 bit units, so if the
  scanner is capable of any amount greater than 8 bits per sample, the
  results are dynamically scaled to fill a 16-bit sample, this process
  is of course reversible (see sBIT documentation).

  Nick.

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