# Re: Scanner Color Shift Problem

From: Steve Underwood (steveu@coppice.org)
Date: Fri Mar 02 2001 - 06:50:24 PST

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  Frederik Ramm wrote:
  >
  > Hi,
  >
  > > This looks like a common colour merging problem. In most scanners there
  > > is a physical separation between the red green and blue sensors. Most
  > > scanners just feed data to the host with this separation, and the driver
  > > needs to shuffle the scan lines to accurately merge the colours. You
  > > will find code to perform this function in several sane backends. A
  > > typical offset between each sensor row is 1/75 inch, but varies between
  > > models.
  >
  > I know about that, and I've done the color merging "by the book" in my
  > driver. Just to be on the safe side, I have changed the driver's
  > offset by +/-1, and each time the error became even bigger. Then I
  > tried the Windows driver that came with the product and it produced
  > the same "error", so I have to assume it is a hardware problem.

  But your scan appears to have an error greater than a pixel. A 1 pixel
  shift in the right direction should surely make the result better than
  your sample scan. You didn't actually say what the resolution of your
  sample is, but there is definitely something wrong. Even cheap scanners
  show no percievable colour fringing at their maximum resolution. Its a
  pretty easy thing to get right.

  Regards,
  Steve

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