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[filmscanners] narrow spike in histogram from SS4000 slide scans


  • To: lexa@lexa.ru
  • Subject: [filmscanners] narrow spike in histogram from SS4000 slide scans
  • From: "S Schwartz" <snsok@swbell.net>
  • Date: Mon, 03 Jun 2002 22:52:59 -0500
  • Importance: Normal
  • Unsubscribe: mailto:listserver@halftone.co.uk

In the last few weeks, histograms of certain scans made on my SS4000 are
showing a very narrow spike (or sometimes 2 spikes) at the lower pixel
levels, usually in blue and usually near level 0, level 1 or some level less
than 9. The images I am scanning that display this spike are generally
outdoor images with some burned out bright yellows flowers.

For example, on the slide I just scanned, Photoshop's histogram display
shows this spike at level 1 where it reports about 520,000 count. That's
nearly 3 times the count in the blue channel than at any other level in the
histogram.

I posted a screenshot of one of Photoshop's histogram here:

http://www.tallgrassimages.com/test/histogram.jpg

This histogram generated by VueScan and by Polaroid's own Polacolor Insight
shows the same phenomenon.

Sometimes when I try to see the count by Photoshop's histogram crosshair
mouse cursor over the spike, the spike does not "register" on the count
line--it's as though it isn't there.

 When I sample the pixels in the bright yellow areas, I don't see any pixels
with a value above 250.  I have Polacolor set for a white point of 255 for
each of the color channels. I had thought these might be pixels that are
beyond the white point, but the shape of the histograms doesn't look like
that.

The scans look OK on the screen. I don't see any anomalies.




Stan Schwartz

snsok@swbell.net

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