Re: filmscanners: VueScan clipping & flat images

[Bob Shomler <bob@shomler.com>]

That vuescan text (below) states that the black point determination uses the 
histogram of each color -- three histograms.  Might the combination of color 
balance / neutral and black point computation result in one or two color 
channels with pixels below the calculated (luminance) black point?  In what 
software/tool is the histogram being viewed?  

In Photoshop a calculated luminosity histogram is displayed by Image->Histogram 
while the logical-or overlay of the three channels is displayed by the RGB 
channel in the levels dialog box.  For Image->Histogram be sure that the 
histogram box shows cache level 1, which can be obtained by Shift+Image-> 
Histogram selection if preferences setting calls for using cache for histograms.

Bob Shomler
www.shomler.com

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>The following is taken from VueScan's help file.  It seems to me that B&W 
>points of 0% should leave all of the pixels in the scan.  (Having said that, 
>when looking at a histogram, it does seem that some pixels either go beyond 
>the black point or there are a mumber of pixels _at_ the black point.)
>...
>Black point (%) 
>The black point is used by the color balance algorithm and is computed by 
>using the histogram of each color in the image. Use this option to leave the 
>black point at the minimum intensity (0%), or to choose the black point such 
>that some percentage of the pixels in the image are below the black point.