Filmscanners mailing list archive (firstname.lastname@example.org)
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: filmscanners: VueScan clipping & flat images
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.
>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.