Re: filmscanners: VueScan clipping & flat images

["Bob Armstrong" <bob.911@btinternet.com>]

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.)

It seems to me that setting B/W to 0% results in what Jawed is calling a flat 
image.  Jawed (if you're reading this!) does a histogram of one of your flat 
VueScan images extend all, or most of the way, from 0 to 255?  I find with my 
flat VueScan mages that do not range across the histogram but leave, 
particularly at the white point end, a lot of unused values.  If that is the 
case with your images I wonder if you would try to increase the white point to 
0.05 or 0.1 and see what that does to the image.  I would be interested in your 
results compared to Nikonscan especially if you set the white point to _just_ 
fill the histogram.  

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.

White point (%) 
The white 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 white 
point at the maximum intensity (0%), or to choose the white point such that 
some percentage of the pixels in the image are above the white point.

Bob Armstrong

Alessandro Pardi wrote:

>Stan, Leif,

>I think you shouldn't use 0% for the white and black point, as this sets the
>deepest shadows to 0 and the brightest lights to 255, and may result in
>clipping. My usual settings are 0.1% for the black point and 0.5% for the
>white point, but I seem to remember a post by Hamrick about this, so you may
>want to dig in the archives.


> From: Goodwin, Leif [mailto:Leif.Goodwin@racalinst.co.uk]
> Sent: giovedì 22 novembre 2001 08.15
> To: 'filmscanners@halftone.co.uk'
> Subject: RE: filmscanners: VueScan and highlight/shadow pixel
> clipping--wh y? (SS4000)
> 
> 
> Stan. I see the same with Vuescan and the Microtek 4000T 
> scanner. Don't know
> why. Leif. 
> 
> > -----Original Message-----
> > From: S Schwartz [SMTP:snsok@swbell.net]
> > Sent: Thursday, November 22, 2001 3:27 AM
> > To: Filmscanners (E-mail)
> > Subject: filmscanners: VueScan and highlight/shadow pixel
> > clipping--why? (SS4000)
> > 
> > I posted this question a few days ago but got no response 
> so I am posting
> > it
> > again.
> > 
> > I like using VueScan with my SS4000 scanner but I am 
> consistently seeing
> > highlight and shadow pixel clipping on my transparency 
> scans. When I use
> > Polaroid's Insight software for scanning, I get a nice 
> histogram with no
> > pixel clipping.
> > 
> > I have tried Vuescan with 0% white point and 0% black point 
> and still get
> > the same clipping. I am using ordinary settings on the color tab:
> > brightness
> > 1.1, gamma 2.2, etc.
> > 
> > Any reason this is happening?
> > 
> > Stan
> 
> 
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