Re: [APML] McBeth Color Card

[Jerry Lodriguss <jml@astropix.com>]

At 10:37 AM 8/1/2002 -0400, you wrote:
>I recently scanned a black and white negative containing an image of a 
>MacBeth color card.  I scanned the film as a positive and negative with a 
>Sprintscan 4000 and saved the uncorrected raw scans in 12 bit mode.  I 
>then compared average pixel values for the different squares of the color 
>chart for each scan.  The results are at:
>http://www.unc.edu/~pedit/chart.gif
>The best fit line is:
>
>negative pixel value = 256 - 1.25 * positive pixel value
>
>Why is the slope -1.25 instead of -1?


Hi Joe,

The scanner is applying a gamma correction to the negative scan.

Raw doesn't always mean really raw to these scanners for some reason. The 
Nikon LS2000 is the same way.

There is absolutely no way to get a true raw scan out of it with the Nikon 
software. But you can with the Vuescan software. And the funny things is, 
if you do a raw scan on the Vuescan software first, and then open the 
NikonScan software (and have it set to what is closest to "raw") then you 
can get a true raw scan out of the Nikon.  Weird.

Jerry

Astronomical photography: http://www.astropix.com




--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>