Proof That
NikonScan
Calculates Scanner Exposure by Reading the Entire Frame
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Load a test
slide for scanning into the scanner
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Using NikonScan
4 focus and autoexpose:
 |
fig. 1 |
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Note the RGB
histogram for the full frame:
 |
fig. 2 |
-
Define a crop
box enclosing a small area of darker tones:
 |
fig. 3 |
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The RGB
histogram of the cropped area appears in the curves window:
 |
fig. 4 |
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Take another
autoexpose
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Regenerate the
preview:
 |
fig. 5 |
That the histogram
is essentially unchanged shows that the exposure function ignored the
crop box. Had NikonScan
calculated
exposure based on
the crop box, the resultant histogram should have changed to look
something like this:
 |
fig. 6 |
In fact, fig. 6 was
obtained through the manual adjustment of analog gain.
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Restore the crop
area to full frame:
 |
fig. 7 |
Note again that the
histogram for the full frame is essentially unchanged from step 3,
additional confirmation that the exposure was based on the full frame.
If the cropped area
is to be the image, proper exposure would have to be set manually by
adjusting analog gain.
Return to Understanding the Exposure
Function
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