Proof That NikonScan Calculates Scanner Exposure by Reading the Entire Frame

  1. Load a test slide for scanning into the scanner
  2. Using NikonScan 4 focus and autoexpose:
Preview scan before cropping fig. 1
  1. Note the RGB histogram for the full frame:
Histogram of above preview scan fig. 2
  1. Define a crop box enclosing a small area of darker tones:
Preview scan with crop box fig. 3
  1. The RGB histogram of the cropped area appears in the curves window:
Histogram of cropped image fig. 4
  1. Take another autoexpose
  2. Regenerate the preview:
Histogram of cropped image after new exposure reading 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:

How histogram of cropped image should appear fig. 6

In fact, fig. 6 was obtained through the manual adjustment of analog gain.

  1. Restore the crop area to full frame:
Full frame histogram after new exposure reading 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.

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