D Poinsett , Mar 24, 2004; 07:31 a.m.
Using a scanner as a densitometer is theoretically possible but two related problems must be overcome. I suspect these problems are at work in the example you have submitted.
1) The scanner itself must be calibrated against known density values before using it to measure unknown denisities. You can scan a Kodak or Stouffer step wedge, but...
2) In order to optimize scan quality, software for many consumer-type scanners cannot disable automatic exposure adjustments. These will undo any calibration.
These unknows must be controlled or you cannot reliably use the results from ordinary scanners to evaluate your film. I have experimented with using a scanner as you propose but have not been to produce results that match those from my densitometer. I've gotten close enough that it seems with reach but have not spent the additional time required to solve the problem. Perhaps others will suggest a solution.