Originally Posted by
Anupam
I was using VueScan the other day and wondered about something that I hope some forum members may help me with. VueScan has a very useful exposure lock feature under the input tab which lets one lock the exposure on the various channels of scanners that support them. Now, doing this means that we can control the exposure from frame to frame and not have the scanner tweak its autoexposure.
So I got to thinking - If I scan a calibrated transmission step wedge - the ones from Stouffer or Kodak - at a locked exposure, and then scan a negative at the same exposure on a flatbed like the Epsons (3200 to v750) comparing the greyscale values in photoshop could give us the density quite accurately.
So, for example, you would lock the exposure at 5 and scan the transmission wedge and then a negative at that same exposure. Now, open both in photoshop in 8bit grayscale (I'm only thinking BW at the moment) and with the dropper tool read the value at a point in the picture where you want to read the density. Now in the scan of the step wedge, find the step which has the closest greyscale value to that slot. Now, of course, since it's a calibrated wedge, you know the actual density of that step and that should also be the density of the point you read in the negative (or pretty darn close).
So, that's the theory. But I am away from home right now and don't have access to the gear to try this out. So if any forum members have a calibrated transmission wedge, Vuescan and a flatbed scanner (preferably one of the Epsons), I'd be grateful if they could try out this little experiment to see if it works.
PS: Please don't ask me to just buy a real densitometer. I already have one. It's just that this seemed like an interesting idea and a valid way to measure densities by comparing to a known density. Thanks for any help on this. Below is the VueScan tab.
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