Densitometers, How do you use this tool?

[T. Duprex]

I have an Epson 4990 photo scanner; Epson Scan as well as the other
scanner programs (Silver Fast and VueScan) have this tool. I've tried
Google and those articles address the real physical densitometers that the
color printing industry uses. IS there a tutorial that describes what this
tool is in the scanning application, and how to use it? My attempts to get
use of the tool by clicking on it and moving around the image doesn't
appear to intuitively direct me to do anything. I would appreciate your
experiences and any useful information on this tool.

TIA

 

[-]

You might enjoy reading this article on using your scanner as a
densitometer:

http://www.mynett.plus.com/ep2450/2450densi.htm

The concept will be the same with your scanner model.

Doug

 

[Bart van der Wolf]

You might enjoy reading this article on using your scanner as a
densitometer:

http://www.mynett.plus.com/ep2450/2450densi.htm

The concept will be the same with your scanner model.

Yes, that's about it. VueScan's 'densitometer' functionality basically
relates the brightest data number in the image to the current data
number under the cursor, and calculates its Relative(!) Optical
Density. Optical density is the Log10 of opacity, and opacity is the
reciprocal of transmission.

It is usable as a layman's densitometer (assuming the scanner's Raw
data is linear), and can be used to check e.g. the base density of
negative film (is an indication of storage+processing), or the density
range of a particular image. If you want to take more accurate
readings, it would require a calibration on a steptablet with known
densities. For the best results one should mask the film carefully to
reduce contrast loss due to internal reflections.

Also, one should exercise care when comparing between films, because
the graininess (especially in silver based B/W film) will alter the
readings with density (Callier effect).