This site is devoted to mathematics and its applications. Created and run by Peter Saveliev.

Optical density

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Q: I ... am wondering if this program is capable of measuring the optical density of images.

A: Pixcavator computes the intensity, not the optical density (OD), of regions in the digital image. You can use either to produce the exact same contours (for gray scale images). If, however, you are used to optical density in your field to evaluate the characteristics of the material, then this may be a problem. For example, if you need to compute the average optical density for a region in the image, then you face this difficulty:

 mean( OD(red), OD(green), OD(blue) ) != OD( mean(red, green, blue) ), and even
 mean( OD(gray) ) != OD( mean(gray) ).

In fact, directly converting the average intensity into the average optical density is impossible. A modification of the algorithm would allow Pixcavator to compute OD as well. This hasn't happen yet simply because the issue never comes up. So, all I can say we'll add this at some point.