Compare Images to Quantify Cleaning Performance

Posted by Frank Robson on Sep 30, 2015; 3:18pm
URL: http://imagej.273.s1.nabble.com/Compare-Images-to-Quantify-Cleaning-Performance-tp5014503.html

Hello,

I'm trying to quantify the cleaning performance of a dishwasher. To do so, I have standardized "dirt test plates" that I clean using the machine.
I take pictures of the test plates before and after cleaning them and want to measure how much dirt got off during the process.
I thougth ImageJ could help me out to do so but the only metric I found for comparision until now are the RGB-values of both images.
I was wondering if there was a better way of doing it.

After the wash, the plate becomes brighter and the stains more grainy.
Pixel to pixel comparision is not possible because the camera is not held still.

Thank you for your help,
Frank