Turning a gray-scale image into a data set - (Jul/21/2012 )

suppose I have a gray-scale image: what I like to do is putting over a grid, and for each parcel the corresponding gray-scale value should be given;

maybe there is something in ImageJ/Fiji...? any contribution is welcome...

ImageJ may do it or you can find such plugin for photoshop. Without a plugin, you can do it manually in PS. You turn on the grids or draw grid over your image, then use the marque selection tool to select individual area, then go to Image -> histogram which will give you the mean value +/- SD, median and # of pixels.

If you know python, or are willing to learn it, you could try using PIL, especially if you are going to do it more than once.

http://www.pythonware.com/library/pil/handbook/imagestat.htm

there are probably things for perl and various other languages but I find the python community nicer and the packages tend to work w/o goofing about with deps.