Re: pixel measurment
Posted by
Olivier Burri on
Aug 25, 2011; 8:58am
URL: http://imagej.273.s1.nabble.com/pixel-measurment-tp3683348p3683354.html
> I want to compare differences in pixel proportions between 2 images.
> Can anyone tell me how to do that? how to measure pixels in a given
> image?
Dear Reena,
Depending on your image and its acquisitions, you're always going to have pretty much the whole picture changed in some minor way (Every noisy pixel will give a count or an intensity change in the background will make the whole background be counted). From what I can gather the simplest thing you can do is to subtract the two images using image calculator, making sure the result is 32-bit.
Subtracting an image at T=0 min to an image at T=20 min yields an image with the following properties:
Brighter regions represent areas where microglial processes appeared, darker regions where they disappeared and gray regions where nothing changed.
You can also threshold your images first.
That way, when you compare pixel values you either have a pixel that belongs to the cell or one that belongs to the background. If you then perform a XOR (Exclusive OR operation) you recover only the pixels that have changed.
You then probably need to normalize those pixels with respect to the cell's areas, but I haven't got the article in front of me.
There are other really fancy methods to do it:
http://bioinformatics.oxfordjournals.org/content/27/4/564I left you a sample of what I'm talking about (for the thresholding here:
https://documents.epfl.ch/users/o/ob/oburri/public/XOR%20example.ijmJust run this macro in ImageJ/Fiji and look at the results. Feel free to use it as a backbone if it's useful.
Good luck!
Oli
Olivier Burri
Engineer, Development in Image Processing
BioImaging and Optics platform (PTBIOP)