how to calculate snr of an image

I am working on images of CT scans. I would like to find out the signal to noise ratio of the image and compare it with other images. How to calculate the snr of the images??

Answer 1

[Rik]

The first hit on Google for me was the Wikipedia page. From this section, it is trivial to write code accordingly:

SNR=mean(CT(:))/std(CT(:));

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