how to merge multiple images into one image?

Hi everyone, I'm trying to use matlab to convert a video into a merged image as described in (Newmann. Z, 2017).

Basically, the video records multiple firing events, like these (At different time point, different area will fire):

I have extract all the frames from the video, but I wonder how should I merge them together and convert the final image into 0-255 gray scale? I want to achieve some thing like this:

Thank you in advance!

Answer 1

[Selva Karna]

Segment each frames, then extract original roi