Binary image from a plot

[Maria Jose Casas Serrano]

Hi, 

I'm struggling with an images comparison task and I would appreciate your tips.

The software I’m doing, prints some plots that I save as .bmp and with -mono and -bestfit parameters. When I read them with “imread” function, I can see that it’s an indexed image and the matrix contains values [0 255]. I would like to convert it to binary but without using the “image” package. 

(Yes, I know that this sounds weird but I would like to find a solution without using it, if possible. It’s due to some incompatibilities with some computers in the lab which cannot be updated to the last Octave version nor installing packages.)

I have to compare images to see the similarity and the easiest way for me it’s to do it with binary values. 

Any tips that you could give me? I’m stuck here…

Thanks!

Maria