I'm trying to add up a few black & white images of the same object in order to amplify the SNR. I'm working on relatively low SNR images (about 1.1) and I wish to amplify it somehow.

My first try was to add up the images grey-levels while removing the noise through a simple threshold but this isn't really working since this threshold isn't quite well defined.

Are there any known algorithms for this kind of task? If so is there any pseudocode or even open source code somewhere?