In this case, it's because I don't want to assume that every dataset that will be used with this code stays in RAM, and it's simpler to handle things on the FS

In this case, it's because I don't want to assume that every dataset that will be used with this code stays in RAM, and it's simpler to handle things on the FS level by adding a new png to the stack, than to keep track of the images in RAM. This way the code can be "simpler"