There seem to be a number of filters that only handle square images and ignore the area outside of the subtended square in rectangular images.
Is there a simple way to edit the filter to fix this? Is it that some earlier functions were limited to square images and if so is there a table of new functions that can be used to replace them?
Yes, it is true that some filters work right ONLY with square images, and if used with rectangular images, the part that gets outside of the square gets deformed or acts weirdly sometimes.
I do not think that normally the filter can be changed to be able to use it on non-square images, as probably the problem is not of the filter, and is of the effect that gives and the components used that must have a square photo.
Although I am not any expert in filter forge, so really I really do not know if it would be possible or not, probably depends on what filter you want to use.
Lets see what other real experts can say about this