How to compare two catalogs?

I have two catalogs a nad b. Catalog a have 1731 jpg images, catalog b have 1711 bmp iamges. Filenames in both catalogs are identical. I want know what files are in catalog a and are not in catalog b. How to do this ?

I'm not sure what catalogue refers to in this context. Directories, libraries, collections, or something different?

When you say the filenames are identical, does that mean every filename exista in both folders, and you need to compare file contents (or dates, or some other attribute)? Or do you mean most of the filenames are the same and you need to find the missing/extra names on each side?

I want this

Folder - a

Folder - b

I want know what files that are in folder a are not in folder.

This is just example. Real filenames are different.

Have a look in the Edit > Select Other menu. There are commands in there to select everything that is or isn't in the other side, and similar.