There are many functions to operate on frames, you can overwrite a frame with the Picture or Out or create a new frame at the top of the stack which is a copy of one of these or an existing Frame. You can adjust the Contrast, Colour and Brightness of Frames and Rectangular regions of Frames. You can alter the size of a Frame. You can make a frame Monochrome or the black areas in it transparent. You can filter an individual Frame.
Several of these functions use the Left and Right Arrow keys to increase and decrease there effect by a small amount. In a similar way 'M' and 'N' do this in much larger steps.
You can also write Macros to do more complex things to Frames e.g. split a frame into it's red green and blue components manipulate them in some way then recombine them, this is how 3d images are created.