The -r/-o/-a/-x flags specify the logical operation to use when doing the paste. They stand for Replace, Or, And, and Xor, respectively. The default is replace.
This tool is most useful in combination with pbmcut(1). For instance, if you want to edit a small segment of a large bitmap, and your bitmap editor is TOO STUPID to edit the large bitmap, you can cut out the segment you are interested in, edit it, and then paste it back in.
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