The result of the swarp superposition is a mosaic

[Snow1Sea]

Hello, I would like to ask a question, that is, the superposition has to go through sex+scamp+swarp, when I use this method to superimpose two pictures, the result is a mosaic, if you directly use swarp to overlay, the result is also a mosaic. What to do in this case, of course, the image is astronomical, thank you.