Screenshot of my "Default" settings for a test (small) version of a panorama stitched from horizontal frames, using the free (demo) version of AutoStitch. Circles outline most important settings -- the rest are program defaults, and I've never changed them. If you have vertical frames which have not been rotated already into portrait orientation, you'll have to change the rotation value over on the right.
Once you want to make a full-resolution version, change the percentage setting in the upper-left, and (if possible) assign more memory (lower-right), and be prepared for it to take "a while" ...
You can see some examples of pictures I've made with this program in this Gallery. I think I've only encountered unacceptable banding once, and I do think it was due to vignetting in the source frames.
P.S.: I think you have to "feed" it JPEG versions of your originals.
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