I have made four or five mosaics with good success. Now suddenly I'm having problems. I have two H-Alpha (mono) images of an area around the Bubble Nebula. I created a synthetic star field and used StarAlignment (Register/Union-Mosaic) to make two new images. I then used GradientMergeMosaic to merge the two images. This is what I get. I did not use dnaLinearFit or LinearFit. Any insight would be appreciated.
https://www.dropbox.com/s/5a5qx1c4e4agz4n/MergeMosaic.jpg?dl=0
