Originally posted by Quazimoto I was wondering if
A) this is indeed that I am not overlapping them enough, so to fix it I'll just use plenty of overlap, right?
B) there is anything that can be done about it for these particular photos that PS has told me can't be aligned?
Hey Quazi,
Here is what I think (based on... uh... 15 years of stitching digital images together (wow)):
A) Photoshop's Photomerge function is very good, but still rather primitive. It only matches details as seen in the lens distorted images you feed it, and even if you select "correct for distortion," there are limits to it's effectiveness. In essence, it will try to "undistort" the image to the best of its abilities, then look for matching details in the overlapping regions. If you use a wide-angle or fisheye lens, it will sometimes give up even if the amount of overlap is good (10-25% is fine, but even 5% is useable), because the Photoshop "distortion corrected" images may include a prominent detail at the extreme edge of one image, which has it's match in the less-distorted interior of the adjacent image. They won't be "undistorted" to the same degree and still won't match up. Without being fully corrected or calculated for, the algorithm gets confused, since that detail object (seen as a group of similar pixels) could still be twice as wide or really curved compared to how the other image captured it.
B) So, it isn't necessarily the overlap %, but the lens you are using. Solution? Don't switch to a less-distorted lens, just use a
(free) dedicated panorama-sticher like Hugin and it will detect your lens by EXIF and use its own internal lens corrections (which are applied to feature matching as variables, not by trying to "undistort" the image and hoping they match), which will almost always stitch something that Photoshop cannot. You might just reserve this tool for those "tough problems" and it will be fine for that. I've stitched images from tilted, circular fisheye lenses with less than 5% overlap using Hugin, so you should be fine!