take two halves of an image too large to captured in its entirety and merge them into a single image.
If the two halves are perfectly aligned and scaled, joining them in any image editor is child's play. However, if the two or more segments are out of alignment (say, rotated slightly), joining them seamlessly can be difficult.
For example, I've had to scan radiographs ("X-rays") or poster-sized items that would not fit onto the flatbed scanner. Some items are so big that one cannot rely on one of the flatbed's straight edges as a guide. If the scanned image has no straight edges within
it, that also takes out any auto-leveling tools, such as the ruler in Photoshop.
(If I have to work manually, I set an upper layer to "Difference" blending, then scale/rotate and transform the upper layer as necessary using the overlap between segments as a guide.)
Photoshop has an automatic "stitching" function called Photomerge which works pretty well most of the time. However, it is not perfect. If you need to merge images into a panorama, say, then you may want a special tool for that.
is available for many platforms, but the downloads on that page are for evaluation purposes only. Various commercial apps derived from Autostitch are available. One variant that I use, mentioned in another thread
, is Kolor's AutoPano Pro
As with so many apps these days, there is a FOSS (free, open source software) alternative. Hugin
is a panorama stitcher designed to work with Panorama Tools