Actually, the good stitching programs do *lots more* than just line up the pixels, such as you might do with Photoshop. I'm not familiar with Image Assembler, but I suspect it's similar to PTMac. (Although PTMac doesn't have that file size limitation.)
I think you're absolutely right there, Jim . However, ImageAssembler, I suspect, is a lot easier to use than Panorama Tools, and a lot faster. On the downside, I get the impression it's not as flexible as Pano Tools because many of the functions are automatic, and the program often gets it wrong. (Such as automatic lens focal length and tilt calculations).
For this reason, I use the 'no frills' image stitch option where the choices are just vertical and/or horizontal alignment, flags or no flags (automatic placing of flags) and force row (or column) of images into straight line etc.
I've given up on the time consuming, frustrating task of trying to compensate for serious parallax errors, which I'm sure Pano Tools is better at doing. (But not quickly and easily).
I only attempt to stitch images that are relatively free of such errors, such as distant scenes with nothing closer than about 200 metres (using my 100-400 zoom), or closer scenes with the Canon TS-E lenses. When the images are right, I can load and stitch a dozen images in about 5-10 minutes using IA, and 3 or 4 TS-E images in about 2 minutes.
I recently tested my TSE 90mm with 1.4x extender in my studio. I placed the tripod about 6 metres from the end of the room and (camera vertical) photographed a row and a half of books and vertically stacked LP albums close to the ceiling where there is a sloping exposed beam. This mixture of vertical, horizontal and diagonal straight lines, and fine print, seemed an ideal test of the stitching capabilities of ImageAssembler with a good source.
The entire stitching process, from loading the source images to saving the final result, took 2 or 3 minutes (automatic positioning of flags). The results looked perfect. All the lines were straight and there were no 'seams' in the sense of no abrupt changes in toality.
However, when one starts pixel-peeping, things are not quite what they seem to be. Sure enough, at 100% magnification on the screen there were two LP albums, slap in the middle of an overlap, that exhibited blurred labelling. The lettering had a shadow. So I used my technique (tip of the year) to get rid of this. I cropped the images so the offending LP album appeared only once in the overlap area.
Did this produce a perfect stitch? Not quite. I'd transferred the blurring to a vertical timber division in the bookcase. Only I would notice it because I'm familiar with the precise grain on that piece of timber .
ps. I had another go at that project because any stitching program worth its salt should be able to produce a perfect stitch with TS-E images, considering the very small parallax errors and lens flaws. This time I used IA's 'lens wizard' to create a lens profile and then stitched the 4 cropped images using that profile. Result? A perfect stitch.