By which I mean curves, rather than ribbons.
I was having problems with joining "bowed" images--i.e. one (or both) of the two halves of the image had a slight concave or convex curve along its "to-join" side, making it difficult to join them together because it left gap(s) along that centre join-line, typically containing distorted-hue (i.e. highly visible) "edge" pixels such as bright oranges/rainbows, etc. Image rotation and Photoshop's Transform -> Skew tools do not fix this, though they do help straighten things beforehand, while the Filter -> Distort -> Lens Correction is too "gross" or "coarse" an effect to be useful here. Likewise with the Pinch filter.
Just now, however, I've discovered that
Filter -> Distort -> Spherize has quite fine control--e.g. right down to just 1% effect, and can be made horizontal-only. For an image scanned at 300ppi, filter effects of ~2-4% can adjust for bows of ~1-3 pixels width, i.e. just enough to be pretty handy.
The only possible loss is a couple of pixels on the "opposite"/outside edge, but that's often just innocuous "background".
/shrug/ Might be helpful for others to know.
Late addition: spherize does not affect the outermost row(s) of pixels in an image, i.e. use that tool
before cropping the image... or paste it into a larger canvas prior to using the spherize tool.