L
Lorenzo J. Lucchini
Maybe. Of course it will depend on how precise the stepping motor of
every individual scanner is.
Anyway, although this is drifting from the original topic... I was
wondering, can this now not-very-useful feature of VueScan be made
better?
Assume the misalignment between any two scans is not sub-pixel. In
this case, it would be easy, although time consuming, to manually
align the scans.
But can you manually align two images that have sub-pixel
misalignment? My intuition says you can, although most image editing
software probably doesn't allow it. Should be a matter of somehow
"moving" a fraction of every pixel value to one neighboring pixel.
Even if this can be done, it remains to be seen if this alignment
process can be automated; otherwise, it would definitely be too
complicated to be practical.
Now, I know there exist programs that can automatically align two
partially or fully overlapping images. I don't think these programs
can do sub-pixel alignment, though.
But I understand that there are ways of measuring the 'sharpness' of
an image: for example, the pamsharpness tool inclued in the latest
version of NetPBM seems to accomplish such a goal.
So, unless something of what I said can't be done, the following
procedure should work to improve the sharpness of a multi-scan:
1) Measure the sharpness of the image formed by combining the two
scans
2) If it is considered satisfactory, then terminate
3) Choose an (x,y), where x and y are fractions of a pixel
4) Shift one of the two scanned images of an (x,y) sub-pixel amount
5) Go back to step 1
This procedure doesn't find the best possible alignment between the
two images, but it at least assures it will make the alignment better
for a sufficient number of iterations.
What's a sufficient number of iterations and what's "satisfactory", of
course, remain to be defined, but you could just say "when sharpness
has improved more than n% from the sharpness measured from the two
unaligned images, then terminate".
by LjL
(e-mail address removed)