[nSLUG] Re: Gimp help? (Re: Image utility for Linux?)

Mike Spencer mspencer at tallships.ca
Wed May 16 04:53:28 ADT 2007

Rich> Have you tried ImageMagick ?

I use display all the time but didn't figure out how to do this
particular task with it or its IM siblings.

Rich> If you know the location of where  you want them to join.

Well, that's part of the problem.  The process of scanning a large
sheets into pairs of overlapping images makes the relation between
images of a pair similar but not precisely alike.  So finding the
matching points is a tedious matter of locating some pixel-sized
landmark in both images, then determining the column indices of that
landmark in both images.  Repeat for each image pair.  I tried that on
a test pair, followed by pnmcut and pnmcat. (SANE produces PGM images
so no conversion is required.) That worked fairly well but it was
tedious and error prone. As well, it didn't allow for correcting tiny
but visually significant rotational differences between images of a
pair that occurred despite best efforts to align the scanned sheets
identically.  I was delighted to find that Gimp could deal so nicely
with the rotational correction.

So no, I didn't use ImageMagick.  But I haven't explored the composite
utility much and your pointer clues me that I should.

BTW, I've made a simpleminded little command line utility that creates
a Gaussian alpha mask to match any given PPM image.  The result can be
used by pnmcomp (and presumably ImageMagick composite) to overlay a
small image on a big one.  I put together a quickie temp web page to
explain this to somebody else whose help I'd solicited:


If this isn't something that everybody but me already knows how to do
more easily, I could post the source.c. (I couldn't find a ready-made
way to do this and it was easier to roll my own than continue the
search.  Before I left hard science, years ago, it was already said
that it was easier to repeat research than to find what was wanted in
the literature.  You'd think that wouldn't be true of code, what with
the net and all....mumble....)

- Mike

Michael Spencer                  Nova Scotia, Canada       .~. 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

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