[MacPerl] Making Thumbnails

[mark@cheers.jsc.nasa.gov (Mark Manning/Muniz Eng.)]

According to mdoub@usa.net:
> 
> I have a lot of jpeg and gif images that I would like to convert into
> thumbnail size images for use in creating an index.  Can anyone give me
> pointers as to how I might do this with macperl?  Are there modules that
> support manipulation and scaling of graphics images?
> 
This is not really a MacPerl question so much as a graphics question.

With that in mind, I have a couple of observations which
I'd like to pass along.  :-)

1. If this is for an HTML web page, all you have to do is
to keep the aspect ratio correct and change the width and
height of the images.  Both Netscape and MSIE will
correctly scale down the image for you.  This is handy in
that you do not have to reload the image in order to see a
full scale one.  Just allow the image to be shown at it's
correct width and height.

2. Smaller images do not necessarily mean that they take up
less space.  It depends upon the complexity of the image.
Thus, a GIF file which contains a single color will stay
approximately the same size for quite a while.  Try it if
you do not believe me.  :-)

3. Scaling in most programs is not really all that good.
What tends to happen is that the picture becomes jagged as
the pixel information becomes more and more compressed.
This is really (to me) rather stupid.  The reason I say
this is because if you have a program like - say Canvas
(which I have).  And you scale down a picture but leave the
dpi at 300, then the scaled down picture looks really
great.  But if you scale down a picture and change the dpi
72 (ie: screen resolution) then the picture looks
terrible.  I tried, for about six months, to get them to
understand that just because the dpi is at 300dpi on one
picture and 72dpi on the other.  That on the screen the two
pictures should look exactly the same.  (Since the screen's
resolution is only 72dpi.)  But I couldn't get them to
understand the concept.  I even tried showing them how the
problem could be corrected (by using the 300dpi resolution,
creating the scaled down picture, and then taking a
snapshot of the screen so the new picture was at 72dpi) all
to no avail.  :-(  But anyway - watch out for jaggies.

Of the programs out there, deBabilizer and Graphics
Converter are your two best bets.  Graphics Converter is
like a really cheap deBabilizer.  It handles batches of
files and can do all sorts of things for you.


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