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I didn't catch anyone else saying it, but the simplest technique for
downsizing screen shots is to reduce the graphics resolution on the machine
from which the screen shots are being taken. Small screen shots of a
640x480 screen will be vastly more legible than from a 1280x1024 screen.
It's easy to blur pictures by accident by scaling them unnecessarily. Having
the wrong settings in Distiller will do it, for instance. Rescaling them to
an arbitrary DPI for an outside shop, only to have the shop rescale them
again, will also do it. Pictures should be rescaled as few times as
possible. Things like screen shots often maintain their integrity better if
you scale them by the stretch/truncate method than by "better" methods,
since it keeps the colors and nice sharp pixel edges intact. JPEG's lossy
compression is bad in this kind of application; lossless compression is
harmless. Anti-aliasing and dithering are also bad.
Realistically, bitmap graphics don't have a "dot-per-inch" size at all --
this is just an entry in a header. Bitmaps are really just an array of
pixels, and as long as you don't change the array size (in pixels) of the
bitmap, nothing bad is likely to happen (unless you forgot to turn off
downsampling or lossy compression in Distiller and when saving the file).
The DPI value is just a suggestion to the application of how big a pixel
ought to be. Changing the DPI doesn't require touching the pixels at all.
That is, a 800x600 bitmap that has its DPI changed from 96 to 150 DPI should
still be 800x600 pixels, and the individual pixels will be untouched. The
reported image size IN INCHES should be reduced to 96/150 of its original
size. It's when you allow the size of the image IN PIXELS to change that
all the artifacting shows up.
