Does anyone out there know of any way that gimp can be used fairly easily to
create 3 or 4 bit grayscale TIFF images (rather than 8 bit)?
Most applications, including gimp, seem to be geared towards 8 bit grayscale
images. But, I'm involved with a hardcopy document archival project where 3
or 4 bit grayscale TIFF images would be preferable for the following
1. 8 bit grayscale files require far too much space.
2. 8 bit grayscale files can't be compressed effectively unless you use a
lossy algorithm such as JPEG. Some loss in image quality IS acceptable for
my project, but JPEG compression can introduce additional artifacts into the
image, and that is NOT acceptable.
3. 1 bit black and white images are not acceptable for my project because
they don't show any intermediate shade variations that may be important for
any number of reasons, including resolving faint handwriting on a form that
includes other very dark features.
4. 3 bit (8 shade) and 4 bit (16 shade) grayscale images are the primary
contenders for my project because they DO provide acceptable identification
of varying shades in the original, and ...
5. The drastic reduction in the number of shades produced by using 3 or 4
bit grayscale instead of 8 bit grayscale makes the images MUCH more
susceptible to LZW and other compression algorithms. A 3 or 4 bit grayscale
image using LZW compression is typically 10 to 20 times smaller than the
corresponding 8 bit image.
So far, I've succeeded in getting gimp to produce indexed tiff images based
on 8 and 16 gray shade pallettes that I've created, and that by itself helps
quite a bit. However, it still introduces sizeable additional overhead into
the tiff file to store the pallete look-up table, that shouldn't be
necessary. It ought to be possible to merely store the images directly as 3
or 4 bit grayscale instead.
Does anyone out there have any ideas or suggestions? Possibly some other
scriptable tool that can manipulate tiff files, other than gimp?
Thanks in advance for any help that you may be able to provide.
Round Rock, Texas
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