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Re: ghostscript questions: JBIG2 compression, embed control, image compression control

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In article <51fc3593-ea22-41e8-8de9-
5d353a9d6ecb@z27g2000prz.googlegroups.com>, dmathog@gmail.com says...
> 
> Three quick questions about current ghostscript.
> 
> 1.  I see libjbig2dec.so linked in my linux version of 8.64.  Is there
> a way to specify jbig2 compression for bw images, or is it only for
> decoding?  The options that I know of for monochrome are only CCITT
> Group 4, RLE, and ZIP.

AIUI the JBIG2 scheme is not royalty-free for encoding of images, just 
decoding. There is currently no means in Ghostscript to encode the 
output using JBIG2. However it is possible to create your own device and 
you could encode the output yourself.
 

> there are both fonts Symbol Type 1 (embedded subset) and Symbol True
> Type.  Even though (or maybe because) this one was created with
> embed=F, subset=T, /printer. If one wanted to block the former, but
> not the latter, could it be done?  Are they not both "Symbol".

Without seeing the source file used to create the PDF I can't be sure, 
but yes, they are probably both called Symbol and therefore you cannot 
choose to embed based on the name.


> 3.  Often most of the pictures in a generated PDF look good with the
> one common compression setting, but some don't.  Is there a way to
> change the compression settings on a picture by picture, or at least
> page by page, basis?

You can alter the settings in PostScript so you can indeed alter the 
settings on an image-by-image basis, but you would need some control 
over the PostScript program generation. In PostScript images may also 
have the /Interpolate flag.

There is no control for this without altering the incoming PostScript.

You can also alter the compression based on whether the image is colour 
monochrome or grayscale. You should probably also consider the 
downsampling threshold and downsampling type applied.



		Ken

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Re: ghostscript questions: JBIG2 compression, embed control, image compression control ken <ken@spamcop.net> - 2011-02-10 07:57 +0000

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