[pdftex] Pdftex compression

Otfried Cheong otfried at cs.uu.nl
Tue Aug 21 12:35:32 CEST 2001

 > In addition to the information I wrote up below, I'm curious
 > whether anyone can shed any light on the following:
 > - AFAICT, there is no native support for PNG images in PDF format.
 >         What does pdftex do with PNG images? Decompress them?
 >         Convert them to JPEG? If it converts them to JPEG, what
 >         compression does it use?

PNG and TIFF images are decompressed into simple bit arrays, and
optionally recompressed with Flate as specified by compression_level.

 > - Does pdftex have any support for CCITT or JBIG2?

Not directly.  Pdftex cannot take an image and compress it in CCITT
and JBIG2.  It can also not generate JPEG by itself (but it can copy
a JPEG file literally into its output).

However, you can achieve the effect by using a tool of your choice to
create a PDF image with any desired encoding (CCITT, JBIG2, JPEG), and
then embed the *PDF* image file.

It is not likely or desirable to add image compression to Pdftex
itself - external tools are much more flexible and powerful.


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