fast image paging

[Camm Maguire]

Greetings!  I have a djvu mode which is designed for scholars reading,
annotating, and cross-referencing many large documents.  Right now I use
pbm formats and create-image.  This makes it easy to highlight and
correlate pixels with text, but the images can get quite large, making
handling sluggish on slower machines.  

Will I improve anything here using a compressed format like png?  Or,
when emacs displays and moves the image, does it decompress the image
anyway into the same sized internal data structure?

Take care,
--
Camm Maguire                                        address@hidden
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"The earth is but one country, and mankind its citizens."  --  Baha'u'llah