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Re: JSTOR and accessibility

From: David Woolley <david@djwhome.demon.co.uk>
Date: Wed, 29 May 2002 07:48:33 +0100 (BST)
Message-Id: <200205290648.g4T6mXd01174@djwhome.demon.co.uk>
To: w3c-wai-ig@w3.org

> I personally cannot see how providing TIFFs (which are essentially
> non-compressed graphic files - ie: pictures) as downloadable files for
> the

Whilst providing TIFFs is essentially slightly worse than using 
PDF files created with Adobe Acrobat capture (with OCR turned off), if
used on material that has never been through a computer in text form,
and considerably worse than using normal PDF on machine readable text
or Acrobat Capture PDF with OCR turned on, it does not produce
uncompressed graphics files.

TIFF is actually a framework for providing information about graphic
files, rather than one particular format.  It can wrap documents in 
essentially JPEG, GIF (LZW), or fax compression modes, as well as
uncompressed documents.  In the case of material consisting of text
and line art only, it can use group 4 fax encoding in two dimensional
mode, which is probably about the best available compression scheme of
all for that sort of material (other than recovering the text).

Different TIFF viewers can support different options, although the
Image Viewer application with recent Windows (Wang/Kodak/name of the day)
can certainly handle group 4 fax - although that is only of interest for
sighted users.

Acrobat Capture is the tool that embeds a scan, but can also embed a 
parallel OCRed at source, text version.  Normal PDF means PDF files 
which instruct the viewer to draw characters and character strings,
imaging them in the viewer, rather than at source.
Received on Wednesday, 29 May 2002 03:10:40 UTC

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