PDF, DjVu, scanned pages, text and line art vs. continuous-tone images (was Re: Many things)

From: Jim Leonard <trixter_at_oldskool.org>
Date: Mon Jan 31 15:15:17 2005

Keep in mind that I am not an advocate of DjVu, I'm just pointing out some
technical details why PDF is not 100% perfect for everything. Read below:

Eric Smith wrote:
>>DjVu has other advantages, such as local/window/viewport decoding of
>>images with ludicrously high dimensions/resolutions but I understand
>>your point.
> I'm not sure I fully understand, but it doesn't sound like anything
> that the PDF format can't support. I would rather invest effort into
> improving the capabilities of free PDF viewer software such as xpdf
> rather than pushing a different standard.

PDF cannot support local decoding (at least, not without some major redesign).
  DjVu supports decoding any local region of a gigantic bitmap, say,
20000x20000. For example, you could pan around said image in a window without
having to download it all.

>>Where are the tools to create DjVu-like PDF files?
> I've been doing it myself with an experimental version of my "tumble"
> program. With that, it's an entirely manual process. I have to split
> the continuous-tone images into a separate layer or file using a
> separate editor (such as Gimp). Then I use tumble to compose a page
> with the background as G4 and the images as JPEG.

You're not exactly helping your argument if you have to write your own software
to do it *and* it's laborious :-)

> I hope to automate the multi-color text problem in tumble using code
> derived from Tim Shoppa's "timify.c". Automating the detection and
> processing of continuous tone images is in my plans as well, but further
> out. There don't seem to be any good published algorithms for image
> detection, so I'll have to experiment with it. As a first step I plan
> to do 2D FFTs on areas of the page; text and line art should predominantly
> have DC and high frequencies, while continuous-tone images should have
> a more even frequency distribution.
> So far I'm doing this work by scanning a page twice, once in bilevel and
> once in greyscale or color. I do that because the published algorithms
> for converting greyscale text and line art to bilevel (thresholding) are
> nowhere near as good as what's done in a good scanner. Picture Elements
> makes a PCI card that can be used to do this (and even works with Linux),
> but it's very expensive so I really want a software-only solution.

All of this sounds like Pagis Pro, a 5+ year old program that interfaced with
scanners beyond 24-bit (most scanners are 30-, 36-, or more). It automatically
recognized text from graphics and encoded appropriately.
Jim Leonard (trixter_at_oldskool.org)                    http://www.oldskool.org/
Want to help an ambitious games project?             http://www.mobygames.com/
Or check out some trippy MindCandy at             http://www.mindcandydvd.com/
Received on Mon Jan 31 2005 - 15:15:17 GMT

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