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Re: JBIG2

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James Dow Allen <jdallen2000@yahoo.com> wrote:
> On Jan 18, 6:58 am, glen herrmannsfeldt <g...@ugcs.caltech.edu> wrote:
>> It seems that JBIG2 isn't a popular topic here, if anywhere.

> I read about JBIG two decades ago.  Was that similar to JBIG2,
> just somewhat simpler?  

JBIG2 is the next edition. I don't know exactly how they compare.

> One minor point on which my recollection differs:

> Gray-scale images, e.g. 4 or 8 bits per pixel, *were* allowed, with
> successive planes encoded.  A *VERY* simple trick was used to get
> a win:
>   Instead of encoding
>     [ b0, b1, b2, b3 ]
> where b0 os MSB and b3 LSB, they encode
>     [ b0, b0 .xor. b1, b1 .xor b2, b2 .xor. b3 ]
> where the k'th developed bit (k > 0) has about the entropy of b{k-1}.

I don't remember that one in JBIG2, but then I wasn't looking
for it, either. JBIG2 does allow for halftone images, though.

There are some IBM manuals that use a (halftone) gray over non-standard
features. It seems to come through in the scanned images I have
(using the generic encoder) though not quite as readable as the
original.

>> Specifically, JBIG2 uses an arithmetic coder with a context of 16
>> different neighbor pixels as predictors....
>> I wonder if anyone else has studied the optimal positions for
>> the AT pixels for different types of input files.

> What kind of predictor do they use?  If it's linear, the win
> by switching to non-linear filter would be bigger
> than optimizing pixel selection.
> (Yes, I realize I'm implying non-conformance.)

I think it is linear, though I am not so sure about that.
Conformance is important. JBIG2 is in PDF 1.4, so I can write PDF files
viewable in all modern viewers. 

-- glen

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JBIG2 glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-01-17 23:58 +0000
  Re: JBIG2 Thomas Richter <thor@math.tu-berlin.de> - 2012-01-18 09:04 +0100
    Re: JBIG2 glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-01-18 12:53 +0000
  Re: JBIG2 James Dow Allen <jdallen2000@yahoo.com> - 2012-01-18 11:55 -0800
    Re: JBIG2 Sebastian <s.gesemann@gmail.com> - 2012-01-18 12:17 -0800
    Re: JBIG2 Thomas Richter <thor@math.tu-berlin.de> - 2012-01-18 21:59 +0100
      Re: JBIG2 glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-01-18 22:22 +0000
    Re: JBIG2 glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-01-18 22:06 +0000

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