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September 2007

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2007.09.23 16:42 "G3 fax: EOL needed at the beginning of each strip?", by Comsquare Martin Osieka
2007.09.24 01:27 "Re: G3 fax: EOL needed at the beginning of each strip?", by Bob Friesenhahn
2007.09.24 05:56 "Re: G3 fax: EOL needed at the beginning of each strip?", by Joris Van Damme
2007.09.24 07:24 "Re: G3 fax: EOL needed at the beginning of each strip?", by Comsquare Martin Osieka
2007.09.24 07:51 "Re: G3 fax: EOL needed at the beginning of each strip?", by Joris Van Damme
2007.09.24 08:01 "Re: G3 fax: EOL needed at the beginning of each strip?", by Andy Cave
2007.09.24 08:32 "Re: G3 fax: EOL needed at the beginning of each strip?", by Joris Van Damme
2007.09.24 08:52 "Re: G3 fax: EOL needed at the beginning of each strip?", by Comsquare Martin Osieka
2007.09.24 08:58 "Re: G3 fax: EOL needed at the beginning of each strip?", by Andy Cave
2007.09.24 08:45 "Re: G3 fax: EOL needed at the beginning of each strip?", by Andy Cave
2007.09.24 09:03 "Re: G3 fax: EOL needed at the beginning of each strip?", by Joris Van Damme

2007.09.24 08:52 "Re: G3 fax: EOL needed at the beginning of each strip?", by Comsquare Martin Osieka

> I'm curious - where in the spec does it indicate strips have to start with

You may interpret this from TIFF 6.0 section 11 "CCITT Bilevel Encoding"

    Strips and Tiles.
    When CCITT bi-level encoding is employed, interaction with
    stripping (Section 3) and tiling (Section 15) is as follows:
    a. Decompose the image into segments-individual pixel arrays 
representing
        the desired strip or tile configuration. The CCITT encoding 
procedures are
        applied most flexibly if the segments each have a multiple of 4 
lines.
    b. Individually encode each segment according to the specified CCITT 
bilevel
        encoding, as if each segment is a separate raster-graphic image.

Means strips should be encoded independent from each other.
I do not have access to the CCITT spec in the moment, but I guess they are 
telling an image must start with EOL.

Still section 10 tells no EOLs needed...
So I would expect T.4 TIFFs containing no EOLs at all are legal.

Martin

----- Original Message ----- 
From: "Andy Cave" <andy.cave@hamillroad.com>
To: "Joris" <joris.at.lebbeke@skynet.be>; "ComSquare Martin Osieka"
<martin.osieka@comsquare.ch>; <tiff@lists.maptools.org>
Sent: Monday, September 24, 2007 10:01 AM
Subject: Re: [Tiff] G3 fax: EOL needed at the beginning of each strip?


> Hi Joris,
>
> I'm curious - where in the spec does it indicate strips have to start with
> EOL? I don't remember it saying so, and checking quickly, I can't find a
> reference to that.
>
> Thanks,
>
> Andy.
>
> ----- Original Message ----- 
> From: "Joris" <joris.at.lebbeke@skynet.be>
> To: "ComSquare Martin Osieka" <martin.osieka@comsquare.ch>;
> <tiff@lists.maptools.org>
> Sent: Monday, September 24, 2007 6:56 AM
> Subject: Re: [Tiff] G3 fax: EOL needed at the beginning of each strip?
>
>
>> Martin,
>> ...
>> The spec clearly indicates strips have to start with EOL. Unfortunately,
>> I've a reasonable amount (i.e. not just a fluke) of testimages where
>> garbage data preceeds the G3 block. LibTiff succeeds on these images by
>> skipping to the first EOL. If we were to change LibTiff to start decoding
>> right away, more unexpected stuff will happen on these images with
>> preceeding garbage data that might just be more frequent.
>>
>> In AsTiff, what I do if the strip or tile doesn't start with an EOL, is
>> actually test and see if a line of desired length can successfully be
>> decoded from the preceeding data, and if that data then is followed by an
>> EOL. If so, I regard that the first line. If not, the code starts at the
>> first EOL instead. This works on both the testimages with random
>> preceeding data, and the testimages that just lack the first EOL. But the
>> LibTiff fax decoder being as it is, a heap of macro's with embedded
>> macro's that nobody at this stage can easilly decipher, it may be hard to
>> make it behave equally intelligent.
>> ...
>
>