Re: FW: JJ2000 bug fix in entropy decoder

Richard,

Thanks for the heads up for the JJ2000 fix. I know you included test data 
but can you tell me which Grib2 files I can use as a test case so i can 
include it in my grib2 testsuite.

Thanks again,
Robb...





On Thu, 4 Sep 2008, Peter, Richard J CTR USAF AFWA AFWA/WDAC wrote:

> Hi Robb,
>
>
>
>   I received your contact from Steve Naples.  Below is a fix for
> JJ2000's entropy decoder that is required for Grib2 decoding.  The
> standard JJ2000 implementation has errors on single bit depth images
> that for the case of landSea mask drop a portion of Canada into the
> ocean.  All single bit-depth Grib2 records have problems when decoded.
> I have tried to feed the change back to the community, but thought you
> might appreciate the info so it could incorporated in a more timely
> manner to your converter.
>
>
>
>
>
> Richard Peter
>
> Sr. Software Engineer
>
> Raytheon - WDAC Project
>
> DSN: 271-9843
>
> Comm: (402) 294-9843
>
>
>
> -----Original Message-----
> From: Peter, Richard J CTR USAF AFWA AFWA/WDAC
> Sent: Thursday, September 04, 2008 11:36 AM
> To: 'address@hidden'
> Subject: JJ2000 bug fix in entropy decoder
>
>
>
> I'm trying to feed back a bug fix for JJ2000.  If I have the wrong
> contact please let me know.  I have a JPEG2000 Codestream that was not
> being properly decoded.  I found the error in the
> jj2000.j2k.entropy.decoder.StdEntropyDecoder.java.
>
>
>
>
>
>
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> I have attached the codestream in question.  It is a simple land/sea bit
> mask.  Using JJ2000 and an image viewer that can shift the image levels
> so that 0 is black and 1 is white, a good portion of Canada is dropped
> into the ocean.  The below change fixes the problem.
>
>
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> Details of fix:
>
>
>
> jj2000.j2k.entropy.decoder.StdEntropyDecoder.java
>
>
>
> line 1990: setmask = (3<<bp)>>1;
>
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>
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> Needs to be
>
>
>
> int one = (1<<bp);
>
>
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> int half = (one>>1);
>
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> setmask = one | half;
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> Must be changed for the case of bp = 30.
>
>
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> bp=30 causes the 3 to be shifted into the msb and when shifted back
> becomes
>
>
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> 0xE000 when it should be 0x6000
>
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> Using unsigned bitshift would also fix case of bp=30, but not sure if
> that would be the correct behavior
>
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> for bp = 31
>
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>
> setmask = (3<<bp)>>>1;
>
>
>
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>
>
> Richard Peter
>
>
>
> Sr. Software Engineer
>
>
>
> Raytheon - WDAC Project
>
>
>
> DSN: 271-9843
>
>
>
> Comm: (402) 294-9843

===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
===============================================================================