[gdal-dev] decoding consistency between JPEG2000 drivers

[Pierre Soille]

On 09/10/2015 20:56, Even Rouault wrote:
> Le vendredi 09 octobre 2015 20:26:34, Pierre Soille a écrit :
>> Dear GDLALers,
>>
>> recently we tested the following 3 JPEG2000 drivers: JP2ECW, JPEG2000,
>> and JP2OpenJPEG.  A jp2 file was opened by all three drivers and we
>> tested whether the decoded image were equal. To our suprise they are
>> not: theJPEG2000 and JP2OpenJPEG lead to the same decoded image but they
>> differ from the one obtained with JP2ECW.  Is this a bug in the
>> implementation of the JP2ECW driver or is there any rationale explanation?
> Pierre,
>
> I don't think the differences come from the GDAL drivers, but rather from 
> differences/bugs/features of the underlying libraries. Regarding JP2ECW, I 
> recall to have observed differences depending if you read component per 
> component or all components together. The version of the JP2 ECW SDK might 
> also have some influence.
>
> Even

Even,

thanks for your reply.  The tested version of the JP2 ECW SDK is 3.3. 
Regarding the comment by Jukka, I ran jhove on the jp2 file and got
(among many other infos) the following:
    CodingStyleDefault:
      CodingStyle: 0
      ProgressionOrder: 0
      NumberOfLayers: 1
      MultipleComponentTransformation: 0
      NumberDecompositionLevels: 5
      CodeBlockWidth: 4
      CodeBlockHeight: 4
      CodeBlockStyle: 0
      Transformation: 1

My understanding is that 'Transformation: 1' refers to a lossless
representation.  If this is confirmed, the JP2 ECW SDK driver v.3.3
should be used with care since it returns values that are not correct. 
Actually, even in the case of lossy compression, I would expect
different drivers to return exactly the same result (as it happens for
the JEG2000 and JP2OpenJPEG drivers in our test).

Many thanks,

Pierre


>
>> Thanks a lot in advance,
>>
>> Pierre
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