[gdal-dev] Possible interlaced 16-bit grayscale PNG read error

[Ray at Daylon]

That did the trick; thanks.

Ray


On 12/28/2024 9:15 AM, Even Rouault wrote:
> Hi,
> 
> This should be fixed per https://github.com/OSGeo/gdal/pull/11553 . This 
> is indeed a 25-year old issue. An indication of how 16-bit interlaced 
> PNGs are popular :-)
> 
> Even
> 
> Le 28/12/2024 à 10:42, Ray at Daylon via gdal-dev a écrit :
>> In GDAL 1.8.0 on little-endian platforms like x64, the PNG driver will 
>> not byteswap pixels from network order (big endian) to little-endian 
>> if the PNG is interlaced (or at least if it's 16-bit grayscale 
>> interlaced).
>>
>> Does anyone know if this was corrected in a future version?
>>
>> In pngdataset.cpp, PNGDataset::LoadScanline() has this code:
>>
>>     if( bInterlaced )
>>         return LoadInterlacedChunk( nLine );
>>
>> The early return causes this downstream byteswapping section:
>>
>>     if( nBitDepth == 16 )
>>         GDALSwapWords( row, 2, GetRasterXSize() * GetRasterCount(), 2 );
>>
>> to be skipped.
>>
>> LoadInterlacedChunk() as far as I can tell even in 3.9.2. doesn't
>> do any byteswapping.
>>
>>
>> Ray Gardener
>>
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>