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

[Even Rouault]

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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