Re: DWA compression: fails due to insufficient buffer size

Vasil -

By any chance do you have an image you can share that trips this problem?
There are a couple of other places where compressBound() would be good to
use.

Thanks!
karl

On Thursday, January 22, 2015, Vasil Minkov <[email protected]>
wrote:

> Hello,
>
> While tracking an error report I found an issue with the DWA compression -
> it fails to compress certain input data.
> The problem is easily reproduced on attempt to store a small (8x8 pixels)
> single-channel (Luma only) EXR image using DWA compression.
> An exception "Data compression (zlib) failed." is thrown in such case. The
> problem also occurs when compressing small and noisy RGB tiles.
>
> It seems that the problem is in ImfDwaCompressor.cpp, in the following
> code fragment:
>
>                 ......
>                 uLongf destLen = (uLongf)
>                     (2 * (*totalAcUncompressedCount) * sizeof (unsigned
> short));
>
>                 if (Z_OK != ::compress2
>                                 ((Bytef *)outDataPtr,
> &destLen,
>                                  (Bytef *)_packedAcBuffer,
>                                  (uLong)(*totalAcUncompressedCount
>                                                 * sizeof (unsigned short)),
>                                  9))
>                 ......
>
> Under certain circumstances compress2() output size may exceed its input
> size, as specified in zlib's docs.
> Here is my fix of the problem:
>
>                 ......
>                 uLongf destLen = (uLongf)
>                     (2 * (*totalAcUncompressedCount) * sizeof (unsigned
> short));
>                 // compress2 requirement:
>                 //   "Upon entry, destLen is the total size of the
>                 //   destination buffer, which must be at least 0.1% larger
>                 //   than sourceLen plus 12 bytes"
>                 // Fulfill the above requirement in integer arithmetic
>                 destLen=((Int64)destLen*1001 + 1000)/1000 + 12;
>                 if (Z_OK != ::compress2
>                                 ((Bytef *)outDataPtr,
> &destLen,
>                                  (Bytef *)_packedAcBuffer,
>                                  (uLong)(*totalAcUncompressedCount
>                                                 * sizeof (unsigned short)),
>                                  9))
>                 ......
>
> zlib's ::compressBound() could also be used to calculate the buffer size.
>
> Regards,
>
> --
> Vasil Minkov
>
> VRay for 3ds Max developer
>
>
> _______________________________________________
> Openexr-devel mailing list
> [email protected]
> https://lists.nongnu.org/mailman/listinfo/openexr-devel
>

_______________________________________________
Openexr-devel mailing list
[email protected]
https://lists.nongnu.org/mailman/listinfo/openexr-devel