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Bink: clip AC coefficients during dequantization.

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Fixes artefacts with Neverwinter Nights WOTCLogo.bik
(http://drmccoy.de/zeugs/WOTCLogo.bik).
Fixes trac ticket #352.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
This commit is contained in:
Reimar Döffinger 2011-07-17 13:03:57 +02:00
parent f04d4345da
commit 47b71eea09
1 changed files with 18 additions and 2 deletions
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20
libavcodec/bink.c
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@ -571,6 +571,22 @@ static inline int binkb_get_value(BinkContext *c, int bundle_num)
return ret;
}
static inline DCTELEM dequant(DCTELEM in, uint32_t quant, int dc)
{
/* Note: multiplication is unsigned but we want signed shift
* otherwise clipping breaks.
* TODO: The official decoder does not use clipping at all
* but instead uses the full 32-bit result.
* However clipping at least gets rid of the case that a
* half-black half-white intra block gets black and white swapped
* and should cause at most minor differences (except for DC). */
int32_t res = in * quant;
res >>= 11;
if (!dc)
res = av_clip_int16(res);
return res;
}
/**
* Read 8x8 block of DCT coefficients.
*
@ -669,10 +685,10 @@ static int read_dct_coeffs(GetBitContext *gb, DCTELEM block[64], const uint8_t *
quant = quant_matrices[quant_idx];
block[0] = (block[0] * quant[0]) >> 11;
block[0] = dequant(block[0], quant[0], 1);
for (i = 0; i < coef_count; i++) {
int idx = coef_idx[i];
block[scan[idx]] = (block[scan[idx]] * quant[idx]) >> 11;
block[scan[idx]] = dequant(block[scan[idx]], quant[idx], 0);
}
return 0;