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go.image/vp8: clamp the UV DC quantization factor to 132. 

This fixes the lossy_extreme_probabilities.webp conformance test.

LGTM=pascal.massimino, r
R=r, pascal.massimino
CC=golang-codereviews
https://golang.org/cl/145600043
This commit is contained in:
Nigel Tao 2014-10-01 09:39:28 +10:00
parent 3bcf25db01
commit 8a2d4aba20
1 changed files with 4 additions and 1 deletions
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5
vp8/quant.go
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@ -49,7 +49,10 @@ func (d *Decoder) parseQuant() {
if d.quant[i].y2[1] < 8 {
d.quant[i].y2[1] = 8
}
d.quant[i].uv[0] = dequantTableDC[clip(q+dquvDC, 0, 127)]
// The 117 is not a typo. The dequant_init function in the spec's Reference
// Decoder Source Code (http://tools.ietf.org/html/rfc6386#section-9.6 Page 145)
// says to clamp the LHS value at 132, which is equal to dequantTableDC[117].
d.quant[i].uv[0] = dequantTableDC[clip(q+dquvDC, 0, 117)]
d.quant[i].uv[1] = dequantTableAC[clip(q+dquvAC, 0, 127)]
}
}