From: "Ronald S. Bultje" <[email protected]>
We operated on 31-bits, but with e.g. lanczos scaling, values can
add up to beyond 0x80000000, thus leading to output of zeroes. Drop
one bit of precision fixes this.
---
libswscale/swscale.c | 18 +++++++++---------
1 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/libswscale/swscale.c b/libswscale/swscale.c
index 29fd08d..74c9225 100644
--- a/libswscale/swscale.c
+++ b/libswscale/swscale.c
@@ -206,7 +206,7 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const
int32_t **lumSrc,
int i;
uint16_t *yDest = dest[0], *uDest = dest[1], *vDest = dest[2],
*aDest = CONFIG_SWSCALE_ALPHA ? dest[3] : NULL;
- int shift = 15 + 16 - output_bits;
+ int shift = 15 + 16 - output_bits - 1;
#define output_pixel(pos, val) \
if (big_endian) { \
@@ -223,24 +223,24 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const
int32_t **lumSrc,
} \
}
for (i = 0; i < dstW; i++) {
- int val = 1 << (30-output_bits);
+ int val = 1 << (30-output_bits - 1);
int j;
for (j = 0; j < lumFilterSize; j++)
- val += lumSrc[j][i] * lumFilter[j];
+ val += (lumSrc[j][i] * lumFilter[j]) >> 1;
output_pixel(&yDest[i], val);
}
if (uDest) {
for (i = 0; i < chrDstW; i++) {
- int u = 1 << (30-output_bits);
- int v = 1 << (30-output_bits);
+ int u = 1 << (30-output_bits - 1);
+ int v = 1 << (30-output_bits - 1);
int j;
for (j = 0; j < chrFilterSize; j++) {
- u += chrUSrc[j][i] * chrFilter[j];
- v += chrVSrc[j][i] * chrFilter[j];
+ u += (chrUSrc[j][i] * chrFilter[j]) >> 1;
+ v += (chrVSrc[j][i] * chrFilter[j]) >> 1;
}
output_pixel(&uDest[i], u);
@@ -250,11 +250,11 @@ yuv2yuvX16_c_template(const int16_t *lumFilter, const
int32_t **lumSrc,
if (CONFIG_SWSCALE_ALPHA && aDest) {
for (i = 0; i < dstW; i++) {
- int val = 1 << (30-output_bits);
+ int val = 1 << (30-output_bits - 1);
int j;
for (j = 0; j < lumFilterSize; j++)
- val += alpSrc[j][i] * lumFilter[j];
+ val += (alpSrc[j][i] * lumFilter[j]) >> 1;
output_pixel(&aDest[i], val);
}
--
1.7.5.4
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