From edf54887e2935a30f9d9a46dd806802c3c867c0e Mon Sep 17 00:00:00 2001 From: Ico Doornekamp Date: Thu, 24 Mar 2016 14:31:38 +0100 Subject: rtpdec_jpeg: fix low contrast image on low quality setting MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The problem is that the argument 'q' is of the type uint8_t. According to the JPEG standard, if 1 <= q <= 50, the scale factor 'S' should be 5000 / Q. Because the create_default_qtables() reuses the variable 'q' to store the result of this calculation, for small values of q < 19, q wil subsequently overflow and give wrong results in the calculated quantization tables. Instead, use a new variable 'S' (same name as in RFC2435) with the proper range to store the result of the division. Signed-off-by: Martin Storsjö --- libavformat/rtpdec_jpeg.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'libavformat') diff --git a/libavformat/rtpdec_jpeg.c b/libavformat/rtpdec_jpeg.c index 15324bf2ba..bc86b159de 100644 --- a/libavformat/rtpdec_jpeg.c +++ b/libavformat/rtpdec_jpeg.c @@ -186,16 +186,17 @@ static void create_default_qtables(uint8_t *qtables, uint8_t q) { int factor = q; int i; + uint16_t S; factor = av_clip(q, 1, 99); if (q < 50) - q = 5000 / factor; + S = 5000 / factor; else - q = 200 - factor * 2; + S = 200 - factor * 2; for (i = 0; i < 128; i++) { - int val = (default_quantizers[i] * q + 50) / 100; + int val = (default_quantizers[i] * S + 50) / 100; /* Limit the quantizers to 1 <= q <= 255. */ val = av_clip(val, 1, 255); -- cgit v1.2.3