mirror of
https://github.com/webmproject/libwebp.git
synced 2024-12-25 13:18:22 +01:00
Updated the near-lossless level mapping.
Updated the near-lossless level mapping and make it correlated to lossy quality i.e 100 => minimum loss (in-fact no-loss) and the visual-quality loss increases with decrease in near-lossless level (quality) till value 0. The new mapping implies following (PSNR) loss-metric: -near_lossless 100: No-loss (bit-stream same as -lossless). -near_lossless 80: Very very high PSNR (around 54dB). -near_lossless 60: Very high PSNR (around 48dB). -near_lossless 40: High PSNR (around 42dB). -near_lossless 20: Moderate PSNR (around 36dB). -near_lossless 0: Low PSNR (around 30dB). Change-Id: I930de4b18950faf2868c97d42e9e49ba0b642960
This commit is contained in:
parent
19f0ba0eb9
commit
4c82284d2e
@ -616,7 +616,7 @@ static void HelpLong(void) {
|
||||
printf(" -noalpha ............... discard any transparency information\n");
|
||||
printf(" -lossless .............. encode image losslessly\n");
|
||||
printf(" -near_lossless <int> ... use near-lossless image\n"
|
||||
" preprocessing (0=off..100)\n");
|
||||
" preprocessing (0..100=off)\n");
|
||||
printf(" -hint <string> ......... specify image characteristics hint,\n");
|
||||
printf(" one of: photo, picture or graph\n");
|
||||
|
||||
|
@ -1,5 +1,5 @@
|
||||
.\" Hey, EMACS: -*- nroff -*-
|
||||
.TH CWEBP 1 "July 30, 2014"
|
||||
.TH CWEBP 1 "Feb 4, 2015"
|
||||
.SH NAME
|
||||
cwebp \- compress an image file to a WebP file
|
||||
.SH SYNOPSIS
|
||||
@ -222,7 +222,7 @@ Encode the image without any loss.
|
||||
Use near-lossless image preprocessing. This option adjusts pixel values
|
||||
to help compressibility, but has minimal impact on the visual quality.
|
||||
It triggers lossless compression mode automatically.
|
||||
Range is 0 (no preprocessing, the default) to 100.
|
||||
Range is 0 (maximum preprocessing) to 100 (no preprocessing, the default).
|
||||
.TP
|
||||
.BI \-hint " string
|
||||
Specify the hint about input image type. Possible values are:
|
||||
|
@ -47,7 +47,7 @@ int WebPConfigInitInternal(WebPConfig* config,
|
||||
config->emulate_jpeg_size = 0;
|
||||
config->thread_level = 0;
|
||||
config->low_memory = 0;
|
||||
config->near_lossless = 0;
|
||||
config->near_lossless = 100;
|
||||
|
||||
// TODO(skal): tune.
|
||||
switch (preset) {
|
||||
|
@ -125,9 +125,14 @@ static void NearLossless(int xsize, int ysize, uint32_t* argb,
|
||||
}
|
||||
|
||||
static int QualityToLimitBits(int quality) {
|
||||
// quality mapping 0..12 -> 5
|
||||
// 13..100 -> 4..1
|
||||
return MAX_LIMIT_BITS - (quality + 12) / 25;
|
||||
// quality mapping:
|
||||
// 0..19 -> 5
|
||||
// 0..39 -> 4
|
||||
// 0..59 -> 3
|
||||
// 0..79 -> 2
|
||||
// 0..99 -> 1
|
||||
// 100 -> 0
|
||||
return MAX_LIMIT_BITS - quality / 20;
|
||||
}
|
||||
|
||||
int VP8ApplyNearLossless(int xsize, int ysize, uint32_t* argb, int quality) {
|
||||
|
@ -1254,7 +1254,7 @@ WebPEncodingError VP8LEncodeStream(const WebPConfig* const config,
|
||||
}
|
||||
|
||||
// Apply near-lossless preprocessing.
|
||||
use_near_lossless = !enc->use_palette_ && config->near_lossless;
|
||||
use_near_lossless = !enc->use_palette_ && (config->near_lossless < 100);
|
||||
if (use_near_lossless) {
|
||||
if (!VP8ApplyNearLossless(width, height, picture->argb,
|
||||
config->near_lossless)) {
|
||||
|
Loading…
Reference in New Issue
Block a user