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add a -z option to cwebp, and WebPConfigLosslessPreset() function

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These are presets for lossless coding, similar to zlib.
The shortcut for lossless coding is now, e.g.:
   cwebp -z 5 in.png -o out_lossless.webp

There are 10 possible values for -z parameter:
   0 (fastest, lowest compression)
to 9 (slowest, best compression)

A reasonable tradeoff is -z 6, e.g.
-z 9 can be quite slow, so use with care.

This -z option is just a shortcut for some pre-defined
'-lossless -m xx -q yy' combinations.

Change-Id: I6ae716456456aea065469c916c2d5ca4d6c6cf04
This commit is contained in:
skal
2014-03-11 23:25:35 +01:00
parent 30176619c6
commit 65b99f1c92
4 changed files with 54 additions and 2 deletions
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20
src/enc/config.c
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@ -138,3 +138,23 @@ int WebPValidateConfig(const WebPConfig* config) {
//------------------------------------------------------------------------------
#define MAX_LEVEL 9
// Mapping between -z level and -m / -q parameter settings.
static const struct {
uint8_t method_;
uint8_t quality_;
} kLosslessPresets[MAX_LEVEL + 1] = {
{ 0, 0 }, { 1, 20 }, { 2, 25 }, { 3, 30 }, { 3, 50 },
{ 4, 50 }, { 4, 75 }, { 4, 90 }, { 5, 90 }, { 6, 100 }
};
int WebPConfigLosslessPreset(WebPConfig* config, int level) {
if (config == NULL || level < 0 || level > MAX_LEVEL) return 0;
config->lossless = 1;
config->method = kLosslessPresets[level].method_;
config->quality = kLosslessPresets[level].quality_;
return 1;
}
//------------------------------------------------------------------------------

10
src/webp/encode.h
View File

@ -20,7 +20,7 @@
extern "C" {
#endif
#define WEBP_ENCODER_ABI_VERSION 0x0202 // MAJOR(8b) + MINOR(8b)
#define WEBP_ENCODER_ABI_VERSION 0x0203 // MAJOR(8b) + MINOR(8b)
// Note: forward declaring enumerations is not allowed in (strict) C and C++,
// the types are left here for reference.
@ -167,6 +167,14 @@ static WEBP_INLINE int WebPConfigPreset(WebPConfig* config,
WEBP_ENCODER_ABI_VERSION);
}
// Activate the lossless compression mode with the desired efficiency level
// between 0 (fastest, lowest compression) and 9 (slower, best compression).
// A good default level is '6', providing a fair tradeoff between compression
// speed and final compressed size.
// This function will overwrite several fields from config: 'method', 'quality'
// and 'lossless'. Returns false in case of parameter error.
WEBP_EXTERN(int) WebPConfigLosslessPreset(WebPConfig* config, int level);
// Returns true if 'config' is non-NULL and all configuration parameters are
// within their valid ranges.
WEBP_EXTERN(int) WebPValidateConfig(const WebPConfig* config);