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MozJPEG chroma subsampling and quality (#235)

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* Adding chroma subsampling for mozjpeg

* Adding separate chroma quality.

* Preact sometimes removes the inline styles, this fixes it.

* Simplifying chroma subsample

* Adding comments
This commit is contained in:
Jake Archibald
2018-11-06 13:46:52 +00:00
committed by GitHub
parent e572b853e2
commit f396a5b784
8 changed files with 114 additions and 20 deletions
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23
codecs/mozjpeg_enc/mozjpeg_enc.cpp
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@@ -29,6 +29,10 @@ struct MozJpegOptions {
bool trellis_opt_zero;
bool trellis_opt_table;
int trellis_loops;
bool auto_subsample;
int chroma_subsample;
bool separate_chroma_quality;
int chroma_quality;
};
int version() {
@@ -119,9 +123,6 @@ val encode(std::string image_in, int image_width, int image_height, MozJpegOptio
*/
jpeg_set_defaults(&cinfo);
/* Now you can set any non-default parameters you wish to.
* Here we just illustrate the use of quality (quantization table) scaling:
*/
jpeg_set_colorspace(&cinfo, (J_COLOR_SPACE) opts.color_space);
if (opts.quant_table != -1) {
@@ -142,11 +143,23 @@ val encode(std::string image_in, int image_width, int image_height, MozJpegOptio
jpeg_c_set_bool_param(&cinfo, JBOOLEAN_TRELLIS_Q_OPT, opts.trellis_opt_table);
jpeg_c_set_int_param(&cinfo, JINT_TRELLIS_NUM_LOOPS, opts.trellis_loops);
// A little hacky to build a string for this, but it means we can use set_quality_ratings which
// does some useful heuristic stuff.
std::string quality_str = std::to_string(opts.quality);
if (opts.separate_chroma_quality && opts.color_space == JCS_YCbCr) {
quality_str += "," + std::to_string(opts.chroma_quality);
}
char const *pqual = quality_str.c_str();
set_quality_ratings(&cinfo, (char*) pqual, opts.baseline);
if (!opts.auto_subsample && opts.color_space == JCS_YCbCr) {
cinfo.comp_info[0].h_samp_factor = opts.chroma_subsample;
cinfo.comp_info[0].v_samp_factor = opts.chroma_subsample;
}
if (!opts.baseline && opts.progressive) {
jpeg_simple_progression(&cinfo);
} else {
@@ -209,6 +222,10 @@ EMSCRIPTEN_BINDINGS(my_module) {
.field("trellis_opt_zero", &MozJpegOptions::trellis_opt_zero)
.field("trellis_opt_table", &MozJpegOptions::trellis_opt_table)
.field("trellis_loops", &MozJpegOptions::trellis_loops)
.field("chroma_subsample", &MozJpegOptions::chroma_subsample)
.field("auto_subsample", &MozJpegOptions::auto_subsample)
.field("separate_chroma_quality", &MozJpegOptions::separate_chroma_quality)
.field("chroma_quality", &MozJpegOptions::chroma_quality)
;
function("version", &version);