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enable YCbCr compresison for jpeg in tiff write 

if we're writing RGB jpeg in tiff, enable YCbCR chrominance subsampling
for a 3x improvement in compression
This commit is contained in:
John Cupitt 2011-09-05 10:53:17 +01:00
parent 7fe104fee6
commit 6f125a6f31
2 changed files with 22 additions and 6 deletions
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1
ChangeLog
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@ -5,6 +5,7 @@
- generate has a 'stop' param to signal successful early termination
- added optional output args, eg. x/y for min
- CLI supports optional output args
- in im_vips2tiff, enable YCbCr compression for jpeg write
10/8/11 started 7.26.3
- don't use G_VALUE_COLLECT_INIT(), many platforms do not have a glib this

27
libvips/format/im_vips2tiff.c
View File

@ -119,6 +119,8 @@
* 12/7/11
* - use im__temp_name() for intermediates rather than polluting the
* output directory
* 5/9/11
* - enable YCbCr compression for jpeg write
*/
/*
@ -464,6 +466,18 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
TIFFSetField( tif, TIFFTAG_ORIENTATION, ORIENTATION_TOPLEFT );
TIFFSetField( tif, TIFFTAG_COMPRESSION, tw->compression );
if( tw->compression == COMPRESSION_JPEG ) {
TIFFSetField( tif, TIFFTAG_JPEGQUALITY, tw->jpqual );
/* Enable rgb->ycbcr conversion in the jpeg write. See also
* the photometric selection below.
*/
TIFFSetField( tif, TIFFTAG_JPEGCOLORMODE, JPEGCOLORMODE_RGB );
}
if( tw->predictor != -1 )
TIFFSetField( tif, TIFFTAG_PREDICTOR, tw->predictor );
/* Don't write mad resolutions (eg. zero), it confuses some programs.
*/
TIFFSetField( tif, TIFFTAG_RESOLUTIONUNIT, tw->resunit );
@ -472,12 +486,6 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
TIFFSetField( tif, TIFFTAG_YRESOLUTION,
IM_CLIP( 0.01, tw->yres, 10000 ) );
if( tw->compression == COMPRESSION_JPEG )
TIFFSetField( tif, TIFFTAG_JPEGQUALITY, tw->jpqual );
if( tw->predictor != -1 )
TIFFSetField( tif, TIFFTAG_PREDICTOR, tw->predictor );
/* Attach ICC profile.
*/
if( embed_profile( tw, tif ) )
@ -523,6 +531,13 @@ write_tiff_header( TiffWrite *tw, TIFF *tif, int width, int height )
TIFFSetField( tif,
TIFFTAG_INKSET, INKSET_CMYK );
}
else if( tw->compression == COMPRESSION_JPEG &&
tw->im->Bands == 3 )
/* This signals to libjpeg that it can do
* YCbCr chrominance subsampling from RGB, not
* that we will supply the image as YCbCr.
*/
photometric = PHOTOMETRIC_YCBCR;
else
photometric = PHOTOMETRIC_RGB;