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default tiff predictor to horizontal

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reduces default tiff lzw / deflate file size by ~20 - 30% at no performance
cost ... thanks @jrochkind

See https://github.com/jcupitt/libvips/issues/777
This commit is contained in:
John Cupitt 2017-10-19 08:50:16 +01:00
parent 6912fe91ed
commit b060883706
1 changed files with 8 additions and 11 deletions
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19
libvips/foreign/tiffsave.c
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@ -10,6 +10,8 @@
* - add properties flag
* 31/5/16
* - convert for jpg if jpg compression is on
* 19/10/17
* - predictor defaults to horizontal, reducing file size, usually
*/
/*
@ -198,7 +200,7 @@ vips_foreign_save_tiff_class_init( VipsForeignSaveTiffClass *class )
VIPS_ARGUMENT_OPTIONAL_INPUT,
G_STRUCT_OFFSET( VipsForeignSaveTiff, predictor ),
VIPS_TYPE_FOREIGN_TIFF_PREDICTOR,
VIPS_FOREIGN_TIFF_PREDICTOR_NONE );
VIPS_FOREIGN_TIFF_PREDICTOR_HORIZONTAL );
VIPS_ARG_STRING( class, "profile", 9,
_( "profile" ),
@ -298,7 +300,7 @@ vips_foreign_save_tiff_init( VipsForeignSaveTiff *tiff )
{
tiff->compression = VIPS_FOREIGN_TIFF_COMPRESSION_NONE;
tiff->Q = 75;
tiff->predictor = VIPS_FOREIGN_TIFF_PREDICTOR_NONE;
tiff->predictor = VIPS_FOREIGN_TIFF_PREDICTOR_HORIZONTAL;
tiff->tile_width = 128;
tiff->tile_height = 128;
tiff->resunit = VIPS_FOREIGN_TIFF_RESUNIT_CM;
@ -488,15 +490,10 @@ vips_foreign_save_tiff_buffer_init( VipsForeignSaveTiffBuffer *buffer )
*
* Use @Q to set the JPEG compression factor. Default 75.
*
* Use @predictor to set the predictor for lzw and deflate compression.
*
* Predictor is not set by default. There are three predictor values recognised
* at the moment (2007, July): 1 is no prediction, 2 is a horizontal
* differencing and 3 is a floating point predictor. Refer to the libtiff
* specifications for further discussion of various predictors. In short,
* predictor helps to better compress image, especially in case of digital
* photos or scanned images and bit depths > 8. Try it to find whether it
* works for your images.
* Use @predictor to set the predictor for lzw and deflate compression. It
* defaults to #VIPS_FOREIGN_TIFF_PREDICTOR_HORIZONTAL, meaning horizontal
* differencing. Please refer to the libtiff
* specifications for further discussion of various predictors.
*
* Use @profile to give the filename of a profile to be embedded in the TIFF.
* This does not affect the pixels which are written, just the way