From 2a51cf23a3caf193a467e21df011a7dbaadb262c Mon Sep 17 00:00:00 2001 From: John Cupitt Date: Wed, 14 Apr 2021 17:34:30 +0100 Subject: [PATCH] better Q computation stolen from cjxl.cc --- libvips/foreign/jxlsave.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/libvips/foreign/jxlsave.c b/libvips/foreign/jxlsave.c index 5e72bf8b..e3586820 100644 --- a/libvips/foreign/jxlsave.c +++ b/libvips/foreign/jxlsave.c @@ -215,11 +215,13 @@ vips_foreign_save_jxl_build( VipsObject *object ) return( -1 ); /* If Q is set and distance is not, use Q to set a rough distance - * value. Q 75 is distance 1.0, Q 100 is distance 0.0. + * value. Formula stolen from cjxl.c and very roughly approximates + * libjpeg values. */ - if( vips_object_argument_isset( object, "Q" ) && - !vips_object_argument_isset( object, "distance" ) ) - jxl->distance = (100 - jxl->Q) / 25.0; + if( !vips_object_argument_isset( object, "distance" ) ) + jxl->distance = jxl->Q >= 30 ? + 0.1 + (100 - jxl->Q) * 0.09 : + 6.4 + pow(2.5, (30 - jxl->Q) / 5.0f) / 6.25f; jxl->runner = JxlThreadParallelRunnerCreate( NULL, vips_concurrency_get() ); @@ -475,6 +477,7 @@ vips_foreign_save_jxl_init( VipsForeignSaveJxl *jxl ) jxl->distance = 1.0; jxl->effort = 7; jxl->lossless = FALSE; + jxl->Q = 75; } typedef struct _VipsForeignSaveJxlFile {