From 156e6a91e4cba186e99b8f48e64325c3bd85513d Mon Sep 17 00:00:00 2001
From: John Cupitt <jcupitt@gmail.com>
Date: Sat, 18 Jun 2022 16:01:51 +0100
Subject: [PATCH] try to improve jxl lossless, again

now seems to handle scrgb and srgb, lossless and lossy, with and without
an ICC profile

see https://github.com/libvips/libvips/issues/2872
---
 libvips/foreign/jxlsave.c | 41 +++++++++------------------------------
 1 file changed, 9 insertions(+), 32 deletions(-)

diff --git a/libvips/foreign/jxlsave.c b/libvips/foreign/jxlsave.c
index ddd84f92..b1fe1b9f 100644
--- a/libvips/foreign/jxlsave.c
+++ b/libvips/foreign/jxlsave.c
@@ -34,8 +34,8 @@
  */
 
 /*
-#define DEBUG
  */
+#define DEBUG
 
 #ifdef HAVE_CONFIG_H
 #include <config.h>
@@ -350,17 +350,21 @@ vips_foreign_save_jxl_build( VipsObject *object )
 		jxl->info.intensity_target = stonits;
 	}
 
-	/* We will be setting the ICC profile, and/or calling
-	 * JxlEncoderSetColorEncoding().
+	/* uses_original_profile forces libjxl to not use lossy XYB
+	 * colourspace. The name is very confusing.
 	 */
-	jxl->info.uses_original_profile = TRUE;
+	jxl->info.uses_original_profile = jxl->lossless;
 
 	if( JxlEncoderSetBasicInfo( jxl->encoder, &jxl->info ) ) {
 		vips_foreign_save_jxl_error( jxl, "JxlEncoderSetBasicInfo" );
 		return( -1 );
 	}
 
-	/* Set ICC profile.
+	/* Set the colour encoding. Either ICC based, or sRGB. 
+	 *
+	 * libjxl will use linear 0 - 1 by default for float, so we
+	 * don't need to call JxlColorEncodingSetToLinearSRGB() or
+	 * JxlColorEncodingSetToSRGB().
 	 */
 	if( vips_image_get_typeof( in, VIPS_META_ICC_NAME ) ) {
 		const void *data;
@@ -381,33 +385,6 @@ vips_foreign_save_jxl_build( VipsObject *object )
 		}
 	}
 
-	/* libjxl will use linear 0 - 1 by default for float, so we don't need
-	 * to call JxlColorEncodingSetToLinearSRGB() or
-	 * JxlColorEncodingSetToSRGB().
-	 */
-	if( in->Type == VIPS_INTERPRETATION_scRGB ) {
-#ifdef DEBUG
-		printf( "setting scRGB colourspace\n" );
-#endif /*DEBUG*/
-
-		JxlColorEncodingSetToLinearSRGB( &jxl->color_encoding, 
-			jxl->format.num_channels < 3 );
-	}
-	else {
-#ifdef DEBUG
-		printf( "setting sRGB colourspace\n" );
-#endif /*DEBUG*/
-
-		JxlColorEncodingSetToSRGB( &jxl->color_encoding, 
-			jxl->format.num_channels < 3 );
-	}
-
-	if( JxlEncoderSetColorEncoding( jxl->encoder, &jxl->color_encoding ) ) {
-		vips_foreign_save_jxl_error( jxl, 
-			"JxlEncoderSetColorEncoding" );
-		return( -1 );
-	}
-
 	/* Render the entire image in memory. libjxl seems to be missing
 	 * tile-based write at the moment.
 	 */