Improve scRGB support (libvips#3623)

ChangeLog

@@ -30,6 +30,7 @@
 - threaded write in tiffsave for tiled JPEG and JPEG2000 [jcupitt]
 - add vips_thread_execute() to the public API [jcupitt]
 - add "keep" flag to foreign savers, deprecate "strip" [a3mar]
+- improve scRGB handling [jcupitt]
 
 18/9/23 8.14.5
 

libvips/colour/LabQ2sRGB.c

@@ -372,8 +372,7 @@ vips_col_scRGB2sRGB_16(float R, float G, float B,
 {
 	vips_col_make_tables_RGB_16();
 
-	return vips_col_scRGB2sRGB(65536, vips_Y2v_16,
-		R, G, B, r, g, b, og);
+	return vips_col_scRGB2sRGB(65536, vips_Y2v_16, R, G, B, r, g, b, og);
 }
 
 /* Turn scRGB into BW. Return or=1 for out of gamut - g will contain an

libvips/colour/sRGB2scRGB.c

@@ -230,18 +230,22 @@ vips_sRGB2scRGB_build(VipsObject *object)
 	if (vips_check_bands_atleast(class->nickname, in, 3))
 		return -1;
 
+	// we are changing the gamma, so any profile on the image can no longer
+	// work (and will cause horrible problems in any downstream colour
+	// handling)
+	if (vips_copy(in, &t[0], NULL))
+		return -1;
+	in = t[0];
+	vips_image_remove(in, VIPS_META_ICC_NAME);
+
 	format = in->Type == VIPS_INTERPRETATION_RGB16
 		? VIPS_FORMAT_USHORT
 		: VIPS_FORMAT_UCHAR;
 	if (in->BandFmt != format) {
-		if (vips_cast(in, &t[0], format, NULL))
+		if (vips_cast(in, &t[1], format, NULL))
 			return -1;
+		in = t[1];
 	}
-	else {
-		t[0] = in;
-		g_object_ref(t[0]);
-	}
-	in = t[0];
 
 	out = vips_image_new();
 	if (vips_image_pipelinev(out,

libvips/colour/scRGB2sRGB.c

@@ -201,6 +201,14 @@ vips_scRGB2sRGB_build(VipsObject *object)
 	if (vips_check_bands_atleast(class->nickname, in, 3))
 		return -1;
 
+	// we are changing the gamma, so any profile on the image can no longer
+	// work (and will cause horrible problems in any downstream colour
+	// handling)
+	if (vips_copy(in, &t[0], NULL))
+		return -1;
+	in = t[0];
+	vips_image_remove(in, VIPS_META_ICC_NAME);
+
 	switch (scRGB2sRGB->depth) {
 	case 16:
 		interpretation = VIPS_INTERPRETATION_RGB16;
@@ -213,14 +221,13 @@ vips_scRGB2sRGB_build(VipsObject *object)
 		break;
 
 	default:
-		vips_error(class->nickname,
-			"%s", _("depth must be 8 or 16"));
+		vips_error(class->nickname, "%s", _("depth must be 8 or 16"));
 		return -1;
 	}
 
-	if (vips_cast_float(in, &t[0], NULL))
+	if (vips_cast_float(in, &t[1], NULL))
 		return -1;
-	in = t[0];
+	in = t[1];
 
 	out = vips_image_new();
 	if (vips_image_pipelinev(out,

libvips/foreign/foreign.c

@@ -1469,7 +1469,6 @@ vips__foreign_convert_saveable(VipsImage *in, VipsImage **ready,
 		in->Type != VIPS_INTERPRETATION_CMYK &&
 		in->Type != VIPS_INTERPRETATION_sRGB &&
 		in->Type != VIPS_INTERPRETATION_RGB16 &&
-		in->Type != VIPS_INTERPRETATION_scRGB &&
 		vips_colourspace_issupported(in) &&
 		(saveable == VIPS_SAVEABLE_RGB ||
 			saveable == VIPS_SAVEABLE_RGBA ||

libvips/foreign/jxlsave.c

@@ -66,6 +66,8 @@
  * - add animation support
  *
  * - libjxl is currently missing error messages (I think)
+ *
+ * - add support encoding images with > 4 bands.
  */
 
 #define OUTPUT_BUFFER_SIZE (4096)
@@ -226,7 +228,7 @@ vips_foreign_save_jxl_build(VipsObject *object)
 {
 	VipsForeignSave *save = (VipsForeignSave *) object;
 	VipsForeignSaveJxl *jxl = (VipsForeignSaveJxl *) object;
-	VipsImage **t = (VipsImage **) vips_object_local_array(object, 5);
+	VipsImage **t = (VipsImage **) vips_object_local_array(object, 2);
 
 #ifdef HAVE_LIBJXL_0_7
 	JxlEncoderFrameSettings *frame_settings;
@@ -282,6 +284,17 @@ vips_foreign_save_jxl_build(VipsObject *object)
 		return -1;
 	in = t[0];
 
+	/* Mimics VIPS_SAVEABLE_RGBA.
+	 * FIXME: add support encoding images with > 4 bands.
+	 */
+	if (in->Bands > 4) {
+		if (vips_extract_band(in, &t[1], 0,
+				"n", 4,
+				NULL))
+			return -1;
+		in = t[1];
+	}
+
 	JxlEncoderInitBasicInfo(&jxl->info);
 
 	switch (in->BandFmt) {
@@ -523,9 +536,7 @@ vips_foreign_save_jxl_class_init(VipsForeignSaveJxlClass *class)
 
 	foreign_class->suffs = vips__jxl_suffs;
 
-	/* This lets throuigh scRGB too, which we then save as jxl float.
-	 */
-	save_class->saveable = VIPS_SAVEABLE_RGBA;
+	save_class->saveable = VIPS_SAVEABLE_ANY;
 	save_class->format_table = bandfmt_jxl;
 
 	VIPS_ARG_INT(class, "tier", 10,