colour: add support for auto-selecting the rendering intent (#4366)

kleisauke · web-flow · commit 917d6f019c04 · 2025-01-29T14:48:56.000Z
* colour: add support for auto-selecting the rendering intent Via the `VIPS_INTENT_AUTO` enum value. Resolves: #3475. * colour: leave room for possible new rendering intents
diff --git a/ChangeLog b/ChangeLog
@@ -6,6 +6,7 @@
 - tiffload: add support for fail_on flag [lovell]
 - tiffload: add support for unlimited flag (requires libtiff 4.7.0+) [lovell]
 - much more reliable operation caching
+- colour: add support for auto-selecting the rendering intent [kleisauke]
 
 8.16.1
 
diff --git a/libvips/colour/icc_transform.c b/libvips/colour/icc_transform.c
@@ -106,6 +106,7 @@
  * @VIPS_INTENT_RELATIVE: relative colorimetric rendering intent
  * @VIPS_INTENT_SATURATION: saturation rendering intent
  * @VIPS_INTENT_ABSOLUTE: absolute colorimetric rendering intent
+ * @VIPS_INTENT_AUTO: the rendering intent that the profile suggests
  *
  * The rendering intent. #VIPS_INTENT_ABSOLUTE is best for
  * scientific work, #VIPS_INTENT_RELATIVE is usually best for
@@ -620,16 +621,18 @@ vips_icc_load_profile_blob(VipsIcc *icc, VipsBlob *blob,
 	}
 
 	icc->selected_intent = icc->intent;
-	if (!cmsIsIntentSupported(profile, icc->intent, direction)) {
+	if (icc->intent == VIPS_INTENT_AUTO ||
+		!cmsIsIntentSupported(profile, icc->intent, direction))
 		icc->selected_intent = (VipsIntent) cmsGetHeaderRenderingIntent(
 			profile);
 
+	if (icc->intent != VIPS_INTENT_AUTO &&
+		icc->selected_intent != icc->intent)
 		g_warning(_("fallback to suggested %s intent, as profile "
 					"does not support %s %s intent"),
 			vips_enum_nick(VIPS_TYPE_INTENT, icc->selected_intent),
 			vips_enum_nick(VIPS_TYPE_INTENT, icc->intent),
 			direction == LCMS_USED_AS_INPUT ? _("input") : _("output"));
-	}
 
 #ifdef DEBUG
 	vips_icc_print_profile("loaded from blob to make", profile);
diff --git a/libvips/include/vips/colour.h b/libvips/include/vips/colour.h
@@ -93,13 +93,18 @@ extern "C" {
 #define VIPS_D3250_Y0 (100.0)
 #define VIPS_D3250_Z0 (45.8501)
 
-/* Note: constants align with those defined in lcms2.h.
+/* Note: constants align with those defined in lcms2.h, except for
+ * VIPS_INTENT_AUTO, which is libvips-specific.
  */
 typedef enum {
 	VIPS_INTENT_PERCEPTUAL = 0,
 	VIPS_INTENT_RELATIVE,
 	VIPS_INTENT_SATURATION,
 	VIPS_INTENT_ABSOLUTE,
+	/* Leave room for possible new rendering intents beyond the
+	 * four standard ones.
+	 */
+	VIPS_INTENT_AUTO = 32,
 	VIPS_INTENT_LAST
 } VipsIntent;
 
