colour: add support for auto-selecting the rendering intent

Introduce the `VIPS_INTENT_AUTO` enum value and use it as the default
for `vips_icc_transform()` and friends.

Resolves: libvips#3475.

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
 

libvips/colour/icc_transform.c

@@ -102,6 +102,7 @@
 
 /**
  * VipsIntent:
+ * @VIPS_INTENT_AUTO: the rendering intent that the profile suggests
  * @VIPS_INTENT_PERCEPTUAL: perceptual rendering intent
  * @VIPS_INTENT_RELATIVE: relative colorimetric rendering intent
  * @VIPS_INTENT_SATURATION: saturation rendering intent
@@ -159,6 +160,8 @@ typedef struct _VipsIcc {
 	int depth;
 	gboolean black_point_compensation;
 
+	VipsIntent selected_intent;
+
 	VipsBlob *in_blob;
 	cmsHPROFILE in_profile;
 	VipsBlob *out_blob;
@@ -446,7 +449,7 @@ vips_icc_build(VipsObject *object)
 	if (!(icc->trans = cmsCreateTransform(
 			  icc->in_profile, icc->in_icc_format,
 			  icc->out_profile, icc->out_icc_format,
-			  icc->intent, flags)))
+			  icc->selected_intent, flags)))
 		return -1;
 
 	if (VIPS_OBJECT_CLASS(vips_icc_parent_class)->build(object))
@@ -596,8 +599,8 @@ vips_image_is_profile_compatible(VipsImage *image, int profile_bands)
  * Don't set any errors since this is used to test compatibility.
  */
 static cmsHPROFILE
-vips_icc_load_profile_blob(VipsBlob *blob,
-	VipsImage *image, VipsIntent intent, int direction)
+vips_icc_load_profile_blob(VipsIcc *icc, VipsBlob *blob,
+	VipsImage *image, int direction)
 {
 	const void *data;
 	size_t size;
@@ -607,7 +610,7 @@ vips_icc_load_profile_blob(VipsBlob *blob,
 #ifdef DEBUG
 	printf("loading %s profile, intent %s, from blob %p\n",
 		direction == LCMS_USED_AS_INPUT ? _("input") : _("output"),
-		vips_enum_nick(VIPS_TYPE_INTENT, intent),
+		vips_enum_nick(VIPS_TYPE_INTENT, icc->intent),
 		blob);
 #endif /*DEBUG*/
 
@@ -617,6 +620,10 @@ vips_icc_load_profile_blob(VipsBlob *blob,
 		return NULL;
 	}
 
+	icc->selected_intent = icc->intent == VIPS_INTENT_AUTO
+		? (VipsIntent) cmsGetHeaderRenderingIntent(profile)
+		: icc->intent;
+
 #ifdef DEBUG
 	vips_icc_print_profile("loaded from blob to make", profile);
 #endif /*DEBUG*/
@@ -634,10 +641,10 @@ vips_icc_load_profile_blob(VipsBlob *blob,
 		return NULL;
 	}
 
-	if (!cmsIsIntentSupported(profile, intent, direction)) {
+	if (!cmsIsIntentSupported(profile, icc->selected_intent, direction)) {
 		VIPS_FREEF(cmsCloseProfile, profile);
 		g_warning(_("profile does not support %s %s intent"),
-			vips_enum_nick(VIPS_TYPE_INTENT, intent),
+			vips_enum_nick(VIPS_TYPE_INTENT, icc->selected_intent),
 			direction == LCMS_USED_AS_INPUT ? _("input") : _("output"));
 		return NULL;
 	}
@@ -654,8 +661,8 @@ vips_icc_verify_blob(VipsIcc *icc, VipsBlob **blob)
 {
 	if (*blob) {
 		VipsColourCode *code = (VipsColourCode *) icc;
-		cmsHPROFILE profile = vips_icc_load_profile_blob(*blob,
-			code->in, icc->intent, LCMS_USED_AS_INPUT);
+		cmsHPROFILE profile = vips_icc_load_profile_blob(icc, *blob,
+			code->in, LCMS_USED_AS_INPUT);
 
 		if (!profile) {
 			vips_area_unref((VipsArea *) *blob);
@@ -763,7 +770,7 @@ vips_icc_class_init(VipsIccClass *class)
 		_("Rendering intent"),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET(VipsIcc, intent),
-		VIPS_TYPE_INTENT, VIPS_INTENT_RELATIVE);
+		VIPS_TYPE_INTENT, VIPS_INTENT_AUTO);
 
 	VIPS_ARG_ENUM(class, "pcs", 6,
 		_("PCS"),
@@ -785,7 +792,7 @@ vips_icc_class_init(VipsIccClass *class)
 static void
 vips_icc_init(VipsIcc *icc)
 {
-	icc->intent = VIPS_INTENT_RELATIVE;
+	icc->intent = VIPS_INTENT_AUTO;
 	icc->pcs = VIPS_PCS_LAB;
 	icc->depth = 8;
 }
@@ -1024,8 +1031,8 @@ vips_icc_export_build(VipsObject *object)
 	}
 
 	if (icc->out_blob &&
-		!(icc->out_profile = vips_icc_load_profile_blob(icc->out_blob,
-			  NULL, icc->intent, LCMS_USED_AS_OUTPUT))) {
+		!(icc->out_profile = vips_icc_load_profile_blob(icc, icc->out_blob,
+			  NULL, LCMS_USED_AS_OUTPUT))) {
 		vips_error(class->nickname, "%s", _("no output profile"));
 		return -1;
 	}
@@ -1188,8 +1195,8 @@ vips_icc_transform_build(VipsObject *object)
 	}
 
 	if (icc->out_blob)
-		icc->out_profile = vips_icc_load_profile_blob(icc->out_blob,
-			NULL, icc->intent, LCMS_USED_AS_OUTPUT);
+		icc->out_profile = vips_icc_load_profile_blob(icc, icc->out_blob,
+			NULL, LCMS_USED_AS_OUTPUT);
 
 	if (!icc->out_profile) {
 		vips_error(class->nickname, "%s", _("no output profile"));

libvips/include/vips/colour.h

@@ -93,8 +93,12 @@ extern "C" {
 #define VIPS_D3250_Y0 (100.0)
 #define VIPS_D3250_Z0 (45.8501)
 
+/* 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_AUTO = -1,
+	VIPS_INTENT_PERCEPTUAL,
 	VIPS_INTENT_RELATIVE,
 	VIPS_INTENT_SATURATION,
 	VIPS_INTENT_ABSOLUTE,

libvips/resample/thumbnail.c

@@ -1031,7 +1031,7 @@ vips_thumbnail_class_init(VipsThumbnailClass *class)
 		_("Rendering intent"),
 		VIPS_ARGUMENT_OPTIONAL_INPUT,
 		G_STRUCT_OFFSET(VipsThumbnail, intent),
-		VIPS_TYPE_INTENT, VIPS_INTENT_RELATIVE);
+		VIPS_TYPE_INTENT, VIPS_INTENT_AUTO);
 
 	VIPS_ARG_ENUM(class, "fail_on", 121,
 		_("Fail on"),
@@ -1060,7 +1060,7 @@ vips_thumbnail_init(VipsThumbnail *thumbnail)
 	thumbnail->width = 1;
 	thumbnail->height = 1;
 	thumbnail->auto_rotate = TRUE;
-	thumbnail->intent = VIPS_INTENT_RELATIVE;
+	thumbnail->intent = VIPS_INTENT_AUTO;
 	thumbnail->fail_on = VIPS_FAIL_ON_NONE;
 }
 
@@ -1273,7 +1273,7 @@ vips_thumbnail_file_init(VipsThumbnailFile *file)
  * input image is broken.
  *
  * Use @intent to set the rendering intent for any ICC transform. The default
- * is #VIPS_INTENT_RELATIVE.
+ * is #VIPS_INTENT_AUTO, ie. use the rendering intent that the profile suggests.
  *
  * Use @fail_on to control the types of error that will cause loading to fail.
  * The default is #VIPS_FAIL_ON_NONE, ie. thumbnail is permissive.

test/test-suite/test_resample.py

@@ -241,7 +241,7 @@ def test_thumbnail(self):
     @pytest.mark.skipif(not pyvips.at_least_libvips(8, 5),
                         reason="requires libvips >= 8.5")
     def test_thumbnail_icc(self):
-        im = pyvips.Image.thumbnail(JPEG_FILE_XYB, 442, export_profile="srgb", intent="perceptual")
+        im = pyvips.Image.thumbnail(JPEG_FILE_XYB, 442, export_profile="srgb")
 
         assert im.width == 290
         assert im.height == 442

tools/vipsthumbnail.c

@@ -296,7 +296,7 @@ thumbnail_process(VipsObject *process, const char *name)
 		interesting = n;
 	}
 
-	intent = VIPS_INTENT_RELATIVE;
+	intent = VIPS_INTENT_AUTO;
 	if (thumbnail_intent) {
 		int n;