From: Carl Hetherington <cth@carlh.net>
Date: Fri, 10 Jun 2022 21:04:54 +0000 (+0200)
Subject: Fix incorrect burnt-in subtitle colours when burning into a DCP source (#2261).
X-Git-Tag: v2.16.14~13
X-Git-Url: https://git.carlh.net/gitweb/?p=dcpomatic.git;a=commitdiff_plain;h=9704833bdfc8c8f104203200be27f714fa677506

Fix incorrect burnt-in subtitle colours when burning into a DCP source (#2261).

dcp::combined_rgb_to_xyz was changed in libdcp (the values are no longer scaled
by 65535) but DoM wasn't changed, and there was no test to catch it.
---

diff --git a/src/lib/image.cc b/src/lib/image.cc
index 7b95e6766..f86c105d4 100644
--- a/src/lib/image.cc
+++ b/src/lib/image.cc
@@ -730,14 +730,14 @@ Image::alpha_blend (shared_ptr<const Image> other, Position<int> position)
 				double const b = lut_in[op[blue]];
 
 				/* RGB to XYZ, including Bradford transform and DCI companding */
-				double const x = max (0.0, min (65535.0, r * fast_matrix[0] + g * fast_matrix[1] + b * fast_matrix[2]));
-				double const y = max (0.0, min (65535.0, r * fast_matrix[3] + g * fast_matrix[4] + b * fast_matrix[5]));
-				double const z = max (0.0, min (65535.0, r * fast_matrix[6] + g * fast_matrix[7] + b * fast_matrix[8]));
+				double const x = max(0.0, min(1.0, r * fast_matrix[0] + g * fast_matrix[1] + b * fast_matrix[2]));
+				double const y = max(0.0, min(1.0, r * fast_matrix[3] + g * fast_matrix[4] + b * fast_matrix[5]));
+				double const z = max(0.0, min(1.0, r * fast_matrix[6] + g * fast_matrix[7] + b * fast_matrix[8]));
 
 				/* Out gamma LUT and blend */
-				tp[0] = lrint(lut_out[lrint(x)] * 65535) * alpha + tp[0] * (1 - alpha);
-				tp[1] = lrint(lut_out[lrint(y)] * 65535) * alpha + tp[1] * (1 - alpha);
-				tp[2] = lrint(lut_out[lrint(z)] * 65535) * alpha + tp[2] * (1 - alpha);
+				tp[0] = lrint(lut_out[lrint(x * 65535)] * 65535) * alpha + tp[0] * (1 - alpha);
+				tp[1] = lrint(lut_out[lrint(y * 65535)] * 65535) * alpha + tp[1] * (1 - alpha);
+				tp[2] = lrint(lut_out[lrint(z * 65535)] * 65535) * alpha + tp[2] * (1 - alpha);
 
 				tp += this_bpp / 2;
 				op += other_bpp;
diff --git a/test/image_test.cc b/test/image_test.cc
index 8d934bdd6..a529a3935 100644
--- a/test/image_test.cc
+++ b/test/image_test.cc
@@ -201,6 +201,44 @@ BOOST_AUTO_TEST_CASE (alpha_blend_test)
 }
 
 
+/** Test Image::alpha_blend when the "base" image is XYZ12LE */
+BOOST_AUTO_TEST_CASE (alpha_blend_test_onto_xyz)
+{
+	Image xyz(AV_PIX_FMT_XYZ12LE, dcp::Size(50, 50), Image::Alignment::PADDED);
+	xyz.make_black();
+
+	auto overlay = make_shared<Image>(AV_PIX_FMT_RGBA, dcp::Size(8, 8), Image::Alignment::PADDED);
+	for (int y = 0; y < 8; ++y) {
+		uint8_t* p = overlay->data()[0] + (y * overlay->stride()[0]);
+		for (int x = 0; x < 8; ++x) {
+			*p++ = 255;
+			*p++ = 0;
+			*p++ = 0;
+			*p++ = 255;
+		}
+	}
+
+	xyz.alpha_blend(overlay, Position<int>(4, 4));
+
+	for (int y = 0; y < 50; ++y) {
+		uint16_t* p = reinterpret_cast<uint16_t*>(xyz.data()[0]) + (y * xyz.stride()[0] / 2);
+		for (int x = 0; x < 50; ++x) {
+			std::cout << "x=" << x << ", y=" << y << "\n";
+			if (4 <= x && x < 12 && 4 <= y && y < 12) {
+				BOOST_REQUIRE_EQUAL(p[0], 45078U);
+				BOOST_REQUIRE_EQUAL(p[1], 34939U);
+				BOOST_REQUIRE_EQUAL(p[2], 13892U);
+			} else {
+				BOOST_REQUIRE_EQUAL(p[0], 0U);
+				BOOST_REQUIRE_EQUAL(p[1], 0U);
+				BOOST_REQUIRE_EQUAL(p[2], 0U);
+			}
+			p += 3;
+		}
+	}
+}
+
+
 /** Test merge (list<PositionImage>) with a single image */
 BOOST_AUTO_TEST_CASE (merge_test1)
 {