Add convert_rgb_gamma().3026-mpeg2-colour

3 files changed, 60 insertions, 3 deletions

diff --git a/src/colour_conversion.cc b/src/colour_conversion.cc
index 5e3da078..b041ba3e 100644
--- a/src/colour_conversion.cc
+++ b/src/colour_conversion.cc
@@ -547,7 +547,9 @@ dcp::combined_rgb_to_xyz(ColourConversion const & conversion, double* matrix)
 PiecewiseLUT2
 dcp::make_inverse_gamma_lut(shared_ptr<const TransferFunction> fn, int scale)
 {
-	/* The parameters here were chosen by trial and error to reduce errors when running rgb_xyz_lut_test */
+	/* The parameters here were chosen by trial and error to reduce errors when running
+	 * inverse_j2k_lut_test and inverse_mpeg2_lut_test.
+	 */
 	return PiecewiseLUT2(fn, 0.062, 16, 12, true, scale);
 }
 
@@ -641,3 +643,38 @@ dcp::rgb_to_xyz(
 {
 	rgb_to_xyz_internal(rgb, dst, dst, dst, size, stride, conversion);
 }
+
+
+void
+dcp::convert_rgb_gamma(
+	uint8_t* rgb,
+	dcp::Size size,
+	int stride,
+	ColourConversion const& conversion
+	)
+{
+	auto lut_in = conversion.in()->double_lut(0, 1, 8, false);
+	auto lut_out = make_inverse_gamma_lut(conversion.out_mpeg2(), 255);
+
+	for (int y = 0; y < size.height; ++y) {
+		auto p = reinterpret_cast<uint8_t*>(rgb + y * stride);
+		for (int x = 0; x < size.width; ++x) {
+
+			/* In gamma LUT */
+			auto r = lut_in[p[0]];
+			auto g = lut_in[p[1]];
+			auto b = lut_in[p[2]];
+
+			/* Clamp */
+			r = max(0.0, min(1.0, r));
+			g = max(0.0, min(1.0, g));
+			b = max(0.0, min(1.0, b));
+
+			/* Out gamma LUT */
+			*p++ = lut_out.lookup(r);
+			*p++ = lut_out.lookup(g);
+			*p++ = lut_out.lookup(b);
+		}
+	}
+}
+
diff --git a/src/colour_conversion.h b/src/colour_conversion.h
index ea470e22..c8439636 100644
--- a/src/colour_conversion.h
+++ b/src/colour_conversion.h
@@ -285,6 +285,14 @@ extern std::shared_ptr<OpenJPEGImage> rgb_to_xyz(
 extern void combined_rgb_to_xyz(ColourConversion const & conversion, double* matrix);
 
 
+extern void convert_rgb_gamma(
+	uint8_t* rgb,
+	dcp::Size size,
+	int stride,
+	ColourConversion const& conversion
+	);
+
+
 }
 
 #endif
diff --git a/test/colour_conversion_test.cc b/test/colour_conversion_test.cc
index aff178f5..9f5476b8 100644
--- a/test/colour_conversion_test.cc
+++ b/test/colour_conversion_test.cc
@@ -273,8 +273,8 @@ BOOST_AUTO_TEST_CASE(rgb_xyz_test)
 }
 
 
-/** Check the piecewise LUT that is used for inverse gamma calculation */
-BOOST_AUTO_TEST_CASE (rgb_xyz_lut_test)
+/** Check the piecewise LUT that is used for inverse J2K gamma calculation */
+BOOST_AUTO_TEST_CASE(inverse_j2k_lut_test)
 {
 	auto conversion = dcp::ColourConversion::rec709_to_dcp();
 	auto lut = dcp::make_inverse_gamma_lut(conversion.out_j2k(), 4095);
@@ -285,6 +285,18 @@ BOOST_AUTO_TEST_CASE (rgb_xyz_lut_test)
 }
 
 
+/** Check the piecewise LUT that is used for inverse MPEG2 gamma calculation */
+BOOST_AUTO_TEST_CASE(inverse_mpeg2_lut_test)
+{
+	auto conversion = dcp::ColourConversion::rec709_to_dcp();
+	auto lut = dcp::make_inverse_gamma_lut(conversion.out_mpeg2(), 255);
+
+	for (double x = 0; x < 1; x += 0.000001) {
+		BOOST_CHECK(std::abs(lut.lookup(x) - lrint(pow(x, 1 / 2.4) * 255)) < 2);
+	}
+}
+
+
 static list<string> notes;
 
 static void