Add an implementation of RPDF dither on the final output.

[movit] / dither_effect_test.cpp

diff --git a/dither_effect_test.cpp b/dither_effect_test.cpp
new file mode 100644 (file)
index 0000000..81f6a24
--- /dev/null
+++ b/dither_effect_test.cpp
@@ -0,0 +1,54 @@
+// Unit tests for DitherEffect.
+
+#include <math.h>
+
+#include "test_util.h"
+#include "gtest/gtest.h"
+
+TEST(DitherEffectTest, NoDitherOnExactValues) {
+       const int size = 4;
+
+       float data[size * size] = {
+               0.0, 1.0, 0.0, 1.0,
+               0.0, 1.0, 1.0, 0.0,
+               0.0, 0.2, 1.0, 0.2,
+               0.0, 0.0, 0.0, 0.0,
+       };
+       unsigned char expected_data[size * size] = {
+               0, 255,   0, 255,
+               0, 255, 255,   0,
+               0,  51, 255,  51,
+               0,   0,   0,   0,
+       };
+       unsigned char out_data[size * size];
+
+       EffectChainTester tester(data, size, size, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR, GL_RGBA8);
+       tester.get_chain()->set_dither_bits(8);
+       tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
+
+       expect_equal(expected_data, out_data, size, size);
+}
+
+TEST(DitherEffectTest, SinusoidBelowOneLevelComesThrough) {
+       const float frequency = 0.3f * M_PI;
+       const unsigned size = 2048;
+       const float amplitude = 0.25f / 255.0f;  // 6 dB below what can be represented without dithering.
+
+       float data[size];
+       for (unsigned i = 0; i < size; ++i) {
+               data[i] = 0.2 + amplitude * sin(i * frequency);
+       }
+       unsigned char out_data[size];
+
+       EffectChainTester tester(data, size, 1, FORMAT_GRAYSCALE, COLORSPACE_sRGB, GAMMA_LINEAR, GL_RGBA8);
+       tester.get_chain()->set_dither_bits(8);
+       tester.run(out_data, GL_RED, COLORSPACE_sRGB, GAMMA_LINEAR);
+
+       // Measure how strong the given sinusoid is in the output.
+       float sum = 0.0f;       
+       for (unsigned i = 0; i < size; ++i) {
+               sum += 2.0 * (int(out_data[i]) - 0.2*255.0) * sin(i * frequency);
+       }
+
+       EXPECT_NEAR(amplitude, sum / (size * 255.0f), 1e-5);
+}