Add proper formats for sRGB without alpha.

[movit] / gamma_compression_effect.cpp

diff --git a/gamma_compression_effect.cpp b/gamma_compression_effect.cpp
index 5581fca32c38c14e15fa7905460761a68d271ddb..079f849e16a62445c6862f6477fa84a511f920be 100644 (file)
--- a/gamma_compression_effect.cpp
+++ b/gamma_compression_effect.cpp
@@ -1,56 +1,116 @@
-#include <math.h>
-#include <string.h>

 #include <assert.h>
 
 #include <assert.h>
 

+#include "effect_util.h"

 #include "gamma_compression_effect.h"
 #include "util.h"
 
 #include "gamma_compression_effect.h"
 #include "util.h"
 

+using namespace std;
+
+namespace movit {
+

 GammaCompressionEffect::GammaCompressionEffect()
        : destination_curve(GAMMA_LINEAR)
 {
        register_int("destination_curve", (int *)&destination_curve);
 GammaCompressionEffect::GammaCompressionEffect()
        : destination_curve(GAMMA_LINEAR)
 {
        register_int("destination_curve", (int *)&destination_curve);

-       memset(compression_curve, 0, sizeof(compression_curve));
-       register_1d_texture("compression_curve_tex", compression_curve, COMPRESSION_CURVE_SIZE);

 }
 
 }
 

-std::string GammaCompressionEffect::output_fragment_shader()
+string GammaCompressionEffect::output_fragment_shader()

 {
        if (destination_curve == GAMMA_LINEAR) {
                return read_file("identity.frag");
        }
 {
        if (destination_curve == GAMMA_LINEAR) {
                return read_file("identity.frag");
        }

-       if (destination_curve == GAMMA_sRGB) {
-               for (unsigned i = 0; i < COMPRESSION_CURVE_SIZE; ++i) {
-                       float x = i / (float)(COMPRESSION_CURVE_SIZE - 1);
-                       if (x < 0.0031308f) {
-                               compression_curve[i] = 12.92f * x;
-                       } else {
-                               compression_curve[i] = 1.055f * pow(x, 1.0f / 2.4f) - 0.055f;
-                       }
-               }
-               invalidate_1d_texture("compression_curve_tex");
-               return read_file("gamma_compression_effect.frag");
-       }
-       if (destination_curve == GAMMA_REC_709 ||  // And Rec. 601, and 10-bit Rec. 2020.
+       if (destination_curve == GAMMA_sRGB ||
+           destination_curve == GAMMA_REC_709 ||  // Also includes Rec. 601, and 10-bit Rec. 2020.

            destination_curve == GAMMA_REC_2020_12_BIT) {
            destination_curve == GAMMA_REC_2020_12_BIT) {

-               // Rec. 2020, page 3.
-               float alpha, beta;
-               if (destination_curve == GAMMA_REC_2020_12_BIT) {
-                       alpha = 1.0993f;
-                       beta = 0.0181f;
-               } else {
-                       alpha = 1.099f;
-                       beta = 0.018f;
-               }
-               for (unsigned i = 0; i < COMPRESSION_CURVE_SIZE; ++i) {
-                       float x = i / (float)(COMPRESSION_CURVE_SIZE - 1);
-                       if (x < beta) {
-                               compression_curve[i] = 4.5f * x;
-                       } else {
-                               compression_curve[i] = alpha * pow(x, 0.45f) - (alpha - 1.0f);
-                       }
-               }
-               invalidate_1d_texture("compression_curve_tex");

                return read_file("gamma_compression_effect.frag");
        }
        assert(false);
 }
                return read_file("gamma_compression_effect.frag");
        }
        assert(false);
 }

+
+void GammaCompressionEffect::set_gl_state(GLuint glsl_program_num, const string &prefix, unsigned *sampler_num)
+{
+       Effect::set_gl_state(glsl_program_num, prefix, sampler_num);
+
+       // See GammaExpansionEffect for more details about the approximations in use;
+       // we will primarily deal with the differences here.
+       //
+       // Like in expansion, we have a piecewise curve that for very low values
+       // (up to some β) are linear. Above β, we have a power curve that looks
+       // like this:
+       //
+       //   y = ɑ x^ɣ - (ɑ - 1)
+       //
+       // Like in expansion, we want to approximate this by some minimax polynomial
+       // in the range β..1. However, in this case, ɣ is typically around 0.4, and
+       // x^0.4 is actually very hard to approximate accurately in this range.
+       // We do a little trick by instead asking for a polynomial of s=sqrt(x),
+       // which means we instead need something like s^0.8, which is much easier.
+       // This warps the input space a bit as seen by the minimax algorithm,
+       // but since we are optimizing for _maximum_ error and not _average_,
+       // we should not add any extra weighting factors.
+       //
+       // However, since we have problems reaching the desired accuracy (~25%
+       // of a pixel level), especially for sRGB, we modify w(x) from
+       // GammaExpansionEffect to remove the special handling of the area
+       // around β; it is not really as useful when the next step is just a
+       // dither and round anyway. We keep it around 1, though, since that
+       // seems to hurt less.
+       //
+       // The Maple commands this time around become (again using sRGB as an example):
+       //
+       // > alpha := 1.055;
+       // > beta := 0.0031308;
+       // > gamma_ := 1.0/2.4;
+       // > w := x -> piecewise(x > 0.999, 10, 1);
+       // > numapprox[minimax](alpha * (x^2)^gamma_ - (alpha - 1), x=sqrt(beta)..1, [4,0], w(x^2), 'maxerror');
+       //
+       // Since the error here is possible to interpret on a uniform scale,
+       // we also show it as a value relative to a 8-, 10- or 12-bit pixel level,
+       // as appropriate.
+
+       if (destination_curve == GAMMA_sRGB) {
+               // From the Wikipedia article on sRGB; ɑ (called a+1 there) = 1.055,
+               // β = 0.0031308, ɣ = 1/2.4.
+               // maxerror      = 0.000785 = 0.200 * 255
+               // error at 1.0  = 0.000078 = 0.020 * 255
+               set_uniform_float(glsl_program_num, prefix, "linear_scale", 12.92);
+               set_uniform_float(glsl_program_num, prefix, "c0", -0.03679675939);
+               set_uniform_float(glsl_program_num, prefix, "c1", 1.443803073);
+               set_uniform_float(glsl_program_num, prefix, "c2", -0.9239780987);
+               set_uniform_float(glsl_program_num, prefix, "c3", 0.8060491596);
+               set_uniform_float(glsl_program_num, prefix, "c4", -0.2891558568);
+               set_uniform_float(glsl_program_num, prefix, "beta", 0.0031308);
+       }
+       if (destination_curve == GAMMA_REC_709) {  // Also includes Rec. 601, and 10-bit Rec. 2020.
+               // Rec. 2020, page 3; ɑ = 1.099, β = 0.018, ɣ = 0.45.
+               // maxerror      = 0.000131 = 0.033 * 255 = 0.134 * 1023
+               // error at 1.0  = 0.000013 = 0.003 * 255 = 0.013 * 1023
+               set_uniform_float(glsl_program_num, prefix, "linear_scale", 4.5);
+               set_uniform_float(glsl_program_num, prefix, "c0", -0.08541688528);
+               set_uniform_float(glsl_program_num, prefix, "c1", 1.292793370);
+               set_uniform_float(glsl_program_num, prefix, "c2", -0.4070417645);
+               set_uniform_float(glsl_program_num, prefix, "c3", 0.2923891828);
+               set_uniform_float(glsl_program_num, prefix, "c4", -0.09273699351);
+               set_uniform_float(glsl_program_num, prefix, "beta", 0.018);
+       }
+       if (destination_curve == GAMMA_REC_2020_12_BIT) {
+               // Rec. 2020, page 3; ɑ = 1.0993, β = 0.0181, ɣ = 0.45.
+               // maxerror      = 0.000130 = 0.533 * 4095
+               // error at 1.0  = 0.000013 = 0.053 * 4095
+               //
+               // Note that this error is above one half of a pixel level,
+               // which means that a few values will actually be off in the lowest
+               // bit. (Removing the constraint for x=1 will only take this down
+               // from 0.553 to 0.501; adding a fifth order can get it down to
+               // 0.167, although this assumes working in fp64 and not fp32.)
+               set_uniform_float(glsl_program_num, prefix, "linear_scale", 4.5);
+               set_uniform_float(glsl_program_num, prefix, "c0", -0.08569685663);
+               set_uniform_float(glsl_program_num, prefix, "c1", 1.293000900);
+               set_uniform_float(glsl_program_num, prefix, "c2", -0.4067291321);
+               set_uniform_float(glsl_program_num, prefix, "c3", 0.2919741179);
+               set_uniform_float(glsl_program_num, prefix, "c4", -0.09256205770);
+               set_uniform_float(glsl_program_num, prefix, "beta", 0.0181);
+       }
+}
+
+}  // namespace movit