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vo_opengl: tone map on the maximum signal component 

This actually makes sure we don't decolor due to clipping even when the
signal itself exceeds the luma by a significant factor, which was pretty
common for saturated blues (and to a lesser degree, reds) - most
noticeable in skies etc.

This prevents the turn-the-sky-cyan effect of mobius tone mapping, and
should also improve the other tone mapping modes in quality.
This commit is contained in:
Niklas Haas 2017-07-27 09:36:48 +02:00
parent e1cc43182c
commit ea76f79e5d
No known key found for this signature in database
GPG Key ID: 9A09076581B27402
1 changed files with 25 additions and 19 deletions
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44
video/out/opengl/video_shaders.c
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@ -581,9 +581,18 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
{
GLSLF("// HDR tone mapping\n");
// To prevent discoloration, we tone map on the luminance only
// Desaturate the color using a coefficient dependent on the luminance
GLSL(float luma = dot(src_luma, color.rgb);)
GLSL(float luma_orig = luma;)
if (desat > 0) {
GLSLF("float overbright = max(luma - %f, 1e-6) / max(luma, 1e-6);\n", desat);
GLSL(color.rgb = mix(color.rgb, vec3(luma), overbright);)
}
// To prevent discoloration due to out-of-bounds clipping, we need to make
// sure to reduce the value range as far as necessary to keep the entire
// signal in range, so tone map based on the brightest component.
GLSL(float sig = max(max(color.r, color.g), color.b);)
GLSL(float sig_orig = sig;)
if (!ref_peak) {
// For performance, we want to do as few atomic operations on global
@ -591,7 +600,7 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
// We also want slightly more stable values, so use the group average
// instead of the group max
GLSLHF("shared uint group_sum = 0;\n");
GLSLF("atomicAdd(group_sum, uint(luma * %f));\n", MP_REF_WHITE);
GLSLF("atomicAdd(group_sum, uint(sig * %f));\n", MP_REF_WHITE);
// Have one thread in each work group update the frame maximum
GLSL(memoryBarrierBuffer();)
@ -619,15 +628,9 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
GLSLHF("const float sig_peak = %f;\n", ref_peak);
}
// Desaturate the color using a coefficient dependent on the brightness
if (desat > 0) {
GLSLF("float overbright = max(luma - %f, 1e-6) / max(luma, 1e-6);\n", desat);
GLSL(color.rgb = mix(color.rgb, vec3(luma), overbright);)
}
switch (algo) {
case TONE_MAPPING_CLIP:
GLSLF("luma = clamp(%f * luma, 0.0, 1.0);\n", isnan(param) ? 1.0 : param);
GLSLF("sig = clamp(%f * sig, 0.0, 1.0);\n", isnan(param) ? 1.0 : param);
break;
case TONE_MAPPING_MOBIUS:
@ -638,15 +641,15 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
GLSLF("const float b = (j*j - 2*j*sig_peak + sig_peak) / "
"max(1e-6, sig_peak - 1);\n");
GLSLF("const float scale = (b*b + 2*b*j + j*j) / (b-a);\n");
GLSL(luma = mix(luma, scale * (luma + a) / (luma + b), luma > j);)
GLSL(sig = mix(sig, scale * (sig + a) / (sig + b), sig > j);)
break;
case TONE_MAPPING_REINHARD: {
float contrast = isnan(param) ? 0.5 : param,
offset = (1.0 - contrast) / contrast;
GLSLF("luma = luma / (luma + %f);\n", offset);
GLSLF("const float lumascale = (sig_peak + %f) / sig_peak;\n", offset);
GLSL(luma *= lumascale;)
GLSLF("sig = sig / (sig + %f);\n", offset);
GLSLF("const float scale = (sig_peak + %f) / sig_peak;\n", offset);
GLSL(sig *= scale;)
break;
}
@ -656,19 +659,21 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
GLSLHF("return ((x * (%f*x + %f)+%f)/(x * (%f*x + %f) + %f)) - %f;\n",
A, C*B, D*E, A, B, D*F, E/F);
GLSLHF("}\n");
GLSL(luma = hable(luma) / hable(sig_peak);)
GLSL(sig = hable(sig) / hable(sig_peak);)
break;
}
case TONE_MAPPING_GAMMA: {
float gamma = isnan(param) ? 1.8 : param;
GLSLF("luma = pow(luma / sig_peak, %f);\n", 1.0/gamma);
GLSLF("const float cutoff = 0.05, gamma = %f;\n", 1.0/gamma);
GLSL(float scale = pow(cutoff / sig_peak, gamma) / cutoff;)
GLSL(sig = sig > cutoff ? pow(sig / sig_peak, gamma) : scale * sig;)
break;
}
case TONE_MAPPING_LINEAR: {
float coeff = isnan(param) ? 1.0 : param;
GLSLF("luma = %f / sig_peak * luma;\n", coeff);
GLSLF("sig = %f / sig_peak * sig;\n", coeff);
break;
}
@ -676,8 +681,9 @@ static void pass_tone_map(struct gl_shader_cache *sc, float ref_peak,
abort();
}
// Apply the computed brightness difference back to the original color
GLSL(color.rgb *= luma / luma_orig;)
// Apply the computed scale factor to the color, linearly to prevent
// discoloration
GLSL(color.rgb *= sig / sig_orig;)
}
// Map colors from one source space to another. These source spaces must be