Gamma Correction for Resident Evil 4 (#81)

* feat(re4remake): add gamma correction, make gamma adjust by channel

- add sRGB -> 2.2 gamma correction
- make bt709Color a float3 as w is unused
- increase DICE ShoulderStart
- compensate for black crush with gamma correction in LUT scaling
- make gamma adjust work by channel instead of by luminance

* feat(re4remake): add gamma correction, make gamma adjust by channel

- add sRGB -> 2.2 gamma correction
- make bt709Color a float3 as w is unused
- increase DICE ShoulderStart
- compensate for black crush with gamma correction in LUT scaling
- make gamma adjust work by channel instead of by luminance

* fix(re4remake): fix gamma correction tooltip

src/games/re4remake/ConvertRec2020PS_0x6737588D.ps_6_6.hlsl

@@ -39,12 +39,15 @@ float4 main(noperspective float4 SV_Position: SV_Position,
             linear float2 TEXCOORD: TEXCOORD)
     : SV_Target {
   if (injectedData.toneMapType != 0) {
-    float4 bt709Color = tLinearImage.SampleLevel(PointBorder, TEXCOORD.xy, 0.0f);
+    float3 bt709Color = tLinearImage.SampleLevel(PointBorder, TEXCOORD.xy, 0.0f).rgb;
 
+    if (injectedData.toneMapGammaCorrection == 1.f) {
+      bt709Color = renodx::color::correct::GammaSafe(bt709Color);
+    }
 #if 1
     DICESettings config = DefaultDICESettings();
     config.Type = 3;
-    config.ShoulderStart = 0.35;
+    config.ShoulderStart = 0.45;
     const float dicePaperWhite = whitePaperNits / renodx::color::srgb::REFERENCE_WHITE;
     const float dicePeakWhite = max(displayMaxNits, whitePaperNits) / renodx::color::srgb::REFERENCE_WHITE;
     bt709Color.rgb = DICETonemap(bt709Color.rgb * dicePaperWhite, dicePeakWhite, config) / dicePaperWhite;

src/games/re4remake/LUTBlackCorrection.hlsl

@@ -20,6 +20,22 @@ float3 AdjustGammaOnLuminance(float3 linearColor, float gammaAdjustmentFactor) {
   return linearColor * (adjustedLuminance / originalLuminance);
 }
 
+/// Adjusts gamma for each color channel, applying the adjustment only for values less than 1.
+/// This function ensures that the color's original sign is preserved and that gamma correction is only applied to values below 1.
+/// At `gammaAdjustmentFactor` = 1.15, it enhances detail in the midtones and shadows without affecting peak whites or clipping any values.
+/// See: https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2408-7-2023-PDF-E.pdf Section 5.1.3.2
+/// @param linearColor The RGB color to adjust.
+/// @param gammaAdjustmentFactor Factor to adjust the gamma for values below 1.
+/// @return The RGB color with adjusted gamma for components below 1, maintaining the original sign and preserving values of 1 and above.
+float3 AdjustGammaByChannel(float3 linearColor, float gammaAdjustmentFactor) {
+  if (gammaAdjustmentFactor == 1.f) return linearColor;  // No adjustment if factor is 1
+
+  // Create a mask to identify components less than 1
+  float3 mask = step(linearColor, float3(1.0f, 1.0f, 1.0f));  // 1 where linearColor < 1, 0 otherwise
+  // Adjust gamma only for components where the value is less than 1
+  return mask * renodx::color::gamma::EncodeSafe(linearColor, 1.f / gammaAdjustmentFactor) + (1.f - mask) * linearColor;
+}
+
 /// Applies a modified `renodx::lut::Sample` that accounts for only black level correction,
 /// leaving peak white untouched as LUTs are already HDR, ensuring no highlight impact.
 /// @param color_input Input color to apply the LUT to.
@@ -30,6 +46,9 @@ float3 LUTBlackCorrection(float3 color_input, Texture3D lut_texture, renodx::lut
   float3 lutInputColor = renodx::lut::ConvertInput(color_input, lut_config);
   float3 lutOutputColor = renodx::lut::SampleColor(lutInputColor, lut_config, lut_texture);
   float3 color_output = renodx::lut::LinearOutput(lutOutputColor, lut_config);
+
+  float3 original_output = color_output;
+
   if (lut_config.scaling != 0) {
     float3 lutBlack = renodx::lut::SampleColor(renodx::lut::ConvertInput(0, lut_config), lut_config, lut_texture);
     float3 lutMid = renodx::lut::SampleColor(renodx::lut::ConvertInput(0.18f, lut_config), lut_config, lut_texture);
@@ -41,6 +60,9 @@ float3 LUTBlackCorrection(float3 color_input, Texture3D lut_texture, renodx::lut
         renodx::lut::GammaInput(color_input, lutInputColor, lut_config));
     float3 recolored = renodx::lut::RecolorUnclamped(color_output, renodx::lut::LinearUnclampedOutput(unclamped, lut_config));
     color_output = lerp(color_output, recolored, lut_config.scaling);
+    if (injectedData.toneMapGammaCorrection == 1.f) {  // fixes crushed blacks with 2.2 gamma correction
+      color_output = lerp(color_output, original_output, saturate(pow(color_output, lutMid)));
+    }
   }
   color_output = renodx::lut::RestoreSaturationLoss(color_input, color_output, lut_config);
   if (lut_config.strength != 1.f) {
@@ -78,4 +100,4 @@ float3 renoDRTSmoothClamp(float3 untonemapped) {
   renoDRTColor = lerp(untonemapped, renoDRTColor, saturate(renodx::color::y::from::BT709(untonemapped) / renodrt_config.mid_gray_value));
 
   return min(1, renoDRTColor);
-}
+}

src/games/re4remake/addon.cpp

@@ -47,6 +47,29 @@ renodx::utils::settings::Settings settings = {
         .tooltip = "Sets the tone mapper type",
         .labels = {"Vanilla", "Vanilla+"},
     },
+    new renodx::utils::settings::Setting{
+        .key = "toneMapGammaCorrection",
+        .binding = &shader_injection.toneMapGammaCorrection,
+        .value_type = renodx::utils::settings::SettingValueType::BOOLEAN,
+        .default_value = 1.f,
+        .can_reset = false,
+        .label = "Gamma Correction",
+        .section = "Tone Mapping",
+        .tooltip = "Emulates a 2.2 EOTF, this is likely what the developers tried to approximate with the vanilla gamma adjustment",
+        .is_enabled = []() { return shader_injection.toneMapType != 0; },
+    },
+    new renodx::utils::settings::Setting{
+        .key = "toneMapGammaAdjust",
+        .binding = &shader_injection.toneMapGammaAdjust,
+        .default_value = 1.f,
+        .label = "Gamma Adjustment",
+        .section = "Tone Mapping",
+        .tooltip = "Adjusts gamma",
+        .min = 0.75f,
+        .max = 1.25f,
+        .format = "%.2f",
+        .is_enabled = []() { return shader_injection.toneMapType != 0; },
+    },
     new renodx::utils::settings::Setting{
         .key = "colorGradeHighlightContrast",
         .binding = &shader_injection.colorGradeHighlightContrast,
@@ -98,18 +121,6 @@ renodx::utils::settings::Settings settings = {
         .max = 100.f,
         .parse = [](float value) { return value * 0.01f; },
     },
-    new renodx::utils::settings::Setting{
-        .key = "colorGradeGammaAdjust",
-        .binding = &shader_injection.colorGradeGammaAdjust,
-        .default_value = 1.f,
-        .label = "Gamma Adjustment (Hue Preserving)",
-        .section = "Color Grading",
-        .tooltip = "Adjusts gamma on luminance, only affects luminance values below 1.",
-        .min = 0.75f,
-        .max = 1.25f,
-        .format = "%.2f",
-        .is_enabled = []() { return shader_injection.toneMapType != 0; },
-    },
     new renodx::utils::settings::Setting{
         .key = "processingInternalSampling",
         .binding = &shader_injection.processingInternalSampling,
@@ -150,6 +161,7 @@ renodx::utils::settings::Settings settings = {
 
 void OnPresetOff() {
   renodx::utils::settings::UpdateSetting("toneMapType", 0.f);
+  renodx::utils::settings::UpdateSetting("toneMapGammaCorrection", 0.f);
   renodx::utils::settings::UpdateSetting("colorGradeToeAdjustmentType", 0.f);
   renodx::utils::settings::UpdateSetting("colorGradeShadowToe", 1.f);
   renodx::utils::settings::UpdateSetting("colorGradeHighlightContrast", 50.f);

src/games/re4remake/shared.h

@@ -9,12 +9,13 @@
 // Should be 4x32
 struct ShaderInjectData {
   float toneMapType;
+  float toneMapGammaCorrection;
+  float toneMapGammaAdjust;
   float colorGradeHighlightContrast;
   float colorGradeToeAdjustmentType;
   float colorGradeShadowToe;
   float colorGradeLUTStrength;
   float colorGradeLUTScaling;
-  float colorGradeGammaAdjust;
   float processingInternalSampling;
 };
 

src/games/re4remake/tonemap_inside_0x1F9104F3.ps_6_6.hlsl

@@ -1416,7 +1416,7 @@ void frag_main()
     SV_Target.w = 0.0f;
 
     if (injectedData.toneMapType != 0) {
-        SV_Target.rgb = AdjustGammaOnLuminance(SV_Target.rgb, injectedData.colorGradeGammaAdjust);
+      SV_Target.rgb = AdjustGammaByChannel(SV_Target.rgb, injectedData.toneMapGammaAdjust);
     }
 }
 

src/games/re4remake/tonemap_outside_HDRPostProcess_WithTonemap_0x973A39FC.ps_6_6.hlsl

@@ -1447,7 +1447,7 @@ void frag_main()
     SV_Target.w = 0.0f;
 
     if (injectedData.toneMapType != 0) {
-      SV_Target.rgb = AdjustGammaOnLuminance(SV_Target.rgb, injectedData.colorGradeGammaAdjust);
+      SV_Target.rgb = AdjustGammaByChannel(SV_Target.rgb, injectedData.toneMapGammaAdjust);
     }
 }