core/colorpipeline: fix tone mapping luminances being switched around

The code from before could never reduce the reference luminance

(cherry picked from commit 1fa3d50e8d)

src/core/colorpipeline.cpp

@@ -346,7 +346,7 @@ ColorTonemapper::ColorTonemapper(double referenceLuminance, double maxInputLumin
     // 50% HDR headroom should be enough for the tone mapper to do a good enough job, without dimming the image too much
     const double minDecentRange = std::min(m_inputRange, 1.5);
     // if the output doesn't provide enough HDR headroom for the tone mapper to do a good job, dim the image to create some
-    m_referenceDimming = 1.0 / std::clamp(outputRange / minDecentRange, 1.0, minDecentRange);
+    m_referenceDimming = 1.0 / std::clamp(minDecentRange / outputRange, 1.0, minDecentRange);
     m_outputReferenceLuminance = referenceLuminance * m_referenceDimming;
 }
 

src/opengl/colormanagement.glsl

@@ -123,7 +123,7 @@ vec3 doTonemapping(vec3 color) {
     // how much dynamic range we need to decently present the content
     float minDecentRange = min(inputRange, 1.5);
     // if the output doesn't provide enough HDR headroom for the tone mapper to do a good job, dim the image to create some
-    float referenceDimming = 1.0 / clamp(outputRange / minDecentRange, 1.0, minDecentRange);
+    float referenceDimming = 1.0 / clamp(minDecentRange / outputRange, 1.0, minDecentRange);
     float outputReferenceLuminance = destinationReferenceLuminance * referenceDimming;
 
     // keep it linear up to the reference luminance