Cycles Denoising: Get rid of halos around bright edges

Previously, bright edges (e.g. caused by rim lighting) would sometimes get
halos around them after denoising.

This change introduces a log(1+x) highlight compression step that is performed
before denoising and reversed afterwards. That way, the denoising algorithm
itself operates in the compressed space and therefore bright edges cause less
numerical issues.

2 files changed, 20 insertions, 0 deletions

diff --git a/intern/cycles/util/util_color.h b/intern/cycles/util/util_color.h
index 83410db13c6..6e61190de6b 100644
--- a/intern/cycles/util/util_color.h
+++ b/intern/cycles/util/util_color.h
@@ -257,6 +257,20 @@ ccl_device float4 color_srgb_to_linear_v4(float4 c)
 #endif
 }
 
+ccl_device float3 color_highlight_compress(float3 color, float3 *variance)
+{
+  color += make_float3(1.0f, 1.0f, 1.0f);
+  if (variance) {
+    *variance *= sqr3(make_float3(1.0f, 1.0f, 1.0f) / color);
+  }
+  return log3(color);
+}
+
+ccl_device float3 color_highlight_uncompress(float3 color)
+{
+  return exp3(color) - make_float3(1.0f, 1.0f, 1.0f);
+}
+
 CCL_NAMESPACE_END
 
 #endif /* __UTIL_COLOR_H__ */
diff --git a/intern/cycles/util/util_math_float3.h b/intern/cycles/util/util_math_float3.h
index 85e9b8114ff..554b7408148 100644
--- a/intern/cycles/util/util_math_float3.h
+++ b/intern/cycles/util/util_math_float3.h
@@ -70,6 +70,7 @@ ccl_device_inline float3 safe_normalize(const float3 a);
 ccl_device_inline float3 normalize_len(const float3 a, float *t);
 ccl_device_inline float3 safe_normalize_len(const float3 a, float *t);
 ccl_device_inline float3 interp(float3 a, float3 b, float t);
+ccl_device_inline float3 sqr3(float3 a);
 
 ccl_device_inline bool is_zero(const float3 a);
 ccl_device_inline float reduce_add(const float3 a);
@@ -349,6 +350,11 @@ ccl_device_inline float3 interp(float3 a, float3 b, float t)
   return a + t * (b - a);
 }
 
+ccl_device_inline float3 sqr3(float3 a)
+{
+  return a * a;
+}
+
 ccl_device_inline bool is_zero(const float3 a)
 {
 #ifdef __KERNEL_SSE__