[Bf-blender-cvs] [558bea22529] master: Cycles Denoising: Add more failsafes for invalid pixels

[Lukas Stockner]

Commit: 558bea225296751b849572122d6202b4ab1fa1cf
Author: Lukas Stockner
Date:   Sun Jun 11 01:44:06 2017 +0200
Branches: master
https://developer.blender.org/rB558bea225296751b849572122d6202b4ab1fa1cf

Cycles Denoising: Add more failsafes for invalid pixels

Now, when there is no usable neighboring pixel for denoising, the noisy value
is preserved instead of producing a NaN.
Also, negative results are clamped to zero.

Note that there are just workarounds that don't fix the underlying problems,
but these issues are very rare and I'm not sure if it's even possible to fix
the underlying problems without introducing a significant slowdown or quality
decrease in other situations.
Because of that and since 2.79 is happening very soon, I just went for these
workarounds for now.

===================================================================

M	intern/cycles/kernel/filter/filter_reconstruction.h

===================================================================

diff --git a/intern/cycles/kernel/filter/filter_reconstruction.h b/intern/cycles/kernel/filter/filter_reconstruction.h
index d6d7639a22d..25a3025056c 100644
--- a/intern/cycles/kernel/filter/filter_reconstruction.h
+++ b/intern/cycles/kernel/filter/filter_reconstruction.h
@@ -81,6 +81,12 @@ ccl_device_inline void kernel_filter_finalize(int x, int y, int w, int h,
 	(void) storage_stride;
 #endif
 
+	if(XtWX[0] < 1e-3f) {
+		/* There is not enough information to determine a denoised result.
+		 * As a fallback, keep the original value of the pixel. */
+		 return;
+	}
+
 	/* The weighted average of pixel colors (essentially, the NLM-filtered image).
 	 * In case the solution of the linear model fails due to numerical issues,
 	 * fall back to this value. */
@@ -93,6 +99,9 @@ ccl_device_inline void kernel_filter_finalize(int x, int y, int w, int h,
 		final_color = mean_color;
 	}
 
+	/* Clamp pixel value to positive values. */
+	final_color = max(final_color, make_float3(0.0f, 0.0f, 0.0f));
+
 	ccl_global float *combined_buffer = buffer + (y*buffer_params.y + x + buffer_params.x)*buffer_params.z;
 	final_color *= sample;
 	if(buffer_params.w) {