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Cycles: Fix occasional black pixels from denoising with excessive radii

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Numerical inaccuracies would cause the XtWX matrix to be no longer
positive-semidefinite, which in turn caused the LSQ solver to fail.
This commit is contained in:
Lukas Stockner
2017-05-08 22:09:35 +02:00
parent f4b7c33c1a
commit 58a0c27546
3 changed files with 6 additions and 3 deletions
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5
intern/cycles/util/util_math_matrix.h
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@@ -176,7 +176,10 @@ ccl_device void math_trimatrix_cholesky(ccl_global float *A, int n, int stride)
* symmetrical positive-semidefinite by construction, so we can just use this function with A=Xt*W*X and y=Xt*W*y. */
ccl_device_inline void math_trimatrix_vec3_solve(ccl_global float *A, ccl_global float3 *y, int n, int stride)
{
math_trimatrix_add_diagonal(A, n, 1e-4f, stride); /* Improve the numerical stability. */
/* Since the first entry of the design row is always 1, the upper-left element of XtWX is a good
* heuristic for the amount of pixels considered (with weighting), therefore the amount of correction
* is scaled based on it. */
math_trimatrix_add_diagonal(A, n, 3e-7f*A[0], stride); /* Improve the numerical stability. */
math_trimatrix_cholesky(A, n, stride); /* Replace A with L so that L*Lt = A. */
/* Use forward substitution to solve L*b = y, replacing y by b. */