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Use custom "cross" filtering.

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Sobel was giving too many false positives. This cross seems to detect
the kinds of edges we care about and avoids the rest of the image, and
it does so on pretty much everything I've tried it on. Very satisfying.
This commit is contained in:
Steven Robertson 2011-10-29 17:36:06 -04:00
parent 0936e34b88
commit b240fc8459
1 changed files with 23 additions and 26 deletions
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49
cuburn/code/filtering.py
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@ -155,29 +155,26 @@ void density_est(float4 *pixbuf, float4 *outbuf,
if (in.w > 0 && den > 0) {
// Compute a Sobel derivative, The Terrible Way! Because I'm Lazy.
// Or more to the point, because even this sloppy mess is such a
// small part of the overall runtime that it's not yet worth
// optimizing. Using a [3, 10, 3] Sobel, normalized to represent
// the density change over a single pixel.
const float corner = 0.0625f; // (3/16)/3
const float main = 0.208333333f; // (10/16)/3
// Compute a fast and dirty approximation of a "gradient" using
// a [[-1 0 0][0 0 0][0 0 1]]/4 matrix (and its reflection)
// for angled edge detection, and limit blurring in those regions
// to both provide a bit of smoothing and prevent irregular
// bleed-out along gradients close to the image grid.
//
// For such a simple operator - particularly one whose entire
// justification is "it feels right" - it gives very good results
// over a wide range of images without any per-flame
// parameter tuning. In rare cases, color clamping and extreme
// palette changes can cause aliasing to reappear after the DE
// step; the only way to fix that is through a color-buffer AA
// like MLAA.
float *dens = reinterpret_cast<float*>(pixbuf);
int didx = idx * 4 + 3;
float v = 0.0f, h = 0.0f, p;
p = corner * dens[didx-{{info.acc_stride*4}}-4];
v -= p; h -= p;
v -= main * dens[didx-{{info.acc_stride*4}}];
p = corner * dens[didx-{{info.acc_stride*4}}+4];
v -= p; h += p;
h -= main * dens[didx-4];
h += main * dens[didx+4];
p = corner * dens[didx+{{info.acc_stride*4}}-4];
v += p; h -= p;
v += main * dens[didx+{{info.acc_stride*4}}];
p = corner * dens[didx+{{info.acc_stride*4}}-4];
v += p; h += p;
float sobel_mag = sqrtf(v*v + h*h);
float x = 0.25f * ( dens[didx+{{info.acc_stride*4}}+4]
- dens[didx-{{info.acc_stride*4}}-4] );
float y = 0.25f * ( dens[didx+{{info.acc_stride*4}}-4]
- dens[didx-{{info.acc_stride*4}}+4] );
float diag_mag = sqrtf(x*x + y*y);
float ls = k1 * logf(1.0f + in.w * k2) / in.w;
in.x *= ls;
@ -192,12 +189,12 @@ void density_est(float4 *pixbuf, float4 *outbuf,
// then scaled in inverse proportion to the density of the point
// being scaled.
float sd = est_sd * powf(den+1.0f, neg_est_curve);
// And for the Sobel...
float sobel_sd = est_sd * powf(sobel_mag+1.0f, neg_est_curve);
// And for the gradient...
float diag_sd = est_sd * powf(diag_mag+1.0f, neg_est_curve);
// If the Sobel SD is smaller than the minimum SD, we're probably
// on a strong edge; blur with a standard deviation of 1px.
if (sobel_sd < fmaxf(est_min, MIN_SD)) sd = fminf(sd, 0.5f);
// If the gradient SD is smaller than the minimum SD, we're probably
// on a strong edge; blur with a standard deviation around 1px.
if (diag_sd < fmaxf(est_min, MIN_SD)) sd = 0.333333f;
// Clamp the final standard deviation.
sd = fminf(MAX_SD, fmaxf(sd, est_min));