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Experimental: real Sobel gradient detection

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This commit is contained in:
Steven Robertson 2011-10-28 08:25:00 -04:00
parent 9b2b3ba011
commit 15f88383b1
1 changed files with 33 additions and 9 deletions
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42
cuburn/code/filtering.py
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@ -153,14 +153,32 @@ void density_est(float4 *pixbuf, float4 *outbuf,
float den;
read_pix(in, den);
float *dens = reinterpret_cast<float*>(pixbuf);
float top = dens[(idx-{{info.acc_stride}})*4+3],
bottom = dens[(idx+{{info.acc_stride}})*4+3];
den = fmaxf(den, fabsf(top-bottom));
float left = dens[idx*4-1], right = dens[idx*4+7];
den = fmaxf(den, fabsf(left-right));
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
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 ls = k1 * logf(1.0f + in.w * k2) / in.w;
in.x *= ls;
in.y *= ls;
@ -174,8 +192,14 @@ 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);
// Clamp the final standard deviation. Things will go badly if the
// minimum is undershot.
// And for the Sobel...
float sobel_sd = est_sd * powf(sobel_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);
// Clamp the final standard deviation.
sd = fminf(MAX_SD, fmaxf(sd, est_min));
// Below a certain threshold, only one coeffecient would be