From 9049902b4f2f415b7311ab101b771917abc7944b Mon Sep 17 00:00:00 2001
From: Steven Robertson <steven@strobe.cc>
Date: Thu, 27 Oct 2011 08:51:40 -0400
Subject: [PATCH] Add a crap gradient detect to make DE less bad.

Use the vertical and horizontal gradients to "detect" when a pixel is
part of an edge that has been softened by grid-shift AA, and avoid
blurring it further. This causes occasional 1px artifacts in stills, but
fixes the truly grotesque DE bleed-out for a net win. A better edge
detector is still needed.
---
 cuburn/code/filtering.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/cuburn/code/filtering.py b/cuburn/code/filtering.py
index 2da5cab..b191c33 100644
--- a/cuburn/code/filtering.py
+++ b/cuburn/code/filtering.py
@@ -156,6 +156,13 @@ 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) {
             float ls = k1 * logf(1.0f + in.w * k2) / in.w;
             in.x *= ls;