[vlc-devel] [RFA] sharpen filter improvement

[Jérémy DEMEULE]

Hi,

First, thanks to the vlc team for their work. The recent nightly seems to 
be more and more stable.
Now I can test the sharpen filter I've coded more intensively :-).

So, I've found some simple but really efficient improvement (about 20-25%).
The idea is to avoid maximum computation with a pre calculus table and 
don't use os/x86 features.

Index: modules/video_filter/sharpen.c
===================================================================
--- modules/video_filter/sharpen.c	(revision 20107)
+++ modules/video_filter/sharpen.c	(working copy)
@@ -84,6 +84,7 @@
 struct filter_sys_t
 {
     float f_sigma;
+    int tab_precalc[512];
 };
 
 /*****************************************************************************
@@ -94,6 +95,16 @@
     return (a > 255) ? 255 : (a < 0) ? 0 : a;
 }
 
+static void init_precalc_table(filter_sys_t *p_filter)
+{
+    float sigma = p_filter->f_sigma;
+    
+    for(int i = 0; i < 512; ++i)
+    {
+        p_filter->tab_precalc[i] = (i - 256) * sigma;
+    }
+}
+
 /*****************************************************************************
  * Create: allocates Sharpen video thread output method
  *****************************************************************************
@@ -121,6 +132,8 @@
     var_AddCallback( p_filter, FILTER_PREFIX "sigma",
                      SharpenCallback, p_filter->p_sys );
 
+    init_precalc_table(p_filter->p_sys);
+
     return VLC_SUCCESS;
 }
 
@@ -207,8 +220,9 @@
                   (p_src[(i + 1) * i_src_pitch + j    ] * v1) +
                   (p_src[(i + 1) * i_src_pitch + j + 1] * v1);
 
-            p_out[i * i_src_pitch + j] =  clip( p_src[i * i_src_pitch + j] +
-                        (p_filter->p_sys->f_sigma * pix) );
+	    pix = pix >= 0 ? clip(pix) : -clip(pix * -1);
+	    p_out[i * i_src_pitch + j] = clip( p_src[i * i_src_pitch + j] + 
+			p_filter->p_sys->tab_precalc[pix + 256] );
         }
     }
 
@@ -241,5 +255,6 @@
     filter_sys_t *p_sys = (filter_sys_t *)p_data;
     if( !strcmp( psz_var, FILTER_PREFIX "sigma" ) )
         p_sys->f_sigma = __MIN( 2., __MAX( 0., newval.f_float ) );
+    init_precalc_table(p_sys);
     return VLC_SUCCESS;
 }

-- 
Jérémy DEMEULE - EPITA SIGL Promotion 2005
Mail: dj_mulder at djduron.no-ip.org

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