sampler2D image;

float pixel = 1.0f / 512.0f;
                                   
float4 main( float4 Pos : POSITION0,
                float2 Tex : TEXCOORD0 ) : COLOR0
{
   int i;
   float4 color;
   float s[8];
   float fx, fy, fxy;
   
   // fetch the original color
   color = tex2D( image, Tex );
   
   // fetch the color from neighbours
   s[0] = dot(tex2D( image, Tex + float2(-pixel, -pixel) ), .33333f);
   s[1] = dot(tex2D( image, Tex + float2( 0.0f,  -pixel) ), .33333f);
   s[2] = dot(tex2D( image, Tex + float2( pixel, -pixel) ), .33333f);
   s[3] = dot(tex2D( image, Tex + float2(-pixel,  0.0f ) ), .33333f);
   s[4] = dot(tex2D( image, Tex + float2( pixel,  0.0f ) ), .33333f);
   s[5] = dot(tex2D( image, Tex + float2(-pixel,  pixel) ), .33333f);
   s[6] = dot(tex2D( image, Tex + float2( 0.0f,   pixel) ), .33333f);
   s[7] = dot(tex2D( image, Tex + float2( pixel,  pixel) ), .33333f);
   
   // compute the Sobel filter
   fx = s[2] + s[7] + 2 * s[4] - s[0] - s[5] - 2 * s[3];
   fy = s[5] + s[7] + 2 * s[6] - s[0] - s[2] - 2 * s[1];
   
   // fxy = fx * fx + fy * fy;
   fxy = abs(fx) + abs(fy);
   
   if (fxy > 0.14)
      color = 0.0f;
      
    return color;
}