/*

     File: kernel.cl

 Abstract: 

 OpenCL compute kernel image filter.

  Version: 1.0

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#define READ_PIXEL(x,y) read_imagef(input_img,CLK_FILTER_NEAREST|CLK_ADDRESS_CLAMP,coord+(int2)((x),(y)))

#define READ_PIXEL_LUM(x,y) convert_to_lum(READ_PIXEL((x),(y)))

float convert_to_lum(const float4 pixel);

kernel void processImage(read_only image2d_t input_img, write_only image2d_t output_img)

{

  const int2 coord = (int2)(get_global_id(0),get_global_id(1));

  const float p0 = READ_PIXEL_LUM(-1,-1);

  const float p1 = READ_PIXEL_LUM( 0,-1);

  const float p2 = READ_PIXEL_LUM( 1,-1);

  const float p3 = READ_PIXEL_LUM(-1, 0);

  const float p4 = READ_PIXEL_LUM( 1, 0);

  const float p5 = READ_PIXEL_LUM(-1,-1);

  const float p6 = READ_PIXEL_LUM( 0,-1);

  const float p7 = READ_PIXEL_LUM( 1,-1);

  const float Gx = p0 - p2 + 2.0f*p3 -2.0f*p4 + p5 - p6;

  const float Gy = p0 + 2.0f*p1 + p2 -p5 -2.0f*p6 - p7;

  const float g = sqrt(Gx*Gx + Gy*Gy);

  float4 pixel = READ_PIXEL(0,0);

  pixel.rgb = g * 8.0f;

  write_imagef(output_img,coord,pixel);

}

float convert_to_lum(const float4 pixel)

{

  return pixel.r*0.2126f + pixel.g*0.7152f + pixel.b*0.0722f;

}