for( i = 1, rows-1) {
    for( j = 1, cols-1) {
      int p1, p2, p3, p4, p5, p6, t;
      p1 = imageIn[( i-1) *303 + j-1];
      p2 = imageIn[( i-1) *303 + j];
      p3 = imageIn[i*303 + j-1];
      p4 = imageIn[i*303 + j+1];
      p5 = imageIn[( i+1) *303 + j];
      p6 = imageIn[( i+1) *303 + j+1];
      t = 128 + p4 + p5 + p6 - p1 - p2 - p3;
      // clip
      if( t < 0) {
        t = 0;
      }
      if( t > 255) {
        t = 255;
      }
      imageOut[i*303 + j] = t;
    }