/// <summary>
/// locates the centre position of a spot
/// </summary>
/// <param name="raw_image_mono">mono image data</param>
/// <param name="raw_image_width">image width</param>
/// <param name="raw_image_height">image height</param>
/// <param name="search_region">region within which to search</param>
/// <param name="black_on_white">whether this image contains dark markings on a lighter background</param>
/// <param name="centre_x">returned x centre position</param>
/// <param name="centre_y">returned y centre position</param>
private static unsafe void LocateSpotCentre(byte* raw_image_mono,
int raw_image_width, int raw_image_height,
polygon2D search_region,
bool black_on_white,
ref float centre_x, ref float centre_y)
{
centre_x = 0;
centre_y = 0;
// get dimensions of the region to be searched
int tx = (int)search_region.left();
int ty = (int)search_region.top();
int bx = (int)search_region.right();
int by = (int)search_region.bottom();
int r = (bx - tx) / 3;
if (r < 1) r = 1;
int search_r = (bx - tx) / 4;
if (search_r < 1) search_r = 1;
// centre of the search region
float search_centre_x = 0;
float search_centre_y = 0;
search_region.GetSquareCentre(ref search_centre_x, ref search_centre_y);
//search_region.getCentreOfGravity(ref search_centre_x, ref search_centre_y);
int image_pixels = raw_image_width * raw_image_height;
float max = 0;
float v;
for (float offset_y = search_centre_y - search_r; offset_y <= search_centre_y + search_r; offset_y += 0.5f)
{
for (float offset_x = search_centre_x - search_r; offset_x <= search_centre_x + search_r; offset_x += 0.5f)
{
float tot = 0;
for (int yy = (int)(offset_y - r); yy <= (int)(offset_y + r); yy += 2)
{
int n0 = yy * raw_image_width;
for (int xx = (int)(offset_x - r); xx <= (int)(offset_x + r); xx += 2)
{
int n1 = n0 + xx;
if ((n1 > -1) && (n1 < image_pixels))
{
if (black_on_white)
v = 255 - raw_image_mono[n1];
else
v = raw_image_mono[n1];
tot += v * v;
}
}
}
if (tot > max)
{
max = tot;
centre_x = offset_x;
centre_y = offset_y;
}
}
}
}