#include <cassert>
#include <vcl.h>

//From http://www.richelbilderbeek.nl/CppGetAverageGreyness.htm
const double GetAverageGreyness(const TImage * const image)
{
  assert(image!=0 && "image must not be NULL");
  assert(image->Picture->Bitmap!=0 && "image bitmap must not be NULL");
  assert(image->Picture->Bitmap->PixelFormat == pf24bit && "image bitmap must be 24 bit");

  //Get the width and height from the source
  const int width  = image->Picture->Bitmap->Width;
  const int height = image->Picture->Bitmap->Height;
  double sum = 0.0;

  for (int y=0; y!=height; ++y)
  {
    assert(y >= 0);
    assert(y < image->Picture->Bitmap->Height);
    const unsigned char * line
      = static_cast<const unsigned char *>(
        image->Picture->Bitmap->ScanLine[y]);
    for (int x=0; x!=width; ++x)
    {
      assert(x >= 0);
      assert(x < image->Picture->Bitmap->Width);
      const double grey
        = static_cast<double>(line[x*3+0] + line[x*3+1] + line[x*3+2])
        / 3.0;
      sum += grey;
    }
  }
  const int surface = width * height;
  assert(surface>0);
  const double average = sum / static_cast<double>(surface);
  assert(average >=    0.0);
  assert(average  <  256.0);
  return average;
}