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

//Get a pixel's greyness
//From http://www.richelbilderbeek.nl/CppGetGreyness.htm
const unsigned char GetGreyness(
  const TImage * const image,
  const int x,
  const int y)
{
  assert(image!=0 && "Image is NULL");
  assert(image->Picture->Bitmap!=0 && "Bitmap is NULL");
  assert(image->Picture->Bitmap->PixelFormat == pf24bit && "Bitmap must be 24 bit");
  assert( x >= 0 && "x coordinat is below zero");
  assert( y >= 0 && "y coordinat is below zero");
  assert( x < image->Picture->Bitmap->Width  && "x coordinat is beyond image width");
  assert( y < image->Picture->Bitmap->Height && "y coordinat is beyond image height");

  const unsigned char * const line
    = static_cast<unsigned char *>(image->Picture->Bitmap->ScanLine[y]);

  const unsigned char red   = line[x*3+2];
  const unsigned char green = line[x*3+1];
  const unsigned char blue  = line[x*3+0];
  const int grey = (red + green + blue) / 3;
  assert(grey >= 0 && grey < 256);
  return grey;
}




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

//Get a line of pixel's average greyness
//From http://www.richelbilderbeek.nl/CppGetGreyness.htm
const unsigned char GetGreyness(
  const TImage * const image,
  const int x1,
  const int x2,
  const int y)
{
  assert(image!=0 && "Image is NULL");
  assert(image->Picture->Bitmap!=0 && "Bitmap is NULL");
  assert(image->Picture->Bitmap->PixelFormat == pf24bit && "Bitmap must be 24 bit");
  assert( x1 >= 0 && "x1 coordinat is below zero");
  assert( x2 >= 0 && "x2 coordinat is below zero");
  assert( y >= 0 && "y coordinat is below zero");
  assert( x1 < image->Picture->Bitmap->Width  && "x1 coordinat is beyond image width");
  assert( x2 < image->Picture->Bitmap->Width  && "x2 coordinat is beyond image width");
  assert( y < image->Picture->Bitmap->Height && "y coordinat is beyond image height");
  assert( x1 < x2);

  const unsigned char * const line
    = static_cast<unsigned char *>(image->Picture->Bitmap->ScanLine[y]);

  const int nPixels = x2 - x1;
  int sum = 0;

  for (int x=x1; x!=x2; ++x)
  {
    const unsigned char red   = line[x*3+2];
    const unsigned char green = line[x*3+1];
    const unsigned char blue  = line[x*3+0];
    const int grey = (red + green + blue) / 3;
    assert(grey >= 0 && grey < 256);
    sum+=grey;
  }
  const int averageGrey = sum / nPixels;
  assert(averageGrey >= 0 && averageGrey < 256);
  return averageGrey;
}




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

//Get a square of pixels' average greyness
//From http://www.richelbilderbeek.nl/CppGetGreyness.htm
const unsigned char GetGreyness(
  const TImage * const image,
  const int x1,
  const int y1,
  const int x2,
  const int y2)
{
  assert(x1 < x2 );
  assert(y1 < y2 );
  const int nPixelsVertical = y2 - y1;
  int sum = 0;

  for (int y=y1; y!=y2; ++y)
  {
    const int grey = GetGreyness(image,x1,x2,y);
    assert(grey >= 0 && grey < 256);
    sum+=grey;
  }
  const int grey = sum / nPixelsVertical;
  assert(grey >=0 && grey < 256);
  return grey;
}