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

//From http://www.richelbilderbeek.nl/CppEnhanceContrast.htm
void EnhanceContrast(const TImage * const image)
{
  //Find lowest and highest value
  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;
  const double averageGreyness = GetAverageGreyness(image);

  double stretch = 1000.0; //Way too much for nearly all images

  for (int y=0; y!=height; ++y)
  {
    const unsigned char * const line
      = static_cast<const unsigned char *>(
        image->Picture->Bitmap->ScanLine[y]);
    for (int x=0; x!=width; ++x)
    {
      const double grey
        = static_cast<double>(line[x*3+0] + line[x*3+1] + line[x*3+2])
        / 3.0;
      const double diff = grey - averageGreyness;
      if (diff < 0.0)
      {
        //pixel was darker then average
        const double newStretch = -averageGreyness / diff;
        assert(newStretch >= 0.0);
        if (newStretch < stretch) stretch = newStretch;
      }
      else if (diff > 0.0)
      {
        //pixel was lighter then average
        const double newStretch = (255.9 - averageGreyness)  / diff;
        if (newStretch < stretch) stretch = newStretch;
      }
    }
  }

  //Enhance the contrast
  for (int y=0; y!=height; ++y)
  {
    unsigned char * const line
      = static_cast<unsigned char *>(
        image->Picture->Bitmap->ScanLine[y]);
    for (int x=0; x!=width; ++x)
    {
      const double grey
        = static_cast<double>(line[x*3+0] + line[x*3+1] + line[x*3+2])
        / 3.0;
      const double diff = grey - averageGreyness;
      const double diffGreyNew = averageGreyness + (static_cast<double>(diff) * stretch);
      const int newGrey = static_cast<int>(diffGreyNew);
      assert(newGrey >=   0);
      assert(newGrey <  256);
      line[x*3+2] = newGrey; //Red
      line[x*3+1] = newGrey; //Green
      line[x*3+0] = newGrey; //Blue
    }
  }
}