Graphics code snippet to calculate the average grey value of a VCL TImage.


#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;

}

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(C++) GetAverageGreyness