(C++) GetAverageGreyness

 

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

 

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#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; }