Go back to Richel Bilderbeek's homepage.

Go back to Richel Bilderbeek's C++ page.

(C++) GetAverageGreyness

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

* View the code of 'GetAverageGreyness' in plain text.

#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;

}

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.