(C++) GetGreyness

 

Graphics code snippet to get the greyness of one or more pixels of a VCL TImage.

 

The greyness of a pixels is the averaged red, green and blue value of it. You can get a single pixel's greyness, or from a square of pixels.

 

To set pixels' their greynesses, use SetGreyness.

 

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#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; }