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.




#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;

}

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(C++) GetGreyness