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(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 the SetGreyness function.

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

#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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