GetPixel is a VCL graphics code snippet to get one single TImage pixel's color.

One version of GetPixel uses RGB values, the other uses a TColor value. The version using TColor is already used for the Win32 API. Therefore, I call the VCL function of GetPixel GetPixelVcl.

For the VCL version of GetPixel, I've also added two functions to obtain the average RGB values of a line and square of pixels.

CLX version of GetPixel


//---------------------------------------------------------------------------

#include <cassert>

#include <QExtCtrls.hpp>

//---------------------------------------------------------------------------

//From http://www.richelbilderbeek.nl/CppGetPixel.htm

const TColor GetPixelClx(

  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 == pf32bit && "Bitmap must be 32 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");

  return static_cast<TColor>(RGB(

    (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+2]), //Red

    (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+1]), //Green

    (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+0])  //Blue

    ));

}

//---------------------------------------------------------------------------

//From http://www.richelbilderbeek.nl/CppGetPixel.htm

void GetPixel(

  const TImage * const image,

  const int x,

  const int y,

  unsigned char& red,

  unsigned char& green,

  unsigned char& blue)

{

  assert(image!=0 && "Image is NULL");

  assert(image->Picture->Bitmap!=0 && "Bitmap is NULL");

  assert(image->Picture->Bitmap->PixelFormat == pf32bit && "Bitmap must be 32 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");

  red   = (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+2]);

  green = (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+1]);

  blue  = (static_cast<unsigned char*>(image->Picture->Bitmap->ScanLine[y])[x*4+0]);

}

VCL version of GetPixel


//---------------------------------------------------------------------------

#include <cassert>

#include <ExtCtrls.hpp>

//---------------------------------------------------------------------------

//Get a pixel's TColor value

//From http://www.richelbilderbeek.nl/CppGetPixel.htm

const TColor GetPixelVcl(

  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]);



  return static_cast<TColor>(RGB(

    line[x*3+2], //Red

    line[x*3+1], //Green

    line[x*3+0]  //Blue

    ));

}

//---------------------------------------------------------------------------

//Get a pixel's RGB values

//From http://www.richelbilderbeek.nl/CppGetPixel.htm

void GetPixel(

  const TImage * const image,

  const int x,

  const int y,

  unsigned char& red,

  unsigned char& green,

  unsigned char& blue)

{

  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]);



  red   = line[x*3+2];

  green = line[x*3+1];

  blue  = line[x*3+0];

}

//---------------------------------------------------------------------------

//Get a line of pixel's average RGB value

//From http://www.richelbilderbeek.nl

void GetPixel(

  const TImage * const image,

  const int x1,

  const int x2,

  const int y,

  unsigned char& red,

  unsigned char& green,

  unsigned char& blue)

{

  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 sumRed   = 0;

  int sumGreen = 0;

  int sumBlue  = 0;



  for (int x=x1; x!=x2; ++x)

  {

    const unsigned char r = line[x*3+2];

    const unsigned char g = line[x*3+1];

    const unsigned char b = line[x*3+0];

    sumRed+=r;

    sumGreen+=g;

    sumBlue+=b;

  }

  const int averageRed   = sumRed   / nPixels;

  const int averageGreen = sumGreen / nPixels;

  const int averageBlue  = sumBlue  / nPixels;

  assert(averageRed   >= 0 && averageRed   < 256);

  assert(averageGreen >= 0 && averageGreen < 256);

  assert(averageBlue  >= 0 && averageBlue  < 256);

  red   = averageRed;

  green = averageGreen;

  blue  = averageBlue;

}

//---------------------------------------------------------------------------

//Get a square of pixels' average RGB value

//From http://www.richelbilderbeek.nl

void GetPixel(

  const TImage * const image,

  const int x1,

  const int y1,

  const int x2,

  const int y2,

  unsigned char& red,

  unsigned char& green,

  unsigned char& blue)

{

  assert(x1 < x2 );

  assert(y1 < y2 );

  const int nPixelsVertical = y2 - y1;

  int sumRed   = 0;

  int sumGreen = 0;

  int sumBlue  = 0;



  for (int y=y1; y!=y2; ++y)

  {

    unsigned char r,g,b;

    GetPixel(image,x1,x2,y,r,g,b);

    sumRed+=r;

    sumGreen+=g;

    sumBlue+=b;

  }

  const int averageRed   = sumRed   / nPixelsVertical;

  const int averageGreen = sumGreen / nPixelsVertical;

  const int averageBlue  = sumBlue  / nPixelsVertical;

  assert(averageRed   >= 0 && averageRed   < 256);

  assert(averageGreen >= 0 && averageGreen < 256);

  assert(averageBlue  >= 0 && averageBlue  < 256);

  red   = averageRed;

  green = averageGreen;

  blue  = averageBlue;

}

//---------------------------------------------------------------------------

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(C++) GetPixel

CLX version of GetPixel

VCL version of GetPixel