(C++) GetPixel

 

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

 

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//--------------------------------------------------------------------------- #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

 

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//--------------------------------------------------------------------------- #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; } //---------------------------------------------------------------------------