(C++) Darken

Darken is a Graphics code snippet to darken a Extctrls::TImage. To bleach a Extctrls::TImage use Bleach.

The tool BarbaImage uses Darken as one of its image operations.

View an example of a composition image demonstrating 'Darken'


#include <cassert>

#include <Extctrls.hpp>



//Darken an image by fraction f

// * f = 0.0 denotes no bleaching  (image untouched)

// * f = 1.0 denotes max bleaching (image black)

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

void Darken(

  const Extctrls::TImage * const source,

  const double f,                   

  Extctrls::TImage * const target)

{

  assert(f >=  0.0);

  assert(f <=  1.0);

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

  assert(source->Picture->Bitmap!=0 && "Image bitmap is NULL");

  assert(source->Picture->Bitmap->PixelFormat == pf24bit && "Image bitmap must be 24 bit");

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

  assert(target->Picture->Bitmap!=0 && "Image bitmap is NULL");

  assert(target->Picture->Bitmap->PixelFormat == pf24bit && "Image bitmap must be 24 bit");

  //Get the width and height from the source

  const int width  = source->Picture->Bitmap->Width;

  const int height = source->Picture->Bitmap->Height;

  //Set the target's width and height

  target->Picture->Bitmap->Width  = width;

  target->Picture->Bitmap->Height = height;



  for (int y=0; y!=height; ++y)

  {

    const unsigned char * lineSource

      = static_cast<const unsigned char *>(

        source->Picture->Bitmap->ScanLine[y]);

    unsigned char * lineTarget

      = static_cast<unsigned char *>(

        target->Picture->Bitmap->ScanLine[y]);

    for (int x=0; x!=width; ++x)

    {

      const int r = lineSource[x*3+2]; //Red;

      const int g = lineSource[x*3+1]; //Green;

      const int b = lineSource[x*3+0]; //Blue;

      const double dist_r = static_cast<double>(r) * (1.0-f);

      const double dist_g = static_cast<double>(g) * (1.0-f);

      const double dist_b = static_cast<double>(b) * (1.0-f);

      const int new_r = static_cast<int>(dist_r);

      const int new_g = static_cast<int>(dist_g);

      const int new_b = static_cast<int>(dist_b);

      assert(new_r >=   0);

      assert(new_r <  256);

      assert(new_g >=   0);

      assert(new_g <  256);

      assert(new_b >=   0);

      assert(new_b <  256);

      lineTarget[x*3+2] = new_r; //Red

      lineTarget[x*3+1] = new_g; //Green

      lineTarget[x*3+0] = new_b; //Blue

    }

  }

}

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