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(C++) Darken

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.

#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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