// returns a masked version of given image where every pixel
// above / below a given value ( in quantum range ) gets transparent
Magick::Image masked( bool below, double value, Magick::Image img )
{
Magick::Image mask = img;
mask.type( Magick::GrayscaleMatteType );
mask.normalize();
double v = below ? value : 1-value;
mask.threshold( v*MaxRGB );
if( below )
mask.negate();
mask.type( Magick::TrueColorMatteType );
mask.transparent( "black" );
Magick::Image masked = img;
masked.composite( mask, Magick::CenterGravity, Magick::CopyOpacityCompositeOp );
return masked;
}
void Magick::negateImage::operator()( Magick::Image &image_ ) const
{
image_.negate( _grayscale );
}