Re: [boost] Generic Image Library (GIL) and floating-point types

From: Lubomir Bourdev (lbourdev_at_[hidden])
Date: 2006-10-17 19:42:56

Tim Shead wrote:
> Suppose that 
> I actually want to convert floating-point RGBA data to 8bpp 
> integer RGB (I'm going to display the alpha separately, say). 
> ... <skipped>
> How would you handle this on a case-by-case basis? 

Hi Tim,

This is described in Section 16 in the design guide. You can create your
own color converters with arbitrary conversion policy. If you want to
change the color conversion in only a few cases, you simply subclass
GIL's default color converter. Color conversion functions take an
optional color conversion object. Pass your converter there.

Lubomir

_________________________

// make the default use GIL's default
template <typename T1, typename C1,   // source      channel type and
base color space
          typename T2, typename C2>   // destination channel type and
base color space
struct my_color_converter_impl : public
color_converter_default_impl<T1,C1,T2,C2> {
};

// provide specializations only for cases you care about
template <typename T1, typename T2>
struct my_color_converter_impl<T1,rgba_t,T2,rgb_t> {
    template <typename P1, typename P2>
    void operator()(const P1& src, P2& dst) const {
        dst.red = channel_convert<T2>(src.red);
        dst.green = channel_convert<T2>(src.green);
        dst.blue = channel_convert<T2>(src.blue);
    }
};

// create a color converter object that dispatches to your own
implementation
struct my_color_converter {
    template <typename SrcP,typename DstP>
    void operator()(const SrcP& src,DstP& dst) const { 
        typedef typename pixel_traits<SrcP>::channel_t SrcChannel;
        typedef typename pixel_traits<DstP>::channel_t DstChannel;
        typedef typename pixel_traits<SrcP>::color_space_t::base
SrcColorSpace;
        typedef typename pixel_traits<DstP>::color_space_t::base
DstColorSpace;
 
my_color_converter_impl<SrcChannel,SrcColorSpace,DstChannel,DstColorSpac
e>()(src,dst);
    }
};

int main(int argc, unsigned char* argv[])
{
    rgba8_image_t a(100, 100);
    rgb8_image_t b(100, 100);
    copy_and_convert_pixels(const_view(a), view(b),
my_color_converter());
}