Re: [Boost-users] Splitting Tiff RGBA into RGB and alpha data ...

Subject: Re: [Boost-users] Splitting Tiff RGBA into RGB and alpha data ...
From: Christian Henning (chhenning_at_[hidden])
Date: 2011-01-15 17:09:36

Hi Corinna,

>
> The alpha transparency data is ok as
> far as I can see, but the RGB data is
> mangled ... presumably I've misunderstood
> how the copy_and_convert_pixels() works.

The default converter for converting a rgba value into anything will
multiply the alpha value to all other channels. That's why the rgb
data looks incorrect.

I suggest you have your own color converter. Here is some code:

#include <boost/gil/gil_all.hpp>

using namespace boost;
using namespace gil;

class convert_rgba_to_rgb
{
public:
    void operator() ( const rgba8_pixel_t& src
                    , rgb8_pixel_t& dst
                    ) const
    {
        get_color(dst,red_t())   = get_color(src,red_t());
        get_color(dst,green_t()) = get_color(src,green_t());
        get_color(dst,blue_t())  = get_color(src,blue_t());
    }
};

int main()
{
    rgba8_image_t img( 640, 480 );

    fill_pixels( view( img ), rgba8_pixel_t( 255, 128, 10, 99 ));

    rgba8_planar_image_t dst_planar_image(img.dimensions());
    rgb8_image_t         dst_rgb_image(img.dimensions() );

    copy_and_convert_pixels( view( img ), view( dst_rgb_image ),
convert_rgba_to_rgb() );

    rgba8_pixel_t v = *view( img ).xy_at( 0, 0 );
    rgb8_pixel_t p = *view( dst_rgb_image ).xy_at( 0, 0 );

    return 0;
}

>
> I'm new to the boost::gil library, and am
> finding the documentation a little
> hard to get to grips with, so any hints
> you could give would be greatly appreciated.
>

Let me know if you have some more issues.

Regards,
Christian