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

Subject: [Boost-users] Splitting Tiff RGBA into RGB and alpha data ...
From: Corinna Kinchin (crin_at_[hidden])
Date: 2011-01-14 11:47:50

Hi there

I have an uncompressed RGBA Tiff file 
(RGB + alpha channel) which I'm trying to
split into two data files, one containing 
the RGB data, and the other 
containing the alpha (transparency) data.

Here's a code snippet showing my (probably misguided) 
attempt at doing this:

image_read_info< tiff_tag > 
        info =  read_image_info(in, tiff_tag());

if ( info._photometric_interpretation == 2 
 && info._samples_per_pixel == 4 ) {

// RGBA
        rgba8_image_t 
                rgba_img;

        // Read RGBA image ...
        read_image(in, rgba_img, tiff_tag());

        // Set up planar image (to extract alpha channel) and rgb image 
        // (to extract rgb data)
        rgba8_planar_image_t
                dst_planar_image(rgba_img.dimensions());
        rgb8_image_t 
                dst_rgb_image(rgba_img.dimensions() );

        // Convert pixels to appropriate view
        copy_and_convert_pixels(view(rgba_img), view(dst_rgb_image));
        copy_and_convert_pixels(view(rgba_img), view(dst_planar_image));

        // Write out data
        ofstream
                out((ofilename+"rbg").c_str(), ios_base::binary),
                alphaout((ofilename +"alpha").c_str(), ios_base::binary);

        out.write(reinterpret_cast<const
char*>(interleaved_view_get_raw_data(view(dst_rgb_image))), 
 info._width * info._height * 3);
        alphaout.write(reinterpret_cast<const
char*>(planar_view_get_raw_data(view(dst_planar_image), 3)), 
 info._width * info._height);

        ...

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.

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.

Thanks a million in advance!

All the best,

 ... Corinna