Re: [boost] [gil] Indexed Images

From: Lubomir Bourdev (lbourdev_at_[hidden])
Date: 2006-11-10 12:25:03

Christian,

I see two problems with this code.
The obvious one is that you are not using indexed_view - this is why its
operator() is not called :-)
Use:
   copy_pixels( indexed_view, view( rgb_img ));

The other problem is that your dereference adaptor returns pixels by
value, so you must not define its reference type to be a pixel
reference. The correct typedefs are:

struct indexed_pixel_deref_fn
{
   typedef indexed_pixel_deref_fn const_t;
   typedef rgb8_pixel_t value_type;
   typedef value_type reference;   // returns by value!
   typedef value_type const_reference;
   typedef reference result_type;

...
};

"const_t" is the type of the immutable equivalent of this type. Since
your adaptor is immutable, it returns its own type.

Lubomir

 

> -----Original Message-----
> From: boost-bounces_at_[hidden] 
> [mailto:boost-bounces_at_[hidden]] On Behalf Of Christian Henning
> Sent: Friday, November 10, 2006 7:05 AM
> To: boost_at_[hidden]; Christian Henning
> Subject: [boost] [gil] Indexed Images
> 
> Hi there, I'm playing around with indexed images in GIL. My starting
> point was an email from Lubomir during the review.
> 
> Here is what I have:
> 
> struct indexed_pixel_deref_fn
> {
>    typedef pixel_traits<rgb8_pixel_t>::reference       reference;
>    typedef pixel_traits<rgb8_pixel_t>::const_reference 
> const_reference;
> 
>    typedef const_reference const_t;
>    typedef reference result_type;
> 
>    typedef rgb8_pixel_t value_type;
>    static const bool is_mutable = false;
> 
>    indexed_pixel_deref_fn( rgb8_pixel_t* table ) : _table( table ) {}
> 
>    rgb8_pixel_t operator()( const gray8_pixel_t& index ) const
>    {
>       return _table[index[0]];
>    }
> 
>    rgb8_pixel_t* _table;
> };
> 
> typedef gray8_view_t::add_deref<indexed_pixel_deref_fn> 
> indexed_factory_t;
> typedef indexed_factory_t::type rgb8_indexed_view_t;
> 
> int _tmain(int argc, _TCHAR* argv[])
> {
>    // create color lookup table
>    rgb8_pixel_t rgb_black( 0, 0, 0 );
>    rgb8_pixel_t rgb_red( 255, 0, 0 );
> 
>    rgb8_pixel_t my_index_table[2];
>    my_index_table[0] = rgb_red;
>    my_index_table[1] = rgb_black;
> 
>    // create indexed image
>    gray8_image_t indexed_img( 10,10 );
>    fill_pixels( view( indexed_img ), unsigned char( 0 ) );
> 
>    rgb8_indexed_view_t indexed_view= indexed_factory_t::make( view(
> indexed_img )
>                                                             ,
> indexed_pixel_deref_fn( &my_index_table[0] ));
> 
> 
>    // color convert the indexed image into an rgb8 image
>    rgb8_image_t rgb_img( indexed_img.dimensions() );
>    copy_pixels( color_converted_view<rgb8_pixel_t>( view( 
> indexed_img ))
>                , view( rgb_img )                              
>            );
> 
>    // save image - it should be all red
>    jpeg_write_view( "test.jpg", const_view( rgb_img ));
> 
> 	return 0;
> }
> 
> I'm not sure if all these typedefs in the deref functor class are
> correct. Esspecially, I don't know what the const_t is for.
> 
> So, my problem is the operator() in my deref isn't called at all. That
> shows me there is something wrong.
> 
> Anyone, any idea why?
> 
> Thanks,
> Christian
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