Hi Eloi, I'm doing some testing and indeed there is something wrong. The following test doesn't work for the alpha channel of the rgba10_pixel_t: #include using namespace boost; using namespace gil; int main() { typedef bit_aligned_pixel_reference< uint32_t , mpl::vector4_c , rgba_layout_t , true > rgba7_ref_t; typedef bit_aligned_pixel_iterator< rgba7_ref_t > rgba7_ptr_t; typedef std::iterator_traits< rgba7_ptr_t >::value_type rgba7_pixel_t; typedef bit_aligned_pixel_reference< uint32_t , mpl::vector4_c , rgba_layout_t , true > _rgba8_ref_t; typedef bit_aligned_pixel_iterator< _rgba8_ref_t > _rgba8_ptr_t; typedef std::iterator_traits< _rgba8_ptr_t >::value_type _rgba8_pixel_t; typedef bit_aligned_pixel_reference< uint64_t , mpl::vector4_c , rgba_layout_t , true > rgba10_ref_t; // A mutable iterator over RGBA10 pixels typedef bit_aligned_pixel_iterator< rgba10_ref_t > rgba10_ptr_t; typedef std::iterator_traits< rgba10_ptr_t >::value_type rgba10_pixel_t; rgba7_pixel_t src_7( 20, 30, 40, 50 ); uint16_t r_7 = get_color( src_7, red_t() ); uint16_t g_7 = get_color( src_7, green_t() ); uint16_t b_7 = get_color( src_7, blue_t() ); uint16_t a_7 = get_color( src_7, alpha_t() ); _rgba8_pixel_t src_8( 20, 30, 40, 50 ); uint16_t r_8 = get_color( src_8, red_t() ); uint16_t g_8 = get_color( src_8, green_t() ); uint16_t b_8 = get_color( src_8, blue_t() ); uint16_t a_8 = get_color( src_8, alpha_t() ); rgba10_pixel_t src_10( 20, 30, 40, 50 ); uint16_t r_10 = get_color( src_10, red_t() ); uint16_t g_10 = get_color( src_10, green_t() ); uint16_t b_10 = get_color( src_10, blue_t() ); uint16_t a_10 = get_color( src_10, alpha_t() ); return 0; } Looking at the packed_pixel's _bitfield member reveals that the it's value is way off. I'll keep investigating the issue. Regards, Christian