[boost] [GIL] Pixel Layout Padding?

Hi there, The current gil::pixel design has a deficiency that you can't specify the align of pixel, for example, you can't have an RGBX pixel in GIL where X is padding. An alternative is to introduce a dummy channel for X, but that doesn't seem to be a good idea as we don't want to mess up the color space. So, maybe it'd be better to extend the current design, say, pixel, to something like pixel. Then we can specify RGBX as pixel, or XRGB as pixel where minus means left justify. Ideas?