i dont know, the hud tbl has been obsolete for ages and you can just get away putting the shield icon in the ships table.
the thing is that the sheild icons use a rather strict pallette. its stored as 8 bit but you only really have 15 shades of grey to work with. index 0 being black and index 15 being white. index is very important so dont let photoshop change your color indicies. best bet is extracting a frame from a shield icon with aniview open the color table in photoshop and save it as a pal file (not an act as they tend to mix up your indicies). then when converting your icon to index, load that pal file photoshop will match to the closest color in the pallette.
the icons are rendered with additive alpha so it makes the sheild segments grow smaller by darkening the pixel colors. if you look at sheild icons you find that the outermost part of the shield is really bright and becomes progressivly darker as it gets closer to the ship. this is so as their darkened they will eventually become zero and will disapear in the additive blending (because theires noting to add), this gives the effect of making the shilds apear thiner as they are weakened.
*feature request*
any chance we can get support for 32bit eff hud icons? rather than using the old meathod of rendering them. what about we give the shield segments alpha chanels and then multiply them (the alpha channels) by the percentage of sheilds in that segment. this would mean you could have color icons and fancyer shield effects. id really like to get away from the old ani format. its working with it tends to burn up a modders time. i dont know about you but i hate working with indexed color.