better 3790 custom icons


I searched and have found people mentioned 8bit or 22x22 and using MS Paint, but I'm a mac user and have no idea how to convert the current icons to show up (without zooming all the way) as I drive like my saved favorites. I have successfully downloaded Starbucks POI's and icons and they do show up, but you have to zoom all the way in in order to see them. Would it be possible to have a category for icons for the higher resolution screen like the 3790's? If not, what do I use on Mac to convert the current icons? When I open the image of the icon, the default on mac is the Preview. I tried resize the icon, but then POI loader won't even load the Starbucks POI's anymore! Thank you.