Re: HGC transparency
The Graphics Asset Converter that is part of the Harmony Graphics Composer only supports 24-bit RGB888 BMPs.
Is the alpha channel information critical in the picture critical to your design? If not, obviously, I would recommend down-converting the original image to 24-bit BMPs and re-import into MHGC.
If it is, you may want to consider converting the image to PNG. Keep in mind, the PNG runtime decoder that comes with the Harmony Graphics stack requires sizable dynamic memory.