Canvas resize

I want to batch process all images in a directory and resize the canvas and/or the image. It needs to detect the current size of the image and canvas and then set the canvas size to be the next biggest power of 2. For example an image which 130 x 305 would have the canvas re sized to 256 x 512 and the image on the canvas would be the same. additionally, the new area of the canvas will be transparent. Also, I want a command line switch to enable me to resize the image as well as the canvas.