As TaeSoo and nrapallo mentioned, you can change the output resolution by modifying two lines of 'config.lua'. You can change the first two lines to these.
Code:
device_width=584
device_height=754
Better yet, you can convert set of image files into LRF using comic2lrf of Calibre. First, make one zip file from the pictures then use a simple script such as
Code:
comic2lrf -c 8 -r 'file.name.here.zip'
I think it will be easier to manage one LRF file instead of hundreds of images.