[xbingo]

Originally Posted by kovidgoyal

And you also have to set the option in MOBI output to not convert images to JPEG.

Thank you for replying
I dig into the source code and found that

 SCRWIDTH, SCRHEIGHT = self.opts.output_profile.comic_screen_size

            try:
                if self.opts.comic_image_size:
                    SCRWIDTH, SCRHEIGHT = map(int, [x.strip() for x in
                        self.opts.comic_image_size.split('x')])
            except:
                pass # Ignore

the width and height should be splited by an 'x', but the chinese simplified help
string mislead me to split it by '*' instead.
All works fine with the origin paperwhite profile after I wrote that option correctly