Glo HD Koreader cannot change the images contrast for epub and mobi comics

I found that koreader has no problem changing the contrast of comic images in pdf/cbz format, but not epub/mobi. It can be seen that the menus are also different, which shows that koreader thinks epub/mobi are text books. So is the contrast change of koreader so unfriendly? Epub/mobi are the two mainstream formats. If I only have epub/mobi,is my only way to convert epub/mobi to pdf/cbz? Also, if I change the file extension from epub to cbz, the sorting of comics will be messed up.
Any suggestions welcome