Manga Generator lets you select a photo from your gallery app and convert it into Japanese MANGA-like image with various free scenes (backgrounds). Yeah, more scenes are available on Google Play for 1 or 2 bucks.
In version 2.0.1, it has 6 filters that let you adjust the image darkness.
Manga Fu Camera is an easy to use app. Choose a scene, take a photo with either the front or back camera and save the Japanese comic image. Unlike Manga Generator, this app comes with only 3 level of brightness adjustment.
Oh, and there’s another app from the same developer called ParaPara Manga Fu Camera. That, I will let you try first.