JPEG <-> PNG Image File Format Converter will change any image on your device into either a JPEG or a PNG image. The process is very straightforward, but the app lacks any directions, or added functions, like export or editing of those images. The result is a one-trick app that, while useful in limited situations, will likely not be needed often.
When you open this app for the first time, you can load any image on your device for conversion. Once it loads, you can choose either JPEG or PNG for saving and it will process the image and convert it. Each conversion takes about two to three seconds and it will then save to your camera roll. The entire app is white with black text, so there is no real interface other than those two buttons and there are no export options when done with an image. The converted images look good and are in the format promised, but you are always guaranteed at least one extra step to get that image wherever you need it to be.
This app is effective at doing what it promises -- converting JPEG files and PNG files on your phone -- but it doesn't do anything else. Still, JPEG <-> PNG is free so if you find you do need to convert an image quickly, it offers a cheap, effective way to get the job done.