I use the Photogene app on my iPad. Works rather like Lightroom...edits are applied when you render a photo to the iPad's Camera Roll (for viewing and/or export), with the original (JPEG) files remaining intact. Photogene can decode RAW data too, but you have no say in how it renders the resulting JPEGs. I find it clips the highlights too much and so use the camera-created JPEG versions of my pics instead. Note that there are also two dedicated RAW converters available for the iPad, PhotoRAW and PiRAWhna, both of which are quite flexible but also very resource-intensive. I can process RAWs from my 16mp Micro 4/3rds cameras, albeit slowly, but Pentax 645D RAWs...err, no.