If you're looking for a professional-grade photo editing app for iPhone or iPad, you have plenty of choice with apps like Lightroom and Snapseed among some of the most popular options.
MaxCurve joins that lineup: it's a photo editing app with support for curves and layers that give you deep control over editing the appearance of a photograph.
This is not your standard curves color adjustment: this app uses 28 different curves to achieve deep control over every aspect of an image. Additionally, it offers supports for layers, so that your edits can be more fine grained, as well as for masks, presets and blend options.
At $4, it is one of the pricier photo apps, but given the advanced features it offers, the price seems well worth it. There are no annoying ads, of course, and no constant prompts to buy things. You can check it out for yourself right below.