If you've been shooting photos with your iPhone as long as I have, then you will probably own (if not heard of) Perfectly Clear from Athentech Imaging.
In the early days of iPhoneography, Perfectly Clear was everyones (including mine) go to app for improving the cameras poorly exposed images, with just 1 click. Then about 18 months ago, disaster struck, as due to developer issues, a seriously buggy version 2.0 of Perfectly Clear hit the App Store, and this once 5 star app rapidly fell to a 1/2 star app.
Well, it may have taken 18 months, but yesterday version 2.4 of Perfectly Clear for the iPhone hit the App Store, and the King of the "Automatic Photo Correction" apps is back, and here is what is new, improved and FIXED :)
If you already own Perfectly Clear for the iPhone or iPad, then you can download version 2.4/1.4 for FREE, but if you've never heard of/seen/tried this app before, then until Friday both apps are on sale for £0.69/$0.99/€0.79/£1.49/$1.99/€1.59, and I can honestly say, having played with the iPhone version, whether you have an iPhone 4 or 4S, "Perfectly Clear is once again a must have app."
A word about Perfectly Clear for the iPad: Disappointedly, version 1.4 will not save above 8 megapixels, so if you edit your digital compact/DSLR photos on your iPad and hoped to be able to add Perfectly Clear for the iPad to your workflow, then you will be sadly disappointed. I have raised this issue with Athentech Imaging, and I have my fingers crossed in hope that they will address this, but until then I can not recommend the iPad version for anything other than lower resolution photos :(