There are many great reasons to edit photos on your iPad. Unless you're a professional photographer or artist, it's almost certainly the best screen you own - especially the third-generation iPad with its fantastic high-resolution Retina display.
The software available makes most of the tweaks you'll want to make to your image as easy as swiping your fingers across the screen. You're easily connected to the majority of social sharing and gallery sites. And, most importantly of all, there's nothing quite like simply touching a screen to add a little digital rouge or add more exposure with a quick tap or two. If you've yet to try it, then it really is high time you did.
But first, here are the things you can't do. RAW editing is out, though for most purposes you can compensate by using the Camera Connection Kit to get a JPEG version of your image to play with (the kit is £25 from the Apple Store and is ideal, even if it's just for backing up your photos as you go).
You can forget about lens correction and automated de-vignetting, and for most of the apps on test, noise reduction is a no-no, too. In each case, there are often individual apps that will handle that (PiRAWnha for instance), but they're not provided as standard in most.
However none of this should matter too much for regular snaps, and you always have the option of bringing the originals into a full-fat editor like Aperture or Photoshop if you need more power. For the overwhelming majority of images, all the tools you need are here, cheap, and amazingly easy to use.
Even if you own a bespoke editing program, the speed at which you can edit photos makes something like Snapseed or iPhoto a handy companion. You can whip holiday snaps into shape immediately rather than having to head home or travel with a separate MacBook. Whether you're an amateur or professional, the iPad is about to become the best photo companion you've ever had. So let's look at the apps available to you…
Test one: Basic edits
Nips and tucks that help any image shine
Every app here offers a very different approach to editing - though they all cover the main tools you need for fixing exposure, pumping up the colour, cropping your images and exporting.
Filterstorm, Photoshop Touch and Photogene are the only tools to offer noise reduction, though all apart from Luminance include sharpening in some form; painted on in iPhoto, a global slider in the others. The trickiest part is often finding where the options are and what they're called - Snapseed calls its sharpen tool 'Details', while other apps can put the tool anywhere. There's no consistency between apps.
Once edited, all tools will export your image as a JPEG. Be warned though, there are export size limitations. On the original iPad, many apps can only handle around 4-6 megapixels; on the iPad 3, you're fine at up to 20 megapixels. Photoshop Touch is the one remaining hold-out, only handling images of 2,048 pixels across.
Test two: Advanced edits
Controls that make so much difference
Despite its size limitations (and current lack of Retina support), Photoshop Touch immediately impresses with its layers, ability to create composites and mask out pieces of photos, and colour-correct with curves instead of simply layers. It's still a little underpowered, and most of what you can do isn't that handy for simple photos, but it's the best with layers so far.
Of the others, Snapseed doesn't have many extras of note, though its main trick - see test four, Ease of use - compensates for that by letting you really get specific about which areas you want to edit.
Somewhat frustratingly, iPhoto does have a good range of edits, but does itself no favours with how it applies them: Sharpen with only three strengths, for instance, or hiding handy options like Vignette as unlabelled icons in its Edit menu.
Still, all these editors have more than a few tricks up their sleeve, including sharpening, and often noise reduction to help with those high-ISO images.
Test three: One-click fixes
Filters and instant presets for easy results
It's a bit of a cheat, but everyone does it. Every iPad editor worth its salt offers a few quick shortcuts to make an image look old, warm, dramatic, noir, and many other styles. All of them except Filterstorm that is, which is very odd considering its name…
Of the rest, Snapseed's are the most limited, using just a handful of textures to not very good value. iPhoto doesn't offer any presets, but does have some handy tools like gradients and oil painting effects, with the major flaw that you have to choose just one instead of being able to combine them.
Luminance wins some points by letting you pick a preset and then tweak it directly, though its selection isn't that great. Photoshop Touch offers some of the best, including Smooth Skin, Lighting and Directional Blur, with the advantage that you can tweak the intensity of each in turn.
None however offer a big selection to one-click transform your photo into something more interesting.
Test four: Ease of use
The speed and pleasure of iPad editing
Two tools stand out here - Snapseed and iPhoto. Snapseed's party trick is that instead of selecting bits of the screen by painting, you tap to add a point (up to eight per image) and it automatically masks out anything around it. You can widen or shrink the active area, apply saturation, brightness and contrast individually to every point, and move the pin at will. It's an amazing way to edit, very fast, and works wonderfully.
Over in iPhoto many tools also benefit from touch, although often not as well. Being able to just tap the sky to edit its blueness is great, though both the amount of stuff on the interface and the mediocre quality of the adjustment brushes often make for a fiddly experience. Trying to apply an effect on a precise area is especially irritating.
The other apps offer convenience over a desktop app, but that's about all in UI terms - sliders and so on that compensate for the lack of a mouse, but don't improve on it.
The Winner: PhotoGene
While it didn't excel in any one single category, iPhoto is a great all-round tool for editing and showing off the benefits of doing it on the iPad. It's accessible and has an excellent toolset, plus support for browsing albums and comparing images.
It's highly recommended but bugs and few issues prevent it from taking top slot - an honour that goes to Photogene, which didn't stand out in any one area, but performed strongly in all tests.
It's easy to use, powerful and even boasts non-destructive editing (a feature usually found only in 'full-size' apps), which helps offset the lack of layers. Photogene is also actively being developed with frequent, feature-packed updates. At just £1.99 it's a great all-rounder.