The rise of smartphones and tablets has provided us with new options for image capturing, editing, sharing and viewing. Especially the latter has sparked not only amateurs' but also professional photographers' interest in mobile devices. After all, when showing off your portfolio to potential clients it's much cooler to elegantly swipe from one digital picture to another on the gorgeous high resolution screens of a latest generation iPad or Google Nexus 10 than carrying prints around in a bulky folder.

The latest generation tablets and even phones are great for presenting your images but if your workflow involves evaluating detail and critical focus on a mobile device the situation is less than ideal. This is because the standard image viewers, such as Apple's Photo app or Android's Gallery app, don't display the actual images but a version that has been reduced in size to maker better use of the mobile devices' limited resources.

This means images look great when viewed at screen size but quality suffers when you zoom in. The zoomed images look pixelated and the zoom factor is usually very limited too. You cannot magnify the images to a 100% view which makes it impossible to check focus and critical sharpness. However, as so often there is an app for that.

Actual Pixels is a great free app for checking the detail in dpreview studio shots. At screen size viewing there's no advantage over the standard Photo App but the difference becomes very obvious when you start zooming in. We've used an iPad 2 for this comparison.
This is the 100% view of our Nikon 36MP D800 Raw box shot in Actual Pixels.
In comparison in the Photo app you cannot zoom to 100% and even at the lesser zoom level the image looks soft which means you cannot reliably judge focus and critical sharpness.

Recent versions of more complex paid imaging apps such as Photosmith or Apple's iPhoto support 100% viewing of images but for those of you who really only need the ability to zoom in all the way there is now a free solution available in the App Store. Actual Pixels works on iPhone and iPad and is very simple. You select an image from the camera roll and can then apply any zoom factor using the pinch gesture. The app displays the image size in pixels and the current zoom factor. There is also a button to easily return to the full-size view.

Actual Pixels is very useful for checking the focus on portraits. However, on this 12MP shot from a Nikon D700 the difference to the default Photo app is not quite as huge as with the 36MP D800 picture above.
Zooming to 100% in Actual Pixels let's you see that the eyes in this portrait shot are perfectly in focus.
Because the original image is only 12MP the gap between the default Photo app preview image and the original file is smaller than in the D800 sample but still not good enough for assessing critical sharpness.

We used an Apple iPad 2 for the comparison between Actual Pixels and the default Photo app but the effect will be similar on other iOS devices. That said, the latest generation iPad with its Retina display will generate a higher resolution preview image for the Photo app, taking it closer to the original image size. Generally Actual Pixels is most useful when assessing high resolution images on low resolution screens but given it's free you can install it on your device without any risk and see if it satisfies your specific needs. You can download and install Actual Pixels from iTunes.

We haven't found an Android equivalent to Actual Pixels yet. Let us know in the comments if you use an Android image viewer that allows you to zoom in to 100% magnification and we'll have a look at it.