Product Reviews

High Dynamic Range Imaging, or HDRI, is taking over Flickr. Search on those four letters and you'll turn up hundreds of thousands of results. Yet they're largely misleading, since most won't be vanilla HDRI at all, but exercises in tone mapping.

HDRI is the process of combining multiple images - usually Raw - taken at different exposures in a single photo. This photo takes reference points from the highlights of the darkest photo and the shadows of the lightest, and combines these with data from all of the other images in the set.

The theory is that you end up with a perfectly exposed shot, with no burnt out highlights, and nothing lost in the shadows. It's ideal for sunset scenes, where the foreground can get lost due to the sky's brightness tricking the camera into cranking down its overall sensitivity. However, as an HDRI file contains far more information than a regular 8- or 16-bit image, you can then go on to stretch various parts of the image's colour spectrum to produce the kind of garish results that often turn up in a Flickr search for HDRI. Whether you'd want to or not is open for debate, but if you do, then you may find Hydra slightly limiting.

Hydra is by far the most attractive HDRI generator

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we've yet come across. It looks like an iLife application, and has an iLife media browser for grabbing up to four source files from your iPhoto library. It'll warp them if they don't quite match up - great if you don't have a tripod - and generate an HDRI result in two clicks.

You can then tailor the results by dragging the divisions between the source images, effectively adjusting the balance of influence that each one exerts on the end result, to bring out your shadows or highlights, and shift the siting of the mid-tones.

It's all highly intuitive and a great introduction for the first timer. It also gives you enormous control over the results, effectively giving you slider-based control over the overall exposure of your image. As such, it's more flexible than even the most advanced DSLR camera.

But in other respects, it's also quite basic. Output can be rendered as a Jpeg or Tiff, but there is no option for tone mapping. If you're shooting a scene with tricky lighting then you should be able to iron out undesirable extremes using Hydra, giving you a more balanced result, and as such it puts professional features into the hands of the consumer, but it's more of a fixing tool than a creative application, as can be seen from the examples here.

Hydra never claims to be anything more than an HDRI rendering utility, and that's exactly what it is. It'll correct your poorly-exposed photos, and help you make the best of less-than-ideal shooting conditions. Just make sure that's all you're after before handing over your money. If you want to add tone mapping into the mix, check out Photomatix Pro ($99, about £50, from hdrsoft.com), the third edition of which is in beta. If you have Photoshop, you already have an HDRI rendering tool, which is under File > Automate > Merge to HDR...