Understanding ALO’S limitations

ALO gives shots a subtle kick – are there any negatives?

While this month’s Canon School has highlighted the benefits that a splash of ALO can bring, there are some caveats that need considering before whacking it up to High.

For a start, it can increase noise, which will be especially obvious in the shadows that have been lightened. If you’ve ever dragged the shadows slider to the right in photo editing software, you’ll know what to expect (although to be fair, it’s not usually as severe). This problem will be worsened if you’ve shot a high ISO.

ALO can also interfere with your exposure. Say you’ve used exposure compensation to make an image darker on purpose – ALO may simply brighten things up again. It’s a similar story with flash exposure compensation. If you have a particular look in mind, it’s better to disable ALO (along with other automatic image processing functions, such as Auto White Balance and Auto Picture Style).

Then, of course, there’s the fact that it can be a bit of a blunt tool. Not having any control over which areas of the picture will be made lighter can be a bit unnerving. Although I would say that, in my experience at least, most of the time it’s been pretty good at working out when something I’ve intentionally made a silhouette should actually be left as a silhouette.

You can at least, thankfully, preview the effect a bit better if you apply ALO to Raw files in Digital Photo Professional

– you can also play with the different strength settings. In fact, you can apply ALO to JPEGS using Canon’s software in post: when you open a JPEG image, most of the image processing options will be greyed out, but you can at least select the Standard option for ALO.

Using the Auto Lighting Optimizer’s Strong setting has increased noise in this low-light image, although noise reduction could help calm it down

DPP allows you to adjust the strength of ALO, and compare results with the original