ISO Sensitivity / Noise levels (contd.)

Noise reduction and fine detail

The Canon EOS 550D offers three levels of in-camera noise reduction (four if you include 'Disable'), which span 'Low' to 'Strong', via 'Standard' - the default setting. Noise reduction is extremely useful if you shoot JPEGs and need smooth, grain-free images, but like all good things, it comes at a cost. The cost is that even the best in-camera NR systems are relatively 'dumb' and all too often, detail is removed along with the noise. This isn't a problem for screen use or if you only want to make small prints, but it means that on close examination, your pictures may not look as sharp and detailed as they might.

With this in mind, the best option for photographers that want more control over noise reduction is to shoot in RAW mode and convert the files in a separate program. Canon bundle Digital Photo Professional with the 550D, but there is a range of third-party raw conversion software available as well, including Adobe's Camera Raw plug-in for Photoshop and Lightroom which we're using here.

To check the effect of noise and noise reduction on low contrast detail we shoot our new studio setup at various ISO and noise reduction settings (where available), then crop an area that's challenging to any camera. The very fine detail in the feathers will help to better judge the effect of noise reduction on fine detail.

Raw vs in- camera JPEG noise reduction low contrast detail comparison

Turning noise reduction to '0' in Adobe Camera Raw gives a fairly good indication of what the 550D's output looks like 'naked'. It is clear from these images that low-contrast detail is very well-preserved in the raw files up to ISO 3200, and noise only starts to swamp detail at ISO 6400 and the highest available setting of 12800. It is no surprise to see that JPEG files don't fair quite so well though, and even with noise-reduction set to 'low' the finest detail in this image is lost by ISO 400. By the time we get to ISO 12800, in-camera noise reduction is masking detail at all settings, but it is clear that 'strong' is the worst offender. This is only to be expected, but it is a shame that set to 'strong', in-camera noise reduction even impacts upon low contrast detail at ISO 100 (albeit very slightly), where there is virtually no noise to reduce.

  RAW (ACR NR Off) JPEG NR Low JPEG NR Standard (default) JPEG NR Strong
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600

ISO 3200

ISO 6400

ISO 12800