Like other recent Canon DSLRs the EOS 7D offers four noise reduction settings - Off, Low, Standard and Strong - and the default setting is Standard. High ISO Noise Reduction settings can be changed via C.Fn II-2. Noise reduction is applied at all sensitivities but gets stronger at higher ISOs. The difference between Off and Low is fairly small and only has an impact on chroma noise. At the standard and strong settings gray and black luminance noise are effected as well. If you are worried about noise the Standard setting is probably best for you. It presents a good compromise between noise reduction and retention of image detail but leans a bit towards the heavy-handed side. Therefore, if image detail is higher up your priority list the Low setting is a good alternative too.
Noise Filter Settings compared
Indicated ISO sensitivity is on the horizontal axis of this graph, standard
deviation of luminosity on the vertical axis.
High ISO Noise Reduction Crops
Noise reduction and fine detail
The biggest issue with noise reduction - especially luminance noise reduction - is that in the process of blurring away the noise it can also have a very destructive effect on the detail in an image, particularly the fine, low contrast detail you might find in hair, fur or grass. To better judge the effect on fine detail lost due to noise reduction we have shot our new studio scene and produced crops from the feathers in the image. We have left out the 'Low' noise reduction setting as it only appears to apply chroma noise reduction which tends to have little impact on detail (fine contrast).
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, 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
As you can see from the crops below even at the 'Off' setting the camera still applies some noise reduction, there is visibly more chroma noise in the RAW shots. The 'High' setting is very strong and blurs detail from the lowest ISO settings. Of course at higher sensitivities it's always going to be a compromise between detail and noise but when you are shooting RAW you have much more control over the application of noise reduction.