Canon 5D Mark III High ISO Noise Reduction
The Canon 5D Mark III offers four High ISO Noise Reduction settings: Disable, Low, Standard (default), and High, allowing you quite a bit of flexibility in choosing how you want to make the tradeoff between subject detail and noise levels in JPEGs. The Canon 5D Mark III manual says noise reduction is applied at all ISOs, working mostly in shadow areas at low ISOs, so we've included crops from ISO 50 up here.
See for yourself how the four noise reduction settings work. Click on any of the crops below to see the corresponding full-sized image.
The above crops show the effects of the four levels of high ISO noise reduction, under the HMI lighting we use to simulate standard daylight. As you can see, the High ISO Noise Reduction setting has little effect below ISO 400. At higher ISOs, the tradeoff between detail and noise can easily be seen. We'd probably tend to shoot with the Disable or Low setting to better preserve detail, especially in subtle reds.