Canon 5DS High ISO NR
Canon 5DS High ISO Noise Reduction
The Canon 5DS's four High ISO Noise Reduction settings ("High, "Standard", "Low" and "Off") provide good flexibility in choosing how you want to make the trade-off between subject detail and noise levels. The camera also offers a Multi Shot Noise Reduction option which takes 4 shots, and then aligns and merges them into one image to average out noise.
See for yourself how the Canon 5DS's "Standard" and "Off" High ISO NR settings compare to RAW without noise reduction under daylight-balanced lighting. (Note that these RAW images also have no sharpening applied, so they're a little softer than camera JPEGs at low ISOs.) Click on any of the crops below to see the corresponding full-sized image. Since the Canon 5DS user manual states noise reduction is applied at all ISOs, we've included crops from the base ISO on up.
The Canon 5DS's default "Standard" High ISO NR setting provides a very good tradeoff between noise and detail at low to moderate ISOs and does a great job at suppressing chroma noise, but it struggles to maintain lower contrast detail at higher ISOs, especially in our red-leaf fabric (as many cameras do). We'd probably shoot with lower settings at higher ISOs and reduce noise ourselves with post-processing (or just shoot RAW). Note how the "Off" setting doesn't disable noise reduction entirely even at low ISOs.