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ISO Sensitivity / Noise levels (contd.)

In-camera High ISO noise reduction

The 1D Mark IV offers four levels of noise reduction Off, Low, Standard and Strong, set using C.Fn II-2. Noise reduction is applied at all sensitivities but gets stronger at higher ISOs. As a camera that is likely to be used in JPEG mode by a fair proportion of its users, this level of control is important. The difference between the Off and Low settings is that the latter applies a slightly greater degree of chroma noise reduction. The default, 'Standard' setting heavily reduces both chroma and luminance noise, from a numerical point of view. As the name suggests, the Strong setting surpresses noise to an even great extent.

  Noise Filter Settings compared
Off
Low
Standard
Strong

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

High ISO Noise Reduction Crops

  Off Low Standard High
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12,800
ISO 25,600
ISO 51,600
ISO 102,400

The image crops tell exactly the story that the noise reduction graphs would lead you to expect: both the Off and Low settings become extremely noisy, while the Standard and Strong settings are increasingly ruthless in terms of reducing both noise and detail. The real differences are at ISO 6400 and above where noise is clearly starting to become problematic. Beyond this point, it's a question of how much detail you're willing to sacrifice in order to get cleaner images.

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

Although it's called 'Off,' it's clear that the JPEG engine is always applying a considerable degree of noise reduction, particularly to counteract color (chroma) noise. Even at ISO 12,800 the off setting looks pretty usable even though the RAWs show that there's plenty of noise to be combated. The NR Strong setting is very aggressive at all ISO settings, so we'd be tempted to use NR-Standard when working above ISO 6400 and Off or Low below that.

  ACR RAW NR OFF JPEG NR-Off JPEG NR-Standard JPEG NR-Strong
ISO 50
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800
ISO 25600
ISO 51200
ISO 102400
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