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ISO Sensitivity / Noise levels (contd.)

In-camera High ISO noise reduction

The Alpha 550 has only two noise reduction options - and neither of them is 'off' (in fact there's very little difference between them), so if you prefer a more light handed approach when dealing with high ISO noise you'll need to shoot raw. As the graphs and examples below show, noise reduction only starts to make a meaningful difference at ISO 1600.

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis (note that the standard deviation scale here is magnified 2x compared to the graphs on the previous page).

High ISO JPEG Noise Reduction vs Raw Crops

  JPEG Standard NR JPEG High NR Raw (no NR)
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800
As you can see, the difference between High and Standard NR is minimal (and appears mostly as a different amount of chroma noise at the highest settings). Looking at the raw output, stripped of as much noise reduction as we can, shows just how much noise the processor is having to work with, and how little there is you could do to improve the top two ISO settings.

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 lovely model and produced crops from the feathers in the image.

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 we saw above the effect of changing the noise reduction setting only kicks in at ISO 1600. As the crops below show, the difference at ISO 200 and ISO 400 is negligible, and at ISO 800 you have to look very closely to see any loss of detail (mainly, it has to be said, because the Alpha 550 can't resolve the finest detail in the feathers). Once you get to ISO 1600 and higher the strong noise reduction blurs away what fine detail there is, though to be fair the raw output at higher settings is so noisy that any detail has been swamped anyhow. The only point I can think you might want to use the A550's output without NR at higher ISO settings is when shooting black and white, when keeping the grain will give you a sharper output.

  ACR RAW NR OFF JPEG NR-Std JPEG NR-High
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400
ISO 12800

What's obvious here is that Sony is having to use a lot of NR at the highest settings, and that the difference between the two NR settings is minimal. you're unlikely to be able to do a much better job with raw when shooting above ISO 1600 - the output is simply too noisy and any fine detail is either swamped or smeared away.

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