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ISO Sensitivity / Noise levels


Standard Test
ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. The works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras).

The image sequence is run through our own proprietary measurement tool which measures the standard deviation (normalized) of the middle gray patch (indicated by the red rectangle above). Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Nikon Coolpix P5100 vs Canon PowerShot G9 vs Nikon Coolpix P5000

Nikon Coolpix P5100
ISO 64
Canon PowerShot G9
ISO 80

Nikon Coolpix P5000
ISO 64

Nikon Coolpix P5100
ISO 100
Canon PowerShot G9
ISO 100

Nikon Coolpix P5000
ISO 100

Nikon Coolpix P5100
ISO 200
Canon PowerShot G9
ISO 200

Nikon Coolpix P5000
ISO 200

Nikon Coolpix P5100
ISO 400
Canon PowerShot G9
ISO 400

Nikon Coolpix P5000
ISO 400

Nikon Coolpix P5100
ISO 800
Canon PowerShot G9
ISO 800

Nikon Coolpix P5000
ISO 800

Nikon Coolpix P5100
ISO 1600
Canon PowerShot G9
ISO 1600

Nikon Coolpix P5000
ISO 1600

Nikon Coolpix P1000
ISO 2000
n/a Nikon Coolpix P5000
ISO 2000
 

Small sensors with high pixel counts usually mean large amounts of noise and the P5100 is no different. It may have a very slightly larger sensor than its predecessor but it also has more sensor sites crammed onto it, so there's no real improvement in performance at high sensitivities. It appears that the P5100 is using marginally higher NR than its predecessor (presumably to counter a slightly noisier sensor), something confirmed in the graphs at the bottom of the page. The net effect is that 'real word' detail is roughly unchanged between the P5100 and its predecessor.

To a large degree this test is more an assessment of the effectiveness (both measurable and visible) of a camera's noise reduction system. Designers have to balance the desire to produce smooth, clean results with the need to retain as much detail as possible (if you blur away the noise, you blur away image detail too). These crops show that all manufacturers find it difficult to produce an acceptable result at anything over base ISO from 12 million pixels crammed into a tiny sensor. By ISO 400 both the P5100 and G9 are showing both noise and a loss of detail from noise reduction. Above that, both do equally badly with noise increasing and detail being lost. Which is not to say that these cameras are bad examples of their kind - we have yet to see a 12MP compact that avoids noise and detail loss at anything above moderate ISO settings. It's interesting to see that at anything over the lowest ISO settings there appears to be very little advantage to the extra pixels the P5100 provides over the P5000 - if anything the softening effect of noise reduction at the highest ISO settings makes the P5100's output actually worse than its predecessor.

Low contrast detail

What the crops and graph don't show is the effect of noise reduction on low contrast fine detail such as hair, fur or foliage. An inevitable side effect of noise removal is that this kind of detail is also blurred or smeared, resulting in a loss of 'texture'. In a new test the crops below show the effect of the noise reduction on such texture (hair) as you move up the ISO range.

100% Crops
ISO 64 ISO 100 ISO 200
ISO 400 ISO 800 ISO 1600
 
ISO 2000 ISO 3200  

No surprises here - at ISO 200 and above noise reduction starts to have an effect on low contrast detail, but we've seen far worse. ISO 400 and 800 are usable for smaller prints, though the light-handed approach to chroma NR means that you are beginning to see colored blotches at ISO 400, getting progressively worse as you increase sensitivity. We'd actually like to see a little less luminance NR and a little more chroma NR, since this would help retain detail and look more pleasant. ISO 3200 (5MP size) uses pixel binning to produce a very smooth, almost featureless result that is, to put it mildly, of limited use.

Luminance noise graph

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

RGB noise graph

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels are on the vertical axis.

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