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ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This 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 (ie. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews.)

Canon PowerShot G9 vs Nikon COOLPIX P5100 vs Canon PowerShot G7

  Canon PowerShot G9
ISO 80
Nikon Coolpix P5100
ISO 64
Canon PowerShot G7
ISO 80
Crops
  Canon PowerShot G9
ISO 100
Nikon Coolpix P5100
ISO 64
Canon PowerShot G7
ISO 100
Crops
  Canon PowerShot G7
ISO 200
Nikon Coolpix P5100
ISO 200
Canon PowerShot G7
ISO 200
Crops
  Canon PowerShot G9
ISO 400
Nikon Coolpix P5100
ISO 400
Canon PowerShot G7
ISO 400
Crops
  Canon PowerShot G9
ISO 800
Nikon Coolpix P5100
ISO 800
Canon PowerShot G7
ISO 800
Crops
  Canon PowerShot G9
ISO 1600
Nikon Coolpix P5100
ISO 1600
Canon PowerShot G7
ISO 1600
Crops

With tiny, high pixel count chips noise is always going to be an issue, and to a large degree this is more a test 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).

When we reviewed the G7 I commented on how much better it would have been had Canon used a lower resolution sensor with larger pixels, but I guess it was kind of inevitable that the G9 would have even more pixels (though to be fair the sensor is also a little larger). At lower ISO settings the difference in the end result (noise-wise) is negligible (the amount of noise and the detail loss through noise reduction are very, very similar). At ISO 800 the G9 looks like it's applying slightly higher noise reduction than its predecessor (presumably because the sensor is producing more noise), and at ISO 1600 the appearance is very different - there's little if any difference in the amount of detail lost, but the G9 result looks softer (and the G7 looks noisier). If anything the G7 actually produces better results at ISO 800 and above, though we're splitting hairs, and you always have the option with the G9 to shoot raw.

Unsurprisingly, given that they almost certainly share the same sensor, the G9 and Nikon P5100 results are very similar (from a noise point of view), with both pretty useless at anything over ISO 400 for serious work. We found that the G9 produced very noisy images at ISO 800 in low light - noisier than these crops might suggest.

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 (fur) as you move up the ISO range.

100% Crops
ISO 80 ISO 100 ISO 200
ISO 400 ISO 800 ISO 1600

We were actually pretty impressed with the G7's performance in the low contrast smearing test, and the G9 is roughly the same at lower ISO settings. Sure there's some loss of detail at anything over ISO 100, but it's less destructive than we've seen with some other high resolution/small sensor compacts recently (don't forget we're looking at 100% crops from a 12MP file here - you'd need to be producing very large prints to be looking this close in the real world). ISO 800 and ISO 1600 are strictly in the 'emergency use only' file (and ISO 400 isn't for anything too detailed), but Canon has to be given credit for retaining a good balance of noise reduction and detail in the ISO 80-200 range.

Real world example

Although most photographers shooting outdoors are going to be looking to avoid using anything but ISO 80 when photographing detailed landscapes, there are always going to be times - in poor light, at the long end of the zoom and so on - when the ability to turn up the ISO in such situations can be very useful. The G9's noise reduction has visible effect at anything over base ISO, but you need to look very closely to see serious blurring of distant foliage at ISO 200, and even at ISO 400 the results are far from unusable. As always you're going to get the best results at ISO 80, but I'd feel perfectly happy going up to ISO 200 for a shot like this if I had to, something you can't say about a lot of today's compact cameras. Note that you can remove the noise reduction totally if you shoot raw and process using Adobe ACR.

100% Crops
ISO 80 ISO 100
ISO 200 ISO 400

Luminance noise graph

Cameras compared:
Canon PowerShot G9, Canon PowerShot G7, Nikon COOLPIX P5100

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

Noise is low up to ISO 400 (thanks to an effective NR system). As you move up the range the G9's stronger noise reduction really kicks in, and at the highest settings measurable (and visible) noise is actually lower than the G7.

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 is on the vertical axis.

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Comments

Silvita
By Silvita (6 months ago)

My super wonderful G9 is going to turn 6 years old soon.

I am grateful to Canon for this sort of masterpiece, despite I have some troubles now due to dust on sensor. But I am sure I'll find the right people that will sort this out.
And I'll keep shooting with her.

Greets to all the reviewers from Italy.

0 upvotes