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ISO Sensitivity / Noise levels

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 (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 1.5 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.)

Fuji FinePix F30 vs FinePix F10 vs Canon PowerShot G7

Fuji FinePix F31fd
n/a
Fuji FinePix F30
n/a
Canon PowerShot SD800 IS
ISO 80
   
Fuji FinePix F31fd
ISO 100
Fuji FinePix F30
ISO 100
Canon PowerShot SD800 IS
ISO 100
Fuji FinePix F31fd
ISO 200
Fuji FinePix F30
ISO 200
Canon PowerShot SD800 IS
ISO 200
Fuji FinePix F31fd
ISO 400
Fuji FinePix F30
ISO 400
Canon PowerShot SD800 IS
ISO 400
Fuji FinePix F31fd
ISO 800
Fuji FinePix F30
ISO 800
Canon PowerShot SD800 IS
ISO 800
Fuji FinePix F31fd
ISO 1600
Fuji FinePix F30
ISO 1600
Canon PowerShot SD800 IS
ISO 1600
Fuji FinePix F31fd
ISO 3200
Fuji FinePix F30
ISO 3200
Canon PowerShot G7
n/a
 

Like the F30 before it the F31fd offers amazingly low noise at ISO 100-400, and at ISO 800 / ISO 1600 it is miles ahead of the competition, offering lower noise and better detail retention. It's interesting to see the difference between the F31fd and the F30 at ISO 1600 and 3200, where the processing has been tweaked very slightly, reducing the amount of noise reduction (and producing a noisier, but less processed looking image). Forget ISO 3200 - it's a stop too far, but ISO 1600 is, in my opinion, a better balance of noise and NR than it was with the F30.

Luminance noise graph

Cameras compared:
Fujifilm FinePix F31fd, Fujifilm FinePix F30, Canon SD 800 IS

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

As seen in our real-world tests, the F31fd has marginally higher luminance noise at most ISO settings, particularly at ISO 1600 and 3200. Both cameras offer lower noise than the 7.2MP Canon, but more importantly they do so with considerably less destructive noise reduction.

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.

The same story for chroma noise; a little higher than the F30 throughout the range (reflecting a very slight tweak of the processing), but still a lot better than the competition despite the less aggressive NR.

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 this 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 100 ISO 200 ISO 400
ISO 800 ISO 1600 ISO 3200

As these crops show there is a gradually increasing smearing of of low contrast detail as you move up the ISO scale, but even at ISO 800 there is some texture preserved (more than many cameras manage at ISO 200!), and there is little - if any - visible noise. Once you get to ISO 1600 - and 3200 in particular - the loss of fine detail is significant enough to restrict the kind of subjects you can expect to shoot with any fidelity.

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