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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 1.4 in this review). (Note that noise values indicated on the graphs here can not be compared to those in other reviews.)

Sony DSC-H7 vs Olympus SP-550UZ vs Panasonic DMC-FZ8

Sony DSC-H7
ISO 80
n/a Olympus SP-550UZ
ISO 50

 

Sony DSC-H7
ISO 100
Panasonic DMC-FZ8
ISO 100
Olympus SP-550UZ
ISO 100
Sony DSC-H7
ISO 200
Panasonic DMC-FZ8
ISO 200
Olympus SP-550UZ
ISO 200
Sony DSC-H7
ISO 400
Panasonic DMC-FZ8
ISO 400
Olympus SP-550UZ
ISO 400
Sony DSC-H7
ISO 800
Panasonic DMC-FZ8
ISO 800
Olympus SP-550UZ
ISO 800
Sony DSC-H7
ISO 1600
Panasonic DMC-FZ8
ISO 1250
Olympus SP-550UZ
ISO 1600
Sony DSC-H7
ISO 3200
Panasonic DMC-FZ8
ISO 3200
Olympus SP-550UZ
ISO 3200

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).

All 'super zoom' cameras struggle with noise since they have particularly small sensors (they have to be small or the lenses would be the size of a trash can) - this is one of the key compromises we have to accept if we want a lightweight camera with a lens this big. Sony's approach to noise reduction seems to be that you can't have enough of it, and once you get to ISO 200 or over the combined effects of noise and heavy NR are enough to cause a serious loss of fine detail. It's not significantly worse than most of its competitors (though the NR - and therefore detail loss - is amongst the heaviest); this is what you get when you stuff eight million pixels into a 1/2.5-inch CCD sensor.

Luminance noise graph

Cameras compared: Sony DSC-H7, Olympus SP-550UZ, Panasonic DMC-FZ8
Note: FZ8 ISO 100-1250 only measured

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

The graph shows what we'd observed in real life photographs: the H7's noise levels at ISO 80-400 are very low. Since Sony doesn't have a magic sensor this can only be the result of heavier than average noise reduction.

RGB noise graph (ISO 50-3200)

Cameras compared: Sony DSC-H7, Olympus SP-550UZ, Panasonic DMC-FZ8
Note: FZ8 ISO 100-1250 only measured

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.

Once again ISO 80-400 noise is very low, thanks to the Bionz noise reduction process, but as our tests show, this comes at a price; the loss of fine detail at anything over base ISO. it's still better than either of the other cameras in this comparison.

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, F3.5
ISO 80 ISO 100 ISO 200
ISO 400 ISO 800 ISO 1600
   
ISO 3200    

These crops illustrate perfectly the extent to which the H7's heavy-handed noise reduction has an increasingly destructive effect on fine, low contrast detail even when photographed from a fairly short distance (these crops show how hair appears in a typical head and shoulders portrait). Even at ISO 80 there is some detail being lost through 'smearing', though it's mainly an issue for distant foliage - and even then only if you're producing prints over 10x8 inches (or of course peeping at pixels like this). Things get increasingly bad as you move up the ISO range, with ISO 200 the point where our 'acceptable' threshold starts to give way. ISO 400 looks distinctly painterly, and ISO 800-3200 may all well be created by a random pixel generator.

So then, if you're shooting landscapes (with lots of distant foliage) or anything with fine, low contrast texture, and you want to produce anything over a postcard sized print you need to stick to ISO 80 or 100, and even then be prepared to lose something to noise reduction. As mentioned earlier in the review, this camera really needs a low NR option for those of us that like to make our own decisions about how much detail we're prepared to sacrifice for a 'smooth' result.

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