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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 1.5 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.)

Sony DSC-HX1 vs Canon PowerShot SX1 IS vs Panasonic Lumix FZ28

Sony DSC-HX1
ISO 125

Canon PowerShot SX1 IS
ISO 100
Panasonic Lumix FZ28
ISO 100

Sony DSC-HX1
ISO 200

Canon PowerShot SX1 IS
ISO 200
Panasonic Lumix FZ28
ISO 200

Sony DSC-HX1
ISO 400

Canon PowerShot SX1 IS
ISO 400
Panasonic Lumix FZ28
ISO 400

Sony DSC-HX1
ISO 800

Canon PowerShot SX1 IS
ISO 800
Panasonic Lumix FZ28
ISO 800

Sony DSC-HX1
ISO 1600

Canon PowerShot SX1 IS
ISO 1600
Panasonic Lumix FZ28
ISO 1600

Sony DSC-HX1
ISO 3200

Canon PowerShot SX1 IS
NA
Panasonic Lumix FZ28
NA

   

The noise reduction on the HX1 starts to kick in at ISO 200, with more sharpening thrown into the mix to keep things from looking totally blurred. The HX1 and the FZ28 perform similarly in terms of noise levels and amount of retained detail, with the HX1 doing marginally better as ISO settings climb. The SX1 IS performs worse than the other two cameras at anything above base ISO (though to be fair these results that look very similar at print sizes, and none is great above ISO 400). The HX1 is at a disadvantage as it is the only camera of the group that cannot record RAW images (to allow you to make a decision on noise reduction and sharpening in post processing). The extra ISO 3200 setting on the HX1 is almost pointless as it is a blurry noisy mess. If the ISO 1600 settings on these cameras are emergency settings, then ISO 3200 is a extra emergency setting, maybe even not enough detail left for a small print.

What you should take away from this is that there is currently no inherent advantage to buying a camera that uses CMOS sensor technology vs CCD technology in terms of noise levels and detail retained at high ISO.

Luminance noise graph

Cameras compared:
Sony DSC HX1, Canon PowerShot SX1 IS, Panasonic Lumix FZ28

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

This graph shows that the current generation of CMOS sensors are just as noisy as CCD sensors, the difference is down to the type and amount of noise reduction a manufacturer decides to apply in camera.

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.

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 125 ISO 200 ISO 400
ISO 800 ISO 1600 ISO 3200

As the noise reduction kicks in at ISO 200, the sharpening is also turned up, meaning that ISO 200 and 400 don't look that different to base ISO (though of course, fine detail is being lost). You can really see the loss of detail between ISO 400 and ISO 800 (to the extent that it almost looks like two different cameras). Once you get to ISO 1600 the output, like virtually all small sensor cameras, is a blurry mess.

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