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

Canon SX100 IS vs Panasonic DMC-TZ3 vs Sony DSC-H3

Canon SX100 IS
ISO 80
n/a n/a

 

 

Canon SX100 IS
ISO 100
Panasonic DMC-TZ3
ISO 100
Sony DSC-H3
ISO 100
Canon SX100 IS
ISO 200
Panasonic DMC-TZ3
ISO 200
Sony DSC-H3
ISO 200
Canon SX100 IS
ISO 400
Panasonic DMC-TZ3
ISO 400
Sony DSC-H3
ISO 400
Canon SX100 IS
ISO 800
Panasonic DMC-TZ3
ISO 800
Sony DSC-H3
ISO 800
Canon SX100 IS
ISO 1600
Panasonic DMC-TZ3
ISO 1250
Sony DSC-H3
ISO 1600

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).

Canon's approach to noise reduction in the past has been unusually light-handed, clear preference was given to detail retention over image 'cleanliness'. More recently Canon's software engineers have modified this approach and there is now clearly more noise reduction applied to images (with a touch of mild smearing of low contrast detail visible even at ISO 80). That said at all settings from ISO 200 to ISO 800 the Canon is doing a decent job of balancing noise and noise reduction.

Ultimately, you can't work around the fact that a 1/2.5 inch sensor simply is prone to noise. There is very mild noise visible in shadow areas even at base ISO, and once you get to ISO 800 there is enough noise to show on even the smallest prints. The amount of noise produced by these tiny sensors won't be much different from manufacturer to manufacturer; the noise reduction algorithms applied however are. Both Canon and Sony are trying to preserve detail by not pushing luminance NR too hard with varying degrees of success across the ISO range (at low ISO settings Canon wins, at higher settings Sony is nosing ahead).

Panasonic has chosen a completely different route, applying an abundance of both chroma and luminance noise reduction resulting in smooth but blurred pictures with comparatively little detail at all higher ISO settings.

Note that the Sony DSC-H3 does not offer manual white balance. For this test we used Cool Fluorescent white balance which produced the best results with our studio lights.

Luminance noise graph

Cameras compared: Canon SX100 IS, Panasonic TZ3, Sony H3

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

RGB noise graph (ISO 80-1600)

Cameras compared: Canon SX100 IS, Panasonic TZ3, Sony H3

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.

Both graphs show what we've observed in both our test shots and our 'real life' samples. - the SX100 IS (still) applies comparatively low levels of noise reduction, so the results are a little noisier than those of some other cameras. On the plus side the SX100 IS retains a little more detail. This is quite evident in comparison to the TZ3 which has significantly lower (measured) noise levels but blurs a lot of detail away. The Sony H3 actually manages to balance noise reduction and detail retention remarkably well - probably the best here.

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

These crops illustrate perfectly how the SX100 IS's noise reduction algorithms smear and blur image detail at higher ISO sensitivities (and that there is a little loss even at the lowest ISO settings). Noise and noise reduction artefacts are clearly visible from ISO 200 upwards. At ISO 400 you really start to lose a lot of detail and at ISO settings higher than that the hair starts to transition into an indefinable yellowish mass - save these settings for emergency use only.

So then, the SX100 IS is not significantly different to most other compact cameras in the noise department. Try and avoid ISO settings higher than 400 and you're ok, the image stabilization should help with that. If you really have to use ISO 800 or 1600 you probably shouldn't print it any larger than postcard size.

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