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ISO Sensitivity / Noise levels


Standard Test
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 (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras).

The image sequence is run through our own proprietary measurement tool which measures the standard deviation (normalized) of the middle gray patch (indicated by the red rectangle above). Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Canon PowerShot S80 vs Olympus Stylus 800 (Mju 800)

note: We have excluded the Stylus 800's 'Bright Capture' ISO 800 and 1600 modes from this comparison (see the Stylus 800 review for more on this), as these modes only produce 3 megapixel files.

  Canon S80
ISO 50
Olympus Stylus (Mju) 800
ISO 64
Crops
  Canon S80
ISO 100
Olympus Stylus (Mju) 800
ISO 100
Crops
  Canon S80
ISO 200
Olympus Stylus (Mju) 800
ISO 200
Crops
  Canon S80
ISO 400
Olympus Stylus (Mju) 800
ISO 400
Crops

As you can see from the crops above there's not a huge difference in the amount of visible noise between these two 8MP compacts (which sport sensors from different manufacturers), though examination of real-world shots leads me to believe the Stylus 800 is using much stronger noise reduction at ISO 200 and 400, meaning less detail in your shots.

Luminance noise graph

Cameras compared:
Canon PowerShot S80, Olympus Stylus 800 (Mju 800), Canon PowerShot SD550, Panasonic LX1

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

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 are on the vertical axis.

It's interesting to see how well the new 8MP sensors are doing when compared to the well-regarded Sony 7MP chip in the S70. There's little real difference between the noise levels of the Stylus (Mju) 800, Canon S70 and Canon S80 - and that's all really down to the strength of noise reduction being applied in each case. Of course the Lumix LX1 is in a class of its own - there's no denying that the Panasonic sensor is so noisy it would wake up the neighbors.

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