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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. 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 (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 SD550 (Ixus 750) vs Olympus Mju Digital 800

  Canon SD550
ISO 50
Olympus Mju 800
ISO 64
Crops
  Canon SD550
ISO 100
Olympus Mju 800
ISO 100
Crops
  Canon SD550
ISO 200
Olympus Mju 800
ISO 200
Crops
  Canon SD550
ISO 400
Olympus Mju 800
ISO 400
Crops

This is the first chance we've had to compare the noise characteristics of the 7MP chip (used in models from Canon, Nikon, Sony and others) and the newer 8MP found in several cameras, including the Olympus Mju 800. As you can see, there's not a lot in it, and most of the difference appears to be down to the nature - and strength - of the noise reduction used. We've said it before, and we'll say it again - this chip is far superior to the 5MP version that came before it, with low noise at the low ISO end of the range, and nothing particularly unpleasant at the higher ISO settings. Considering it's size - and the size of the chip - the SD550 gives little reason for serious complaint when it comes to noise.

Note: the Olympus Mju 800 has ISO 800 and ISO 1600 settings, but these are not saved at full resolution, and feature very heavy noise reduction.

Luminance noise graph

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.

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