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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.

Olympus SP-310 vs Canon PowerShot S80

  Olympus SP-310
ISO 64
Canon SD550
ISO 50
Crops
  Olympus SP-310
ISO 100
Canon SD550
ISO 100
Crops
  Olympus SP-310
ISO 200
Canon SD550
ISO 200
Crops
  Olympus SP-310
ISO 400
Canon SD550
ISO 400
Crops

The SP-310 exhibits slightly more visible noise than the at ISO 200 and 400 but there's not a lot in it, as the graphs below show. This is hardly surprising given that the cameras almost certainly share the same Sony sensor. Up to ISO 100 noise is very low indeed, something we've noted before with 7MP cameras, and even at ISO 400 the results are perfectly usable (though the SP310's higher chroma noise will be more visible).

Note: the SP-310 has a 'Noise Reduction' option, but this only kicks in for exposures of 0.5 seconds or longer when activated.

Luminance noise graph

Cameras compared: Olympus SP-310, Canon SD550, Canon S80, Fujifilm FinePix F10.

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. As these graphs show there really isn't a huge difference between the luminance noise levels for the SP-310 or the two Canon PowerShots (though if you look closely you can see that the SP-310 has lower noise at low ISO and higher noise at high ISO. For a zoomed version of this graph click here). All three are put to shame by the Fuji F10 at ISO 400, and of course the F10 goes all the way to ISO 1600 too (not shown here).

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.

Again it's interesting to see that the SP-310 has very low chroma noise at low ISO settings - even beating the Fuji F10 - but less impressive at higher sensitivities, particularly at ISO 400, where it is producing noticeably more noise than the other cameras here.

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