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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 ISOs. 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 SD450 (Ixus 55) vs Fujifilm FinePix F10 (to ISO 400 only)

  Canon SD450
ISO 50
Fuji FinePix F10
ISO 80
Crops
  Canon SD450
ISO 100
Fuji FinePix F10
ISO 100
Crops
  Canon SD450
ISO 200
Fuji FinePix F10
ISO 200
Crops
  Canon SD450
ISO 400
Fuji FinePix F10
ISO 400
Crops

The SD450 is, like all the 5MP compacts we've tested, pretty noisy at the high end of the ISO range (particularly ISO 400), whereas the F10 has been praised here and elsewhere for its low noise.

Luminance noise graph

Cameras compared:
Canon SD450 (5MP), Fuji F10 (6MP), Kodak P850 (5MP), Canon S80 (7MP)

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

As the noise measurements show, the SD450 has very similar noise characteristics to most other 5MP cameras - it's pretty noisy at ISO 400, and the difference between most models comes down to the strength (and effectiveness) of the noise reduction systems more than the sensor itself. As mentioned earlier in the review, Canon's indicated ISO values are usually 2/3 to 1 stop lower than the measured sensitivity, and this needs to be taken into consideration when looking at these results.

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.

Unsurprisingly chroma noise is higher than the Fuji F10 and the Canon S80 (which sports the newer 7MP sensor), but is broadly similar at ISO 400 to most other 5MP cameras (including the Kodak P850, shown here).

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