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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-500UZ vs Kodak EasyShare P850

  Olympus SP-500UZ
ISO 80
Kodak P850
ISO 50
Crops
  Olympus SP-500UZ
ISO 100
Kodak P850
ISO 100
Crops
  Olympus SP-500UZ
ISO 200
Kodak P850
ISO 200
Crops
  Olympus SP-500UZ
ISO 400
Kodak P850
ISO 400
Crops

Noise - especially chroma noise - is pretty well controlled at all ISO settings, and is roughly on a par with the better 5MP cameras. Looking at 'real world' ISO 400 shots it would certainly seem that the new 6MP chip in the SP-500UZ is marginally less noisy than the older 5.0MP sensors used in most of its competitors.

Note: the SP-500UZ 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-500UZ Ultra Zoom, Kodak P850, Panasonic DMC-FZ20

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 SP-500UZ exhibits fairly low noise at lower ISO settings, staying on the low side of average as you move up the scale to ISO 400. What the figures don't show is that the noise reduction used is fairly low, meaning you lose a lot less detail than with most 5MP super zoom models.

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.

Chroma noise is broadly similar to the other cameras in this class, slightly higher than the other two cameras here, but again this is more to do with noise reduction than actual noise (the SP-500UZ loses far less detail at ISO 200+ than the P850 or FZ20).

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