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ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor to enable faster shutter speeds and/or better performance in low light. The way this works in a digital camera is by "turning up the volume" on the CCD's signal amplifiers. Nothing is without its price however and doing so also amplifies any noise that may be present and often affects colour saturation.

The Coolpix 4500 provides four selectable ISO sensitivities of ISO 100, 200, 400 and 800. The latter is noted as not producing optimum results (high noise) and so appears in red when selected.

Our noise comparison test involves shooting a colour patch chart (a GretagMacBeth ColorChecker) at the full range of ISO sensitivities and then measuring luminance and RGB noise at a 'mid' grey patch.

Note that this is a modification to our previous noise test which only measured luminance noise. The new test now provides a graph of luminance noise for each selectable sensitivity as well as individual RGB channel noise.

Nikon Coolpix 4500 vs. Canon PowerShot G2

Image sharpening set to 'Normal' on both cameras, white balance preset other settings as default. Measurements taken at approximately 21°C (~70°F). Lighting was daylight.

  ISO 50
Nikon Coolpix 4500
n/a
Canon PowerShot G2
1/40 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 100
Nikon Coolpix 4500
1/51 sec, F4.7
Canon PowerShot G2
1/100 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200
Nikon Coolpix 4500
1/111 sec, F4.7
Canon PowerShot G2
1/160 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400
Nikon Coolpix 4500
1/216 sec, F4.7
Canon PowerShot G2
1/400 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 800
Nikon Coolpix 4500
1/454 sec, F4.7
Canon PowerShot G2
n/a
 Original crop
 Red channel
 Green channel
 Blue channel

At first glance the Coolpix 4500 does seem cleaner at each sensitivity than the G2, also worth noting is the fact that the Coolpix 4500's noise is more evenly spread across each channel. This is probably due to its use of a CYGM color filter array, the 'double green' of the G2's GRGB color filter array produces clean greens but more noise in other channels.

But, what's in an ISO number?

To be fair, it's worth noting is the G2's apparent sensitivity compared to the selected ISO setting. At ISO 100 the Coolpix 4500 exposes at 1/51 sec, F4.7, the G2 at 1/100 sec, F4.5, virtually a stop faster. This indicates what we've observed before that the G2's ISO sensitivities are indicated extremely conservatively. As you can see setting the G2 to 'ISO 400' produces the same amount of sensitivity as the Coolpix 4500 at 'ISO 800'. It would be a fair guess that the G2's ISO 50 is probably nearer to ISO 64 and that the 4500's ISO 100 is nearer to ISO 80.

Luminance noise graph

Note that ISO sensitivity is on the horizontal axis of this graph. As the above graph indicates luminance noise at the selected sensitivity appears to be lower on the Coolpix 4500 but does suddenly jump at the 'not recommended' ISO 800.

RGB noise graph

Note that ISO sensitivity is on the vertical axis of this graph. Here we can see that the Coolpix 4500 does a fairly good job of keeping noise levels between each channel fairly similar (again probably an advantage of the CYGM color filter array), this will lead to less obvious noise occurring in particular colour areas of an image.

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