Previous page Next page


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 5700 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 5700 vs. Minolta DiMAGE 7i

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 100
Nikon Coolpix 5700
1/56 sec, F4.4
Minolta DiMAGE 7i
1/60 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 200
Nikon Coolpix 5700
1/111 sec, F4.4
Minolta DiMAGE 7i
1/125 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 400
Nikon Coolpix 5700
1/208 sec, F4.4
Minolta DiMAGE 7i
1/250 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel
 
  ISO 800
Nikon Coolpix 5700
1/428 sec, F4.4
Minolta DiMAGE 7i
1/500 sec, F4.5
 Original crop
 Red channel
 Green channel
 Blue channel

As far as we know these two cameras use the same 2/3" CCD sensor, and as you can see they produce very similar levels of noise, although obviously different image processing delivers slightly different 'looking' noise. The D7i has much more visible at ISO 100 than the 5700, more so than is indiciated by the crop above. The 5700's noise doesn't increase that much at ISO 200, at ISO 400 noise is visible (although shooting to reduce in size later this wouldn't show up). At ISO 800 noise becomes much more dominant and would be only useful in extreme situations.

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 is very similar with the 5700 exhibiting less noise than the D7i at ISO 100 and the two drawing level at ISO 400.

RGB noise graph

As we'd expect both cameras exhibit less noise in the green channel (because there are double the number of green pixels on a GRGB Bayer pattern CCD), both cameras exhibit most of their noise in the red channel. Red channel noise tends to be most visible in light blue skies.

Previous page Next page

Comments