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 noise and can also affect colour saturation.

The PowerShot G3 provides four selectable sensitivities of ISO 50, 100, 200 and 400.

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.

Canon PowerShot G3 vs. PowerShot G2

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

	ISO 50
	Canon PowerShot G3 1/30 sec, F5.0	Canon PowerShot G2 1/30 sec, F5.0
Original crop
Red channel
Green channel
Blue channel
	ISO 100
	Canon PowerShot G3 1/60 sec, F5.0	Canon PowerShot G2 1/50 sec, F5.0
Original crop
Red channel
Green channel
Blue channel
	ISO 200
	Canon PowerShot G3 1/125 sec, F5.0	Canon PowerShot G2 1/100 sec, F5.0
Original crop
Red channel
Green channel
Blue channel
	ISO 400
	Canon PowerShot G3 1/250 sec, F5.0	Canon PowerShot G2 1/200 sec, F5.0
Original crop
Red channel
Green channel
Blue channel

As you can see from the patch crops above and graphed data below there is virtually no difference in ISO noise between the PowerShot G3 and G2. Indeed the subtle differences here could easily be accounted for in the slight differences between sensors manufactured at different times. However it is worth noting that the G3 appears to be approximately 0.3 EV (a third of a stop) more sensitive than the G2 at the same selected ISO.

Luminance noise graph

Note that indicated ISO sensitivity is on the horizontal axis of this graph.

Canon PowerShot G3 vs. Nikon Coolpix 4500

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

What is ISO 50?

As we've noted previously Canon's indicated ISO 50 is fairly conservative, indeed for the G3 I would put that indicated sensitivity closer to ISO 80. Comparing this to the Nikon Coolpix 4500 we find that the G3 is just over 0.3 EV (a third of a stop) more sensitive than the 4500 at the same indicated ISO. Thus the comparison below must be made with matching indicated ISO sensitivity (for the fairest possible comparison).

	ISO 50
	Canon PowerShot G3 1/30 sec, F5.0	Nikon Coolpix 4500 n/a
Original crop
Red channel
Green channel
Blue channel
	ISO 100
	Canon PowerShot G3 1/60 sec, F5.0	Nikon Coolpix 4500 1/46 sec, F4.9
Original crop
Red channel
Green channel
Blue channel
	ISO 200
	Canon PowerShot G3 1/125 sec, F5.0	Nikon Coolpix 4500 1/97 sec,F4.9
Original crop
Red channel
Green channel
Blue channel
	ISO 400
	Canon PowerShot G3 1/250 sec, F5.0	Nikon Coolpix 4500 1/184 sec,F4.9
Original crop
Red channel
Green channel
Blue channel
	ISO 800
	Canon PowerShot G3 1/160 sec, F4.5	Nikon Coolpix 4500 1/386 sec, F4.9
Original crop
Red channel
Green channel
Blue channel

As expected the G3 delivers low noise levels at ISO 50, but interestingly only as good as the Coopix 4500 at ISO 100 where the G3's noise levels are noticeably higher (which is a real pity). Things start to draw closer at ISO 200 and by ISO 400 the G3 is just nudging ahead. Of course the Coolpix 4500 can go one better with ISO 800, although noise level are very high here.

Luminance noise graph

Note that indicated ISO sensitivity is on the horizontal axis of this graph.

RGB noise graph

Note that indicated ISO sensitivity is on the vertical axis of this graph.