ISO Sensitivity / Noise levels

Standard Test

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 SD100 provides four selectable sensitivities of ISO 50, 100, 200 and 400. Our noise comparison test involves shooting a color patch chart (a GretagMacBeth ColorChecker) at the full range of ISO sensitivities and then measuring luminance and RGB noise at a 'mid' grey patch.

Canon's conservative approach

As we have previously reported, Canon tend to take a conservative approach to their labeling of ISO sensitivity. If you glance at the exposure details below the SD100 was consistently shooting one stop (1 EV) faster than the Optio S at the same 'ISO'. This means that the SD100's ISO 50 is equivalent to ISO 100 on the Optio S. You must bear this in mind especially when viewing the comparison graphs at the bottom of this page.

Canon PowerShot SD100 vs. Pentax Optio S

Measurements taken at approximately 21°C (~70°F). Lighting was daylight. Manual white balance.

	ISO 50
	Canon PowerShot SD100 1/200 sec, F3.9	Pentax Optio S 1/125 sec, F3.5
Original crop
Red channel
Green channel
Blue channel
	ISO 100
	Canon PowerShot SD100 1/400 sec, F3.9	Pentax Optio S 1/250 sec, F3.5
Original crop
Red channel
Green channel
Blue channel
	ISO 200
	Canon PowerShot SD100 1/125 sec, F9.0	Pentax Optio S 1/500 sec, F3.5
Original crop
Red channel
Green channel
Blue channel
	ISO 400
	Canon PowerShot SD100 1/250 sec, F9.0	Pentax Optio S n/a
Original crop
Red channel
Green channel
Blue channel

At first the results look good for the Optio S, until you consider the stop difference in sensitivity advantage that the SD100 carries and then it's clear that it has less noise at the same equivalent sensitivity (especially from ISO 100 upwards).

Luminance noise graph

Note that indicated ISO sensitivity is on the horizontal axis of this graph. (The SD100's ISO 50 is just as sensitive as the Optio S ISO 100).

RGB noise graph

Note that indicated ISO sensitivity is on the vertical axis of this graph. (The SD100's ISO 50 is just as sensitive as the Optio S ISO 100).