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 HP 850 provides just two sensitivities of ISO 100 and ISO 200.

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.

HP Photosmart 850 vs. Canon PowerShot G3

This test was made more complicated by the G3's higher than reported sensitivity. In effect the G3 was a full stop more sensitive than the HP 850 at the same indicated ISO, this meant that the G3 was shooting with a 1/50 sec, F4.0 exposure at it's ISO 50, the HP 850 had a similar exposure at ISO 100. Thus we must compare crops from each camera a stop of sensitivity apart. Because the HP 850 has only two selectable sensitivities we won't be graphing the results, instead the standard deviation (a measurement of luminance noise) is shown below each crop.

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 100	ISO 50
	HP 850 1/42 sec, F4.1	Canon PowerShot G3 1/50 sec, F4.0
Original crop
Red channel
Green channel
Blue channel
Std. dev.	1.27	1.68
	ISO 200	ISO 100
	HP 850 1/84 sec, F4.1	Canon PowerShot G3 1/100 sec, F4.0
Original crop
Red channel
Green channel
Blue channel
Std. dev.	1.72	2.50

Very interesting results, at the same effective sensitivity the HP 850 exhibitted lower noise levels than the PowerShot G3. It's unclear if this is down to noise reduction or simply better noise management. Either way an impressive performance from the HP, considering these low noise levels it's a pity that HP didn't choose to extend the selectable sensitivity levels up to ISO 400 and 800.