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.
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