ISO Sensitivity / Noise levels

Standard Test

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. The works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (ie. ISO 200, 1/200 sec for consistency of exposure between cameras).

The image sequence is run through our own proprietary measurement tool which measures the standard deviation (normalized) of the middle gray patch (indicated by the red rectangle above). Additionally we now have a 'detail crop', this is currently a postage stamp (lots of fine detail) but we may replace this at a future date. Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Canon EOS 20D: Parameter 2

The EOS 20D's default parameter set is now 'Parameter 1' which sets contrast, sharpness and saturation to +1, this provides punchier 'out of the camera' performance but in this test we're looking to compare the 20D's with its "neutral" setting which is 'Parameter 2'; this is the same as the EOS 10D's default setting.

Test notes:

• Shots taken at approximately 25°C (~77°F)
• Lighting was simulated daylight measured as 10.1 EV (at ISO 100)

Canon EOS 20D vs. Canon EOS 10D (ISO 100 - 3200)

• Canon EOS 20D : Canon 50 mm F1.4 lens, Aperture Priority (F4), Manual WB,
  Parameters 2 (neutral), 50 mm F1.4, JPEG Large / Fine
  
• Canon EOS 10D: Canon 50 mm F1.4 lens, Aperture Priority (F4), Manual WB,
  Default Parameters (neutral), 50 mm F1.4, JPEG Large / Fine

	Canon EOS 20D ISO 100, 1/100 sec, F4	Canon EOS 10D ISO 100, 1/100 sec, F4
Crops
	Canon EOS 20D ISO 200, 1/200 sec, F4	Canon EOS 10D ISO 200, 1/200 sec, F4
Crops
	Canon EOS 20D ISO 400, 1/400 sec, F4	Canon EOS 10D ISO 400, 1/400 sec, F4
Crops
	Canon EOS 20D ISO 800, 1/800 sec, F4	Canon EOS 10D ISO 800, 1/800 sec, F4
Crops
	Canon EOS 20D ISO 1600, 1/1600 sec, F4	Canon EOS 10D ISO 1600, 1/1600 sec, F4
Crops
	Canon EOS 20D ISO 3200, 1/3200 sec, F4	Canon EOS 10D ISO 3200, 1/3200 sec, F4
Crops

Despite a two megapixel increase in pixel count (and hence a reduction in photosite size) the EOS 20D manages to deliver lower noise with better sharpness at higher sensitivities than the EOS 10D. Very interestingly the final production camera we had for review wasn't quite as good as the pre-production unit, however it's fair to say that at higher sensitivities (above ISO 800) the EOS 20D has between a two thirds and one stop noise advantage over the EOS 10D.

What we have observed visually is pretty much supported by our noise measurements, that from ISO 100 to 400 noise levels are virtually the same (which means very low) and from ISO 800 upwards the EOS 20D is cleaner. The considerably more expensive (and more capable) EOS-1D Mark II (8 MP Canon CMOS) delivers a similar level of noise at ISO 100 (ie. virtually nothing) but maintains a lower noise level at ISO 200, 400 and 800. Only at ISO 1600 and 3200 does the level of noise from the EOS 20D begin to match the 1D Mark II.

Luminance noise graph (ISO 100 - 3200)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity (normalized image) on the vertical axis.

RGB noise graph (ISO 100 - 3200)

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of each of the red, green and blue channels (normalized image) are on the vertical axis.