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Noise Measurement
By Phil Askey

Standard Test Chart

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).

dpreview.com Noise Measurement Tool version 1.4

The biggest change introduced with the latest version of our noise measurement tool is the measurement of standard deviation of the black patch as well as the inclusion of a crop of the patch in the review visualization. The black patch is a fairly good representation of noise typically seen in dark 'shadow' areas of an image, certain cameras which may have a relatively good mid-tone noise profile perform less well in the shadows.

Our current noise measurement tool performs the following functions:

Measures luminance noise of the middle gray patch
Measures luminance noise of the black patch ('shadow noise')
Measures chroma noise of the middle gray patch
Takes crops of the gray, black and detail and provides these for review visualization
Outputs result data for production of luminance and chroma noise graphs

Learn : Glossary : Reviews : Noise Measurement