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ISO Sensitivity / Noise levels

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 noise measurement tool (version 1.4 in this review). Click here for more information. (Note that noise values indicated on the graphs here can not be compared to those in other reviews.)

Panasonic DMC-FZ7 vs Panasonic DMC-FZ5

  Canon A700
ISO 80

Panasonic DMC-FZ7
ISO 80

Crops
  Canon A700
ISO 100
Panasonic DMC-FZ7
ISO 100
Crops
  Canon A700
ISO 200
Panasonic DMC-FZ7
ISO 200
Crops
  Canon A700
ISO 400
Panasonic DMC-FZ7
ISO 400
Crops
  Canon A700
ISO 800
Panasonic DMC-FZ7
ISO 800
Crops

Noise at lower ISO settings is low enough not to be an issue, and Canon has decided to use a fairly low noise reduction to preserve detail. At ISO 400 noise isn't too intrusive (especially in good light), which helps when using the long end of the 6x zoom in less than perfect light, though you wouldn't want to produce prints larger than about 5x7 inches without first using some noise reduction software. At ISO 800 the results are fairly 'gritty', though it's nice to see that luminance noise - particularly blotches of color - is fairly well controlled without too much loss of detail through noise reduction. That said, unless you produce very small prints I can't see the ISO 800 setting being of much use except to get you out of a tight spot where there isn't an alternative.

Luminance noise graph

Cameras compared:
Canon PowerShot A700, Panasonic DMC-FZ7, Canon PowerShot A620

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

At lower ISO settings luminance noise is low (measurably lower than the 7MP PowerShot A620), and up to ISO 400 it remains on the low side of the average for this class of camera (which means its a lot better than most 5MP cameras, and similar to most 7.2MP models). At ISO 800 things get a lot noisier, but this reflects Canon's decision to resist the temptation to turn the noise reduction up to ridiculous levels. On a side note, our measurements would seem to indicate that noise reduction kicks in at ISO 100.

RGB noise graph

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

Again the noise levels are on the low side of the average for 6 and 7MP cameras, only really leaping up at ISO 800.

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