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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). Note that noise values indicated on the graphs below should not be compared to those in other reviews.

Panasonic Lumix DMC-LX1 vs Canon PowerShot SD550 (Ixus 750)

  Panasonic DMC-LX1
ISO 80
Canon SD550
ISO 50
Crops
  Panasonic DMC-LX1
ISO 100
Canon SD550
ISO 100
Crops
  Panasonic DMC-LX1
ISO 200
Canon SD550
ISO 200
Crops
  Panasonic DMC-LX1
ISO 400
Canon SD550
ISO 400
Crops

Even a cursory glance at the crops reveals that the LX1 has higher levels of noise at all ISO settings, though the difference is most pronounced at ISO 200 and 400. Once the noise has been measured and plotted on a graph (see below) the difference is stark. Compared with the 7MP Canon SD 550 and the new 8MP Olympus Mju Digital 800 the LX1 has much higher levels of both luminance and chroma noise. Note that all tests were performed with the noise reduction set to it's default ('STD').

Note: the Olympus Mju 800 has ISO 800 and ISO 1600 settings, but these are not saved at full resolution, and feature very heavy noise reduction.

Luminance noise graph

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

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 are on the vertical axis..

Effect of Noise Reduction at ISO 400

Unlike most compact cameras the LX1 allows some control over the amount of noise reduction applied in-camera. There are three settings; low, standard (the default) and high. As these 100% crops from our standard studio test scene show, there isn't much to choose between any of the settings, though there is marginally more detail preserved at the low setting. If you don't like Panasonic's noise reduction system (and frankly who would?) there is always the option to shoot raw and use Adobe Camera Raw (ACR) to convert the images.

Image below shot at 1/500th sec.

  Low Standard High
ISO
400
ISO
400
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