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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 1.5 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-FX01 vs Canon SD 630 (Ixus 65)

  Panasonic DMC-FX01
ISO 80

Canon Ixus 65
ISO 80

Crops
  Panasonic DMC-FX01
ISO 100
Canon Ixus 65
ISO 100
Crops
  Panasonic DMC-FX01
ISO 200
Canon Ixus 65
ISO 200
Crops
  Panasonic DMC-FX01
ISO 400
Canon Ixus 65
ISO 400
Crops
  Panasonic DMC-FX01
ISO 800
Canon Ixus 65
ISO 800
Crops
  Panasonic DMC-FX01
ISO 1600
Canon Ixus 65
n/a
Crops

In good light the FX01 doesn't really have a noise problem until you hit ISO 400. You can see from the crops above that the Canon SD630 (which uses the new generation Sony 6MP CCD) has an inherently less noisy chip, meaning it needs less noise reduction to produce an acceptable result, and my only problem with the FX01 is that I'd prefer a slightly lower level of noise reduction at all ISO settings (or at least an option). This is particularly true when shooting in low light, when even ISO 100 images have excessive noise reduction that limits the size you can print the files. At ISO 200 and 400 in low light the images have the familiar 'watercolor' noise reduction that blights most recent Panasonic models.

High Sensitivity Mode

This year manufacturers have woken up to the fact that all the pixels in the world won't help an image shot in very low light that suffers from camera shake, and have started to include high sensitivity (high ISO) options to their new models. Unfortunately the sensors used in most compact cameras simply aren't very sensitive to light, and there's only so far you can amplify the signal before noise swamps the detail in the image. The FX01, like many other models featuring a 'high sensitivity' mode, uses a technique called 'pixel binning' - where four or more neighboring pixels are combined to make a single 'super pixel' with higher sensitivity. Obviously this reduces the pixel count of the image proportionately, which is why most such modes are only available at lower resolutions. Panasonic took the unusual step of keeping its high ISO setting at full (6MP) resolution - which means the images must be interpolated back up once the image has been captured. The results can be seen below.

There's not a lot you can say about these images really; the process of pixel binning, followed by noise reduction and sharpening, then re-sizing back up to 6MP produces results that - though virtually free of noise - are also virtually free of detail. To be fair, Panasonic makes no claims for the quality of the high ISO mode, but it seems particularly pointless to resize them back up to 6MP; a process that simply amplifies the lack of detail and makes the sharpening halos look enormous. On the plus side, this mode will allow you to get a shot you might not be able to take any other way, but the result will look terrible printed anything bigger than a postcard. Of course for party snaps the quality of result is a lot less important than getting the shot, but when compared with cameras such as the Fuji F10 (or even the ISO 800 result from the Canon SD630 above) it's hard to get too excited about the FX01's low light capabilities.

ISO 800
100% crop
ISO 800 studio scene
(note there is no manual white balance option in this mode)

Luminance noise graph

Cameras compared:
Panasonic DMC-FX01, Canon SD630 (Ixus 65), Fujifilm FinePix F10

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

Up to ISO 200 there's not a huge difference between these three models in terms of measurable noise (though looking at the images themselves you'll see the FX01 uses by far the highest amount of noise reduction). Of course the huge drop at ISO 800 and 1600 are simply a result of the pixel binning process.

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.

The FX01 has the highest chroma noise of this trio at ISO 80-400, but there's not a huge difference up to 200 (which would cover virtually all daytime photography). At ISO 400 the F10's class-leading performance leaves the other two standing, but the FX01 and SD630 are both within the boundaries expected from this class of camera, and are perfectly usable at ISO 400 as long as you don't want to print too large.

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