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SO 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 (i.e. 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.

Ricoh GX100 vs Nikon Coolpix P5000 vs Panasonic DMC-LX2

Ricoh GX100
ISO 80
Nikon Coolpix P5000
ISO 64
n/a
 
Ricoh GX100
ISO 100
Nikon Coolpix P5000
ISO 100

Panasonic LX2
ISO 100

Ricoh GX100
ISO 200
Nikon Coolpix P5000
ISO 200

Panasonic LX2
ISO 200

Ricoh GX100
ISO 400
Nikon Coolpix P5000
ISO 400

Panasonic LX2
ISO 400

Ricoh GX100
ISO 800
Nikon Coolpix P5000
ISO 800

Panasonic LX2
ISO 800

Ricoh GX100
ISO 1600
Nikon Coolpix P5000
ISO 1600

Panasonic LX2
ISO 1600

With tiny, high pixel count chips noise is always going to be an issue, and to a large degree this is more a test of the effectiveness (both measurable and visible) of a camera's noise reduction system. Designers have to balance the desire to produce smooth, clean results with the need to retain as much detail as possible (if you blur away the noise, you blur away image detail too).

For the GX100 Ricoh's approach to noise reduction is to keep it fairly low until you hit the higher ISO values, then to turn it up to the max. At ISO 80-400 the results have slightly more luminance noise than we're used to seeing, which means they look quite grainy (and to be honest at ISO 400 there seems to be no corresponding benefit when it comes to detail). ISO 800 uses heavy noise reduction so looks blurry and soft, whereas ISO 1600 produces a blurry and noisy result.

JPEG/RAW

Using Camera Raw to process ISO 800 and 1600 DNG files reveals just how much detail is being lost to noise reduction or, if you want to look at it the other way round, just how much noise the GX100's image processor is removing before it saves its JPEGs. For grainy black and white shots I'd shoot raw (for color work ISO 800 and 1600 are essentially unusable).

 
ISO 800 JPEG
ISO 800 RAW
(ACR 3.7, default)
 
ISO 1600 JPEG
ISO 1600 RAW
(ACR 3.7, default)

Low contrast detail

What the crops and graph don't show is the effect of noise reduction on low contrast fine detail such as hair, fur or foliage. An inevitable side effect of noise removal is that this kind of detail is also blurred or smeared, resulting in a loss of 'texture'. The crops below show the effect of the noise reduction on such texture (hair) as you move up the ISO range.

100% Crops
ISO 80 ISO 100 ISO 200 ISO 400
   
ISO 800 ISO 1600    

As noted elsewhere noise reduction really kicks in at ISO 400 (and is so high at ISO 800/1600 that all low contrast detail has been obliterated), though you can see the effect starting to turn detail to mush even at ISO 100. To eke the very most detail from the GX100 you really need to stick to ISO 80 (or if you must shoot at anything higher, try to use raw and be prepared for some fairly extensive post processing).

Luminance noise graph

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

You can clearly see the high shadow noise levels at up to ISO 400, dropping dramatically as you hit ISO 800 (when the noise reduction really kicks things up a notch).

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.

Chroma noise is much more consistent, and is almost identical to the similarly-specified Coolpix P5000.

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