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.)

Ricoh GR-Digital vs Casio EX-Z850

	Ricoh GR-D ISO 64	Casio EX-Z850 ISO 50
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	Ricoh GR-D ISO 100	Casio EX-Z850 ISO 100
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	Ricoh GR-D ISO 200	Casio EX-Z850 ISO 200
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	Ricoh GR-D ISO 400	Casio EX-Z850 ISO 400
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	Ricoh GR-D ISO 800	Casio EX-Z850 ISO 800
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	Ricoh GR-D ISO 1600	Casio EX-Z850 ISO 1600
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We've criticized many cameras recently for heavy-handed noise reduction that destroys fine detail from the image itself, and the GR-D takes things to the other extreme, with unusually low noise reduction. For one thing this shows just how noisy the result of squeezing 8 million pixels onto a 1/1.8 inch chip is, and how much unsurprised we should be when we see noise reduction so heavy it leaves the image looking soft and detail-free. Ricoh's approach is to avoid sacrificing detail for noise, which is in many ways admirable; these are considerably more 'honest' images than many competitors (the Casio shown here for comparison being a good example), but it does leave you with very, very noisy images at anything over ISO 100, (noise is visible in flat tones even at ISO 64).

As for the noise itself (which at higher ISO's is higher than any camera we've tested in the last few years), I've seen it described as being 'film grain-like', and to a certain extent I agree; the luminance noise is grainy rather than blotchy, and at lower ISO's isn't terribly offensive. As you move up the ISO range the chroma noise becomes more and more intrusive, so that by the time you're at ISO 400 or higher all the shadow areas have a blue tint. You can fairly easily remove chroma noise if you know what you're doing (using something like Neat Image or Photoshop), and if you're not printing too large, the luminance 'grain' isn't a major problem at lower ISO settings.

Ultimately, though, the GR-D is too noisy at higher ISO settings; and I can't help thinking it would be a far better camera with a lower pixel count, lower noise sensor. Shooting at higher ISO's in black and white mode gives a nice 'gritty' effect, that does look like a fast B&W film, but let's be honest; it's a lot easier to put noise into an image in post-processing than it is to remove it.

Luminance noise graph

Cameras compared:
Ricoh GR Digital, Canon PowerShot S80, Casio EX-Z850

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

As the graph shows the noise is - as observed above - slightly higher than average at ISO values up to 200, and at ISO 400 shadow noise really leaps up. The noise reduction is obviously ramped up slightly at ISO 800 and 1600, but noise is still very high.

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, color noise is higher than average for this class of camera at 'standard' ISO settings (64-400), though as noted above this is due to lower noise reduction, rather than any inherent differences in the sensor itself. At higher ISO settings, despite stronger NR, the chroma noise is again, high.