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ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This 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 ISOs. 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). Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Sigma DP2 vs. Olympus E-P1 vs. Sony DSLR-A330 vs. Ricoh GR Digital IiI

  • Sigma DP2: Aperture Priority, Manual WB, Default Parameters,
    JPEG Hi / Fine
     
  • Olympus E-P1: Olympus Zuiko 50 mm F2.0 Macro lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), SHQ JPEG
     
  • Sony Alpha 330: Sony 50 mm F1.4 lens, Aperture Priority, Manual WB,
    Default Parameters (Normal), High ISO NR (Normal), JPEG Large / Fine
     
  • Ricoh GR Digital III: Aperture Priority, Manual WB, Default Parameters (Normal),
    JPEG Large / Fine
  Sigma DP2 Olympus E-P1 Sony DSLR A330 Ricoh GRD III
ISO 50/64    
ISO 100
ISO 200
ISO 400
ISO 800

It's unusual for us to compare such different cameras but the DP2 is such an unusual offering that it has no direct peers. So here it lines up against the Olympus E-P1, which has a similarly sized sensor but interchangeable lenses, the Ricoh GRD III which has a sensor over six and a half times smaller but a brighter, wider-angle lens, and the Sony DSLR A330, which represents the APS-C sensor sized DSLRs that make up the majority of DSLR sales.

The DP2's level of detail is astonishing, despite its lack of absolute resolution (it may only produce 4.7 megapixel files but every pixel is made to count). The Olympus shows how well a large conventional, Bayer-pattern sensor can do and is capturing a similar amount of detail such that the results are likely to be pretty comparable if down-sized. The Ricoh also does well but its small sensor (in comparison to this company - it's pretty big for a compact camera), can't compete as the ISO rises.

The Sigma does a good job of keeping chroma noise under control, with luminance noise appearing only at the (rather modest) highest ISO setting - particularly in the dark regions.

  Sigma DP2
Chroma
Black
Gray

RAW noise

Sigma appears confident that RAW conversion software, with access to greater computing power than is available within the camera, can give better high-ISO results and allows access to the ISO 1600 and 3200 modes that are unavailable in JPEG mode.

  Sigma DP2 Olympus E-P1 Sony DSLR A330 Ricoh GRD III
ISO 50/64    
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200  

Looking at the camera's noise with noise reduction reduced to a minimum in Adobe Camera Raw, it become obvious why Sigma limits its JPEG output to ISO 800 - noise rises drastically after that point. It's still not terrible (in these well-lit conditions) though the it's hard to get the full picture, since blacks are artificially clipped at ISO 1600 and 3200. Also these figures measure noise at the pixel level and there is such a disparity in pixel numbers, that the amount of noise in the whole image is not likely to be significantly different, overall. The provided SPP software can get better results out of them, though with no control over the noise reduction settings, you'll generally want to stay at ISO 800 or below.

  Sigma DP2
Chroma
Black
Gray
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