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ISO Sensitivity / Noise levelsISO 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). Room temperature is approximately 22°C (~72°F), simulated daylight lighting. Sony DSLR-A350 vs. Canon EOS 450D vs. Pentax K20D
The differences in performance between the three cameras are visible at ISO 400 with both luminance and chroma noise appearing in the Sony and Pentax crops. The response to this noise varies between the three manufacturers with Pentax doing very little to rein it in, while the Sony smoothes it away fairly aggressively and the Canon balances its noise reduction to stay relatively noise-free up to ISO 1600. The results of the Sony approach do not appear to have too damaging an effect at sensitivity levels up to ISO 400 but it blurs away an increasing amount of detail above that level. And unfortunately, the noise reduction doesn't so much reduce the noise as share it with adjacent pixels. The results at ISO 3200 are frankly dismal, obliterating detail in such a way that it limits post-processing options yet still doesn't produce noise-free images. Thankfully, unlike the more expensive A700, the A350 does not appear to apply noise reduction to its RAW files, as we'll see on the next page. * It's worth noting that these results are with the cameras in their default modes, the EOS 450D for example has an optional stronger High ISO noise reduction option which delivers images with almost no chroma noise. Noise graphsLuminance noise graphIn numerical terms, the A350 seems to do well against the Pentax K20D in terms of both Gray and Chroma noise. However, the crops above (and the studio examples later in the review), show that this is mainly because of much more aggressive noise reduction that is smearing away detail from ISO 400 upwards.
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis. Chroma (color) noise graph
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of color on the vertical axis. |
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