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 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 1.4 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.)
Canon PowerShot S3 IS vs Panasonic DMC-FZ7
| Canon PowerShot S3 IS ISO 80 |
Panasonic DMC-FZ7 |
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| Canon PowerShot S3 IS ISO 100 |
Panasonic DMC-FZ7 ISO 100 |
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| Canon PowerShot S3 IS ISO 200 |
Panasonic DMC-FZ7 ISO 200 |
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| Canon PowerShot S3 IS ISO 400 |
Panasonic DMC-FZ7 ISO 400 |
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| Canon PowerShot S3 IS ISO 800 |
Panasonic DMC-FZ7 ISO 800 |
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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). These crops show two manufacturers with very different approaches (particularly at higher ISO settings); Panasonic (which has a noisier sensor to start with) uses fairly heavy noise reduction, Canon's approach appears to be more subtle, and much less bothered about luminance noise (the graininess is a lot less visually offensive than color blotches). There is some softness as the noise reduction really kicks in at ISO 200, ISO 400 is quite grainy, and I think it's safe to say ISO 800 is for 'emergency use only' but overall these results are pretty good for a small sensor camera (it is also worth noting that ISO 800 looks a lot noisier as the light levels drop).
Canon PowerShot S3 IS vs Canon PowerShot S2 IS
| Canon PowerShot S3 IS ISO 80 |
Canon PowerShot S2 IS |
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| Canon PowerShot S3 IS ISO 100 |
Canon PowerShot S2 IS ISO 100 |
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| Canon PowerShot S3 IS ISO 200 |
Canon PowerShot S2 IS ISO 200 |
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| Canon PowerShot S3 IS ISO 400 |
Canon PowerShot S2 IS ISO 400 |
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The S3 IS is undoubtedly an improvement on its predecessor at higher ISO settings, both in the amount of measurable noise and in the visual impact of that noise on the resultant images. At lower ISO settings the differences are minimal, and it's worth mentioning again that the S3 IS has ISO ratings that are much more accurate than the S2 IS (which understates its ISO ratings; it's a lot more sensitive at ISO 400 than the new camera).
Luminance noise graph
Cameras compared:
Canon PowerShot S3 IS, Canon PowerShot S2 IS, Panasonic DMC-FZ7
Note: ISO 50-800 only (the FZ7's ISO 1600 mode is almost identical to its ISO 800).
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis.
As usual what we're really looking at here isn't 'noise' as much as noise reduction; all three cameras produce similar results at lower ISO settings, but the Panasonic has much heavier noise reduction at higher settings. It does seem, however, that the S3 IS sensor has lower inherent noise than the S2 IS, even taking into account the differences in sensitivity. As noted from visual assessment of the gallery shots it appears that the noise reduction really kicks in at ISO 200.
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.
Chroma noise is very well controlled at lower ISO settings, and is around the average at ISO 400, though at ISO 800 it is very strong (here the Panasonic result can be more or less ignored as the results are so lacking in detail that the absence of noise is irrelevant).
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