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ISO / Sensitivity accuracyThe actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). We found the G11, LX3 and G10 all produced slightly darker images than we'd expect, with each of them very close to one third of a stop underexposed compared to the expected brightness. We've previously found that the GF1's indicated sensitivity when shooting JPEGs (standard settings) to be around a thirds of a stop (averaging ~0.4EV) lower than the actual sensitivity (in other words, the GF1 is around a third of a stop more sensitive than it says it is).
* Default settings. ISO Sensitivity / Noise levelsISO 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 1.5 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.) Canon PowerShot G11 vs Panasonic Lumix DMC-LX3 vs Panasonic DMC-GF1 vs Canon PowerShot G10
The G11 does a good job in keeping noise at bay but it does it at the expense of fine detail, which is increasingly blurred by noise reduction as the sensitivity rises. Above ISO 400 there is very little in the way of fine detail, in stark contrast to the comparable LX3, which doesn't suppress noise so aggressively and hence is noisier but retains more detail. The other difference is that the LX3 offers a degree of choice over the amount of noise reduction applied in JPEGs, whereas the G11 doesn't. With its smaller sensor, the G11 can't compete with the GF1 at high ISO. The G11 seems to be a pretty good match for the G10 though - retaining at least as much detail but with cleaner output at all ISOs. Low contrast detailWhat 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 (feathers) as you move up the ISO range.
The fine detail recorded at ISO 80 and 100 begins to get lost at as low a setting as ISO 200. By ISO 800, all the subtle detail has been completely lost and, by ISO 3200, everything is a rather vague mess. However, when you consider that more APS-C sensors struggle once you get to ISO 3200, despite them being eight and a half times larger (and hence receiving eight and a half times as much light per exposure). It also makes clear the extent to which 'good high ISO performance' is dependant on clever noise reduction - even on the highest level professional DSLRs the fine detail is one of the first victims of using very high ISO settings. Luminance noise graphCameras compared:
Measured ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis. As the crops would suggest, the G11 has the lowest noise pretty much across the board (though, as we've seen, this is partly because its noise reduction is so strong that it has blurred away most of the fine detail). RAW noise
It's interesting to see that the amount of chroma noise coming from the G11 is more similar to the GF1 than either of its peers with similarly-sized sensors.
Measured ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis. Visually, as well numerically, the G11's noise levels appear to be closer to those of the GF1 than those of the other two cameras with similarly sized sensors (the LX3 and G10). This is a really impressive result for a compact camera and means you're likely to be able to create images with a much better balance between noise and detail than the out-of-camera JPEGS by processing from RAW. |
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