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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. Fuji FinePix S8000fd vs Panasonic Lumix FX18 vs Olympus SP560-UZ
Fuji has used a conventional CCD in the S8000, rather than its higher sensitivity Super-CCD technology (the acclaimed sensor used in the S6000fd would result in an 18x zoom the size of a dustbin). This leaves the S8000fd using essentially the same technology as its two most obvious competitors. As a result, the differences between the cameras are more to the balance between noise and noise reduction being struck by their manufacturers. Fujifilm has clearly decided that it's better to allow a little noise to appear than to eliminate all the detail (though how well it succeeds in this is questionable). The S8000fd has marginally higher chroma and luminance noise than its competitors, and shows visibly less loss of detail at ISO 200-400. Once you get to ISO 800 the differences are mostly aesthetic, with Fuji trying hard to keep the noise down whilst retaining some sharpness - something it does to a degree, but only by adding some pretty unpleasant painterly noise reduction. That said the results at ISO 400 and 800 make for better looking small prints than you'd get from either competitor. All three cameras produce fairly shoddy results at ISO 1600 The Fuji starts to combine information from several photosites (pixel binning) to produce a lower-resolution IS0 3200 image. The results aren't going to please anyone who wants to actually look at their photos but it's there if you really want it. The Olympus doesn't resort to pixel binning but this doesn't help it produce anything readily tolerable. At ISO 6400 you'd be better off putting the camera away and remembering how the scene looked, rather than filling your memory cards with pre-school watercolors that these cameras produce in very low light. Luminance noise graphCameras compared:
Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity is on the vertical axis. 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. 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'. In a new test the crops below show the effect of the noise reduction on such texture (fur) as you move up the ISO range.
This test attempts to re-create the conditions that appear in real-world images. Whether it's grass, distant leaves, hair or fur, fine detail of a similar color can easily confuse noise reduction routines, which just smear all of the results together and remove or distort fine texture in the final images. Here you can see that the detail starts to degrade at ISO 200 and is totally gone by the time you reach ISO 800. As we've already seen, ISO 3200 and 6400 favor blobs of color over detail. That all said, to Fuji's credit the ISO 64-400 results are a lot better than many we've seen. |
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