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ISO Sensitivity / Noise levels

ISO 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 (die. 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.)

Olympus SP560-UZ vs Panasonic Lumix FX18 vs Fuji FinePix S8000fd

Olympus SP-560UZ
ISO 50

n/a

Fujifilm FinePix S8000fd
ISO 64

Olympus SP-560UZ
ISO 100
Panasonic Lumix FZ18
ISO 100
Fujifilm FinePix S8000fd
ISO 100
Olympus SP-560UZ
ISO 200
Panasonic Lumix FZ18
ISO 200
Fujifilm FinePix S8000fd
ISO 200
Olympus SP-560UZ
ISO 400
Panasonic Lumix FZ18
ISO 400
Fujifilm FinePix S8000fd
ISO 400
Olympus SP-560UZ
ISO 800
Panasonic Lumix FZ18
ISO 800
Fujifilm FinePix S8000fd
ISO 800
Olympus SP-560UZ
ISO 1600
Panasonic Lumix FZ18
ISO 1600
Fujifilm FinePix S8000fd
ISO 1600
Olympus SP-560UZ
ISO 3200
n/a Fujifilm FinePix S8000fd
ISO 3200
Olympus SP-560UZ
ISO 6400
n/a Fujifilm FinePix S8000fd
ISO 6400

Like all such cameras the SP-560UZ struggles with noise at anything but the lowest ISO setting, and once you get beyond ISO 400 the output is firmly in the 'emergency use only' camp.

Compared to its main competitors the SP-560UZ does a pretty good job of suppressing chroma noise up as far as ISO 1600. Some luminance noise starts to creep into the gray and black samples from ISO 200 upwards and appears to have been blurred somewhat by noise reduction, reducing contrast and definition from the image sample. A fraction less luminance noise reduction might have left more detail, even if it resulted in 'grainy' noise.

Noise reduction really kicks in at ISO 800 with the amount of chroma noise visibly dropping and no real rise in luminance noise visible compared to the ISO 400 image. Unfortunately, this means the amount of detail in the image is drastically reduced and only suffers more from then onwards.

Luminance noise graph

Cameras compared:
Olympus SP560UZ, Fujifilm FinePix S8000fd, Panasonic FZ18

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 detail

What 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.

100% Crops
ISO 50 ISO 100 ISO 200 ISO 400
ISO 800 ISO 1600 ISO 3200 ISO 6400

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 can just smear all of the results together and remove or distort fine texture in the final images. With the SP-560UZ you can see the definition of the hair starts to reduce at ISO 200 - the brightest and darkest details are still well represented but everything in between is starting to posterize to one or two shades.

By ISO 800, as the previous test would lead us to expect, all the detail begins to get swirled together and, although not visible in the ISO test, blotches of chroma noise are starting to appear. At ISO 1600 and above, I defy anyone to guess what the item being photographed was.

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