Project: Noise

For the purposes of this exercise, I chose a scene with some detail, an (almost) textureless surface in shadow and in light and a surface in between.

Here are the pictures at the range of ISOs

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ISO 100

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ISO 200

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ISO 400

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ISO 800

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ISO 1600

These don’t show too much noise so to analyse it, I have taken a crop of each image around the top of the raffia box.

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ISO 100

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ISO 200

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ISO 400

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ISO 800

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ISO 1600

Taking a close look at the final picture, there is some noise in the white material, particularly becoming more noticeable deeper into the shadow. The noise is not particularly apparent in the folded blanket or the raffia work. To take a closer look I have made more crops of just the noisy area.

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ISO 100

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ISO 200

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ISO 400

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ISO 800

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ISO 1600

This shows clearly how the noise intensifies with increasing ISO sensitivity. ISO 100 and 200 are noise free, ISO 400 shows some noise which gradually increases to ISO1600. This is as to be expected from the course notes, the noise is at its worst in the shadowy areas and increases with increasing ISO.

Grain in film can be used as a creative tool, digital noise rarely adds to the image and is generally to be avoided. For this reason, I have always tried to avoid using ISO1600 for this reason, however this exercise has shown that even at this ISO setting, the noise might be acceptable – it is barely discernable in the full size picture. If it’s the difference between getting the shot or not, or a choice between noise and motion blur, ISO1600 is worth using. The Art of Photography had a similar exercise investigating the effect of noise and it led me to very much the same conclusion.

From a quick internet search on digital image noise I have drawn the following summary:

· Noticeable noise is a result of a low signal to noise ratio (SNR)

· Level of noise is fairly constant so in bright light a high SNR so noise not a problem

· Low light = low signal so SNR is lower

· Small photo sites gather less light than big ones ie low signal and low SNR. Therefore:

o Big sensors are a good thing (larger photosites) (notice how full frame sensor cameras seem to have higher max ISOs)

o High resolution sensors tend to have smaller photosites so not good

· Electronic circuitry introduces noise

http://www.cambridgeincolour.com/tutorials/image-noise.htm

http://www.trustedreviews.com/opinions/digital-photography-tutorial-image-noise-and-noise-reduction_Page-2

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