Exercise 7: Your tolerance for noise.

This exercise enabled me to find out how my camera reacts when using high ISO settings, the difference between each setting and how much tolerance I personally have towards digital artifacts in my images.

The remit was to take an image indoors using daylight, the image had to contain a combination of sharp detail and textureless areas, with some of the textureless area in shadow.

The camera was set on a tripod and using the AV setting a series of shots were taken using ISO 100 through to ISO 1600. The cream wall has no features, whilst the wooden vase and Russian dolls provide both texture, detail, colour and shadow against the wall. I shot at f5.6 so that the images were not too under-exposed or I did not incur overly long shutter speeds.

None of the following images were processed so that the true impact of the ISO adjustments can be seen.



ISO100




ISO100 Shadow and detail

 At ISO100 the image is a little under-exposed but when viewed at 100% the details are sharp and there are no artifacts in the shadows or darker areas. When the exposure was adjusted in RAW the details remained sharp and the shadows "clear".


ISO200



ISO200 Shadow and detail

 There appears to be very little difference between ISO100 and ISO200.


ISO400






ISO400 Shadow and detail

 At ISO400 the exposure is slightly better but noise is begiing to become apparent in the shadow area and the details on the Russian dolls/vase are not so sharp.

ISO800



ISO800 Shadow and detail

  The noise increases at ISO800 both in the shadow and is visible in the textureless area of the wall.

ISO1600



ISO1600 Shadow and detail


With exposure increased in raw the coloured artifacts become more noticable.

At ISO1600 the noise is very apparent and does not make for a very satisfactory image at all. Depending on what people are trying to capture sometimes it is better to obtain the shot than have no record whatsoever. Sometimes a little grain can add interest to an image especially if the image is converted to monochrome so the discolouration is less obvious.

The conclusion reached is that at a push I personally would not try to use a higher ISO than 800, but possibly would use 1600 if I desperately wanted to capture a specific event. The 400D seems to manage fairly well up to ISO400.

Noise

Digital noise is a grainy distortion that spoils pictures shot in low light conditions with high ISO settings or when using a long exposure. Noise appears as speckles which can be black,coloured or bright depending on the scene and the exposure. It is usually worst in the shadows but can also been seen as pink,purple and other colour speckles in what should be a blue sky. A large amount of noise in an image reduces the overall sharpness and clarity of the picture.

Selecting a higher ISO amplifies the output signal from the sensor. The amplification process has difficulty with finding the difference between image signal and noise therefore the noise is also amplified. This helps to explain why high ISO images are always more noisy than ones taken with a lower setting.
In digital cameras this noise can also be affected by a variety of factors for example imperfections in the electronic components of which the camera is made, also the electronic components can  be affected by background electrical fields and electromagnetic radiation. The size of the sensor within a camera and the number of pixels crammed on the sensor will have a huge impact on the amount of noise generated.
Occasionally temperature can affect the amount of noise produced.

The major cause of noise is when there is simply not enough light hitting the sensor causing a sampling error.

Useful information was found the following websites :o)

http://www.photoxels.com/tutorial_noise.html

To try and reduce noise, if at all possible, avoid using long exposures and high ISO settings. There are several noise reduction software applications on the market and some image editing software has a noise reduction filter built in. Adobe Camera Raw offers noise reduction during RAW conversion. (The Noise Reduction section of the Detail tab has controls for reducing noise. Image noise includes luminance  noise, which makes an image look grainy, and chroma (colour) noise, which is usually visible as coloured artifacts in the image.)The Luminance control reduces grayscale noise, and the Colour control reduces chroma noise. Moving a slider to zero turns off noise reduction.

Most DSLR's have a noise reduction feature which can be turned on when required. On the Canon 400D this function comes under the heading of "Custom Functions" with the Long Exp. noise reduction known as C.Fn-2. It is accessed through the Menu button and selecting the Tools 2 tab.