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Digital photography jargon n is for...
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“Noise” in the context of digital photography, is random unwanted digital data that becomes converted to colour and/or brightness levels that do not correspond to the original optical image.
All digital images contain noise – the issue is when noise levels become high enough to have an adverse impact upon image quality.
During exposure, the image sensor is electronically activated to record the light signals falling upon it. However even in the absence of any light, the sensor will generate random data - the longer the sensor is activated the greater the quantity of this random background “noise”.
At the end of the exposure recorded light signals are amplified before being converted to digital data – any background noise is also subjected to this amplification.
In simple terms – the greater the quantity of light that is recorded compared to the inherent background noise , the less the adverse effect on the quality of the image.
This light signal versus background noise is known as the signal to noise ratio.
Listed below are the various factors that result in a low signal to noise ratio and therefore result in noisy images.
Digital noise is a fact of life. There are however various post processing options that can be used to reduce noise in images. Adobe photoshop and camera raw both have noise reduction filters and there are also specialist “plug in” software programmes designed specifically to reduce noise.
Noise is most prevalent when light data is scarce – so it follows that the darker areas of an image are likely to be most noisy. So brightening shadow areas to correct exposure in post processing will create noisier images compared to darkening slightly over exposed images. Care needs to be taken not to over expose to the point where highlights are “clipped” as then there will be no image data to recover.
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