Noise . . . ?

  • Thread starter Thread starter CJS
  • Start date Start date
We get noise in digital cameras because of the smallness of the photodiodes.

Each tiny diode generates an electrical signal dependant upon the light falling on it but these signals are tiny and have to be amplified.

When you amplify such a tiny signal you also amplify the noise inherent in all electrical components (even passive components such as resistors generate noise).

The larger the amplification the larger the noise.

When you increase the ISO sensitivity on your camera all you are really doing is increasing the level of amplification.

Since most scenes will have a range of tones from dark to light the noise levels will be greatest in the dark tones since these tones generate the least electrical signal.

So when you underexpose a scene you get more noise and if you grossly underexpose a scene then attempt to recover it in PP you can get greater noise then a properly exposed scene at a higher ISO.

Which is why using a histogram to get proper exposure will also help to keep your noise levels down.

Hope this helps you a little.

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CJS said:
Quote from: 'Noise issues with Canon 5D':

. . . 'Yep underexposed will always be so much more noise. You will probably get a much cleaner shot at 800-1600 ISO that is exposed well than an underexposed shot at 200 ISO.

http://www.talkphotography.co.uk/forums/showthread.php?t=310767

Can someone explain to a simpleton:thinking: 'why and how' . . . ? :shrug:

CJS
Click to expand...

In brief ...

Assume a sensor can capture a six stop dynamic range, recording a 12 bit image will allow it to record 4,096 tonal values. Each stop records half the amount of info as the previous one, with the brightest recording the most.

So the brightest stop would record 2048 levels, and the darkest only 64 levels.

There is more info to manipulate in the brighter areas than the darker areas of the image, as you start pushing the darker areas the editing software has only 64 bits of info to work with, so you have bigger steps between each tone of the image.

Buy a copy of "Digital Exposure Handbook" by Ross Hoddinott it will answer most questions in plain simple terms, and is probably the most useful book I have read with regard to digital exposure.
 
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