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Old Sep 26, 2003, 12:44 AM   #1
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Default grain & noise difference

Can somebody please tell me what is the difference between noise & grain. Are they one & the same.
I understand that grain is related primarily to high ISOs (giving a grainy photo). Is noise just another name?
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Old Sep 26, 2003, 7:12 AM   #2
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The source is different (of course, since grain comes from the film) but the results are basically the same. Speckels in the picture where detail should have been.

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Old Sep 26, 2003, 8:55 AM   #3
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It was my understanding that it is basically the same thing but, grain pertained to film cameras where, noise pertains to digital cameras.
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Old Sep 27, 2003, 9:18 AM   #4
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The "effect" is similar, but the cause is quite different. Ditital photo technology revolves around the sensor and its "photosites" which collect light. Unfortunately, in any electronic device there are two issues to contend with (Signal and Noise). The more favorable to signal the ratio between signal and noise, the less noise will appear in the image. ISO on a film camera is film type dependent with smaller, finer grain film producing higher ISO ratings. With digital, ISO is simply the result of amplification. The amplification of the signal to give some "equivalency" which makes sense to the ISO ratings of film. The more we amplify the signal, the more we amplify the noise.

Noise has various causes in digital photo technology, but mostly there are three factors. The amount of light collected per photosite (size and depth of the individual photosite wells), what is commonly referred to as "dark current" which resides in each photosite, and the ambient temperature. The higher the temperature, the more noise. In CCD's used for celestial photography, super cooling allows long exposure, low noise captures. In our typical digicams, we don't have this advantage so we go to larger sensors which allow more space for individual photosites which collect more signal to counter the more or less fixed amount of noise, and we use sophisticated algorithms in firmware to filter the noise when established patterns of noise distribution are known or can be analyzed.

With film we use larger particles of silver halide to increase ISO but at the expense of actually seeing these particles when generous enlargements are made. So fine grain film requires more light, but gives greater enlargement potential before the grain appears visible while coarse grain film requires less light but fosters the appearance of grain sooner in the enlargement process.

Both grain and noise can be ameliorated with sophisticated software such as Neat Image.

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