Discussion:
Which definition of decibels in camera signal-to-noise ratio?
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m***@uga.edu
8 years ago
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When calculating the signal-to-noise ratio in a (linear) digital image, should one define the decibel as 10*log10 or 20*log10 ?

The case for 10*log10 is that the values represent luminous intensity, which is power.

The case for 20*log10 is that the values represent voltages in the CCD cells.

I see some people doing it either way. Which is best? Is there a standard?
Phil Hobbs
8 years ago
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Post by m***@uga.edu
When calculating the signal-to-noise ratio in a (linear) digital image,
should one define the decibel as 10*log10 or 20*log10 ?
The case for 10*log10 is that the values represent luminous intensity, which is power.
The case for 20*log10 is that the values represent voltages in the CCD cells.
I see some people doing it either way.  Which is best?  Is there a standard?
I always use electrical dB, i.e. 10 log(I**2 R). That's what spectrum analyzers and so on use, for a start. For another thing, there are electrical contributions to the SNR, and it's unphysical to convert them all into optical dB. (What would you do about 1/f noise in optical dB?)

Of course that doubles the quoted SNR numbers. Some folks may suspect specsmanship, so in talks and papers I mention early and often that I'm using electrical SNR.

Cheers

Phil Hobbs

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