E-M5 has DR 13!

Started Apr 13, 2012 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,717
Re: hard to get 13 bits of DR from 12-bit RAW files [n/t]

SphericalAberration wrote:

Let me have a go at trying to put this straight :
Signal to noise ratio is not the same as dynamic range.

If the sensor full scale corresponds to 13EV of light above dark = 6.02 x 13 dB = 78.26 dB = FS.

Likewise for an ADC the best possible FS SNR = 6.02N + 1.76 dB

For 12 bit it's not possible to have signal to noise ratio SNR better than 74dB.

However notice that the SNR plots from the cameras are way below this number e.g. 42dB.

That is because each ADC bit change corresponds to more than 6dB or 1EV change in light level.

SNR results in the range of 40 dB (or so) are because the SNR of the opto-electronic transducers (the image-sensor photo-sites themsleves when fully illuminated) are limited by primarily by Photon Shot Noise that is known to be a property of the opto-electronically converted light energy itself.

Each ascending (more "significant") bit in a common ADC corresponds to a power of 2 - which is equal to 6.02 dB (or 1.0 EV, or 1.0 "stop") change in whatever input signal is converted. There do exist logarithmic ADC designs weighting the bits to the power of a different base other than 2.

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