E-M5 has DR 13!

Started Apr 13, 2012 | Discussions thread
Bart Hickman Veteran Member • Posts: 7,256
More a function of how they define DR

A 12-bit raw file gives 12-bits of DR over the full resolution (or max spatial frequency range). This type of dynamic range is a measure of how small of a max frequency signal (1 pixel dark, 1 pixel light alternating pattern) the sensor can distinguish from noise. This type of DR corresponds with SNR and is limited by the 12-bit raw if the hardware were perfect. I think the latest FF and APS-C cameras are actually getting so good, 12-bit quantizing noise is just starting to be measurable--thus the offering of 14-bit.

I believe these 13EV DR numbers we see are a measure of output range of the transfer curve of the sensor. This is a totally different type of DR and will not be limited by the quantizing noise of the raw file because I think they measure it by averaging the value of a grey patch over many pixels (or at least, it appears this is what dpreview does.) Eg, if you average just 4 pixels together, you reduce all noise (including quantizing noise) by 1 stop. These grey patches probably have 100's of pixels in them at least, so you could increase the SNR by 20dB or more beyond the 12-bit ideal.

Even the first definition of SNR varies with resolution--you can filter and down-sample an image by 2x in each direction and also boost SNR by 6dB.


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