E-M5 has DR 13!

Started Apr 13, 2012 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,683
Re: More a function of how they define DR

Bart Hickman wrote:

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.

The pixel-binning techniques that you describe work on uncorrelated spatially-distributed random noise (such as Photon Shot Noise), but to the extent that Read Noise (the dominant component of the noise-floor in specifying Dynamic Range) is not entirely random (but is instead periodic) on the level of (within the area of) the pixels binned, those relationships do not hold to be true ...

John Sheehy wrote:
There is no camera on the market with uncorrelated read noise.


Pixel binning is only useful to save storage space, or it can cut read noise by some amount if it is done before reading the photosites, in camera (and not with all technologies at all ISOs - binning at ISO 400 would serve no noise purpose whatsoever on an analog CMOS sensor like the ones Canon uses in their DSLRs). IOW, multiple pixels' charges are combined and read out as a single pixel. That would help reduce image-level read noise. However, any noise created by cameras after readout will be worse with hardware pixel binning, because less pixels have the same added noise each.


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