What's so special about 3x3 binning in 5D III video?

Started Mar 3, 2012 | Discussions thread
DSPographer
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Re: How the 5D2 Reads the sensor for video
In reply to zerozeronine, Mar 6, 2012

I explain the 5D2 video read-out here:
http://forums.dpreview.com/forums/read.asp?forum=1032&message=40673471

The color aliasing artifacts of the 5D2 video shows that the De-Bayer processing happens after down-sampling. The moire frequencies of the aliasing shows that the initial down-sampling is 3 to 1 for both horizontal and vertical directions. The magnitude of the horizontal and vertical aliased response shows that the sensor is binned horizontally but not vertically so 2 of every 3 rows are skipped on read-out.

The read-out speed is of a sensor is one the the primary drivers of its design. It is very unlikely that Canon is able to read the full 22 Mpix of the 5D3 at video rates since its architecture is similar to the 5D2 architecture. They did double the read channels though so with a slightly higher video read-out speed than the still photo read-out speed the sensor could read every line if it used 3:1 column binning like the 5D3. But it might also use a very different read out scheme such as 2:1 horizontal and 2:1 vertical binning/decimation. We really need to wait for test samples from the 5D3 before we find out how Canon achieves video read speeds using 8 channels.

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