How do you arrive to this value?

This is really simple. In my example I was skipping every second pixel (horizontal and vertical). When sampling only one out of four pixels the resolution will drop to one-fourths. This equals to 21MP/4 => 5.25MP ≈ 5MP.

If an image is projected to the sensor which has details small enough to fall between two active pixels, aliasing will occur. The function of the OLPF is to spread such small details so it always hits an active pixel.

See Nyquist Shannon sampling theorem - Wikipedia for details about sampling.

To be clear I don’t say the 5DMKII skips every second pixel. This was just an example. But it is save to say the Canon 5DMKII does some sort of sub sampling and it is also obvious that the OLPF is too weak in this situation.

Yeah but it´s pretty obvious that the 5D2 uses every third pixel of every third row!
That pretty much fits the pixel count 1920x3 = 5760.

Using every second pixel of every second row would bring us only blue and red (or just green) pixels of the bayer patterns!
Sampling every third pixel in every third row brings us another perfect bayer-pattern again!

From the images posted at Reduser, I think they use every pixel on every third row. There doesn't seem to be aliasing of vertical lines. It's horizontal lines that cause the problem.

This could be implemented with a simple low pass filter before the A/D as the lines are read, providing inexpensive horizontal filtering with a potentially ideal aliasing/resolution result in that dimension. In the vertical dimension, it's another story. By skipping every third row, we get aliasing issues.

Oh well. This isn't an issue if we shoot sunrises. Zooming in on herringbone suits could be another story...

I can´t believe that they would be reading out 7MP 30times per second - that would be a very high pixel rate.
And it would be a pity - because if they were able to read 3 out of 9 pixels in 30 fps it was too close to 4 of 9 pixels which would provide us a totally new possibility:
http://www.gamsig.com/geheim/Bayer2.gif

I think the solution is to find the right soft/diffusion filter that reduces aliasing without reducing the resolution by too much. Frankly, a solid 720p image is probably enough for most of us. Vimeo is 720p. Unless we're making Blu-ray discs or showing at a film festival, I'd think most of us would be happy with aliasing-free 720p. (That and 24 fps and Exposure Simulation that actually sticks in video mode...)

Yes Jon adding a low pass filter before ADC will help reducing horizontal aliasing. But if canon uses a usual Bayer pattern this method will average blue and green or green and red pixels. I’m not sure if this can be corrected by a clever de-Bayer algorithm. May be Canon managed to only average pixels form the same color. If not, I think the color separation will be a problem.

As for read out speed: In burst mode the 1DmkIII can capture 5 images per second. If the 5DmkII has the same sensor, we should be safe to say that the read speed is at least 105MP/s.
If the mechanical shutter or the DSP / CPU are the limiting factors, then the sensor may be read even faster.

Reading every pixel at every third line would result in 210MP/s which is very fast. At the moment I don’t really care how canon exactly reads the pixels. It is more important to know how we can work around this issue. I think some sort of optical filter will be the only clean solution. I don’t have access to a 5Dmk2 so I have to wait for test results.

Exactly what I think. This will be - in the short term - the way to go. A filter might even add some organic bokeh, similar to 35mm adapters. Not everybody's choice but some will like it.

I hope we will find out about the best filter ASAP - and one thing is positive:
Even with the sharpness parameter of the 5D2 all down, filterless video looks tack-sharp.
So with the right soft-filter in the "sweet-spot" between aliasing and softness, the in-camera sharpening should be able to compensate for the filter.

We could also sharpen in post, but considering the AVC-encoder of the 5D2 the results might even be better with moderate in camera-presharpening.

a cheap solution for the antialiasing problem could be black Tulle. like this:
Tulle Netting Black Wedding Favor Netting Spools 6" wide 75' / 25 yards for $2.88
just put one or two layers of black Tulle in front of the lens.

professional people photographers use this to get soft portraits...

Yes this could be the solution. Very smart.

My personal moire showcase ;-)
 

To keep the search for the best workaround alive,
here´s my personal showcase for "5D2 moire":

ALIASING on the Canon 5D mark II on Vimeo
Aliasing is way uglier in the original 1080p-file that´s downloadable at the bottom of the page.

While shooting portrait-style with wide-open bokeh nearly 98% of the footage is decent.
As I took a winter walk, only 4 of 20 scenes looked ok.
If you got roofs or cars in the frame and you´re doing a wideangle shot, chances for aliasing are very high.

Andreas: If you shoot in urban environments you will almost always have hard edge ore fine repeating detail where the 5DMk2 will fail. May be I am hypersensitive for image artifacts but what can I do. I can’t stand the rainbow effect of DLP Beamers. I do not like the sharpening artifacts of cheap digital cameras. I’m less than unhappy with rolling shutter artifacts of my HV20. I do not like the motion artifacts of 100Hz / 120Hz TV sets……
All of this technology fails in one ore the other situation. Once spotted it attracts my eye all the time.

I was curious about the Tulle method Ralph mentioned. But then I got nervous about affecting the bokeh. So I did this quick test with my HV20 and a tee sieve. This method fails unless you use a very fine mesh.

-Street light in focus no filter
-Street lights out of focus no filter
-Street lights out of focus Tee sieve right before lens (4mm)

Has someone jet tested the diffusion filters? Footage?

This thread is too important to let it sink into oblivion. There's still no satisfying answer of how to reduce the sometimes annoying aliasing of the 5D. (Not only here on dvinfo but on other sites, too) Besides the struggle for better manual controls and 30p to 24p conversion, this is the 3rd most worrysome issue with the 5D. I would love to know that there's a solution before buying the 5D next month.