I decided to work out the numbers. if 4/3 is 18.0 x 13.5 mm and the same pixel density, then to get the 16/9 using Panasonic pixel count (their count gives a slightly smaller diagonal—about 1 percent), the sensor would be 19.6 x 13.5 mm with the corners cut off. So the published sizes don't make sense since the sensor should be this ratio for the GH1 pixel counts. (The pixel count for 16/9 is stated to be 4352x2448 and for 4/3 4000x3000.)

A drawing shows the situation a bit better here: http://www.dpreview.com/reviews/panasonicdmcgh1/. Although I think the rotating gif on the bottom of the page is wrong.

I should add that all of this isn't terribly important, the results are what counts. And as you originally pointed out the GH1 doesn't crop from a 4/3 sensor, but uses others parts of a sensor with more pixels resulting in more pixels in the 3:2 and 16:9 formats than those formats in the other u4/3 cameras.

Amin,

What are the dimensions of the sensors? The white boxes don't have any dimensions. And what is the source for the size of the white boxes? Panasonic and dpreview say the sensors are the same size for the G1 and GH1, even if they don't agree on the dimensions. My original link may have had an error http://www2.panasonic.com/webapp/wcs/stores/servl...

And more pixels doesn't necessarily make the sensor bigger.