Canon 7D downscale full size to 1080p

Canon 7D has a 22.3 x 14.9 mm sensor (5,184 × 3,456 pixels) with 4.3um pixel size. Its HD 1080p recording's format is 1920 x 1080 pixels. Would somebody tell me how the camera downscale the full size to the 1080p?

As 3456/1080 = 3.2, can I say each pixel of 1080p is the average of 3.2 x 3.2 pixels of the full size? And the pixel size of 1080p is equivalent to 3.2 x 4.3um = 13.76um?

Thanks.

Most probably, they only use 3*1080 = 3240 pixels for the video.

The sensor has a special design that allows it to read out scanlines at a lower resolution and getting multiple scanlines summed while reading - this saves a lot of time when needing to read out images at the full video frame rate. But it doesn't support any fractional scaling vertically.

Thanks for your reply.

In horizontal, 5184/1920 = 2.7, does that mean camera reads out every two scanlines because cameras don't support fractional scaling? If scaling factor is 2 in horizontal and 3 in vertical, pixel number for the FOV would be 1920 x 2 = 3840 pixels in H and 1080 x 3 = 3240 pixels in V. Is this correct? i'm kind of confused.

eric_qian wrote in post #16793574
Thanks for your reply.

In horizontal, 5184/1920 = 2.7, does that mean camera reads out every two scanlines because cameras don't support fractional scaling? If scaling factor is 2 in horizontal and 3 in vertical, pixel number for the FOV would be 1920 x 2 = 3840 pixels in H and 1080 x 3 = 3240 pixels in V. Is this correct? i'm kind of confused.

I'm really not sure. But 1920x1080 has square pixels so they must use the same scaling in both directions, so my previous post can't be correct. Maybe they settle for using 3840x2160 pixels.

It should be quite quick to test what horisontal field-of-view you get in 1920x1080 video mode compared to the field-of-view you get in stills mode.

Even in Canon's own technical "inside this or that" information, they state that Canon Japan doesn't reveal how this is done. Thus it's up to us to guess, since there is most likely no relevant informaton available. Canon consider it a trade secret.