Info on sensor crop for video?


Jul 6, 2017
Davidson, NC
I have a general question about how various Canon cameras use their sensors to capture video. I've picked up some vague ideas along the way as I've read forum messages, and I would like to fill in some gaps in my understanding.

Obviously various cameras are not going to use their whole sensors to capture video, since the sensor has a 3:2 (or maybe 4:3) width to height, and video is normally 16:9 these days (or maybe wider for some purposes).

I get the impression that different bodies might take different approaches to using available pixels to produce video. Perhaps some might use the full sensor width and scale down to 1080p. Some might even use just the central 1920 x 1080 pixels, or maybe cameras do something between those two extremes.

Is there an online guide somewhere that explains how different models approach this task? My interest would be primarily in Canon products, and of course specifically in the ones I use regularly for video now, the 6D2 and the G7X II. But of course a more general discussion, and even better, a comparison of different approaches would be interesting.

But even if you don't know anything comprehensive, some general clarification would be welcome.
Aug 23, 2013
Bahia Brazil
Canon does not inform (or other manufacturers) which down conversion process it uses in each camera model specifically.
Camera reviewers then need to compare sensor specifications and output format, and use some math to get to conclusions.
This does not always give certainties, but moiré observation helps to make assumptions that lead to logical conclusions.

For example, 70D, 7D ii, 5D ii has a high incidence of moiré in its 1080P video, which shows that Canon reads the sensor by jumping lines. That is, read line 1, jump the 2, read line 3, jump the 4, etc.

Top-of-the-line models like 1DX and 1DC read the entire sensor and this uses a large processing capacity and generates a lot more heat than the tactics of Canon's more "popular" models.

In order not to cause overheating with 4K video in 5D iv, Canon preferred to optimize processing capacity by concentrating the work in a small area in the center of the sensor, and created the 1.7x crop factor and not overload the image processor with all 30 megapixel.
Aug 23, 2013
Bahia Brazil
In fact, Sony reads the entire sensor and uses the image processor to convert to the video output format. This is the reason why the Sony A7 line suffers from overheating and high battery consumption.