Video crop mode

[Janke]

Maybe this has been discussed before, sorry for duplicating in that case, but I just did some experimenting with my EOS-M, and noted that the video crop mode uses only 1720 x 968 pixels of the sensor, not the full 1920x1080. (It's the same in other EOS cameras, too. AFAIK...)

Why use a smaller area and scale it up?

Wouldn't it even be less processor-intensive to use the unscaled 1920x1080, or is this impossible to implement for some reason ?

[a1ex]

We are not Canon engineers, so we can't explain why they decided to do this or that.

[Frank7D]

Hi Janke,

How did you determine that this is happening?

Edit:  I assume by comparing FOV?

[Janke]

@ a1ex: 

I first thought that the cropping was done in ML...  But why, indeed did Canon implement the crop like this?  (As a matter of fact, the crop feature is disabled in the EOS-M, even though it is available in other EOS models!)


@ Frank7D:

I did it by comparing a still in full resolution, then a frame grab from a crop video, both shot with the exactly the same lens setting.

Superimposing them in Photoshop, I noted that they didn't match pixel-by-pixel (which they should, if the video crop had been a plain, unscaled crop).

Changing the size of the video crop image until they superimposed perfectly, I found that the cropped area is exactly 1720 x 968, but resized to 1920x1080.

[Frank7D]

Thanks, when I get a chance I'll do a similar test with my 7D.

[a1ex]

https://bitbucket.org/hudson/magic-lantern/src/tip/src/crop-mode-hack.c

All ML does here is to enable a hidden setting.

Raw recording is different: from a single-buffered raw stream implemented by Canon as a debug feature, we wrote the rest (starting with cropping the video stream, buffering for near-optimal writing speeds, user interface and so on, until the conversion to DNG).

A strong hint is to look at the file format used by the feature. If it uses Canon file formats (MOV or CR2), it's Canon code creating it (maybe with minor tweaking of some parameters, but the codebase is still Canon's). If it's DNG, that's a open format, it's well documented, so we can create such files from scratch. If it's RAW or MLV, these are file formats designed by us (first was the simplest thing that worked, second is a bit more advanced).

You can also tell by the look and feel of the feature. If the graphics and fonts look nice, antialiased and consistent, it's probably Canon code. If it has jagged edges and looks like an old DOS program, it's ML code

And the strongest hint here: if it works without ML, it's clearly Canon code (try it).

@Frank7D: this feature is not available on 7D, so I'm not sure what you are going to test

[Frank7D]

@Frank7D: this feature is not available on 7D, so I'm not sure what you are going to test

I thought we were talking about the crop mode where you push the 5x zoom button and then shoot raw/mlv video. I do that on my 7D all the time.