Author Topic: Canon M , record cropped 2.35:1 improves rolling shutter compared to 16:9  (Read 483 times)

2blackbar

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Hey guys is it possible to record mov files cropped  and save some cpu cycles?
I noticed i have less rolling shutter when im recording raw 2.35:1 compared to recroding 16:9 even in mov h264.
That pre recording crop for sure lest camera record faster, when i use crop 2.35:1 so it doesnt have to sweat as much as when recording 16:9, so is it possible to record actual 2.35:1 to h264 mov files ? That improves rolling shutter and would be worthy from what i see.
What do You guys think ?

Levas

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As far as I know, there is no possibility to change recording resolution (and aspect ratio) in h.264, although I'm not really sure  ???

But what I do know is that the sensor readout speed timing is not changing when aspect ratio is changed.
So if you see improvement between 2:35:1 and 16:9 , you will see the same improvement when recording 16:9 in h.264 and crop it to 2:39:1 in post on computer.

Since readout timing from sensor is not changing, I think the rolling shutter is not actual getting better with 2:39:1 compared to 16:9, it probably just looks less worse because the image height is less.

2blackbar

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I see the difference with naked eye, looks better when raw is turned on, it might be because i use fps override with raw and it makes rolling shutter look better but when i use fps override in h264 then it doesnt look as good as raw when i look at rolling shutter.

a1ex

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Best guess: in standby (or also when recording raw video), EOS M runs its LiveView at 720p (yes, even if you have 1080p selected in their menu). Of course, rolling shutter is lower in that mode.

The FPS override menu also displays accurate figures of the rolling shutter.

Kharak

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I have been wondering the same, and I dont feel it got answered or asked well enough here.

for instance the 5d3. Is the sensor readout time the same in full 3:2 as in for instance 2:39.1? In fps override it says 21,5 ms for 1932x1290 at 24.000 fps. In fps override the 21.5 ms does not change if I lower vertical resolution.
In 3x3 mode does the read out “scan” always go from full height of sensor (1932x1290) to bottom even if I was recording say 2:39.1 (1920x804)? Or is it only active captured area where the “scan” is being performed?

And is the readout time the same in crop_rec 3x3 60p (720p mode) 1920x800 as normal 3x3?

In fps override under Rolling shutter it says multiply us/line (16,6) by vertical resolution, i am not particular good at math and probably misunderstood something because i got a very high number which I don’t know what to do with.
once you go raw you never go back

Levas

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In normal magic lantern raw recording, the whole sensor is readout from top to bottom.
You can select different resolution/aspect ratio's in menu, but the whole sensor is readout from top to bottom, and only the selected resolution/aspect ratio is saved to memory card.
So resolution/aspect ratio selection has no influence on rolling shutter.

There is also a module called 'crop_rec' recording within Magic Lantern, with this module you can select different 'presets' of resolutions with a fixed frame rate.
The crop_rec presets only readout maximum resolution selectable within the crop_rec preset, so not the whole sensor is readout from top to bottom.
This makes it possible to achieve higher resolutions or higher frame rates then standard Canon options.

But I think, which is not made use of yet, it is also possible to create presets with less rolling shutter.
Only downside is, with most of these presets, Canon live view is not working, so you don't have the normal liveview, you can however get a slower low resolution liveview created within magic Lantern.
Now the question is, would you sacrifice normal Canon live view to get less rolling shutter ?
Because I think it is possible, but probably not very useful due lack of proper working liveview.

You can look at it as creating a readout mode like 50fps/720P, but using it for 25fps (so keep the speed of the B timer, but changing A timer to get 25fps, B-timer is responsible for rolling shutter).
This way you will have the rolling shutter of 720p mode, but now with 25 fps recording.


Kharak

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Thank you, Levas!

I am quite familiar with the crop_rec module, but have not experimented with Fps timers. Seems as though the crop_rec module doesn't work too well with fps override. Except for 3.5k mode, there I have changed either the A or B timer to get accurate 1/48 shutter.

once you go raw you never go back

Levas

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Crop_rec module won't work properly with FPS override function, both try to alter A and B timers, I don't know which one of the two wins  :P

You can try and ask if somebody in the 5d3 forum topic can make you a custom crop_preset for 5d3 with like 1920 x 800 resolution at max (in 3x3 readout mode, so no crop/zoom).
So instead of the standard 1920x1280 mode, a 1920 x 800 mode, that way, they can lower the B timer, which is normally set to be able to deliver 1280 vertical resolution, after that, A timer needs to be increased to get 24/25 fps again.
This way there are roughly 35% vertical lines less to be readout. So sensor readout speed is increased with 35% (sort of, because we're cheating by not reading out the whole sensor  :P)