Author Topic: Aperture change during one single frame or photo -> temporal AA filter  (Read 4455 times)

Levas

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A1ex is talking about a temporal antialiasing filter. See quote at the bottom of this post.

I like the idea and was wondering if it is possible to control the aperture in video mode during one single frame ?
Let's say you're filming in PAL (25fps).
Is it possible to use a shutter of 1/25th of a second and for example use:
f22 for 1/100th of the time
f4.0 for 1/50th of the time
f22 for 1/100th of the time.
Which results in one single frame which took 1/25th  of a second?

Or, does anyone know if it's possible to use this in full res silent picture mode.
Let's say, time-lapse with 10 seconds interval. Can I get a 10 seconds single exposure, where the diafragma is f22 in the first and last few seconds of exposure and in the middle a seconds of f8 exposure ?

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Quote from A1ex in topic: www.magiclantern.fm/forum/index.php?topic=11787.150;topicseen

Another neat trick that can be done with a high-fps sensor, even if the final output has a low fps: temporal antialiasing filter.

Other companies did it in a different way, but the end result would be pretty similar:
http://tessive.com/time-control-faq/
http://www.red.com/learn/red-101/cinema-temporal-aliasing

and it was discussed here as well:
http://www.magiclantern.fm/forum/index.php?topic=5074
http://www.magiclantern.fm/forum/index.php?topic=8555.msg82898#msg82898

I'm going to implement this in ML for timelapse, with these functions. It will probably drain the battery pretty fast (because the sensor will be capturing light all the time), but it should give a very nice motion blur. Didn't try, but the theory makes sense.

This is also possible in post, but not practical (you would have record at say 300 fps and transcode to 24).

gerk.raisen

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #1 on: October 06, 2014, 06:35:00 PM »
UAO...
Great Levas, interesting project...
I will pleased to test when just ready ...or almost ready  ;)

dmilligan

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #2 on: October 06, 2014, 07:46:44 PM »
Sounds like a good way to wear out/destroy the aperture blade motor(s) in the lens, and I strongly suspect it's not possible for us to move them that quickly.

It might be possible for silent picture timelapse, but there's a much better/easier way: just take multiple sub-exposures for each single timelapse "frame" and average them with appropriate weights (using the newly discovered EekoAddRawPath functions). Something along these lines is probably what a1ex is thinking of implementing. For example, for a "10 second" exposure, you would take 10 - 1 second silent pictures and average them with appropriate weights such that the first and last subexposure gets the least weight, and ramp up to the middle exposure which gets the most weight.

You could also get some interesting effects for single long exposure photography with this technique (in addition to eliminating the need for strong ND filters during the day). The averaging is also going to do stuff like lower the noise and increase DR.

Levas

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #3 on: October 07, 2014, 12:22:59 AM »
"Sounds like a good way to wear out/destroy the aperture blade motor(s) in the lens"

Was thinking about that after I typed and posted it...  :-[ :P
switching aperture more than 3 times per frame on 25fps...that will be a lot of click/clack aperture changes, maybe it's a new way to create fire  :P
So forget it for video.

I assume that A1ex approach will be a frame blending technique with EekoAddRawPath functions.
Which is even better then this posted idea...

But I'm still wondering if diafragma can be controlled during exposure of one single photo  :-\
Wonder what the effects are if you have a long exposure which starts at f2.8 and ends with f22 and vice versa start with f22 and end with f2.8.
Probably creates something like soft focus effect ???.

Audionut

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #4 on: October 07, 2014, 02:21:13 AM »
But I'm still wondering if diafragma can be controlled during exposure of one single photo  :-\
Wonder what the effects are if you have a long exposure which starts at f2.8 and ends with f22 and vice versa start with f22 and end with f2.8.
Probably creates something like soft focus effect ???.

http://www.magiclantern.fm/forum/index.php?topic=12703.0

a1ex

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #5 on: October 07, 2014, 10:30:03 AM »
[...] just take multiple sub-exposures for each single timelapse "frame" and average them with appropriate weights (using the newly discovered EekoAddRawPath functions). Something along these lines is probably what a1ex is thinking of implementing. For example, for a "10 second" exposure, you would take 10 - 1 second silent pictures and average them with appropriate weights such that the first and last subexposure gets the least weight, and ramp up to the middle exposure which gets the most weight.

Exactly.

Levas

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Re: Aperture change during one single frame or photo -> temporal AA filter
« Reply #6 on: October 07, 2014, 11:53:25 AM »
"such that the first and last subexposure gets the least weight, and ramp up to the middle exposure which gets the most weight."
Even better!

Sounds great for time lapses  :D