Author Topic: Dual Exposure (NOT ISO!) in video  (Read 2002 times)

ineffable

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Dual Exposure (NOT ISO!) in video
« on: July 25, 2015, 04:24:56 PM »
Hello ML,

Is it possible to record video at alternating exposure rates per frame (1 frame at 1/48 @ ISO 400,  the next frame at  1/400 @ ISO 3200).

Recording the above should be at 48FPS - alternating between 24 frames @ 1/48 and 24 frames @ 1/400

The idea behind this is to capture the slower exposure frames to be used as the video source (24fps at 1/48 - or whatever), and use the intermediate 1/400 (or faster) frames to significantly help motion capture tracking programs (this is aimed towards faster moving objects/scenes that generate significant motion blur). The 1/400 frames are there to freeze the motion - not to be used in final production, so the quality can be less-than-perfect.

If the image files are imported into a NLE using odd/even file numbers to distinguish, the separate rates *should* load into the correct video track (dropped frames may cause issues, but the frame details are stored in the metadata so all is not lost)

Offset the fast exposure frames correctly and the motion tracking points should be able to overlay the video track to be used.

Kind Regards
Ineffable

dmilligan

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Re: Dual Exposure (NOT ISO!) in video
« Reply #1 on: July 25, 2015, 04:54:41 PM »
It would be extremely difficult to configure the sensor in such a manner even if 1) such complicated configuration is even possible with the hardware and 2) we were to be able to figure out how to control the sensor and electronic shutter in a low level manner.

Think about rolling shutter and how that complicates things. Each line is readout one by one. A 1/48s frame takes longer than 1/48s to capture the entire image from start of top line to end of bottom line. When your shutter angle is near 360 (e.g.1/48s @ 48 FPS), the top line of the next frame begins exposing before the bottom line of the current frame finishes reading out.

My initial guess would be that this is simply impossible. Feel free to do some reverse engineering and prove me wrong. A good place to start learning would be really digging into the current FPS override implementation and understanding exactly how all the timers work (something I haven't really done myself).