How to render optical flow between two non-adjacent frames?

[ootts]

Describe your feature request

Suppose we have three frames, where either objects or camera moves, resulting optical flow.
Let's say we have frame1, frame2, and frame3. Using blenderproc, we can obtain flow1 and flow2, where flow1 connects frame1 and frame2, and flow2 connects frame2 and frame3.
But I am wondering if it is possible to render a flow image that connects frame1 and frame3?

Describe a possible solution

A possible solution without blenderproc would be warpping flow2 using flow1, resulting in warped_flow2, and then add warped_flow2 with flow1 to obtain the flow image between frame1 and 3. But this would involve interpolation. If we have a large number of frames and we do a chain of warping, there may be error accumulation. Thus, a native support from blenderproc would be nicer.

[cornerfarmer]

Hey @ootts,

unfortunately, blender does only allow rendering optical flow for non-adjacent frames. Therefore the only recommendation I can give you is to change the keyframes such that the frames of which you want to render the optical flow are next to each other