Fixing backward flow timestep bug in DAIN_slowmotion

[kmbriedis]

The calculation of timesteps for the backward flow computation in DAIN_slowmotion is incorrect if the timestep is not 1/N. Therefore the simple array reversal time_offsets[::-1] must be replaced by [1 - t for t in time_offsets]

Example: If timestep=0.15: time_offsets = [0.15, 0.3, 0.45, 0.6, 0.75] And currently calculated offsets from the second keyframe are [0.75, 0.6, 0.45, 0.3, 0.15] while they should be [0.85, 0.7, 0.55, 0.4, 0.25] and are all off by 0.1 which lead to a slightly unaligned warp for the second image and worse quality of the output.

[VelocityRa]

Is there a reason this hasn't been merged?

[AlphaGit]

I have incorporated these changes into my fork of this repository.