Editing 24p (section)

=== The Optical Flow Method ===

This is currently the highest quality method of converting 60i footage to 24p. It involves using [[optical flow]] to extrapolate 24 frames of information from 60 frames while compensating for the time displacement between the two. For example, in one second of 60i footage, each image is captured at 1/60 second, which does not perfectly align with images that would have been captured 24 times per second. Simply "cherry picking" 24 images out of 60 does not present 24 frames with perfect temporal consistency, since more or less time may have elapsed between frames. The result is a slightly jittery picture, which appears to jitter in a cyclic fashion. Optical flow algorithms will analyze the footage and make corrections to the picture in order to better "fit" each frame into the new 24 frame sequence. The resulting footage is much smoother because it simulates equal exposure time between frames.

For best results, footage should be deinterlaced and frame-doubled to 60p. This preserves all of the footage's temporal information, which is key in determining what the "missing" points in time should look like when converting to 24 frame/s.

The last step is to compensate for the lack of [[motion blur]] in the 60i footage. Since the images were captured at 1/60 second, there is less motion blur between images than there would have been if shot at 24 frame/s with a 180° shutter (i.e. 1/48 second exposure time). Optical flow is used to introduce motion blur between frames, mimicking the motion blur present when shooting the standard 180° shutter angle. This method of creating motion blur is far more realistic than simple frame blending, which is simple to implement and usually a standard feature in most non-linear editing programs.

The optical flow method also works with 30p footage and is currently the best option for 30p to 24p conversion.