Stop motion slow motion; different results from normal slo-mo

johnmeyer wrote on 4/9/2002, 1:13 AM
I can't get slow motion to work correctly on stop motion video (video created from a series of still images). Here is the test I performed:

1. I captured a series of still images of an object moving across a table. I used several different still image capture techniques (i.e., capturing individual frames into JPEG files and then creating an AVI file; or capturing using a stop motion capture program that takes individual snapshots and automatically creates the AVI file).

2. I used VF capture program to capture a normal video of my hand moving the same object across the table at approximately the same "speed" as my series of stop motion captures.

I then loaded each of these two AVI files into VF, slowed each clip down to 60% of its normal speed, and then rendered a new file for each of the two original clips. The clip captured directly in VF creates beautiful slow motion, with the intermediate frames almost indistiguishable from the original frames. However, on the clip captured from stop motion, I get ghosting and interlace artifacts on the in-between images.

I tried first rendering the stop motion file back to a new AVI file (using VF) to make sure there wasn't something unusual in the AVI format created by the stop motion software. This didn't make any difference. I think the problem may have something to do with interlacing, but I can't quite figure it out.

Does anyone have any suggestions?

Thanks!

John

Comments

Chienworks wrote on 4/9/2002, 5:47 AM
I'm sure interlacing is the key. The video captured in "real-time" is actually made of 60 fields per second (well, 59.94, but anyway ...) and Video Factory therefore has twice as many samples to draw from when rendering to slow motion. True, each of these fields is only half the resolution of a full frame image, but when there is movement, the eye fills in the lost detail for you. The version you made with still images doesn't have this interlacing. Worse yet, Video Factory forces it into an interlaced version when it's rendered. Since there wasn't any interlacing to begin with, this has to be "made up" and it can lead to the ghosting you saw. Try the same experiment again but force the output formats to Progressive instead of Interlaced. You may see the results switch the other way around.
johnmeyer wrote on 4/9/2002, 2:52 PM
I'm almost certain that you are correct. My challenge now is to find a way to either convert the stop motion video to an interlaced format that will allow VF to produce acceptable slow motion, or else find a stop motion capture technique that produces video that is more normal. VirtualDub will probably hold the key.

BTW, what I'm actually doing is converting Super8 movie film one frame at a time. I then post-process using a product called Steadyhand to remove the residual shutter jitter (from the film registration errors in the original camera). If I can solve the slo-mo problem (which should produce much better results than the traditional telecine), I should have absolutely stunning results that actually will look better than the original projected footage.
johnmeyer wrote on 4/9/2002, 3:20 PM
One addition to my previous reply. I just did some more research, and I think I am close to understanding the problem, although I am no closer to finding a solution.

NTSC video consists of roughly 60 fields per second (actually twice 29.97, and even that isn't exactly correct -- but it's close enough for this discussion). Normally each field represents a slightly later moment in time than the previous field so that each frame of video contains two different moments in time. However, in my stop motion capture, both fields of each frame are exactly identical. I'm not sure whether this is identical to progressive, since the video header in the file is probably still telling the software to render the frame as if it were interlaced.

Thus, I think my challenge is to either synthesize an interlaced video frame that contains fields from two different moments in time and then feed that to VF for the slow motion render, or else see if I can convert my stop motion video to true progressive and then get VF to create good slo-mo from that (which it may not be capable of doing).

Any further suggestions, anyone?

John
gminnick wrote on 7/22/2003, 12:06 PM
I am having the same problem. Except in my case, I took some video and used virutual dub to only process every tenth frame to create a stop motion effect. It looks great when I play the clip by itself and it looks great in VF when I am previewing. But when I render I get ghosting. I am not sure if this is an interlace problem yet or not. It is almost like VF is trying to fill in from one frame to another to smooth it out.
gminnick wrote on 7/22/2003, 12:25 PM
Ok, I used Virtual Dub to remove every odd (or even, cant remember) to create a progressive clip and processed every 10th frame. I used that in a test clip on VF and it looks great. So it does seem to be an interlacing problem. However, taking the clip that has the ghosting that VF makes and useing Virtual Dub to go frame by frame, something is just not right. When it goes from one still scene to the next it looks like 2 pics with a faded transition. Using the interlaced clip, it seems VF is trying to fade from one stop motion scene to the next. I hope that makes sense.
gminnick wrote on 7/22/2003, 1:20 PM
Ok, I think I have a solution. At least it worked for me. When I made my deinterlace clip by removing the odd (or even) field, it shrunk to 640x240. I was squished, but played fine in the rendered clip. I chose to enlarge to 640x480 and I got the problem again. I decied to resize the 640x240 non-int clip to 320x240 this time. I rendered in VF and it came out perfect.

Interlacing is the biggest headache cause you never really know what the software is doing at times. I know there are options in VF for choosing interlacing and doing every frame or at certain time intervals (but this does not seem to be avail when doing mpg).

I also noticed that deinterlacing a 640x480 clip by combining fields so it does not get squished did not help in VF. Maybe it inernally interlaces a clip that is x480 and not one x240 right before it sends it off to be compressed. And then maybe when it renders for TV, it interlaces during that part, which would mean it may interlace a x480 clip twice: (once during processing and then when compressing depending on the output).

Who knows!!!! Hope this helps.