8mm Forum: The John Meyer Method of Telecine

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Posted by Ian Brennan (Member # 3583) on September 25, 2013, 10:44 PM:

[Tip of the hat to you JohnMeyer]
[cross-posted to Doom9]

Like many of you, I’m getting enjoyment both in keeping our movies alive and in the experence of developing a telecine model. I wanted to pay back for the help I’ve had in exploring my telecine project.

I came across John Meyer’s method about six months ago and I’ve been hooked on the simplicity of the model. I wanted to share my experiences.

Back in 2002 John shared a brainwave and invented a model for Telecine. You can read it here http://forum.doom9.org/showthread.php?t=106837

In essence, his insight was that if the shutters were removed from the projector a camcorder running at a reasonably high speed would be able to record both the frame moving into position as well as the steady state of the frame when it settles in tho the gate.

Using AviSynth, he would then process the complete video and extract out the frames from the clutter. You would end up with a video with no interlace and no duplicates.

The beauty of this method is that you don’t need to track the projector’s mechanical progress, don’t need modified mice or any microswitches, magnets etc. You set up your video camera and away you went. As long as the camcorder ran at more than twice the fps of the projector this would work.

I contacted John recently and he generously shared his model. John’s method used TFM to identify the blur found when the film is in motion. His method processed the resulting log file in Excel.

Even though he shared his tools and insights with me, I could never get the quality that he did using his method. I have no idea why.

After a number of false starts, I’ve built on his idea but used “DeDup” to show where duplicate frames are. But the model is essentially his.

Here’s some of my footage on YouTube using John’s capture method http://youtu.be/2neBYuF3lgA - you will get the idea after a few moments, so pause when you’re ready, we’ll come back to the video later. You can see there are periods of blur as the film progresses across the gate. [Ignore the quality of the capture – this was a quick and dirty experiment].

Let me jump to the detail to show graphically what DeDup logs for that footage. Here’s the graph http://flic.kr/p/g9JUE3

DeDup identifies the percentage change between sequential camcorder frames.

The large spikes are where the movie frames transition into the gate – the transition from a stable image to a blur and then stability when the next frame comes to rest as shown in the movie above.

In the above capture, the camcorder was running at 50 fps and the projector was running about 1/4 of that speed. That is, there are four spike areas every 50 frames.

My solution processes DeDup logs looking for peaks, then wait for the next sequence of low values and pick one of them as the frame to include in the final movie.

The log file is processed with a short VBSCRIPT. My code sets a threshold over which it assumes all values are frame transitions – in the graph above, anything over 5% would be assumed to be frame movement. Anything below that value is assumed to be a stable frame.

The transition between frames can, in the graph above, can cover two or video frame, depending on the moment where the video captures the transition. This is addressed by looking for a number of consecutive “lows” values, which means all film motion have stopped. I leave it to the reader to speculate what the trough represents.

The code then skips subsequent "low" values until it detects another set of low-> high transitions and then starts the process again.

If you continue with the youtube video you can see the resulting movie. http://youtu.be/2neBYuF3lgA

There are some limitations to this method. If the film/capture is seriously over or under exposed then the transition may not show clear peaks. Raising or lowering the threshold can address this, but runs the risk of clipping real frame sequences, or including frame transitions into the final sequence.

I’ve tried this across a number of captures and a number of cameras – including webcams, microscopes and DSLRs. As long as there is good exposure you get the capture.

If you’re interested I’ll share the AviScripts and VBScripts.

Thanks again John for your inspiration.

Posted by Janice Glesser (Member # 2758) on September 25, 2013, 11:47 PM:

Ian...thank you so much for you detailed explanation of John's method. I'm very familiar with his work...but have to admit that when he came up with this real-time capture method I got lost. I could see the results...but didn't understand all the details of the process.

I would very much be interested in the scripts. I use AVI Scripts now for enhancing my captures...but really like to take a stab at John's method. I'll PM you my email address.

Posted by Ian Brennan (Member # 3583) on September 26, 2013, 06:27 PM:

Hi, the source files and descriptions are posted on http://sdrv.ms/186zWXO

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