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BMCC 4K Gets 50/60i?


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Seems like a good time to ask. What is the point of interlaced footage?


Actually it's non-moving shots that interlacing helps. For a given bit rate, you have a certain amount of resolution you can represent. On progressive scan you have to show every line in the same frame, so there's less information you can squeeze into that bit rate. If you instead skip every other line for one frame and do them on the next, and back and forth, you can represent the same resolution at half the bit rate. However, when your footage is in motion, there will be scan lines on the edges of the motion as you are combining two different frames where the subject was in two different places.


That's an ugly artifact and for fast-motion shots you would often rather do 720p than 1080i. But for still shots with no changes from frame to frame 1080i is essentially just as good as 1080p yet half the bandwidth, and for the same e.g. 50Mbps bandwidth the 1080i will actually be better than what you can do 1080p at least with an intraframe codec. Long GOP codecs like H.264 relieve a lot of that problem by incorporating information from multiple frames, but introduce other artifacts of their own.


You can interpolate 1080i60 to 1080p60 for slo-mo but you do run the risk of the interlacing artifacts on edges. This is how you can get slo-mo on the C100 for instance. All the 4K modes for the BMD listed are progressive and therefore can't be used for slo-mo other than with something like Twixtor if that supports 4K now.

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A lot of misconceptions about interlacing here. Interlacing is a method to get 50/60 fps into the same bandwidth as 25/30 fps. It just basically halves the resolution. Because they way interlaced televisions showed the image (one line after the next) it looked pretty much as running at 50/60 fps. Except the resolution was lower.


But the thing is. It's not fake. It actually is 50/60 fps. So you can get slowmotion out of the C100 and BMCC (if it can do 50/60i) if you handle the interlacing properly. The end resolution would be 1920x540 per frame. 


There isn't supposed to be artifacts anywhere if the interlacing is handled properly.

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I used to use this trick to get 60p from 60i footage on my Sony EX-F1.... The resolution drop really isn't that noticable, it will be usable for certain shots.


It's a free little feature, so just test it and see if you like it. If i were delivering a wedding video or something, a few 60i to 60p shots would probably work well and i doubt anywould would notice the drop in resolution, because they would be enjoying the slow motion effect.

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That kind off attitude means you won't be shooting anything worth seeing.


Fortunately a few distributors have thought differently, and they all demanded 1080p. :)


Getting a 4k camera to shoot half 1080p res is kind of missing the point, don't you think?

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