When shooting high speed video (or film), it’s common to run into problems with flickering lights. In addition to all of the usual suspects such as fluorescents and the like, fixtures that we don’t normally think of as being “flickery”? such as smaller tungsten bulbs and all household incancesdents actually flicker quite a bit at high speeds.

Of course the best solution to this is to use flicker-free sources, but sometimes there’s no choice but to shoot with flickery lights, and in those situations the deflicker tools that are part of the Furnace kit from The Foundry can work miracles.

Here is an example of a clip shot at 300fps with a Phantom V7.3 under stadium lights and what I was able to do with it.

The HPM110 (the updated P2 mobile), especially with the AVCI board, is 4 boxes in one - a portable D5-quality recorder, a frame rate converter, a format converter, and a gamma corrector.

Workflow With Panasonic HD and Final Cut Pro HD

There is one minor technical inaccuracy, in that the article states that only footage shot at 23.98 can be captured through firewire. In fact, it doesn’t matter what the frequency of the camera was. What matters is the frequency of the _deck_. If the frequency of the camera was 60Hz (meaning the 24 setting is actually 24, not 23.98), then the captured footage will be 0.1% slower than shot. Sync with external sources may need to be adjusted, but capturing *is* possible.

Otherwise, this is a good how-to.

To understand the issue it is necessary to understand the process of adding and removing pulldown to 24 frame footage, as well as how 4:2:0 subsampling works. First, a brief refresher on pulldown:

If you expose 24fps footage (e.g. on a film camera) and transfer it to NTSC video, it is necessary to turn 24 images into 30 video frames, each of which consists of 2 fields. This is done by adding what is know as 2:3 pulldown. It turns your first 4 frames of film:

| A | B | C | D |

into 5 frames of video by repeating certain fields like this (each letter here represents one field of video):

| AA | BB | BC | CD | DD |

at which point the sequence repeats itself. In order to get back to 24 frames you need to pull out 2 fields for each original frame. The A, B and D frames are easy (since there are already complete frames for those), but the C frame must be reconstructed from the second field of the BC frame and the first field of the CD frame. This is where the 4:2:0 issue comes in.

Many (some?) people are familiar with 4:2:2 and 4:1:1 subsampling, where the frequency of chroma samples is 50% and 25% respectively of that of luma. All subsampling in those cases is horizontal: every field is subsampled identically. In 4:2:0 subsampling, however, chroma is subsampled by 50% both horizontally _and_ vertically. Vertical subsampling is more complicated that horizontal subsampling. With progressive frames it is fairly straightforward: samples are arranged like this:

|C| |C| |
| | | | |
|C| |C| |
| | | | |

For interlaced footage, however, a different scheme is needed or else one field will have chroma information from the preceding field (and out of sync with the Luma). In this case the field from each field is subsampled separately, like this (black lines are from the odd field, red from the even):

|C| |C| |
|C| |C| |
| | | | |
| | | | |

The problem of properly encoding 2:3 pulldown is now becoming apparent: Ideally, since we wish to end up with progressive frames, we would use the progressive form of vertical subsampling. This would make it impossible (or at least extremely difficult) to remove the pulldown, since there will be cross-frame chroma contamination in the BC and CD frames, making a clean extraction of the C frame difficult. In order to avoid this problem, we need to subsample the video as interlaced video, but this results in significant loss in vertical chroma resolution in the progressive frames, since our chroma samples are now out of order.

Clearly, then, with any format that uses 4:2:0 subsampling ( _cough_ *HDV* _cough_), it is best for the interlaced to stay interlaced and the progressive to stay progressive and to leave it at that.