DVL-Digest 803 - Postings: Index DV to Film (DV at all?) DV to Film (DV at all?) - "Perry" Stephen posted: >Despite all the info out there, this is perhaps one of the most confusing issues ever to confront film and video types since the advent of sound. Let's keep the discussion open and free-flowing.< I couldn't agree more! How about this micro-essay of some facts: Current NTSC and PAL television is interlaced video. The vast majority of current video tape formats support interlaced video including DV, DVCAM and DVCPRO25 and 50. Interlaced video has a movement 'animation' speed of 60 or 50 pictures per second, and a full vertical frame resolution spread over two fields. This system gives an image which most folk find avoids flicker and gives very fluid movement rendering. The system breaks down slightly on fast moving edges where there is 'stair-stepping' due to the half resolution but this is minimised by motion blur as long as short camera shutter times are avoided. Pictures with high vertical resolution will 'twitter' due to frame rate flicker, where the edge information is only on alternate fields; this is normally minimised by averaging line pairs on the CCD output. In general the system works very well and was a very good use of available resources when designed in the mid 20th century. Movie film is a progressive system, normally running at 24frames/sec. This is only sufficient to give fluid movement as long as you restrict the speed, and results in a choppy impression called motion judder. Some folks think this gives film a dream like quality which adds to the story telling values. Personally I just see choppy motion! Projection of movie film needs to have the flicker rate increased, usually by installing a two bladed shutter which effectively shows each frame twice and increases the flicker to 48Hz. This is sufficient in the special environment of a movie theatre. Movie films get shown on television, and therefore need to be translated to interlaced video. This is normally done in a telecine suite. In NTSC areas, the film is converted using 3:2 pulldown, where each film frame contributes the image for alternatively 3 and 2 video fields. This crunches the motion rendering even more but has the advantage of 'fitting' almost exactly. In PAL areas, the film is normally run 4% fast and each frame supplies the image for the two fields in a video frame. This works very well and the audio can be pitch converted to avoid the wrath of musicians with perfect pitch! (It also has the advantage that turgid movies are that much shorter:}) Movie films thus have a unique 'look' on television. This look can be associated with the production values of the best of the movie industry, and the unique color rendering capabilities of a telecine scenario to produce a goal that many producers aspire to. I like to compare it to the typical US stretched limo, it is one of the most impractical cars I have ever travelled in but there is no doubt it has 'Hollywood Style'. This 'look' is also prevalent in 'The West' for most television commercials, where even more money than for movies is spent on image quality. There is thus an understandable desire to create the 'look', but an equally understandable desire to avoid the costs of film production and telecine transfers. This now needs to fit into the bigger world of Hi-Def television and electronic movie production. There are two particular areas of probably most interest to this List: 1) Using video to create a television program with the 'look' of a film production. 2) Using video to create a physical film. The two are quite different in technical requirements and should not be confused. They are common in being unfulfilled with off the shelf video kit that best serves their needs. They also have in common a detachment from 'reality' or 'accuracy' and are therefore very difficult to 'measure' or 'define'. Moving media is a conjuring trick, and interlaced television does a pretty good job of mimicking reality in a sort of looking through a telescope way. Hi-Def video does an even better job and will definitely be the way to go when we can all afford it. Movie film is not about reality (even for documentaries) and is much more about 'creating magic'. In this aim it relies on the viewer to a much greater extent, and each of us will have a quite different experience. Current technology is on the edge of our physiology so 'One man's meat etc.' definitely holds true. So with this in mind, I'll happily join in the fun. Most of what we buy and use is severely crippled by economic restraints; it is either too expensive or it is compromised by mass market requirements. We can all aspire to a better system for our particular needs, but getting the manufacturers to make it is quite a different thing. As an indication of this, one factoid is that nearly all current video cameras use progressive scan CCD sensors; it is how they then process the signal that determines the final image quality. This processing can often be designed into the CCD chip set(s) and cannot be easily changed. Perry Mitchell Video Consultant http://www.perrybits.co.uk (diese posts stammen von der DV-L Mailingliste - THX to Adam Wilt and Perry Mitchell :-) [up] |
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