High Def and Standard Def
The existing North American system for broadcasting is called NTSC. This is now known as “Standard Definition”. “High Definition” is a totally new standard requiring different cameras, capture mediums, playback machines, transmission facilities and TVs. The broadcast term “Digital TV” can also be misunderstood. Standard Def can be delivered in Digital or Analog. HD is always Digital.
The main criterion of these formats is the number of lines that make up the picture—the more lines, the sharper the picture. When TV started in North America we chose 525 lines, whereas Europe chose 625 for its PAL system. HD systems can range from 720 to 1080 lines. My opinion is that we really did miss the mark with 525 lines; there seems to be a quality threshold just beyond this. PAL’s 625 lines looks so much better—so much so that PAL broadcasters are not as concerned about upgrading to HD right now. These scanning line numbers are actually an oversimplification. TV engineers use “lines of horizontal and vertical resolution” and those figures truly show the increased resolution of HD which is more than five times Standard Def! Pixel count and “megabytes per second” are other systems for rating picture information.
In Canada, most of us are still looking at Standard Def pictures. HD is only available on a limited numbers of channels which require an HD television set and conversion box to be viewed properly. Shooting in HD will help future sales. It’s too bad most broadcasters aren’t willing to pay an extra premium for HD shows!
LITTLE i AND BIG P
When you see “1080i” and “24P”, the letters refer to another element in the scanning system. Until recently, all TV pictures were interlaced or “i”. That means that, if there are 525 lines, lines #1, #3,#5, #7 (up to #525) are presented as a “field,” then after that is finished (in 1/60 sec.), lines #2, #4, #6 (up to #524) are inserted as the next field. This breaks up the picture and causes certain issues in post. “P” is for progressive—when all the lines are shown in the same scan. This results in a better picture and suits tape-to-film transfer because the video frame is a total entity, like the film frame. Progressive gives a better image, but do some research—some progressive systems are not truly progressive.
FRAME RATE
Standard Def in North America offers up frames at the rate of 30 frames a second (with interlace, that’s 60 fields so that format is called 60i—with progressive that’s 30 frames or 30P). There has been a big problem when transferring 30 frames of video to film’s 24 frames; you have to lose information. It’s much easier to stretch out film’s 24 frames to video’s 30 by repeating some parts of the frames (called 3-2 or 2-3 pulldown). PAL’s frame rate is 25 which is very close to film. When HD was introduced, Sony made a video camera which captured at 24 fps. There are two ways of using this feature:
1. It can be used for what it was intended—to transfer to film, frame for frame.
2. It can be used as an effected image on video productions. Shoot at 24 and get an effect of the raw video output which creates a blurry stuttered motion. This is very popular with producers because it looks different from clean smooth running video and looks more like film. Ever since video was invented, whether it makes sense or not, people have been trying to make video look like film.
Certain video cameras can provide variable frame rates up to 60 fps. With these variable frame cameras, you select a frame rate, have the proper interface to translate this, and get genuine fast or slow motion on video. You can also get altered motion in post with any video but you don’t get a true slow mo effect. If you just use the unaltered raw video with variable speed cameras, you can get blur or strobing effects (as in #2 above).
Don’t confuse the above with shutter speed settings, although there certainly is some overlap in the look achieved. Video cameras can offer slower or faster shutter speeds than the standard 1/60 sec. This will generate a blur or strobing effect, but will not alter frame output as with the frame rate.
This frame rate/shutter adjust can be a complex techno warp, but just try different settings, play them back in the finished format and see what works best for you. Or research other shows and use the rates they used. With all these options it’s best to consult with the DOP, the manufacturer, rental house personnel or an engineer/colourist. Options are changing with each new camera model so the information in this article will probably be out of date by the next issue!
