by Bill Elliott, HD Director of Photography

Motion pictures are made up of a series of still images projected one after the other in rapid sequence. When those individual pictures are projected fast enough, 24 pictures per second (also referred to as 24 frames per second), your brain sees the action in those frames as one continual motion. If the film were to be played back at a slower frame rate, you would start to see "jitter" in the motion. Motion picture camera manufacturers have settled on 24 frames per second because your brain can't detect much of a difference if the film frame rate is faster. Also, using film at a faster frame rate dramatically increases the cost of the film used since the faster the frame rate, the more film that is required to show any given time sequence. The cost to the motion picture producers would dramatically increase. When we shoot HDTV, the cost per minute of videotape is only a fraction of the cost per minute of motion picture film. This lower cost allows us to utilize the variable frame rates that HD cameras can shoot without creating budget issues. In the world of HDTV program origination, some of the recording formats we use allow us to shoot frame rates from 5 frames a second all the way up to 60 frames per second. For our discussion here, we'll restrict our discussion to 24 frames per second, the motion picture film standard, and 30 frames per second, the traditional analog video standard. (Note: Actually, the analog video frame rate standard is 29.97 frames per second but, for simplicity, we'll refer to it as 30 frames per second.)

Thanks to the flexibility of digital video, HD television program producers can pick the format and frame rates that will best help them create the look and feel that they are looking for, whether it be 24 frame interlaced, 24 frame progressive, 30 frame interlaced, or 30 frame progressive. The "P" in 24P stands for progressive. Many feature film producers, who originate their movies on HD but plan on showing them in theatres, prefer to shoot at 24 progressive frames per second. This allows them to transfer one frame of video for every frame of film. Shooting 24 progressive frames per second also emulates the look of motion picture frames. When viewed side by side to the same action shot in 30 frames per second, the 24 frames per second rate seems to have a very slight flicker. That sight flicker is the "temporal" feel that many people refer to as "film look." Many programs that are created for television or direct to home video are originated in 30 interlaced frames per second since that's the frame rate that NTSC televisions in the U.S.A. had historically been designed to display. And that allows the producers to edit electronically with video editing equipment, which has historically been a much faster and cheaper process, than physically editing film. Which frame rate is the best to use depends on the subject matter, the look the program producers want, budget, and how the program will be viewed. For years, artists have been able to chose from oils, water colors, acrylics, chalk, pen, and pencils among other mediums to create their art. Now, motion picture and television producers have their own variety of "palettes" to choose from. No one frame rate, format, scanning rate, etc. is better than the rest. It's simply a matter of artistic taste and final presentation medium.

The same digital technology that's allowing broadcast HDTV its wide flexibility is also allowing consumer video equipment manufacturers to offer low cost digital cameras & recorders that are also capable of different frame rates and progressive or interlaced scanning. More and more manufacturers are introducing HDTV equipment to the professional and consumer market every day. The prices are coming down and features are growing. It's up to the consumer to be educated and understand what is available and, most importantly, how they want to use it. There's no doubt that digital television is much better than the old NTSC analog system. But, with the ever-increasing selection of new video products and programs available, we must remember that even though HDTV is digital, not all digital television is HDTV.