WHAT IS HD?

One of the most frequent questions I am asked is which HD format should I use? The answer depends on what you are trying to do.

As a general rule, the better the original video recoding, the better the final product will be. Keep in mind that it is very possible to record terrible high definition video. HD does not guarantee quality. In fact HD doesn’t exactly guarantee a particular resolution.

The following are the most common forms of consumer and broadcast HD available today:

RESOLUTION
Today, resolution can mean one of several things: the number of vertical lines of resolution, the number of frames per second or whether the image is progressive or interlaced. Resolution will typically be expressed as either (frames-per-second)-(interlaced vs progressive) 24p 30p 60i or (vertical resolution)-(interlaced vs progressive) 480p 720p 1080i .

PROGRESSIVE VS INTERLACED
Two of the most confusing terms used in video production are progressive frame rate and interlaced video. Simply put, a progressive frame rate is the absence of interlaced video. Interlaced video is the standard video used up to the current HD or ATSC standards.

INTERLACED VIDEO
Television as we know it is saddled with a limitation known as field refresh rate. Basically, each individual image is presented to you in two phases – even and odd fields each refreshing thirty times a second. Because the even and odd fields are presented separately - even field first, the image is refreshed sixty times a second. The result is an image that flickers at a rate of sixty times a second while the frame rate is reportedly only thirty frames a second.

If this system worked in exactly that way, NTSC television or 60i would have a vertical resolution of 480 lines from top to bottom.

It doesn’t.

In reality, NTSC television captures a distinct image sixty times a second - each field is a distinct image. The hitch is that the images are captured at a resolution of 240 vertical lines but on alternating fields. Likewise these frames are displayed on the screen at sixty times a second on alternating fields. To the human eye, the 240 line images appear to merge forming a 480 vertical line image. The only problem is that these fields were captured 1/60th of a second apart. They do not match. If, for example, you were photographing a football being kicked across the screen, when the two fields combined to make a single 480 line image, the football would appear to be a jumble of mismatched lines. This is the fuzziness you notice with moving objects on a standard definition screen.

a moving football (English version) - interlaced

PROGRESSIVE VIDEO
Progressive video, on the other hand, is more like traditional film. Each image, at any resolution, is complete in and unto itself. Regardless of whether you photograph moving images at 60, 30 or 24 frames per second, each frame is a complete image refreshed in its entirety at the rate denoted by the setting used (60p, 30p, 24p). It should be noted that still images captured from progressive video will also look better than those derived from interlaced video as no field interpolation is necessary to create a complete image.

4:3 vs 16:9
Simply put 4:3 is the standard television or NTSC square format. 16:9 is the standard wide screen format favored by HD television. Essentially, if an image is acquired using NTSC format cameras, wide screen can only be achieved by “letterboxing” or placing black bars at the top and bottom of the image. By contrast, a 16:9 image is already rectangular and always contains more pixels than a 4:3 image. To display a 16:9 image on a 4:3 display the source image must be reduced in size until the width of the 16:9 image fits exactly the width of the 4:3 monitor. The gap at the top and bottom are filled with the “letterbox”.

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60i
60 frames per second, interlaced video. Can be one of several vertical resolutions. Specifically, this is an image refreshing alternating fields sixty times every second. The most common forms of 60i are standard NTSC television and 1080i HD television.

60p
60 frames per second, progressive video. This can be any of a number of resolutions. The most common are 480p, 720p and 1080p.

24p
24 frames per second, progressive video. This can be any of a number of resolutions. The most common are 480p, 720p and 1080p.

24f
24f is an aging intermediate process between true progressive 24p video and NTSC 60i playback. Without exploring the origins of 24f and 24PsF formats and standards, it is enough to say that video recorded in 24f on Sony and Cannon video equipment will not enjoy the absolute clarity as systems using true progressive video technology such as 24p.

480p
720 horizontal pixels by 480 lines of resolution. Known  as EDTV or Enhanced Definition Television or HD Lite, 480p is simply normal NTSC television without interlacing. As a result, 480p is exactly twice the resolution of standard TV. Initially, the American broadcasters wanted to make 480p the US standard of HDTV in a failed compromise with the FCC and the proposed ATSC. Today 480p is standard for most non HD DVD systems, gaming consoles and standard definition consumer digital recording equipment. Interestingly, the difference between 480p and standard NTSC television (480i or 60i) is more striking than the difference between 480p and 1080i HD. Some viewers prefer 480p on larger screens to 1080i due to the lack of a “saw toothed” edge on laterally moving images. Typically 4:3 resolution, 480p can be shot 16:9 using either cropping or anamorphic compression. 480p is commonly available in 24, 25 (PAL) and 30 frame per second modes.  Some systems can shoot 480p at 60 frames per second allowing for limited conversion to slow motion effects in 24, 25 and 30fps modes.

720p
A high definition format favored by Panasonic. The full resolution is actually 1280 horizontal pixels by 720 vertical lines of resolution. 720p is always in a 16:9 aspect ratio or wide screen.  720p is the most common progressive format HD image in use.

1080i
1920 horizontal pixels by 1080 lines of vertical resolution, interlaced video. 1080i is the most common form of broadcast HD video. It is also the most common form of prosumer HD video or HDV. The main drawback of recording in the 1080i format is that once interlacing is accounted for, your actual resolution is only 1920 x 540. 1080i is a 16:9 wide screen format commonly available in 24, 30 and 60 frame per second modes.

1080p
1920 horizontal pixels by 1080 lines of vertical resolution, progressive video – also true HD or real HD. 1080p is the most impressive of all HD formats available to professional video production. Formerly only the Sony CineAlta systems shot in the 1080p realm, now many prosumer cameras are offering 1080p video with impressive results. Because of the information density of 1080p images, 1080p is still most commonly used as a final or “post” format – 1080i or 720p images being “upressed” to 1080p with varying degrees of quality. The problem with 1080p in small format video capture is that the image is incredibly compressed. Care should be taken in preproduction to determine whether your project will benefit from 1080p acquisition. 1080p is a 16:9 wide screen format available in 24, 25, 30 and in a few cases 60 frame rates.

480, 720 and 1080 resolution comparisons

 

CONSUMER, PROSUMER, CARD MEMORY

In addition to all these choices and caveats, you have to consider whether a professional, large format camera is necessary or a more flexible prosumer camera will facilitate your production. Also, the tape format itself is a consideration imposing varying degrees of compression into the production pipeline. Even the capture format – tape, drive or memory card – has implications for duration, power requirements and resolutional limitations. Depending on the length, location and format of your project, care will be given in choosing a camera and format. Ultimately your final product will dictate the tools we use. One size does not fit all.

 

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