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Figure 3.1

A frame of 1080 HD video is almost twice as big as a frame of 720 HD video, but 720 can have a frame rate of 60p, which is double that of 1080. 2K is bigger still, but not by much.

WHAT TO WATCH

Broadcast network TV—ABC broadcasts 720p and all the other networks broadcast 1080i.

Be sure to look at network original programming, such as the news and not the commercials.

Components of Digital Video

At the simplest level, all digital video is a collection of electronic signals recorded by a camera onto a piece of media: videotape, optical disk, hard drive, or flash memory. No matter how the signals are stored, all digital video consists of tracks, frames, scan lines, pixels, and audio samples.

Tracks

During a shoot, your video camera captures video and audio information, converts it into electronic data, and stores it onto its recording medium. All of this data is laid down in separate tracks (sometimes called channels or streams), typically one video track and two audio tracks. (Some cameras and audio recorders can record four or more tracks of audio.) In addition, most digital cameras record some form of data track that includes information such as the time of day, timecode, camera settings, and so on.

Frames

The video track consists of a series of still images, or frames, that, when played in sequence, appear to be moving. Frames of video are similar to frames of film, except that you can’t see them by holding them up to the light. Instead, you need a computer to decode the electronic information that constitutes each frame and display it on a monitor.

Each second of video contains a specific number of still images in order to give the illusion of motion. The number of still images, or frames, per second is called the frame rate. When motion picture film was invented, it originally ran at a frame rate of 18 frames per second (fps). With the advent of sound, the frame rate had to be increased to 24fps to get audio that was in sync with the picture.

There are many different frame rates associated with HD. The reason is that when HD was developed, it needed to be compatible with a variety of existing media: film, American analog broadcast video, and European analog broadcast video. Each of these three potential sources for HD defines a subset of HD frame rates:

n24p and 23.976p. Frame rates based on film.

n29.97p, 30p, 59.94i, 60i, 59.94p, and 60p. Frame rates based on American television.

n25p and 50i. Frame rates based on European television.

As you’re trying to decide which frame rate to use when you shoot, you can narrow down your options by using this list. For example, if you are doing a project in the United States, there is no reason to shoot 25p or 50i.

24P

24p is used when shooting video footage that will eventually be transferred to film. It is also used when transferring projects shot on film to HD for broadcast. Some argue that shooting 24p results in more film-like footage even if it is never transferred to film. 24p can be either 720 or 1080, so be sure to specify!

Scan Lines

Each individual frame of video is composed of a series of horizontal lines that are scanned across the screen starting at the top. With some types of video, these scan lines start at the top and work their way down to the bottom, filling the screen entirely, a process called progressive scanning (p).

With other types of video, the scan lines start at the top but only draw the even-numbered lines until they get to the bottom; then the odd-numbered lines are filled in from top to bottom (see Figure 3.2), a process called interlaced scanning (i). Each pass across the monitor is called a field, and each frame of interlaced video consists of two fields. The order in which the fields are drawn can change, depending on how the video is recorded.

If you are wondering which one is better, there’s no clear answer, but progressive scanning is definitely simpler and more intuitive, so given the choice, most filmmakers these days opt for progressive scanning. However, if your project is destined for broadcast television, the network may require that you use a form of HD with interlaced scanning.

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Figure 3.2

Interlaced video uses two fields to make up a complete frame of video; progressive scan video does not have fields.

Pixels

A pixel, short for “picture element,” is the smallest component of a video image. A frame of 720 HD video consists of a grid of 1280 pixels in width and 720 pixels in height. A frame of 1080 HD video contains a grid that’s 1920 pixels wide and 1080 pixels tall. These pixel dimensions are one way that people describe the resolution of a frame of video.

Vertical Resolution

The number of horizontal lines that fit on the screen is known as the vertical resolution. Some of the horizontal lines in each video frame are used to convey information that isn’t part of the visible image, something you don’t really need to worry about. For example, the vertical resolution of 1080 HD actually consists of 1125 vertical lines, of which 1080 are visible.

Horizontal Resolution

When it comes to image quality, you hear a lot of talk about “resolution,” especially when discussing video cameras. When speaking of resolution, people are usually referring to the horizontal resolution—that is, how many individual pixels (or dots) there are in each one of those horizontal lines. The vertical resolution mentioned earlier is fixed, but the horizontal resolution is variable.

Due to the way in which the human eye works, a set of alternating black-and-white lines, like those in Figure 3.3, will look like gray mush if the lines are small enough. Horizontal line resolution measures how many alternating black-and-white lines can fit in a video image before turning into an indistinct gray mass. Due to its subjective nature, horizontal line resolution is not a hard-and-fast figure. It varies according to such factors as the monitor, the camera hardware, how bright the room where the monitor is, how far you are from the monitor, and how good your vision is. Some cameras, lenses, and monitors have a greater capacity for displaying distinct vertical lines, and these devices are considered to have better “resolution.”

Figure 3.3

The number of vertical lines that fit into a frame of video is called the horizontal resolution. If the horizontal resolution is great enough, a group of black-and- white vertical lines like these will look like a solid grey mass.

Film Resolution

The resolution of 35mm film is higher than the resolution of 1080 or 720 HD video. Film is an analog medium so it doesn’t have pixels, but nevertheless it is considered to have a minimum resolution of 2048 1080 pixels, or 2K. In other words, in order for a digital video format to approximate the resolution of 35mm film, it must have a resolution of 2048 1080 pixels or higher. Digital video formats that have this resolution are often referred to as digital cinema formats, rather than HD. The resolution of digital cinema formats range from 2K to 4K (or 4096 2160). The RED One is a digital video camera that acquires footage in the digital cinema range, which is why it is often used for shooting feature films.

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WHAT TO WATCH

Slumdog Millionaire won the Academy Award for best cinematography and was mostly shot in a digital cinema format.

Aspect Ratio

The ratio of the width of an image to its height is called the aspect ratio (see Figure 3.4). HD video (both 1080 and 720) and 35mm film formats have a widescreen native aspect ratio, 1.78:1 (aka. 16:9) for HD video and 1.85:1 for most 35mm film. Typically, wider is considered more “cinematic.” Shooting in a wider format lets you put more information across the screen and is a truer representation of the way our field of vision works. Older SD and analog television displays and older computer monitors have a native aspect ratio of 4:3, or 1.33:1. In addition, 16mm, 8mm, and Super8 film all have a native aspect ratio of 4:3.

Figure 3.4

The larger rectangle has a 16:9 aspect ratio, while the smaller rectangle has a 4:3 aspect ratio.

Pixel Shape

Most newer digital video formats use square pixels but some older formats, like DV and HDV use non-square pixels. If your video uses non-square pixels, you might have to go through some extra steps in postproduction. For a more in-depth information, look at the pixel aspect ratios document at www.thedigitalfilmmakinghandbook.com.