Last updated: 5/07/06

CHAPTER 07: VIDEO TECHNOLOGY

Introduction to Video Technology

Converting Processes from Analog Video Into Digital Video

Video Compression

Introduction to Video Technology Video is usually composed of visual images depicting

live action with an accompanying audio soundtrack.

Video is simply moving still images / pictures (moving from one frame to another frame in a given time).

Digital video, of course employs digital methods to capture, store, and present video.

Digital video creates the illusion of full motion by displaying a rapid sequence of changing images on a display device.

Computer video differs from traditional video.

The signals driving computer monitors are different from the video standards used in television VCRs.

Introduction to Video Technology Digital video combines features of graphics and audio to

create dynamic content for multimedia products.

Several parameters are implicit in the video standard, which makes it possible to freely interconnect various video devices such as camcorders, VCRs, and monitor.

1. True video operates at a fixed frame rate.

2. under the cosmetic front mask to the edge of the picture

tube.

3. A video frame is actually made up of two interlaced fields

consisting of the even and odd scan lines respectively.

Interlacing creates a similar problem when thin parallel lines appear on screen.

Introduction to Video Technology Watch some video where the subject is wearing a

striped shirt, and you’ll notice that the stripes on the shirt appear to crawl or shimmer.

This effect, called a moiré pattern, is caused by interlacing.

Introduction to Video TechnologySources of Digital Video Digital video consist of

movie clips

recordings of live action

a series of graphic images played in rapid succession

still images taken from film, video tape, or live action

Introduction to Video TechnologyBroadcast Video Standards Three analog broadcast video standards commonly

used around the world: NTSC, PAL, and SECAM.

In US, the NTSC standard is being phased out, replaced by the ATSC Digital Television Standard.

Because these standards and formats are not easily interchangeable, it is important to know where your multimedia projects will be used.

Each system is based on a different standard that defines the way information is encoded to produce the electronic signal that ultimately creates a television picture.

Introduction to Video Technology1. NTSC (National Television Standards Committee) Used by US, Canada, Mexico, Japan, and many other

countries.

Standards that define a method for encoding information into the electronic signal that ultimately creates a television picture.

A single frame of video is made up of 525 horizontal scan lines drawn onto the inside face of a phosphor-coated picture tube every 1/30th of a second by a fast-moving electron beam.

The drawing occurs so fast that your eye perceives the image as stable.

The electron beam actually makes two passes as it draws a single video frame, first laying down all the odd-numbered lines, then all the even-numbered lines.

Introduction to Video Technology Each of this passes (which happen at a rate of 60 per

second, or 60 Hz) paints a field, and the two fields are combined to create a single frame at a rate of 30 fps.

This process of building a single frame from two fields is called interlacing, a technique that helps to prevent flicker on television screens.

2. PAL (Phase Alternate Line) Used in the UK, Western Europe, Australia, South

Africa, China, and South America.

Used in the U.K., much of Europe, Australia and South Africa.

Consists of 625 scan lines drawn every 1/25 second.

PAL is interlaced at 50 cycles per second

Introduction to Video Technology3. SECAM (Sequential Color with Memory) Used in France, Eastern Europe, the former USSR, and

a few other countries.

Although it is a 625-line, 50 Hz system, it differs greatly from both the NTSC and the PAL colour systemsin its basic technology and broadcast method.

Often, however, TV sets sold in Europe utilize dual components and can handle both PAL and SECAM systems.

4. ATSC DTV (Advanced Television Systems Committee Digital Television)

Started as the High Definition Television (HDTV) , changed first to the Advance Television (ADTV) initiative and then finished as the Digital Television (DTV) initiative.

Introduction to Video Technology This standard slightly modified from the Digital

Television Standard (ATSC Doc. A/53) and Digital Audio Compression Standard (ATSC Doc A/52), moves U.S television from an analog to digital standard and provides TV stations with sufficient bandwidth to present four or five Standard Television signals (STV, providing the NTSC’s resolution of 525 lines with a 3:4 aspect ratio, but in a digital signal) or one HDTV signal (providing 1080 lines of resolution with a movie screen’s 16:9 aspect ratio).

For multimedia producers, this emerging standard allows for transmission of data to computers and for new ATV interactive services.

Converting Processes From Analog Video Into Digital VideoAnalog Video Video information that is stored using television video

signals, film, videotape or other non-computer media.

It defines where the digital content will come from and what will be required for the computer to access it.

Each frame of the video is represented by a fluctuating voltage signal known as an analog wave form or composite video.

Composite analog video has all the video components : brightness, colour, and synchronization combined into one signal.

Converting Processes From Analog Video Into Digital Video

Converting Processes From Analog Video Into Digital VideoDigital Video Is captured from television, VCR, and camera sources.

Relies on devices called controllers, which are used to control VCR, videodisk, camera, and other video devices.

Controllers - electronic devices that enable computers to control the operation of video equipment.

Is based on specialized video capture hardware that accepts video input and turns it into a digital format.

Video capture -process of transforming a video input signal (from a VCR or camera) into a series of graphic images that can be stored on a computer.

Converting Processes From Analog Video Into Digital VideoCharacteristics of Digital Video1. Frame Rate Number of images displayed within a specified amount

of time to convey a sense of motion (always described in frames per second -fps).

Standard rate = 24 to 30 frames per second. It must be projected at a constant rate.

In some cases (television),frames are also known as cells.

Converting Processes From Analog Video Into Digital Video2. Frame Size The height and width of each individual frame or

image.

However,the size of the image also determines the quality and size of each frame displayed.

Larger frame size = best quality but must pay more for processing the image.

Smaller frame size = lessened image quality but less processing is required.

Converting Processes From Analog Video Into Digital Video3. Color Depth / Resolution The amount of colour for each pixel within each frame

or image.

1 bit (2 colours), 8 bits (256 colours), 16 bits (65,535 colours), and 24 bits (16.7 million colours).

A factor to consider for storage space and processing.

24-bit colour to achieve optimal colour reproduction.

8-bit (greyscale) reducing file size but still maintaining an acceptable image resolution.

Converting Processes From Analog Video Into Digital Video

Video Frame 1

Video Frame 2

Video Frame 3

Video Frame 4

Frame Rate: number of frames displayed over a period of time (sec)

Colour Depth: number of colours per image,related to number of bits per colour (24 bits for 16 million colours) Frame Size: height and

width of a frame (measured in pixels)

Video Frame 1

Video Frame 2

Video Frame 3

Video Frame 4

Frame Rate: number of frames displayed over a period of time (sec)

Colour Depth: number of colours per image,related to number of bits per colour (24 bits for 16 million colours) Frame Size: height and

width of a frame (measured in pixels)

Converting Processes From Analog Video Into Digital VideoAnalog Versus Digital1. Easily Scalable It is portable to a variety of computer systems that

may vary in performance measures. Analog video does not have this luxury. The systems that display and use analog video must match those that produced it.

2. Randomly Accessible Users can jump to parts of a digital movie without

having to search through the entire sequence. In contrast, the media used for analog video store it sequentially.

Converting Processes From Analog Video Into Digital Video3. Stored and Transmitted Efficiently Digital video data may be stored efficiently and

accurately using standard secondary memory technologies. Tapes and films are subject to wear and aging, but such storage media as CD-ROMs preserve the original source without these defects. Video may also be transmitted over computer networks as well, creating new opportunities for delivering video and applications.

4. Powerful Editing Capabilities Digital editing exploits the power of the computer to

insert, delete, combine, copy, and move frames like any other form of data. The process is quick and painless, but even better, the results are precise and predictable.

Converting Processes From Analog Video Into Digital Video5. Additional Playback Features Besides forward and reverse, video sequence can be

dropped to simulated fast play. Random access allows starting and stopping at arbitrary points in the video sequence.

6. Interactive Potential The computer already controls video playback so it can

just as easily make decisions affecting that control based on feedback from the user. In other words, the content of what is viewed can be effected by interacting with the user as it viewed.

Converting Processes From Analog Video Into Digital VideoConverting Processes Video is usually recorded and played as an analog

signal therefore it must be digitized.

A video source, such as a video camera, VCR, TV or videodisc, is connected to a video capture card n computer.

As the video source is played, the analog signal is sent to video card and converted into a digital file that is stored on the hard drive.

At the same time, the sound from the video source is also digitized.

Converting Processes From Analog Video Into Digital VideoVideo CaptureComponents of a video capture system: Video source: Camera, Video Cassette Recorder.

Analog to digital converter: circuitry for converting the analog video stream into a digital video stream – a series of bits and bytes that represent the images from a video source.

Audio capture circuitry: Sound capture device that operates concurrent with the video capture system.

Hardware compression chip: A digital signal processing chip and associated supporting hardware for implementing a compression algorithm on the raw video stream.

Converting Processes From Analog Video Into Digital VideoProcessing Digital Video for Playback Digital video is a sequence of frames that is usually

displayed with synchronized, accompanying sound.

Accordingly, most video formats store data for both sights and sounds in the same file. That is why we have to take sounds into consideration when calculating the file size for a digital video.

Processing digital video for playback is based on the following criteria: Frame Resolution / Size (pixel) Color Depth (bit) Frame Rate ( fps) Audio Requirements (Kbits)

Converting Processes From Analog Video Into Digital Video

Video data size = Frame size * Frame rate * Colour depth * Time

Example:

Frame Resolution = 320 x 240Color Pixel = 16 bitsFrame rate = 15 per secondsAudio Requirements = monaural, sample rate 11.025 KHz,

8 bits resolution

Converting Processes From Analog Video Into Digital VideoThe data that the CPU must process for each second of

playback:

Video data size (Kbits/sec) = visual Kbits/sec + audio Kbits/sec

Visual Kbits/sec = 16 bits per pixel X 320 X 240 pixels per frame X 15 frames per sec

= 18432000 bits / 1024 (1K = 1024 bits)

= 18,000 Kbits/sec

Audio Kbits/sec = 8-bit sample size X 11,025 samples/sec X

1 mono channel = 88,200 bits / 1024 = ~ 86 Kbits/sec

Video data size = 18,000 + ~86 = ~18,086 Kbits/sec OR ~2.2

Mbytes/sec

Converting Processes From Analog Video Into Digital VideoShooting and Editing Video Tipsa) Don’t underestimate the importance of smooth camera

work.

b) Use a good tripod or placing the camera on a stable platform.

c) Always strive for adequate lighting.

d) Move the subject, not the lens.

e) Make backups of your tapes.

f) After recording, break off the write protection tab to prevent accidental erasure.

g) Do not reuse tapes.

Video Compression Compression is necessary when working with video on

computers.

Compression is performed by a compression/decompression scheme called a codec.

Uncompressed digital video has a data rate of approximately 20 MBps.

Many computer hard drives cannot handle this data rate.

Video Compression

1. JPEG (Joint Photographic Experts Group) This compression standard, developed for use with still

images, has a compression ratio of about 20:1 before visible image degradation occurs.

JPEG is one of the most popular compression standards used in the Macintosh, PC, and Amiga platforms.

JPEG 2000 is an initiative that will provide an image coding system using compression techniques based on the use of wavelet technology.

Video Compression

2. MPEG (Moving Picture Experts Group) It was developed specifically for motion images.

There are five MPEG standards being used or in development (MPEG-1, MPEG-2, MPEG-4, MPEG-7, and MPEG-21).

Each compression standard was designed with a specific application and bit rate in mind, although MPEG compression scales well with increased bit rates.

At a 50:1 compression rate before image degradation occurs, MPEG compression allows fast compression of video and audio, and decompression occurs in real time.

MPEG is capable of decompressing data at a rate of 1.2 to 1.5M per second.

Video Compression

3. DVI DVI compression/decompression technology is based

on the Intel i750 chip set.

DVI’s compression algorithms can compress full-motion, full speed 24-bit video at a rate between 80:1 to 160:1.

At these compression rates, DVI can deliver 30 frames per second full screen, full motion video with the support of specially designed boards.

JPEG delivers 30 frames per second but at a quarter screen size

Video CompressionOptimizing Video for Playback from a CD-

ROM CD-ROMs are today’s choice for distributing video; they

are inexpensive to mass-produce, and they store 650M of data.

Because they are based on recent technological developments, CD-ROMs have higher data transfer rates.

You can take advantage of the higher transfer rates by preparing your digital video file properly.

Here are some suggestions:

Limit the synchronization of video and audio; synchronization reduces the video file size and increases the data transfer rate.

Specify an appropriate software compression algorithm.

Video Compression Be conservative in the use of high quality sound.

CD-quality sound (16-bit, 44 Khz) as opposed to 11MHz requires a larger file size.

Record or edit the sound track of the video at 8 or 11 Mhz.

Use the smallest video window that you can without losing effectiveness.

The size of the video window and the frame rate you specify dramatically affect performance.

The smaller the size of the video window, the smaller the amount of data to be compressed and the faster the data transfer rate.

The software compression algorithm you specify makes a dramatic difference in performance.