Multimedia Building Block : Video

Week - 12

Lecture Outline• Video consideration• Analog vs. digital video• Obtaining video clip• How video works• Color encoding for video transmission• Broadcast video standard• Integrating Computers and video• Shooting and editing video• Video recording format• Digital video• Video compression

Video consideration• Video can add great impact to your multimedia

presentation due to its ability to draw people attention.• Video is also very hardware-intensive (require the

highest performance demand on your computer)– Storage issue: full-screen, uncompressed video uses

over 20 megabytes per second (MBps) of bandwidth and storage space.

– Processor capability in handling very huge data on real time delivery

Video Consideration• To get the highest video performance, we should:

– Use video compression hardware to allow you to work with full-screen, full-motion video.

– Use a sophisticated audio board to allow you to use CD-quality sounds.

– Install a Super fast RAID (Redundant Array of Independent Disks) system that will support high-speed data transfer rates.

Analog vs. Digital Video• Digital video is beginning to replace analog in both

professional (production house and broadcast station) and consumer video markets.

• Digital video offer superior quality at a given cost.• Why?

– Digital video reduces generational losses suffered by analog video.

– Digital mastering means that quality will never be an issue

Obtaining Video Clip• If using analog video, we need to convert it to digital

format first (in other words, need to digitize the analog video first).

• Source for analog video can come from:– Existing video content

• beware of licensing and copyright issues – Take a new footage (i.e. shoot your own video)

• Ask permission from all the persons who appear or speak, as well as the permission for the audio or music used.

How video worksVideo basics– Light passes through the camera lens and is converted

to an electronic signal by a Charge Coupled Device (CCD)

– Most consumer-grade cameras have a single CCD.– Professional–grade cameras have three CCDs, one for

each Red, Green and Blue color information.

How video worksVideo basics– The output of the CCD is processed by the camera into

a signal containing three channels of color information and synchronization pulse (sync).

– If each channel of color information is transmitted as a separate signal on its own conductor, the signal output is called RGB, which is the preferred method for higher-quality and professional video work.

How video worksTransmission mode

– Composite video transmits the whole signal in a single cable (all three color information and the sync signals are mixed together).

• Yield less precise color definition• Colors cannot be manipulated or corrected• A coaxial cable or RCA connector are usually used.

– S-Video separates color and brightness information over two wires.

• S-Video cables use a unique S-Video connector.

How video works

Transmission mode– Component video separates color (chrominance) and

brightness (luminance) information over three wires. • Two chrominance and one luminance signals• Chrominance = information on colors• Luminance = information on brightness

– Luminance and chrominance are used to encode color during transmission.

How video works• Video frames for television are interlaced

– Each frame consist of two separate fields : odd and even fields.

– The technique of mixing the two fields together to create one image is called interlacing.

How video works• Video is recorded onto magnetic tapes (analog)• Audio is recorded on a separate straight-line track at

the top of the videotape.• At the bottom of the tape is a control track containing

the pulses used to regulate speed.

Diagram of tape path across the video head for analog recording

Diagram of tape path across the video head for digital recording

Color encoding for video transmission1. RGB signal

– Consist of separate signals for red, green and blue– Other colors can be coded as a combination of these

primary colors• e.g. white = R + G + B

Color encoding for video transmission2. YUV signal

– Separate brightness (luminance) component Y– Color information (3 chrominance signals U and V)

• Y = 0.3R + 0.59G + 0.11B• U = (B-Y) * 0.493• V = (R-Y) * 0.877

Color encoding for video transmission3. YIQ signal

– Similar to YUV– Basis for the NTSC format

• Y = 0.3R +0.59G + 0.11B• I = 0.60R – 0.28G + 0.32B• Q =0.21R – 0.52G + 0.31B

4. Composite signal– Individual component (RGB, YUV or YIQ) must be

combine into one signal.

Broadcast video standard• Four broadcast and video standards and recording

formats commonly used around the world are:• NTSC• PAL• SECAM• High Definition Television (HDTV)

• 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.

Broadcast video standard• NTSC (National Television Standard Committee)

– This standard is used in North America, South America and Japan.

– NTSC video has 525 interlaced lines of horizontal resolution.

– The frame rate is 30 frames per second (fps)

Broadcast video standard• PAL (Phase Alternate Line)

– This standard is used in Australia, South Africa and most of Europe.

– PAL video has 625 interlaced lines of resolution.– The frame rate is 25 fps.

Broadcast video standard• HDTV (High Definition Television)

– Six HDTV formats exist• Resolution vary from 720 to 1080 lines• Frame rates vary from 24 to 60 fps.• Format can either be interlaced or progressively scanned.

– The aspect ratio of HDTV is 16:9• Aspect ratio for NTSC, PAL, SECAM and computer monitor

is 4:3– The aspect ration of 16:9 is sometimes called

“widescreen”

Broadcast video standard

4:3 aspect ratio

Broadcast video standard

16:9 aspect ratio

Broadcast video standard• SECAM (Sequential Color and Memory)

– This standard is used in France, Russia and a few other countries.

– SECAM video has 625 interlaced lines of resolution.

Integrating Computers and Televisions for Video

We will look at:• Differences between computer and television video

– Overscan and safe title area– Video color– Interlaced and progressive scanning– Interlacing effect

• Working with text and titles

Differences between computer and television video

1. Overscan and the safe title area– Every analog TV displays the picture differently– Common practice for the television industry to

broadcast an image larger than the the standard TV screen so that the “edge” seen by viewer is always bounded by the TV’s physical frame, or bezel.

– This is called overscan

Differences between computer and television video

– In contrast, Computer monitor displays a smaller image (underscan), leaving a black border inside the bezel.

– When a digitized video image is displayed on the RGB screen, there is a border around the image, and when computer screen is converted to video, the outer edges of the images will not fit on a TV screen.

Differences between computer and television video– It is advisable to scale the video within the “safe title

area” as shown below so that the image will not be affected by over scanning.

Differences between computer and television video

2. Video color– Computer monitors uses RGB color.– Video uses YUV color.

• A YUV signal includes separate red, blue and luminance (brightness) information.

– Many RGB colors will not display in the YUV color space.

– High-end video editing applications offer filters to help you identify and correct ‘illegal’ RGB colors in the YUV color space.

Differences between computer and television video

3. Interlaced and progressive scanning– Television uses interlaced scanning– Computer employs progressive scanning

Differences between computer and television video

4. Interlacing effect– Lines that are one pixel thick will flicker on a TV due to

interlacing.– Make sure fonts and other lines are thicker than one

pixel.

Working with text and titles.

Use plain, sans serif fonts

Use light text over a dark background

Do not kern the letters too tight

Remember to avoid single-pixel-thick lines.

Avoid parallel lines, boxes, and tight concentric lines

Keep the graphics and title within the title safe area Leave titles on screen long enough to be read

Shooting and Editing Video 1. Shooting platform

– Use steady shooting platform to avoid shaky camera work.

– Use a tripod or place the camera on a stable platform– If must shoot handheld, use a camera that has an

electronic image stabilization feature for static shoot such as “steady-cam” balancing attachment.

Shooting and Editing Video2. Lighting

– Lighting can make a major different between amateur and professional shooting

– Always strive for adequate lighting– A standard studio lighting arrangement includes

• Fill• Key• Rim• background

Shooting and Editing Video• The “Lighting Lab” software

Shooting and Editing Video3. Blue Screen

– Blue screen key editing is used to superimposed subjects over different backgrounds.

– Blue screen is popular because expensive sets are not required.

– The blue background color will be replaced by the background image, frame by frame.

– e.g. Star Trek movie.

Shooting and Editing Video• The following figure shows frames taken from a video of an actor shot against

blue screen on a commercial stage. The blue background was removed from each frame, and the actor himself was turn into a photo-realistic animation that walked and jumped over the computer desktop.

Shooting and Editing Video4. Composition

– Consider the delivery medium when composing shots• For playback from CD-ROM or the web in small computer window,

avoid wide panoramic shots.• Use close-up or head-and-shoulder shooting.

– Consider the amount of motion in shot• The more scene changes from frame to frame, the more

“information” need to be transferred from the computer memory to the screen, unless you have a very good compression algorithm to handle this.

– Keep the camera still, let the subject move, not the camera.

Video Recording format1. S-VHS

– This format offers color and brightness quality superior to regular VHS

– Hi-8 also used this recording format– S-VHS is not considered broadcast quality.

Video Recording format2. Component (YUV)

– This format is used by professional-level analog equipment such as Betacams.

– This format is generally considered broadcast quality– YUV produces an image using three signals:

• Luminace (Y)• Blue minus luminance (U)• Red minus luminance (V)

Video Recording format3. Component digital (D-1 standard)

– To record NTSC signal in digital form– Digital video is used where signal was converted to

digital information before it was recorded as bits and bytes.

– Advantages include:• Better color and image resolution• Ability to make many copies without loss of quality

– Using 19mm (3/4-inch) tape– Comes with extremely high price tag.

• Only being used for super-high-end broadcast project

Video Recording format4. Composite digital

– More affordable than component digital, this format is becoming a new standard for the broadcast industry.

– To reduce the cost, other less expensive formats were developed to record NTSC composite signal into digital form, namely D-2 and D-3

– Modern DV (Digital Video) cameras use the composite digital format.

Video Hardware Resolution• Video horizontal resolution is the number of lines of details a

camera is able to reproduce, not the vertical scan lines on a TV set.• This resolution is determined by the number, size, and quality of the

CCDs used.Video Type Resolution

8 mm 230

VHS 240

3/4-SP 330

S-VHS 400

Hi-8 400

Digital 500+

Beta-SP 550

MII 550

Broadcast quality 1000

Consumer-grade equipment– Consumer-grade equipment is usually built to a price– Lower priced equipment usually exhibits lower quality

and fewer features.– The equipment is easier to use, but less robust and

lower quality– Editing with consumer-grade VCRs will produce

unacceptable glitches and low quality.

Making tape copies• Avoid copying from VHS to VHS• Master copy should come at least from Hi-8, S-VHS or

DV .

Digital Video– Computers and video technology have been merging for

several years now.– Digital video may either be captured directly from a

camera, or indirectly from the video tape recorder (VTR), or from the broadcast signal (be careful with the legal issue)

– Digital VTR record digital signal, while analog VTR record analog signal.

– To display analog video on computer, it needs to be digitized first.

– Digitized video is then compressed as the size of uncompressed video is large.

Digital Video– To digitize a video using computer, a video capture

card is required.• Analog signal is fed into this video capture card attached to

the computer.• Within this card, the analog signal is converted to digital form• The resulting digitized data is compressed in the card before

being passed on for storage on disk or transmission over the network.

– Alternatively, the analog signal can be digitized and compressed using circuitry inside a camera.

• The purely digitized data will then be transmitted to the computer via a high speed interface called FireWire.

Digital Video• There are two significant advantages in using computer

based digital video.– The ability to randomly access the video.– The ability to compress the video.

• These advantages are significant particularly when editing the video, transporting, and storing video for multimedia project.

Characteristics of digital Video• The frame is the basic feature of digital video and has

some of the same characteristics as two dimensional computer graphics including height, width, and color depth.

• A frame is a single image in a video sequence and is the same as single cell of movie film.

Characteristics of digital Video• Three basic characteristic of digital video are

– Frame rates - number of images displayed within a specified amount of time to convey a sense of motion.

– Frame size - the height and width of each individual frame or image.

– Color Depth or Resolution - the amount of color for each pixel within each frame or image.

• The size of a digital video file directly related to the frame rate, size, and color depth.

Frame Rate & Computer Frame Display• Frame rate is based on presenting a series of images so

rapidly that the brain processes the image collectively instead of as single images.

• Usually measured in frame per second ( 30,or 24 frame per second .)

• The frames of movie film, called cells, are moved past a light source at constant rate.

• A computer monitor uses a process called progressive scan to update the computer display one line at a time.

• The entire frame is displayed 30 times every second (for 30 fps) and is referred to as non interlaced video.

Frame Size• The size of the image determines the quality of the image

displayed and the processing involved to display that image.

• The larger frame size is obviously the best for resolution and image quality.

• The key is to fine the acceptable quality within performance capabilities.

Color depth or resolution• Digital video attempts to reproduce the highest quality

image possible. • Color depth and resolution refer to the number of colors

displayed on the screen at one time• Ranging from 1 bit up to 8 bit ,16 , 24 or even 32 bit per

pixel• Color resolution is a factor for storage space and

processing. – 24 bit color to achieve optimal color reproduction– 8 bit black and white or 256 color for a reduction in file size

while maintaining an acceptable image resolution.

Quality• Quality directly related to frame size, frame rate and color

depth. • Quality also depends on content. Motion picture needs

higher frame rate. • Must balance digital video quality, based on subjective

look and feel, with the amount of digital video

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.