Multimedia Building Block : Video * 07/16/96 Multimedia Building Block : Video Week - 12 *

Lecture Outline Video consideration Analog vs. digital video * 07/16/96 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 *

* 07/16/96 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: * 07/16/96 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 * 07/16/96 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 *

* 07/16/96 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 works Video basics * 07/16/96 How video works Video 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 works Video basics * 07/16/96 How video works Video 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 works Transmission mode * 07/16/96 How video works Transmission 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 * 07/16/96 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 * 07/16/96 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) * 07/16/96 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 * 07/16/96 Diagram of tape path across the video head for analog recording *

Diagram of tape path across the video head for digital recording * 07/16/96 Diagram of tape path across the video head for digital recording *

Color encoding for video transmission * 07/16/96 Color encoding for video transmission 1. 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 transmission * 07/16/96 Color encoding for video transmission 2. 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 transmission * 07/16/96 Color encoding for video transmission 3. 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 Broadcast video standard 4:3 aspect ratio *

Broadcast video standard * 07/16/96 Broadcast video standard 16:9 aspect ratio *

Broadcast video standard * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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. * 07/16/96 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 * 07/16/96 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 Video * 07/16/96 Shooting and Editing Video 2. 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 * 07/16/96 Shooting and Editing Video The “Lighting Lab” software *

Shooting and Editing Video * 07/16/96 Shooting and Editing Video 3. 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 * 07/16/96 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 Video * 07/16/96 Shooting and Editing Video 4. 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 format * 07/16/96 Video Recording format 1. 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 format * 07/16/96 Video Recording format 2. 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 format * 07/16/96 Video Recording format 3. 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 format * 07/16/96 Video Recording format 4. 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 * 07/16/96 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 Digital 500+ Beta-SP 550 MII Broadcast quality 1000 *

Consumer-grade equipment * 07/16/96 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 * 07/16/96 Making tape copies Avoid copying from VHS to VHS Master copy should come at least from Hi-8, S-VHS or DV . *

* 07/16/96 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. *

* 07/16/96 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. Video capture card is used to convert analog to digital signal Compression is done via codec. *

* 07/16/96 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 * 07/16/96 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 * 07/16/96 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 * 07/16/96 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. *

* 07/16/96 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 * 07/16/96 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. *

* 07/16/96 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 *

* 07/16/96 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. *