Video Technology and Animation

5. Video Technology - Copyright © Denis Hamelin - Ryerson University

Video Technology

and Animation


Video Technology Basics

A video signal is usually generated by a display monitor, a piece of electrical equipment which displays viewable images generated by a computer without producing a permanent record.

The representation of video signals comprises three aspects: visual representation, transmission and digitization.


Visual Representation

The goal is to present a realistic image. To achieve this goal, the television picture must convey accurately the spatial and temporal elements of the scene.

Vertical distance and Viewing Distance:

The geometry of a television image is based on its width (W) and height (H). The conventional ratio W/H is 4/3 (1.33). Also called the aspect ratio. 16/9 is also a standard aspect ratio.


Viewing Distance

The viewing distance (D) determines the angular field of view. This angle is usually calculated by the ratio D/H.

The smallest detail in a picture is a pixel, but it is unavoidable that some pixels fall between scan lines. This is the loss of vertical resolution (only 70% of vertical details are in a scan line – Kell factor). It is independent of resolution.


Picture Detail

Scan lines are either sequential (progressive) or alternate (interlaced).

The number of horizontal elements is equal to the product of the vertical resolution and the aspect ratio.

In a television signal, not all lines or columns are visible. They are used to transmit additional information.


Depth Perception

In nature, humans perceive a third dimension, depth, by comparing the images perceived by each eye.

In a flat television picture, depth perception is achieved by perspective appearance.

Perspective effects are influenced by the choice of the camera lens (focal length).


Luminance

Color perception is achieved by three signals, proportional to the relative intensities of red, green and blue light (RGB) present in each portion of the scene.

These are conveyed to the monitor separately and the tube reproduces them at each point in time.


Perception of Motion

In contrast to the continuous pressure waves of an acoustic signal, a discrete sequence of individual still pictures is perceived as a continuous sequence.

This property is used in films, television and video in computer systems.

The impression of motion is created by presenting a rapid succession of barely different images in rapid succession.



Between each still picture (frame), the light is cut off briefly.

To represent visual reality, two conditions must be met: First, the rate of repetition must be high enough

to ensure continuity of movements.

Second, the rate must be high enough that the continuity of perception is not disrupted by the dark intervals between pictures.



It is known that continuous motion is only perceived as such if the frame rate is higher than 15 frames per second.

To make motion appear smooth, at least 30 fps must be used.

Films using only 24 fps often appear strange, especially when large objects move quickly and close to the viewer, as in pan shots.



Showscan is a technology for producing and presenting films at 60 fps using a 70 mm film.

The standard rate for television in Canada is NTSC (National Television Systems committee) is 29.97 Hz. The scanning equipment uses 24 Hz but is translated at 29.97 for reproduction.

The European standard PAL (Phase Alternating Line) uses 25Hz for both.


Raster-Scan System


Color CRT

A raster-scan system


Liquid Crystal Display (LCD)

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer.


LCD Color Displays

In color LCDs each individual pixel is divided into three cells, or subpixels, which are colored red, green, and blue, respectively, by additional filters (pigment filters, dye filters and metal oxide filters). Each subpixel can be controlled independently to yield thousands or millions of possible colors for each pixel.

Color components may be arrayed in various pixel geometries, depending on the monitor's usage. If the software knows which type of geometry is being used in a given LCD, this can be used to increase the apparent resolution of the monitor through subpixel rendering. This technique is especially useful for text anti-aliasing.


Plasma Displays

Many tiny cells located between two panels of glass hold an inert mixture of noble gases (neon and xenon). The gas in the cells is electrically turned into a plasma which then excites phosphors to emit light.

In color panels, the back of each cell is coated with a phosphor. The ultraviolet photons emitted by the plasma excite these phosphors to give off colored light. The operation of each cell is thus comparable to that of a fluorescent lamp.

Every pixel is made up of three separate subpixel cells, each with different colored phosphors. One subpixel has a red light phosphor, one subpixel has a green light phosphor and one subpixel has a blue light phosphor. These colors blend together to create the overall color of the pixel


Plasma Displays


Flicker

If the refresh rate is too low, a periodic fluctuation of the perceived brightness can result. This is called the flicker effect.

In films, the light itself is interrupted an additional three times to produce a flicker-free image even at 16Hz (three times = 48Hz).

In TV, interleaved scanning lines send half the picture at a time with interlaces scans.

For computer monitors, refresh rate is increased (70Hz).


Interlaced Scan Lines

Interlaces scan lines achieve a simulated refresh rate of 60 Hz (NTSC) or 50Hz (PAL).


Signal Formats

A video signal is decomposed into three sub signals: one luminance signal and two chrominance (color) signals).

In NTSC and PAL systems, the component transfer of luminance and chrominance in a single channel is accomplished by specifying the chrominance carrier to be an odd multiple of half the line-scanning frequency. Chrominance and luminance and interleaved.


Color Encoding

RGB Signal: Consists of separate signals for red, green and blue. Every color can be encoded as a combination of these three primary colors using additive color mixing. Values are normalized so that R+G+B=1 (White).


YUV Signal

Since human vision is more sensitive to brightness than to color, a more suitable encoding separates the luminance from the chrominance (color information). Instead of separating colors, the brightness information (luminance Y) is separated from the color information (channels U and V). For reason of compatibility with B&W receivers, luminance must be transmitted.


YUV Signal

Y = 0.30R + 0.59G + 0.11B U = (B – Y) x 0.493 V = (R – Y) x 0.877 An error in Y is more

serious than an error in U or V, so Y is encoded using a larger bandwidth.

YUV is also called the (4:2:2) for the ratios of bandwidths.


YIQ Signal

A similar encoding exists for the NTSC's YIQ signal.

Y = 0.30R + 0.59G + 0.11B

I = 0.60R – 0.28G - 0.32B

Q = 0.21R – 0.52G – 0.31B

I stands for in-phase, while Q stands for quadrature, referring to the components used in quadrature amplitude modulation. Some forms of NTSC now use the YUV color space, which is also used by other systems such as PAL.


NTSC System / YIQ Signal


Television Systems

NTSC: The U.S. Standard in use in Canada. It uses a refresh rate of 30Hz and a picture of 525 lines.

SECAM: Used primarily in France and Eastern Europe, It is based on frequency modulation instead of amplitude modulation like NTSC and PAL. 25Hz / 625 lines.

PAL: European standard, 25Hz/625 lines.


Television Systems


System Comparisons

Video professionals and television engineers jokingly referred to NTSC as "Never The Same Color" or "Never Twice the Same Color". Reception problems can degrade an NTSC picture by changing the phase of the color signal, so the color balance of the picture will be altered unless a compensation is made in the receiver. This necessitates the inclusion of a tint control on NTSC sets, which is not necessary on PAL or SECAM systems.


System Comparisons

The mismatch between NTSC's 30 frames per second and film's 24 frames is well overcome by an ingenious process which capitalizes on the field rate of the interlaced NTSC signal, thus avoiding the film playback speedup used for PAL and SECAM at 25 frames per second (which results in audio distortion).

There is no question the NTSC system reflects the technology of its originating era, but its compatibility and flexibility has been the key to its longevity over seven decades. The coming of digital television and high-definition television may end the need for analog television systems.


Composite Signal

All information is composed into one signal.

To decode, you need modulation methods for eliminating interference between luminance and chrominance components.


HDTV

Improved vertical resolution (>1000 lines), improved luminance (higher video bandwidth: 5x the conventional systems) produce an image close to 35mm film.

16:9 image ratio.

Progressive scanning instead of interlaced mode.

Since the vertical resolution is twice as large, the viewing distance can be halved.


HDTV (1080i)

1080 interlaced; one of two formats designated as high-definition television in the ATSC DTV standard, with 1,080 vertical pixels by 1,920 horizontal pixels. The i stands for interlaced, as opposed to progressive scanning, used in the second HDTV standard, 720p.

1080i has more scanning lines but also suffers the disadvantages of interlaced scanning. In the USA, 1080i is used by CBS, NBC, HBO, Showtime and Discovery HD due to the crisper picture particularly in non-moving shots. In Canada, all broadcasters use 1080i.


HDTV (720p)

720 progressive. Comprises 720 vertical pixels and 1,280 horizontal pixels. The p stands for progressive.

Contrary to myth, 720p is not inferior to 1080i; 720p has fewer lines but also has the advantages of progressive scanning and a constant vertical resolution of 720 lines, making it better able to handle motion. 720P is used by ABC, Fox and ESPN because the smoother image is desirable for fast-action sports telecasts.


HDTV (1080p)

The number 1080 represents 1,080 lines of vertical resolution, while the letter p stands for progressive scan or non-interlaced. 1080p is considered a HDTV video mode. The term usually assumes a widescreen aspect ratio of 16:9, implying a horizontal (display) resolution of 1920 dots across and a frame resolution of 1920 × 1080 or about 2.07 million pixels.


HDTV (1080p)

1080p is sometimes referred to in marketing materials as "True High-Definition" or "Full High-Definition". 1080p is currently the digital standard for filming digital motion pictures. The best technology commercially available is 1080p, soon to be superseded by 2160p.

Various television networks in the world broadcast HDTV programming in 1080i and 720p; no 1080p broadcasting exists at this time. (Blu-ray disks have the capacity to support 1080p).


1080p vs. 1080i

1080i and 1080p signals actually contain the same information. Both 1080i and 1080p represent a 1920x1080 pixel resolution.

In 1080i each frame of video is sent or displayed in alternative fields. The fields in 1080i are composed of 540 rows of pixels or lines of pixels running from the top to the bottom of the screen, with the odd fields displayed first and the even fields displayed second. Together, both fields create a full frame, made up of all 1,080 pixel rows or lines, every 30th of a second.


1080p vs. 1080i

In 1080p, each frame of video is sent or displayed progressively. This means that both the odd and even fields (all 1,080 pixel rows or pixel lines) that make up the full frame are displayed together. This results in a smoother looking image, with less motion artefacts and jagged edges.

Most Blu-ray players read the 1080p/24 signal off the disc, then it actually reinterlaces the signal to 1080i, and then deinterlaces its own internally made 1080i signal in order to create a 1080p/60 signal for output to a 1080p input capable television.


EDTV(480p) / SDTV(480i)

Enhanced Definition Television. Also used to describe plasma and other fixed-pixel displays that have 852x480 resolution. They can show an HDTV image but don't provide as much detail as higher-resolution displays.

Form of standard-definition digital television (SDTV) not considered high-definition television (HDTV), though 480p is discernibly cleaner and slightly sharper than analog television. The native resolution of DVD is 480p, but that resolution can be seen only if a DVD player outputs a progressive-scan signal and the set has progressive-scan or component-video inputs.

For PAL systems, the standards are 576p and 576i.


HDTV vs. SDTV


Digitization

Refers to sampling the gray/color level in the picture.

Once points are sampled, they are quantized into pixels.

Sampled value is mapped into an integer (steps).

Quantization level is dependent on number of bits used to represent resulting integer, like 8 bits per pixel or 24 bits per pixel.


Digitization

Need to create motion when digitizing video

Digitize pictures in time.

Obtain sequence of digital images per second to approximate analog motion video.


Digitization

Component Coding: The elements that make up a video signal, consist of luminance and two separate chrominance signals. (Less cross-talk, more std, less bandwidth).

Composite Coding:Analog video signal that includes vertical and horizontal synchronizing information. Since both luminance and chrominance signals are encoded together, only a single connection wire or jack is needed. (Simpler).


Bandwidth and Video

Uncompressed video: Image size x frame rate

Compressed video: depends on compression scheme.

HDTV quality video uncompressed: 345.6Mbps, compressed using MPEG (34 Mbps with some loss of quality).


Computer-Based Animation

Drawings are digitized to create key frames (important and different positions).

Individual frames are completed by using image composition techniques to add backgrounds and foregrounds.

Animation of movement requires new frames with intermediate positions. These are computer generated.


Computer-Based Animation

Linear interpolation “lerping” is the simplest method but creates only straight lines.

Splines use curves to produce smoother transitions.

Other methods involve polygons and shape recognitions.

In-between frames are very complex to create.


Animation Languages

Three categories of computer languages for animation:

Linear-list notations: command-like instructions containing a beginning frame number, an ending frame number, an action (event) and its arguments.

Ex: 42, 53, B, ROTATE “PALM”, 1, 30.

Rotates the “Palm” 30 degrees on axis 1 between frames 42 and 53.

Ex: Scefo (Scene Format).


Animation Languages High-Level Programming Language Notations: Embedding

animation control in a general-purpose programming language.

Ex: ASAS and LISP.

(grasp my-cube) ;cube is current object

(cw 0.05) ;clockwise rotation

(grasp camera) ;camera is current object

(right panning-speed) ; move it to the right

http://www.red3d.com/cwr/papers/1982/ASAS82.html for more...


Animation Control

There are various techniques to control animation: Explicitly Declared Control: the animator provided

a description of all events like transformations and scalings. Can be provided by joystick or data glove.

Procedural Control: animation is determined by properties of different objects on the screen.

Constraint-Based Control: animation is determined by positions of different objects on the screen.


Animation Control

There are various techniques to control animation: Control by Analyzing Live Action: real

movements are emulated using rotoscoping (filming of the live character) or by using indicators on the body of the live character.

Kinematic and Data Control: takes care of the physical dynamics (gravity, acceleration, inertia...).


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Video Technology and Animation