"Basic TV and Video Systems" by Grob & Herndon Flashcards
What is a pixel?
Pixel stands for picture elements and is the smallest unit of light or shade in an image.
What do you call imagery that is in one “color”?
An image that is on one “color”, meaning it consists of white, gray, and black, is called monochrome.
How is a television picture presented, in a nondigital format?
A television is scanned in a sequential series of horizontal lines, one under the other, just as you would read lines text from a book. Starting from the top left, scanning in successive order, from left to right and top to bottom in a method known as horizontal linear scanning.
How many lines per frame of video?
The standard is 525 scanning lines for one complete picture or frame.
How many frames per second in video?
The time to form one complete frame (525 scanning lines) is 1/30th second. This equates to a picture repetition “rate” of 30 frames per second.
What is the purpose of a video signal?
The purpose of a video signal is to get the picture information from the output of the camera to the input of the picture tube. Common methods include closed-circuit television, video recording, on magnetic tape, or a laser disc, television broadcasting, cable television, satellite television, and video converted or stored in a digital format.
How many frames per second in standard movies?
A repetition of 24 frames per second is used in motion-picture practice.
What is the minimum number of frames needed to perceive motion?
Greater than 16 frames per second, any fewer and the scene looks jerky.
What makes up a field of video?
A field in video is half of a frame, containing either the group of odd or even horizontal scanning lines in a frame.
Why did the US choose 30 frames per second
A television picture is scanned in a sequential series of horizontal lines, one under the other. The standard is 525 scanning lines for one complete picture of frame. The time to form one complete frame (525 scanning lines) is 1/30th second, therefore the frames are repeated at a rate of 30 Hz, which is one-half the AC powerline frequency of 60 Hz. The frame repetition rate of 30 is chosen in television because homes in the U.S. are supplied with 120 V 60 Hz ac power. When the frame rate is 30 per second, the field rate equals the powerline frequency of 60 Hz. This is because televisions convert ac to dc with either a half-wave or full-wave power supply. The ripple frequencies are harmoniously related to the 30 Hz frame rate.
Why is there vertical and horizontal synchronization in video (TV)?
When the electron beam scans the screen of the picture tube at the receiver, the scanning must be exactly timed in order to assemble the picture information in the correct position. Horizontal syncing controls the timing of each horizontal line on the screen. A pulse is sent at the end of each line, when the electron beam is tracing to the beginning of the next line. Without horizontal synching, the image would appear distorted with diagonal lines. Vertical synching controls the timing of when a new frame is drawn on the screen. A pulse is sent at the end of each field when the electron beam is retracing to the top of the screen. Without vertical synchronization, the image would appear to be rolling. Proper synchronization is crucial for a smooth, flicker-free viewing experience on a display. By coordinating the timing of each frame, synchronization prevents judder during fast motion sequences.
What is the Chrominance signal?
The video signal that contains the color information.
Define Brightness
The overall, or average, intensity of illumination.
Define Contrast
The difference in intensity between black and white parts of the reproduced picture.
Define Resolution
How clear and detailed the image appears, determined by the number of pixels contained within each frame of video. A higher resolution indicates more detail in the video.
Define Saturation
The amount of color added which is varied by controlling the level for the chrominance signal.
Define Hue
An object’s color which depends on the phase angle of the 3.58-MHz chrominance signal.
Define Aspect Ratio
The width-to-height ratio of the picture frame.
What is considered the best viewing distance?
Four to eight times the picture height. This allows the viewer to be close enough to see the details in the image, without being so close that we see the individual scanning lines, color dots, and grain of the picture reproduction.
How did older cameras capture images?
With mechanical scanning, a photoelectric tube was combined with a rotating wheel to scan the picture element.
What is a CCD?
CCD stands for a charge-coupled device and is a common type of camera pickup transducer. It is a solid-state device using vertical columns and horizontal rows of photodiodes to convert light into electrical charges. The charges are stored and then transferred to the output stage of the device. The charges corresponding to the light level are clocked out of the device as a video signal.
CCDs are less expensive, lighter, consume less power, last longer, avoid image burn, and have low lag time when compared to tube devices.
If sensors do not see color how do they reproduce color?
Light from the color passes through the camera’s lens and the sensor stack, and finally lands on the color filter array, where certain wavelengths of light are filtered by three filters – red, green, and blue. Then it is detected by the sensor itself, which has it own spectral sensitivity curve. In a CCD, a different color is located above each photodiode In the CCD image sensor. The cyan filter passes blue and green and filters out red. The yellow filter passes red and green and filters out blue. The magenta filter passes red and blue and filters out green. The fourth color filter is green, so green is passed while red and blue are filtered out.
Why do video cameras need an infrared filter?
CCD image sensors have a wider wavelength response than the human eye, especially in the longer wavelengths of 700 nm and greater (known as infrared). To maintain a response similar to the human eye, an IR filter is placed in the light path in front of the CCD pickup.
What is white balance?
White balance is when the camera shows a picture of a white card as neutral white, and not as some identifiable hue.
What is one footcandle?
The standard reference for luminous intensity has been the candle. The candela (cd) is a more recent unit based on electrically repeatable devices and is practically equal to the candle. The light lux falling on a surface is directly proportional to the candlepower and inversely proportional to the square of the distance. The light lux on the surface is its illumination. One footcandle is the light lux intercepted by a one-foot-square surface that is one foot from a one-candlepower source.
What is a lux?
Lux measures the amount of light falling on a surface per unit area. A footcandle and a lux are both units of illumination, they differ by an approximate factor of 10 (10.87, to be exact).
What does FM stand for?
FM stands for frequency modulation.
How is writing speed determined?
The relative speed between the head gap and the moving tape determines the writing speed.
What is a helical-scan and why is it used?
A helical-scan is a technique to use tape more efficiently for a longer playing time. The tape crosses the head gap at an angle, instead of being linear. The magnetic recording is made on diagonal paths across the tape.
What does VHS stand for?
Video Home System
What does DVD stand for?
DVD stands for digital videodisk but is sometimes referred to as digital versatile disk.
Can DVDs be used for different aspect ratios?
Yes, 4:3 or 16:9 options are available with the DVD format.
Why are DVDs used to store computer files?
DVDs are used to store computer files due to the large storage capacity.
What does LCD stand for?
LCD stands for liquid crystal display
How are computer monitors different from TVs?
Monitors are similar to computer monitors, except a monitor does not need the RF tuning circuits of a television receiver because monitors use baseband video signals or RGB signals. Monitors also have control that prevent overscan, which is when important information is lost at the edges of the picture. TVs are usually set for a little overscan to insure full-screen coverage. In TV, the overscan helps make the picture information look a little bigger. Another difference is that the color level and tint controls in monitors are often determined by the computer’s software or video card.
What is the difference between interlaced and progressive scanning?
Interlaced scanning is a method for doubling the frame rate of a video display without taking up additional bandwidth. With this method, each frame is split into odd and even lines that are transmitted for 1/60th of a second, each of which constitutes a field. Interlaced videos are great for broadcasting as video images can be processed onto the screen with very little bandwidth. Because of this, it has been used for a long time in analog television broadcasts based on the NTSC (U.S.) and PAL (European) formats. While it is significantly faster, it may result in some flickering. In fast motion, the image may appear blurred as only half of the image is captured at a time. Monitors are unable to use interlaced scanning because the picture would contain vertical jitter and flicker in small areas of the picture.
In progressive scanning, horizontal lines are scanned in sequential order, but the horizontal sweep rate is increased. Progressive scanning produces a better picture quality but requires longer to scan.
What is the definition of sampling?
Sampling is a process by which a “snapshot” is taken of the input waveform, thousand of times in one second.
What does DCT stand for?
DCT stands for the digital cosine transform process which uses a trigonometrical formula derived from Fourier theory to transform data into blocks described by 8 x 8 pixel segments of the picture.
What does MPEG stand for?
Motion Picture Experts Group
Explain MPEG-2, include what a GOP and B,P and I frames are.
MPEG-2 is a compression scheme by which large amounts of information are compressed into data packets. To do this, something must be removed for there to be a space-saving effect. “Redundant” data is removed to provide the reduction in information required to make a sequence of pictures. Therefore, a process of intraframe compression or spatial compression is sued on every frame of video encoded into MPEG-2.
Three data frames are used in the MPEG-2 picture sequence. The B frames are the bi-directional predictive pictures. The P frames are the predictive coded pictures. The I frames are intracoded pictures. This I frame is present in all forms of MPEF-2. It is required by the decoder to interpret the information in the data packets and present an “apparent” motion sequence from subsequent frames. The I frame is also the first frame transmitted/encoded in a group of pictures (GOP) sequence. It is the lead frame in describing a scene to be decoded and displayed by the B and P frames. As much redundant information is removed from the picture as possible to reduce the space and time necessary to encode/decode the information.
The P frame is based on data in the I frame. B pictures are based on data from both I and P frames. The GOP sequence is usually 12 pictures in length.
