"Basic TV and Video Systems" by Grob & Herndon Flashcards
(40 cards)
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.
