This set of Video Engineering Multiple Choice Questions & Answers focuses on “Television Fundamentals – Scanning, Picture Frame, Flicker, Interlaced Scanning and Fields”.
1. The pixel elements are not spread over the entire picture in scanning.
Explanation: The above statement is false. The pixel / picture elements are spread over the entire picture. Each pixel represents particular light intensity and color variation. If each picture is transmitted simultaneously, it will require a large number of channels for transmission.
2. The human eye sees the light for 60 ms (microsecond) even after the light is removed.
Explanation: Persistence of vision means the eye can retain the sensation of an image for a short time even after the actual image is removed. The human eye sees the light for 60 ms even after the light is removed. This allows the display of a video as successive frames. As long as the frame interval is shorter than the persistence period, the eye will see a continuously varying image in time.
3. What is termed as the process of exploring a video picture image in quick succession?
a) Picture frame
Explanation: Scanning refers to the process of exploring a video picture image (also called as frame) in quick succession. Scanning starts from the left, proceeds to the rightmost element and returns to the left of next lower line. This takes place till the entire image is scanned. This is just like reading a page word by word.
4. Which signals are applied to the horizontal and vertical deflection circuits of the camera tube in scanning?
b) Unit impulse
Explanation: Scanning of the elements is done in a very fast pace. This process is repeated a large number of times per second to create an illusion of simultaneous pickup and transmission of picture details. Sawtooth signals are applied to the horizontal and vertical deflection circuits of the camera tube.
5. What is the word used by TV engineers for one complete scanning from left to right and top to bottom and then again to the top?
a) Picture frame
b) Picture image
c) Picture video
d) Picture audio
Explanation: TV engineers use the word ‘picture frame’ for one complete scanning from left to right and top to bottom and then again to the top. By opening and closing the shutter, 24 frames are formed in one second.
6. How many scanning lines per frame are there for Indian PAL system?
Explanation: 25 frames are formed every second in the TV system. There are 625 scanning lines per frame for Indian PAL (Phase Alteration by Line) system. Hence there are 15625 (625 × 25) scanning lines per second. In US, NTSC (National Television Standards Committee) system is used.
7. What happens to the image if the space between pictures is longer than the period of persistence of vision?
d) Interlaced scanning
Explanation: Due to some biological reason, the brighter the still image presented to the viewer, the shorter is the persistence of vision. So, bright pictures require more frequent repetition. If the space between pictures is longer than the period of persistence of vision, then the image flickers (moves waveringly).
8. What is the field rate for PAL system?
a) 15 Hz
b) 75 Hz
c) 2 Hz
d) 50 Hz
Explanation: The basic idea is that a single frame is scanned twice. The first scan includes only the odd lines, the next scan includes only the even lines. With this method, the number of ‘flashes’ per frame is two, and the field rate is double the frame rate. Thus PAL system has a field rate of 50 Hz (25 × 2).
9. What is the term for even and odd fields that are scanned alternately?
a) Interlaced scanning
Explanation: The electron beam scans every alternate line instead of scanning its successive line. So, the total lines are divided into two groups. These two groups are known as fields. The names of these two groups are: Even field and Odd field. Both fields are scanned alternately. This type of scanning is known as interlaced scanning.
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