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Picture Quality – Black & White TV Broadcast

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PICTURE QUALITY – BLACK & WHITE TV

BROADCAST

 

In the early ‘30s the thought of combining movie theatre experience with radio broadcasting in order to bring

home full audio video entertainment occupied the mind of innovative thinkers at the time.

 

Whereas movies were being projected onto a large screen one picture at the time, 24 images per second,

the same notion would not work getting that feed into individual households. What had been working then was

radio frequency transmission.

 

The idea of television consisted of capturing an image electronically one dot at the time given its amount of

generated luminosity between white to black and the entire intricate grey scale in-between, transmitting it

over-the-air, receiving it and displaying it on the TV monitor. In a similar fashion one could relate understanding

concept of newsprint.

Due to frequency spectrum limitation the Federal Communication Commission (FCC) mandated no more

than 6MHz per channel/station regardless radio or television.

 

NOTE: 6MHz signifies 6 Mega Hertz. One hertz is a unit of cycle per second. 6MHz means there can be up to

6,000,000 different electrical impulses sent per second.

 

Accommodating mandated restrictions, engineers believed they needed to deliver 30 images per second

given that movies got away with 24. Each images required be scanned 525 lines top to bottom, 45 of which

kept invisible hence the 480 standard. Each scan line would consist of 370 pixels, 40 of which invisible.

The equation:

 

     30 images per second  x  525 scan lines  x  370 pixels  =  5,827,500 Hertz

 

 

When first tested in studio there was so much flickering appearing on screen it blinded the engineers forcing

them to turn away or turn off the monitor. There was no way that prototype would make it into any American

household without being trashed in seconds flat.

 

Going back to the improvement methods made in film, engineer proceeded to increase the number of images

per second until eliminating flickering. 40 images per second did the trick.

 

The second phase of the experiment consisted in moving the studio receiver monitor in somewhere close by in

the neighborhood yet distant to test broadcast reception. No matter how much they tried the experiment bombed.

Realizing they were exceeding allowable bandwidth and cognizant they couldn’t return to 30 images per second,

a clever engineer proposed sending half the image at the time. Not top, bottom, top, bottom and so forth but odd

lines, even lines, odd lines, even lines and so forth. Interlaced scanning was invented. 2 fields equalled one full

image. Plus, broadcasting 60 fields per second matched North American electrical standard of 60Hz.

       

So if you ever wondered why in the age of analog TV broadcasting it didn’t take long feeling a headache

materializing further to watching too much television, it was because although eyes were fooled in seeing

motion, the brains however had to strain and work overtime recreating the missing information.

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