Modern displays use a grid of pixels that emit light to create images, controlled by circuits and transistors. Old-school TVs, like CRTs, didn't use pixels or digital circuits but still displayed images using cathode rays and phosphors. CRTs manipulate an electron beam's brightness and position with magnetic fields to draw lines on the screen, creating an image through persistence of vision. The TV signal includes blanking intervals that are 'blacker than black' to help synchronize the image, and audio is transmitted as FM radio. Overscan hides the blanking intervals, ensuring the whole screen is used.
Here are the key facts extracted from the text:
1. A modern display uses a grid of millions of pixels to create an image.
2. Each pixel can have instructions sent to it to control its brightness.
3. The instructions are divided into three values for red, green, and blue to create different colors.
4. Analog television predates World War II.
5. CRT stands for cathode ray tube.
6. The cathode ray tube was invented by Johann Hittorf and William Crookes.
7. The electron gun generates a stream of electrons in a CRT.
8. The flyback transformer generates an extremely high voltage to attract electrons to the front of the screen.
9. The inside surface of the tube is coated with a special powder called a phosphor.
10. When electrons hit the phosphor, it emits light via fluorescence.
11. The deflection yoke is responsible for moving the electron beam around the screen.
12. The yoke contains two electromagnets that work together to move the beam.
13. The electron beam is deflected left and right 15,750 times per second in NTSC televisions.
14. The electron beam is deflected at a frequency of 60 Hz in NTSC countries.
15. The refresh rate of a television is determined by the frequency of the AC electricity.
16. A CRT television has a refresh rate of 60 Hz in NTSC countries and 50 Hz in PAL countries.
17. The image on a CRT television is made up of lines, not pixels.
18. There are roughly 525 lines that make up the NTSC signal.
19. The deflection yoke draws a pattern on the screen called a raster.
20. The raster is drawn 60 times a second in NTSC countries.
21. The screen is only completely redrawn 30 times a second.
22. The principle behind interlaced video is that the screen is drawn from top to bottom 60 times a second.
23. The vertical deflection is not happening in steps, but is a constant downward motion.
24. The deflection yoke is mounted to the tube slightly crooked to counteract the downward motion.
25. The constant downward travel is how the interlacing is accomplished.
26. The TV signal contains triggers to assist the TV in grabbing hold of the image and keeping it in one place.
27. The blanking intervals between scan lines are used as a reference for the beginning and end of a scan line.
28. The blanking intervals are used to prevent anything from being drawn on the screen as the deflection yoke sweeps the electron beam back to the left-hand side.
29. The TV signal contains a vertical blanking interval, which is used to allow the deflection yoke time to get back to the top of the field.
30. The vertical blanking interval contains special pulses to differentiate between the odd and even numbered fields.
31. The CRT is scanning outside the borders of the face of the tube, which is called overscan.
32. Overscan is done to hide the blanking intervals and ensure the whole screen is being used.
33. Closed captioning was added to television broadcasts using the overscan area.
34. A decoder inside the television set could read digital text information from the overscan area and place text graphics on top of the image.
35. Audio in a CRT television is transmitted at a set offset frequency from the video source.
36. The audio signal is always in sync with the video signal because they are transmitted together.