Polarman
Joined: 24 Jun 2005
Posts: 55
Location: Barbados |
| Week 2 - Television |
 |
|
Please add answers to these questions below
1. How are moving pictures created using film?
2. What is persistence of vision?
3. How many images per second are necessary to give the illusion of smooth motion?
4. If the frame rate is sufficient to ensure smooth motion, what problem remains?
5. What flicker rate is necessary so that the image is perceived by the eye to be constant brightness?
6. How is the necessary flicker rate achieved in film?
7. Are these frames and flicker rates totally adequate?
8. In television, what is the problem in transmitting a picture via a wire or single broadcast channel?
9. What is scanning?
10. What is a line?
11. What are pixels?
12. What is a raster?
13. What is a frame?
14. What is a sync pulse (line sync and field sync)?
15. What is the frame rate for PAL?
16. What is the frame rate for NTSC?
17. How were these frame rates derived?
18. How is the flicker rate increased in TV?
19. What is a field?
20. What is the blanking interval?
21. Describe field sync pulses.
22. How many lines are there in a frame (PAL and NTSC?
23. How many lines are visible (PAL and NTSC)?
24. What is bandwidth?
25. What is the bandwidth of a TV signal (PAL and NTSC)?
26. Describe the monochrome video waveform?
27. What is the range of voltages used?
28. What is the voltage of the sync pulse?
29. What is the voltage of range of the image portion of the signal?
30. What is the front porch?
31. What is the back porch?
32. Why are the porches necessary?
33. How does the eye perceive colour?
34. What are the additive primaries?
35. Compare sodium vapour yellow with the yellow produced by a street lamp.
36. What is RGB?
37. Why are television images not transmitted in RGB?
38. When colour television was invented, why did transmissions have to be compatible with monochrome receivers?
39. Describe luminance and chrominance.
40. How was the colour information slotted in to the existing signal?
41. Describe NTSC
42. Why was the frame rate changed for NTSC?
43. Describe PAL
44. Describe Y = 0.3R + 0.59G + 0.11B
45. Describe U = 0.49(B - Y) and V = 0.88(R - Y)
46. Compare I (orange-cyan 1.3MHz) and Q (green-purple 0.4MHz)
47. Describe how the chrominance signals can be recombined with luminance to produce RGB.
48. Describe the problems with NTSC and the solutions in PAL.
49. Draw the colour television waveform.
50. Describe the action of the colour burst.
51. Describe SECAM |
Sun Mar 12, 2006 8:53 pm |
|
|
JakoBee
Newbie
Joined: 19 Apr 2007
Posts: 4
|
|
|
|
Please add answers to these questions below
1. How are moving pictures created using film?
By putting a series of still pictures together and displaying them, fast enough for the eye to conceive them as a moving.
2. What is persistence of vision?
The theory of the human eye’s retina, keeping images for split seconds, for the brain to conceive the image. When pictures are displayed fast enough it perceives the illusion of movement.
3. How many images per second are necessary to give the illusion of smooth motion?
8-12 images are needed to create the sense of motion, but for the sense of smooth motion you’ll need 24-30 frames pr. Second.
4. If the frame rate is sufficient to ensure smooth motion, what problem remains?
Flicker perception.
5. What flicker rate is necessary so that the image is perceived by the eye to be constant brightness?
I’m not sure how to understand the term - constant brightness –
Could be when no black periods are seen.
In this case the answer would be: 40-60. Depending on the amount of light in the room you are weiving the screen.
6. How is the necessary flicker rate achieved in film?
Via Interlacing. Adding one frame of bright light, pr. frame, so the flickering isn’t perceived. In cinema they use two flashes pr. Frame, so the total fps. in cinema is 76
7. Are these frames and flicker rates totally adequate?
To most people yes, however there are some people who still experiences flickering at those framerates. Again it all comes down to the external lighting.
8. In television, what is the problem in transmitting a picture via a wire or single broadcast channel?
Power consumption.
9. What is scanning?
Scanning is done to create an interlaced video display, for us to see the TV picture.
The process of taking images apart and putting them back together again is called scanning.
10. What is a line?
Each frame consists of lines, in PAL 625 NTSC 525. The more lines, the better the resolution.
The lines are what the scanning reads to project a picture.
11. What are pixels?
PICture Element. the smallest spot on the screen that can be resolved as having a different brightness or color from what is next to it.
12. What is a raster?
The electronic beam that scans the regtangular area of the TV screen, and thereby creates the TV picture we see.
13. What is a frame?
The complete picture, consisting of all the lines.
14. What is a sync pulse (line sync and field sync)?
Line sync: The sync pulse is inserted horizontally at the end of every line, telling the Raster beam to draw the next line.
Field sync:
Is When a field is complete a vertical pulse is transmitted, telling the beam to draw a new field.
15. What is the frame rate for PAL?
25
16. What is the frame rate for NTSC?
30
17. How were these frame rates derived?
NTSC By the US Government and Industry Committee
PAL- was developed by Walter Bruch at Telefunken in Germany in 1963
18. How is the flicker rate increased in TV?
By interlacing. Every picture divided into 2 fields, which is drawn twice as fast. Resulting in twice as many flashes thereby, flicker rate is increased.
19. What is a field?
Either the odd or even lines of an image (Half the picture)
20. What is the blanking interval?
The short period where the electron beam is shut down, to avoid stray marks onscreen when it returns to the top or left side of the screen.This short period is also used to carry data.
21. Describe field sync pulses.
Vertical sync Pulse
Field sync occurs at each retrace of the beam.
22. How many lines are there in a frame (PAL and NTSC?
PAL - 625. NTSC - 525
23. How many lines are visible (PAL and NTSC)?
PAL - 576 NTSC – 483 – They can both vary.
24. What is bandwidth?
Refers to the frequency range, from the lowest to the highest signal frequency.
25. What is the bandwidth of a TV signal (PAL and NTSC)?
NTSC – 4,2 - 6,75Mhz - PAL - 5Mhz
26. Describe the monochrome video waveform?
The monochrome video signal is a combination of two signals, the sync pulses and the black and white intensity information called luminance.
27. What is the range of voltages used?
Where?
28. What is the voltage of the sync pulse?
0.3 V
29. What is the voltage of range of the image portion of the signal?
?
30. What is the front porch?
The few milliseconds of zero signal after a scanline. (top to bottom)
Its purpose was to allow voltage levels to stabilise in older televisions, preventing interference between picture lines.
31. What is the back porch?
The few milliseconds of zero signal after a scanline. (left to right)
It was originally allocated to allow the slow electronics in early televisions time to respond to the sync pulse and prepare for the active line period
32. Why are the porches necessary?
Porches is used to establish a reference for black level. And to stabilize the signals for older TV’s.
33. How does the eye perceive colour?
Through the three different conetypes, one for reddish, one for greenish and one for blueish colors.
34. What are the additive primaries?
Red, Green and Blue
35. Compare sodium vapour yellow with the yellow produced by a street lamp.
Well it is the same basically. Theres low pressure sodium and high pressure sodium. High pressure sodium lamps contain mercury, which gives it a different color when started, these are the ones used for streetlights and security lights.
36. What is RGB?
A colorstandard, where other colors are produced when mixing Red Blue and green.
37. Why are television images not transmitted in RGB?
This would require a bandwith 3 times the size of the current bandwith.
38. When colour television was invented, why did transmissions have to be compatible with monochrome receivers?
Cause monochrome was still the standard broadcast transmission, therefore most people had monochrome receivers in their TV sets.
39. Describe luminance and chrominance.
Chrominance=Color. Luminance= Black and White
40. How was the color information slotted in to the existing signal?
Via the Chrominance signal (C)
41. Describe NTSC
National Television System Committee – 525 lines. 30 Fps. Used mainly in the USA and Japan.
42. Why was the frame rate changed for NTSC?
It was changed from 30 fps. To 29,97 Fps. when the color TV was introduced. It was done to implement the color information.
43. Describe PAL
Phase Alternate Line. Used in most of the world, primarily in Europe.
625 lines. 25 Fps.
44. Describe Y = 0.3R + 0.59G + 0.11B
Video signal representing Luminance. RGB Used by NTSC Before color TV.
45. Describe U = 0.49(B - Y) and V = 0.88(R - Y)
U and V is 2/3 of the signal YUV, which actually is the component video signal. The YUV is a way to convert the RGB signal to reduce the transmission and storage requirement. and it is said to be without any losses of quality, because the human eye cannot percept it.
46. Compare I (orange-cyan 1.3MHz) and Q (green-purple 0.4MHz)
I and Q are synonyms for U and V
47. Describe how the chrominance signals can be recombined with luminance to produce RGB.
Via the YUV somponent video signal the the U and V are integrated into the the Chrominance signal (C). The TV-reciever reproduces that signal to RGB when projecting the signal.
48. Describe the problems with NTSC and the solutions in PAL.
Reception problems, can cause a colordegrade or alteration of phasecolors. Unless a Tint Control device is used on the TVset. This is not necessary on PAL.
Colorburst is a signal transmitted in NTSC to tell the receiver how to recombine the colors. Not necessary in PAL.
49. Draw the colour television waveform.
** - Draw where?
50. Describe the action of the colour burst.
Colorburst is a signal used to keep the chrominance subcarrier synchronized in a color television signal.
By synchronizing an oscillator with the colorburst at the beginning of each scan line, a television receiver is able to restore the suppressed carrier of the chrominance signals, and in turn decode the color information.
51. Describe SECAM
A 625 line 50 interlaced field per second analog broadcast standard used in Europe, primarily in France. |
|
Thu May 03, 2007 12:38 pm |
|
|
|
|
AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
|
| Good week |
|
|
A very good start you have made here, really excited to have seen your work, and so quickly!
If you feel good please continue, also note we generally have time towards the end of the course to ensure that we have clean up any areas if we need.
So far so good!!
_________________
It's all in the ears. - Learn the concepts not the software.
Audio Courses is a way into the music business for you
|
|
Mon May 07, 2007 1:15 am |
|
|
 
|
|
All times are GMT. The time now is Sat May 17, 2008 6:01 am
|
|
|
|
| |
