Frame Rate:
Frame rate (also known as Frame Frequency) is a measurment to show how many unique consecutive images (frames) are produced in one second.
Movies/Cartoons will appear continuously (optical illusion) if they are equal or above 10 frames per second. The usual frame rate is 24 frames per second.
We have a few different standard frame rates that we will list them in this tutorial.
Flicker Fusion Frequency:
The frame rate is related to but not equal to flicker fusion rate.
Light that is pulsating below this rate is seen by human eye as "flickering" and light that is pulsating above this rate is seen as being continuous.
Few people will see flickering above 75 hertz.
So what's the connection between Flicker Fusion and Frame Rate?
The common frame rate of 24 fps (Frames Per Second) produces 48 or 72 pulses of light per second which the flickering will not be seen by most people most of the time.
Progressive and Interlace:
We have two methods to produce frames.
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Progressive: Images are produced using one pass only.
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Interlaced: Images are produced using two passes called fields.
Each field contains half of the lines in a complete frame (odd or even-numbered lines.) So when we are using 25 or 30 complete frames per second, they appear by a flicker fusion frequency of 50 or 60 Hz (50 half frames are shown in a second for 25 fps system and 60 half frames are shown in a second for 30 fps systems). The reason in the US they use 30 fps is for their 60 Hz power and same with Europe (25 fps) for their 50 Hz power.
Video systems use a more complex method called Interlaced video (which we discussed above).
So, NTSC runs at 30 fps, PAL and SECAM run at 25 fps (SECAM has 100 field lines more than PAL).
Have you ever paused on a taped video and seen that the image is flickering between two images? Yes, you have paused between two (interlaced) fields!
Modern dvd players use progressive scan. Also all computer monitors use progressive scan so the video formats are generally progressive.
NTSC, PAL and SECAM stand for?
NTSC: National Television SYstem Committee
SECAM: Sequential Color And Memory
PAL: Phase Alternating Line
More about Frame Rates:
There are three main frame rate standards in TV and movie industry.
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24p or 23.976 progressive frames per second is also a noninterlaced format. This frame rate is widely used in the movie (theater) industry and video makers because of it's cine look (blurry or motion blur look specially in action scenes.) and also because it's cheaper. If they use 30p frame rate, the movie print will be longer by %20! Why longer? Well add 6 frames for each second. Do the math! ;)
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50i is 50 interlaced fields per second and is used in Europe because of their 50Hrz power (it will produce 25 complete frames...).
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25p is 25 progressive frames per second and again is used in Europe only.
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60i or 59.94 interlaced fields per second is the standard video field rate per second (60 interlaced fields which equals to 30 complete frames). This has been used for a long time from broadcasting to camcorders and DVDs.
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30p or 29.97 progressive frames per second, will produce video at 30 complete frames per second and is a noninterlaced format.
35 mm films also use the 24p frame rate.
I'm confused! So who uses what?
I know it's just useless and stupid! Couldn't they just make ONE standard frame rate? Well I guess they couldn't!
Anyways!
PROBLEM!:
The problem is computers can play ANYTHING. They can even produce REAL 30 fps or REAL 24 fps. But in order to play it on a tape or on TV, you have to convert real 30 fps to 29.97 (or 24 to 23.976).
I'm sure you have seen both 30 fps and 29.97 fps (or 24 and 23.976) in After Effects or similar programs. That's why!
The method to convert frame rates is called simply "Frame Rate Conversion".
Frame Rate Conversion:
Ok! We have to explain another Jargon!
Remember what fps stands for? Yeap, Frames Per Second or the number of frames which will be displayed in one second.
Now we have frc.
So what is "frc"?
It stands for "Frame Rate Code". This is directly related to fps and it is used when we're dealing with fractional frame rates. It is a more convenient and accurate to give transcode a code.
Pulldown:
There are two different methods to convert the 24 fps of film to the local video standard.
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24 to 25: To convert film to European standard, the film should sped up by 4% and then matched frame per frame to video. It is also known as 2:2 pulldown because each frame of film is matched to 2 fields (1 frame) of video (Beucause of that 4% sped up, there is a slight pitch change in audio).
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24 to 29.97:
3:2 Pulldown (also known as 2:3 or 2:3:2:3 pulldown): 60i devided by 2 is 2.5 so this means that each frame of film needs to last for 2.5 fields of video. To do that first the film is slowed down to 23.98 fps. Obviously we can't have half a field so instead we alternate between frames of film lasting 3 or 2 fields in duration to make that necessary 2.5 fields.
The most commonly used codes are:
1: 23.976 (24000/1001.0)
3: 25 (25000/1000)
4: 29.970 (30000/1001.0)
Now don't get confused. For example by changing the frame rate from 29.9 to 23.9 (to watch it on TV!) the movie will not get shorter! Every frame will be displayed for a longer time period. Why? Because there will be fewer frames in the final converted movie and the display time of each frame will be longer. And the movie WILL HAVE THE SAME RUNNING.
FPS and Display Time:
|
frs |
fps |
Display Time (Sec) |
Milliseconds |
| 1 |
23.97 |
1 / (24000/1001) |
41.71 |
| 3 |
25.00 |
1 / (25000/1000) |
40.00 |
| 4 |
29.97 |
1 / 30000/1001) |
33.37 |
Things to remember:
Remember if you change a frame rate to another, the quality, shrink or size of it might need to improve too.
Future...:
Everybody's waiting for the digital TV and the new gadgets that will bring with it. I'll put the last chart to compare the TVs that we have right now that the future digital TVs.
|
Standards |
SDTV (Analog) |
HDTV (Digital) |
| Total Lines |
525 |
1125 |
| Active Lines |
480-486 (maximum visible on the screen) |
1080 (maximum visible on the screen) |
| Sound |
Two channels (Stereo) |
5.1 Channels (Surround) |
| Maximum Resolution |
720 x 486 |
1920 x 1080 |