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Scoob

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Could someone explain the significance of these or link an article which explains them and the importance of them in relation to HD video?

namechamps

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Quote:
Originally Posted by Scoob /forum/post/0

Could someone explain the significance of these or link an article which explains them and the importance of them in relation to HD video?

fps = frames per second

hz = measure of rate with interval length of 1/interval per second.

A movie has 24fps, if changes frames at 24hz

TV operate at 60fps, changes images at 60hz.

While not exactly right fps and hz can be used interchangeably.

Why this is important to movies & HDTV is that unless the TV can accept an input and display in a multiple of 24 then there will be some jerkiness in the playback due to 3:2 pulldown. Some people never notice it. I can only see it on slow pans across a repeating background.

Why this happens?

Movies on HD DVD & BD are stored as 24fps. Most (99%+ TV in US) run at 60hz. To output 60fps a 3:2 pull down applied.

Frames on Disk: A B C D E F (6 frames = 1/4 sec @ 24fps)

Frame in output: AAA BB CCC DD EEE FF (15 fames = 1/4 sec @ 60fps).

To simply the issue the jerkiness comes from the fact that in the above example the A C E frames are displayed on your TV longer than the B D F fames. In the original film all frames are displays the same amount of time = 24hz (1/24 second).

Some BD players can output 24fps. To take advantage of this your TV would need to accept a 24fps input and have a panel that can run at a multiple of 24fps. No TV displays 24fps because it is too slow and would cause flickering. If the TV displays at 72hz or 120hz it is an exact multiple of the original film. In the above example a 72hz display would output each frame 3 times (AAABBBCCCDDDEEEFFF). A 120hz display would output each frame 5 times.

Some TV as a marketing tool will accept a 24fps input but their panel runs at 60hz. They essentially just perform the 3:2 pull down internally. To get true 24fps playback the source, output, input and display must all be 24fps.

120hz panels could be considered the most compatible panels because 120 is an exact multiple of 24, 30, 60 the 3 most common methods of film/video distribution.

benwaggoner

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Also, note that "24p" for video content is normally 24/1.001, typically rounded to 23.976 (but really 23.97600239760023976...).

Craig F

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Quote:
Originally Posted by namechamps /forum/post/0

each frame last for 24hz.

That makes no sense. Each frame lasts for 1/24 of a second at 24 Hz. Otherwise, good post

namechamps

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Quote:
Originally Posted by Craig F /forum/post/0

That makes no sense. Each frame lasts for 1/24 of a second at 24 Hz. Otherwise, good post

Corrected this film changes frames at 24hz.

Robert George

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120hz panels could be considered the most compatible panels because 120 is an exact multiple of 24, 30, 60 the 3 most common methods of film/video distribution.

It is now being reported that at least some of the new 120Hz panels are in fact not refreshing a 24Hz signal natively, but are actually simply doubling the normal 60Hz refresh rate. In other words, the same video processing for 60Hz is used but the panel refresh is doubled to look a bit smoother.

Scoob

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Thanks everyone, that was very informative.

namechamps

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Quote:
Originally Posted by Robert George /forum/post/0

It is now being reported that at least some of the new 120Hz panels are in fact not refreshing a 24Hz signal natively, but are actually simply doubling the normal 60Hz refresh rate. In other words, the same video processing for 60Hz is used but the panel refresh is doubled to look a bit smoother.

Yeah I saw that on the new samsungs. Very disapointing.

It will be a while before 24fps is mainstream.

zambelli

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Quote:
Originally Posted by namechamps /forum/post/0

Corrected this film changes frames at 24hz.

At recording time, yes. At projection time, it's projected at 72 Hz (triple-blade shutter) or 48 Hz (double-blade shutter). Never at 24 Hz.

ChrisWiggles

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Quote:
Originally Posted by namechamps /forum/post/0

fps = frames per second

hz = measure of rate with interval length of 1/interval per second.

A movie has 24fps, if changes frames at 24hz

TV operate at 60fps, changes images at 60hz.

While not exactly right fps and hz can be used interchangeably.

TVs do not operate at 60frames per second. Video is 30fps interlaced, at 60hz. fps and hz cannot be used interchangeably. fps is the framerate, the latter is the refresh rate. They are not the same thing.

denness544

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So what displays can handle 24fps perfectly?

namechamps

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Quote:
Originally Posted by ChrisWiggles /forum/post/0

TVs do not operate at 60frames per second. Video is 30fps interlaced, at 60hz. fps and hz cannot be used interchangeably. fps is the framerate, the latter is the refresh rate. They are not the same thing.

Most HDTV are progressive and display 24 or 60fps content at 60hz. They are almost never interlaced. My TV takes a 60fps input and outputs it at 60fps. The TV refreshes at 60hz. Going forward the number of HDTV that are interlaced will approach 0%.

ChrisWiggles

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Quote:
Originally Posted by namechamps /forum/post/0

Most HDTV are progressive and display 24 or 60fps content at 60hz. They are almost never interlaced. My TV takes a 60fps input and outputs it at 60fps. The TV refreshes at 60hz. Going forward the number of HDTV that are interlaced will approach 0%.

My point is that video is not 60fps, which you seem to maintain. It is 30fps. You are correct that this is likely displayed at 60hz.

John Mason

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My year-2000 CRT HDTV (Philips 64PH9905), like many consumer-electronics TVs, displays 1080/60i HD at 60 fields per second and my eyes/brain merge two TV fields/frame into a frame rate of 30 Hz. Such interlaced displays show 1080i at 60 fields per second whether 2-3 pulldown (duplicate fields) is being used to deliver 24p movies or 1080/60i (30i) images from TV cameras (or 720p converted to 1080i by my cable STB). Glimmie has pointed out that some digital projectors for theaters only display at 24 Hz (since progressive flat panels or microdisplays needn't be refreshed to avoid flicker).

In table 6.1, Charles Poynton's 2003 Digital Video and HDTV lists the refresh (flash) rates of TV at 50 or ~60 Hz, with frame rates of 25 or ~30 Hz, respectively. For cinemas, the table lists the refresh (flash) rate of 48 Hz and a frame rate of 24 Hz. As mentioned above, sometimes films are projected at higher refresh rates.

My RPTV only deinterlaces 480/60i to 480/60p with a Genesis microcircuit. Later CRT RPTVs, to trim manufacturing costs, began displaying 480i at 540p and other formats. -- John

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