All You Wanted To Know About Resolution...Maybe (1 Viewer)

[Alex Antin]

I have been reading posts that deal with the question of Resolution of HDTV, 35 MM Film, etc. I thought it might be helpfull to put down some of the facts...and myths of Resolution.

First off, resolution is determined by 3 factors:

1. How many lines make up the image (called Vertical Res.)

2. How many Pixels can fit on a line (called Hort. Res.)

3. How many images are shown in a second of time (called Frame Rate.)

35 MM film according to Eastman Kodak is measured at 2000/2500/24. That means 2000 lines with 2500 pixels per line at 24 frames per second. Sounds impressive but where film falls off is the size of the image that is projected at the local Cinema. To fill the screen the frame of 35 MM film has to be blown up to over 200,000 times its normal size. In large theaters like in LA and NYC to it over 300,000 times.

HDTV is 1080/1920/30. This is considered 1080P with the P meaning Progressive. This means that a complete frame is shown once every 30th of a second. 1080I is interlace which in reality shows a complete frame every 15th of a second. It is the interlace process that fools the eye into seeing a higher frame rate than actually exists.

These are the 2 most popular types of HDTV and it is really too bad that the third type 720/1280/60 has fallen by the wayside because if you look at the last number...the 60...it represents 60 frames per second which is the highest frame rate ever used for commerical purposes.

Douglass Trumbull, a former special effects master (2001, Blade Runner, Star trek The movie) invented a film process called Showscan. It used 70 MM film running at 60 frames/sec. For anyone who has ever seen this and I have, It is reality...period. It matches the resolution of what the human eye can see. It was to be showcased in the movie Brainstorm but was not used. It became a short lived blip on the radar screen of film technology dominated by IMAX ( as far as quality of image).

So what is "enough" resolution? Can you see the difference between 1080I and 1080P? The answer is yes...and no. It depends on the size of your viewing screen. On a 50"...maybe. On a 144" ..definitely...on a 34"..I don't think so.

Hope this helps.

 

[Allan Jayne]

A few minute details:

For film, lines of resolution counts just the black lines upon a white background. For video the white spaces of background in between the black lines are counted as lines also when counting lines of resolution. So the comparison with video is 2000 for film versus 540 for video, or 4000 for film versus 1080 for video.

Since the film projected in your local theater is a 4'th or 5'th generation copy, the picture is of course not as sharp as what was filmed in the camera. So picture details that were indeed 1/2000'th the frame width could well be fatter and, if juxtaposed close enough, blurred together on the film copy you are viewing although still distinguishable on the original film.

1080i shows all 1080 scan lines every 1/30'th of a second. Half of them (either the odds or the evens) are shown every 1/60'th of a second.

To reduce the human eye's perception of flicker, the 24 frames per second as shown in the theater are actually presented as 48 flashes per second, each frame flashed twice.

Film converted to video, whether 720p@60 or 1080i@30, still has 24 unique frames per second. To achieve 60 fps for 720p or 60 fields (half pictures) per second for 1080i, the film frame content is repeated, with each film frame's content used either twice or three times.

Video hints:
http://members.aol.com/ajaynejr/video.htm

 

[Holadem]

This isn't quite correct.

The interlaced picture never displays the full frame.

Alternatively even and odd lines.

Your mind does the rest.

--
H

 

[ChrisWiggles]

??? 720p hasn't fallen by the wayside at all...

It's also not really a "3rd" type if you talk about broadcast HD which is just 720p and 1080i basically in practice. 1080p content is rare, but hopefully forthcoming in larger quantities with HD-DVD and BRD.

 

[ChrisWiggles]

I forgot to add that the encode resolution label does not always represent the content resolution and form. Allen was getting at this with how film content is 3:2 encoded at video rates. It still remains 24fps content encoded at a different rate. This can also become confusing with specific exmaples like PsF (Progressive Segmented Frame) encoded content, which can appear as for instance 1080i48 but the content itself is 1080p24, as the interlaced fields are not taken from temporally-distinct captures, they are taken of the same image and split into two temporally distinc interlaced fields for transmission purposes only, but should be re-combined to progressive for display since the capture is not temporally distinct between the two fields.