60i or 24P?

[Ron Evans]

Originally Posted by Bob Willis

I don't believe so Shaun.

"The field rate of 1080i is typically 60Hz for NTSC countries (such as United States, Canada and Japan) or 50Hz for PAL/SECAM countries (such as in Europe, Australia, much of Asia, Africa). Because of this the two most common frame rates are 30 frames per second or 25 frames per second. Both variants can be transmitted by both major digital television formats, ATSC and DVB. The frame rate can be either implied by the context or specified after the letter i, such as "1080i30". The European Broadcasting Union (EBU), prefers to use the resolution and frame rate separated by a slash, as in 1080i/30 and 1080i/25, likewise 480i/30 and 576i/25."

See what I mean about confusion!!!! As I said in my earlier post field rate of 60 is the rate at which the camera operates ie 60 frames a second but it only transmits half the vertical resolution in a field. You can't add two consecutive fields and get a frame, they are 1/60sec( or 1/50 in Europe/PAL countries) apart!!!! One can CALL this a frame by convention but to assume this is a technical fact is incorrect. An interlace stream is missing half the information and without the other designed end of the chain( the CRT phosphors and our eyes and brain) the process doesn't work the way it was intended. IT was designed to have the motion characteristics of a higher frame rate than film ( ie 60fps) but only use half the bandwidth. One might call it an analogue compression decompression scheme. Deinterlacers that assume these interlaced fields are from the same frame to produce, 30P or 25P, output terrible results with juddering motion as expected. The only way to get close to the image produced by a CRT is to delinterlace to the equivalent of 60P or 50P for display on a modern flat panel display. Hence the move to 120hz LCD and the sub field drives of the Plasma displays. A side benefit is these refresh rates are nice whole numbers of 24fps for correct reproduction of film transfers as well.

Ron Evans

[Shaun Roemich]

Thanks for the clarification Chris. There are SO many half truths about displays and video in general out there I try to nip the ones that are not entirely accurate in the bud. WAY too many of my clients have required "deprogramming" over the years because of something they read on the internet...

[Shaun Roemich]

Originally Posted by Ron Evans

As I said in my earlier post field rate of 60 is the rate at which the camera operates ie 60 frames a second but it only transmits half the vertical resolution in a field.

Again, not accurate. The camera (assuming interlacing) images the half resolution 60 times per second (for NTSC) AND THEN grabs the alternating lines on the next pass. Your statement about not having a temporally complete frame is accurate but any discussion of NTSC video being 60 FRAMES per second is wrong. PERIOD. 60 fields/30 frames. I'm sorry to be difficult on this but any misrepresentation of fields and frames is wrong.

[Ron Evans]

Originally Posted by Shaun Roemich

Again, not accurate. The camera (assuming interlacing) images the half resolution 60 times per second (for NTSC) AND THEN grabs the alternating lines on the next pass. Your statement about not having a temporally complete frame is accurate but any discussion of NTSC video being 60 FRAMES per second is wrong. PERIOD. 60 fields/30 frames. I'm sorry to be difficult on this but any misrepresentation of fields and frames is wrong.

I have a full understanding of fields and frames. I did not say NTSC is 60 frames a second. NTSC is 60i. The missing fields are permanent. You can't add consecutive fields and get 30 full frames. I said the camera is taking pictures at a rate 60 frames a second ( which it is, whether that is half the resolution,a field or full like some of the latest cameras and then decide what they will output the Panasonic HMC150 for example if I am to believe the information) Each camera operates differently. How the camera images the scene is irrelevant only that it transmits a field every 1/60 a second. Frame rates to me mean full progressive frames just like a film camera would take. NTSC 60i is NOT 30P. By convention it is 30 frames( two fields = a frame) which bears no resemblance to the temporal motion of 30 frames a second it just happens to be numeric,60 fields divided by 2 = 30frames. The temporal motion is that of a 60 frames per second capture not a 30 frames per second capture. Hence the terrible confusion and technology problems of deinterlacing for flat panel displays. We are getting hung up on whether a frame is FULL or partial. To me if the camera shutter opens 60 times a second and the camera records this, it is operating at 60 frames a second. What it records is something else, it could be a field or a full frame and what it transmits/records to tape or memory could be something else entirely.
I too am sorry for continuing this topic but there is a big difference between 60i(30frames) and 30P. IF the NTSC 30frames isn't 30P what is it? IT isn't 30i because that would be 15frames..........I will accept the convention. 60i is 30frames as a name only because 2 fields is 1 frame( even if they didn't come from the same full progressive frame).

Ron Evans