Need to know about 60i, 30P, and 24P

[Melissa Van Groenenbergh]

Can some one explain the difference between60i, 30P, and 24P? We have only ever shoot in 60i, and we have a shott coming up and I was wondering how 30P works. Can some one help me? Everything I can find on the Internet hasn't helped explaining the difference.

[John Ealer]

With the SDX-900, you need to keep in mind that the camera sampling mode (60i, 30p, 24p) is separate from the VTR recording mode. The VTR in the camcorder always records 59.94 fields per second, so no matter what mode you shoot in (60i, 30p, 24p) you have a NTSC signal on tape that can be viewed on any NTSC television. The different camera signals (60i, 30p, 24p) are converted to 59.94i for recording. For the purposes of this explanation, I'm not going to get into the .1% speed difference between 60i and 59.94i.

 

When the camera is set to 60i, the camera samples 60 interlaced fields (212.5 lines) a second, in the odd-even alternation you're accustomed to. Keep in mind two consecutive fields, while part of the same frame, are temporally offset by 1/60 of second; i.e. the odd field is a picture of what happened 1/60 of second after the even field.

 

When the camera is set to 30p, the camera samples 30 complete 525-line (480-active line) frames a second. These complete frames are then divided into odd and even fields before being recorded as interlaced fields by the VTR. In 30p mode, the odd and even fields as recorded on tape are not temporally offset whatsover. Both fields are samples of the exact same moment in time.

 

When the camera is set to 24p, the camera samples 24 complete 525 lines (480 active line) frames per second. These complete frames are then "pulled down" via a traditional 2:3 pulldown process to before being recorded to tape at 59.94i. In 24p, the first frame will be placed into the first two fields, the second frame will be put onto the next three fields. [When the camera is set to 24pa mode, the "advanced" pulldown scheme of 2:3:3:2 is used.]

 

I've shot all these modes with the camera many times. 60i obviously feels very much like "video". 30P has a more "filmic" (a dangerously abstract term, I know) look, but has less of the flickering artifacts that 24p might have. They all look good, depends on what you're going for.

 

J

[Gordon Highland]

Do you understand difference between interlace and progressive?

 

Interlace (i) uses two fields per frame, one containg the odd-numbered lines and one with the even-numbered lines. Put these together, and you get pretty realistic motion with that "video look" you're so accustomed to seeing on the news and reality programming and such. Progressive (p), whether 24 or 30, is produced one whole frame at a time by the sensors (like film), however, it is still recorded onto the tape at 29.97 fps by distributing those 24 images over 60 fields in one second using a pattern called pulldown. Upon capture, your editing software removes this pulldown, giving you the actual full frames to work with, and in the case of 24p, a 20% smaller file size.

 

Progressive-scan images sometimes suffer from a stuttery, strobed kind of look when there's a lot of action or camera movement (like film), but tends to look more dramatic and higher-resolution as well (it also requires a little more light in 24p). Still images look better in progressive mode, and sometimes in interlace you'll get a still image that looks very jaggy because the two fields you're seeing represent two slightly different places in time on every other line.

 

EDITED: Yeah, what he said. :) Dontcha hate it when you get beat to the punch?

Edited August 8, 2005 by Gordon Highland

[Steve Ford]

Is it just me, or does the picture look more rich in progressive mode. I see deeper colors and richer blacks without a muddy look.

[Daniel Andreas]

Can some one explain the difference between60i, 30P, and 24P?  We have only ever shoot in 60i, and we have a shott coming up and I was wondering how 30P works. Can some one help me? Everything I can find on the Internet hasn't helped explaining the difference.

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This link be helpful to visualize the concept of Interlaced v.s. Progressive imaging.

 

http://www.avdeals.ca/classroom/Proscanexplained.htm