720p59.94 to 1080i29.97

[Sean Oneil]

[Tom Brooks] “To my mind, 1080i is always going to be, in effect or in a manner of speaking, “540p60″ as it is displayed on a progressive monitor.”

That is absolutely not true. Much, if not most, 1080i is displayed as 1080p30 on a progressive monitor. Anything originating from film, for example, gets reverse telecined and converted to 1080p30.

[Tom Brooks] “If a camera is to record 1080i it will record fields that are half the resolution of the full frame”

Depends on the camera and the recording mode. Some will record 1080i with 60fps per second. But some will record 30fps. I have two video projects on our SAN right now that were shot natively on video at 1080i. One is the “540p60” type format. That was shot on HDCam. The other was shot on HDV, and that is a “1080p30” type format.

All 1080i masters originating from film is a 1080p30 type format. It is not 540×60. It is 1080 lines times 30 (with pulldown meaning there are 12 duplicate fields). Of course both “types” are the same 1080i timing signal. But one has segmented 60 half-frames, the other has segmented 30 full frames.

If you check my other posts I confirmed that the Kona 3 does indeed create a 1080p30-type format for most conversions to 1080i. It only does the 540p60-type format when the source is 720p60. Which makes sense.

[Tom Brooks] “One interesting point that all of this brings up is that any of the formats that sacrifice frame rate to achieve progressive frames (24P and 30P) also end up preserving all 1080 lines of resolution at all times (as long as you keep them away from interlaced NTSC displays). But at the expense of motion smoothness or frame rate. “

I’m under the impression that the vast majority of content is shot at 24 or 30fps. 60fps is not too common from what I can tell. I’m just going on anecdotal perception though. I really don’t know for sure.

[Tom Brooks]

Sean, I really appreciate the feedback. It has been interesting for me. Hope chrispy doesn’t mind the diversion of the thread! One area about which I have not yet found much information on the web is the way that LCD and other progressive displays process video. What are their refresh rates? What exactly is refresh rate? I’ve heard it said that most flat panels have a 60Hz refresh rate. Does that mean they put a new image on the screen every 60th of a second? Is there a period of time when the screen is black between frames? When you say an LCD displays 1080p30, does that mean that the panel has a 30Hz refresh rate? Or is it storing the frame and then displaying it twice at 60Hz? Little bits of this have been mentioned on the Cow and other places, but I need MORE. I don’t expect to find that knowledge right here and now–just making mention of the subject. Thanks for all your effort on this topic.

[Sean Oneil]

Well there’s always Wikipedia :). I’m not an engineer or anything, but from what I understand you are right. Most LCDs have a max refresh rate of 60hz. Some newer consumer TVs are 120hz. The reason for this is that 120 is an even multiple of both 30/60 and 24. This allows stutter-free playback of native 24p signals (like from a blu-ray player).

LCDs don’t flicker or display black between frames or anything like the way CRTs work. Feed it an image and it will display it indefinitely as a constant stream of light – like a lightbulb. 60 times a second it will “refresh” to see if the image has changed.