1080i/60p

[Timothy Lou Ly]

1080i AND 60p? I don't understand this.

 

Just to clarify some things:

 

1080 is the resolution of the video correct? The "i" means that it is being recorded in interlaced format or will be broadcasted in interlaced format?

 

60p? 60 frames per second in progressive? If it were 60i it would really be mean 60 fields/30 fps right?

 

So how can it be recording 60 fps progressively, yet have 1080 interlaced resolution? Does it just mean that the 60p will be converted into interlace format and become something like 120i or 120 fields?

 

What am I not understanding here, or what is it that I'm getting wrong?

 

Please help!!!

Edited April 10, 2009 by Timothy Lou Ly

[John Sprung]

Indeed you're right. This combination of terms is nonsense. It's impossible for something to be both progressive and interlaced at the same time. It's like those TV commercials where somebody wants a cab ride to the airport and downtown at the same time.

 

However, there is one major manufacturer of consumer equipment that uses that revolting verbiage. What they mean by it is pretty much the same thing that Sony means by "Segmented frame". The image content is actually progressive. But they read the data out as if it were two fields, which can be re-assembled to make a complete frame. That lets them send progressive images through the legacy interlaced plant. If you were to display it as interlace, it would have interline flicker like crazy unless the actual content was soft.

 

The way the numbers work is that they have 30 true progressive frames, 30p, which they record as 60 "Segments" in Sony's use of the term, or as if it were 60i, which it isn't.

 

So, rejoice -- you're smarter than some camera companies. ;-)

 

 

 

 

-- J.S.

[Timothy Lou Ly]

Indeed you're right. This combination of terms is nonsense. It's impossible for something to be both progressive and interlaced at the same time. It's like those TV commercials where somebody wants a cab ride to the airport and downtown at the same time.

 

However, there is one major manufacturer of consumer equipment that uses that revolting verbiage. What they mean by it is pretty much the same thing that Sony means by "Segmented frame". The image content is actually progressive. But they read the data out as if it were two fields, which can be re-assembled to make a complete frame. That lets them send progressive images through the legacy interlaced plant. If you were to display it as interlace, it would have interline flicker like crazy unless the actual content was soft.

 

The way the numbers work is that they have 30 true progressive frames, 30p, which they record as 60 "Segments" in Sony's use of the term, or as if it were 60i, which it isn't.

 

So, rejoice -- you're smarter than some camera companies. ;-)

 

-- J.S.

 

Hmm. I'm still trying to grasp this, here. So what they simply mean by 60p is that it really is 30 true progressive frames but will be sent out as 60 "segments" so it can be read by 1080i, and that this isn't truly 60 progressive frames?

 

As you said, it can be re-assembled to make a complete frame, which would end up to be 30 frames. Now how does that differ from 60i? Is it just that the recording process truly does record in progressive instead of interlace right off the bat? Oh, and also when it's re-assembled, is it compatible with 1080p as well as 1080i?

Edited April 10, 2009 by Timothy Lou Ly

[John Sprung]

Hmm. I'm still trying to grasp this, here. So what they simply mean by 60p is that it really is 30 true progressive frames but will be sent out as 60 "segments" so it can be read by 1080i, and that this isn't truly 60 progressive frames?

 

As you said, it can be re-assembled to make a complete frame, which would end up to be 30 frames. Now how does that differ from 60i? Is it just that the recording process truly does record in progressive instead of interlace right off the bat? Oh, and also when it's re-assembled, is it compatible with 1080p as well as 1080i?

 

Right, 60 progressive frames is twice as much data as 30p or 60i. It's a stretch to do 60p in high end pro gear, let alone consumer stuff. So, they're definitely not talking about real 60p. They mean 30p, but recorded as if it were 60i. Yet another reason why this is dumb and disgusting.

 

The big differences between true 60i and 30p recorded in the 60 "segments" that work sort of like fields method are:

 

1. The segments that make up a progressive frame are both from the same time sample. Moving objects are in the same position in both segments. Interlaced fields represent two different times, 1/60 second apart. Moving objects are in different places in the two fields of interlaced TV, so if you try to just put them together, their edges get "mouse teeth".

 

2. The image content of 60i has to be low pass filtered to a lower resolution than 30p, because the Nyquist limit for 60i is lower. To do it absolutely right, you'd have to cut the i resolution to exactly half of the p resolution. But, funny thing, people accept a little bit of interline flicker, which means that you can get away with more like 65% instead of just 50%. That's the whole reason for interlace in the first place. That's a kind of lossy compression that works in analog, so it was a useful way to get sharper pictures back in the 1930's when this stuff was developed. Interlace was the right answer for half a century. Now that we have digital compression, it does more harm than good. We can do better compression with less loss, interlace just interferes with that.

 

 

 

-- J.S.

[Timothy Lou Ly]

Ah, I understand now! Thanks a ton!!!

 

One more thing though...

So how about the 25f or 25p (which is the official term?) that the Canon XH-A1 has? Is that 25 true progressive frames? Also, I heard or read somewhere (can't remember which) that it wasn't compatible with FCP - is that true?

[Phil Rhodes]

25f is a simulation of 25p that has somewhat lower resolution than real 25p would have under otherwise identical circumstances.

 

Actually the Canon 25f isn't completely disgusting, but it's not ideal.

 

P

[Mei Lewis]

I have a related question someone may be able to answer.

 

In Premiere Pro CS3 all of the project presets relating to 1080 HDV (which I assume is just short for High Definition Video) have non square pixels,

"Pixel Aspect Ratio: HD Anamorphic 1080 (1.333)". The two 720 options have square pixels. Why is this?

 

I was trying to make a project with some files from my Canon 5Dmk2 which I shot at full HD 24p, which I think is 1920x1080, progressive, with square pixels, and actually 23.976 frames per second prgressive. I wanted the output to be the same as the input and had to make up a custom preset.

 

Is the non-square pixel issue something to do with a broadcast format?

[John Sprung]

This particular one, with a 1.333:1 pixel aspect ratio, doesn't come from a broadcast format. I don't know why anyone would mess around with non-square pixels any more.

 

Back in the standard definition days we used the same horizontal count for both NTSC and PAL/SECAM: 720 x 483 for NTSC and 720 x 576 for PAL. This yields pixel aspect ratios of 1.12:1 and 0.94:1. They're not as far out of square, and therefore not as inefficient as 1.333:1.

 

 

 

 

-- J.S.

[Mei Lewis]

So what's is the 1.333 ratio all about?

[Jim Hyslop]

So what's is the 1.333 ratio all about?

From what I've seen, it's a way some cameras cheat to get 1080x1920 resolution. They actually record at 1080x1440, with a pixel aspect ratio of 1.33:1. Map every 3 camera pixels into 4 monitor pixels and you get 1920 pixels horizontally. Kind of like a digital version of anamorphic lenses.

 

It's also used with NTSC DV, to get a 16:9 image out of an NTSC signal. Same principle.

 

--

Jim