Newbie Question Regarding 1080i to 720p.
 

Hi all,

I asked a question a while ago about changing 1080i to 1080p of which I found out that I'll lose half my resolution. If I filmed at 1080i but rendered as 720p would I retain full resolution? Also - What are the advantages of actually filming 1080p instead of filming 1080i and rendering as 720p?

I ask this, as i'm looking to buy a new camera, and am torn between the V1, Z1 or Z5... I'm leaning towards the Z5, as it has all the features as the others, but does have the 1/3" chips rather than the 1/4" ones in the V1 and does have progressive. But i'd like to find out more about progressive before spending a lot of money!

I look forward to your feedback!

Ollie

From your current post and what I recollect of your other one it seems that you'd prefer to shoot progressive. If you are going to deliver progressive then shooting that way is the best way to preserve your resolution. There are some who think that there's really no reason to shoot interlaced any longer and in most situations I agree with them. The only reason I still shoot interlaced is because for action sports having fields available is good for creating slow motion footage. Without fields, you could still slow footage down but it wouldn't look as smooth.

Hello Ollie, I will try to offer what I think about these questions.

1080p has the most resolution but it is limited to two framerates, 24p/25p and 30p.

1080i has the screen size of 1080p but takes each frame, cuts it in half using every other horizontal line of pixels and alternates showing these to parts to achieve the look of a faster framerate. In PAL this would be 50 frames per second.

720p has less resolution but offers more framerates - 24p,25p, 30p, 50p and 60p

No the real important thing to consider is that the Blu-ray spec only allows for 1080p24, 1080i or 720p60, 720p50, 720p25 and 720p24.

DVD is safest as interlaced only as only some players do progressive.

The big advantage to progressive shooting is that the entire frame is intact as opposed to interlaced breaking up every other line. This offers better compression when exporting, allows for better slo-motion effects, better still frame capture and overall has a much more filmic, pleasing appearance.

When shown on an HDTV, 1080i and 720p will show basically the same amount of detail unless there is no motion then the 1080i will act like 1080p until there is motion again.

1080p on an HD tv is the best, but you have to shoot in 24p to get 1080p.

In this SD/HD crossover period, going to DVD is a real consideration and some formats translate better than others. Here is what my testing has found:

720p60 or 720p50 translate the best to DVD.
1080i can translate well if the source footage is full raster 1920x1080, not 1440x1080.
1080p24 translates well if you use the 2:3 pulldown.

I prefer shooting in progressive because it gives you more options and I like the look of it.

Interlaced has a very definite, present video look.

Welcome to the world of HD. Many options, but that means you have so much more to know to be on top of your game.

Hope this helps!

Hi Tripp,
Thanks very much for your input once again - From what you've said, it seems like it's a 'handy' thing to have being able to switch from interlaced recording and progressive? If so the Z5, still seems to be in favour.

Tim, that is so helpful - thanks ever so much!!

Here are a few questions related to your post, that are bound to open up another can of worms!

1) If I was to shoot 1080i 50 - can I render this as 720p or would this not work (If yes, then what would the FPS be? - 50?)
2) Is there any advantage to rendering a 1080p video for a standard DVD or is it only really useful for Bluray?
3) Relating to question 1, If I shot at 1080p 25, is there a way of "converting" it for DVD use to say 720p, or would it be best just to shoot at 1080i for a DVD?
4) If I wanted to film something for multiple formats e.g a stage show, would I be best to shoot progressive or interlaced? Am I right in thinking that if I shot 1080i 50, it would mean I could render interlaced for DVD, and then 720p for youtube and bluray whilst retaining good quality?

Thanks a lot for your help, I know these are newbie questions - but I want to make sure I make the right decision and know what I'm on about in the long run!

Ollie

Ollie,

A lot of your questions are dependent upon your editing software.

1) You can put 1080i footage on a 720p timeline, but the quality of your software will determine how good it looks.

2) There is an advantage to shooting 1080p for DVD. More detail in, more detail out.

3) DVD use for say 720p is sort of off here. DVD is lower resolution than 720p, so you would want to make the DVD file from oyur original 1080 content. Going to 720p would not help anything here.

It is all about capturing in a given format and trying not to change it until output to Blu-ray, DVD or web. The more your change formats, the more your software has to interpolate and the jaggies and softness start appearing.

So it is important to think of your final delivery whan you choose what framerate to shoot in.

4) Well I would shoot in a progressive format if the web is in the mix. This is another benefit of progressive shooting that I did not mention. Computers display video in a progressive manor, so having original material in progressive lets them playback in their native state.

Interlaced video can be put on the web, it is done all of the time, but it it has to be de-interlaced in the web encoding process.

I shoot events at 720p60. The footage even looks good if I throw it on a 24p timeline which makes it look like I shot it at 24p.

Most of all, you need to experiment to see the different framerates and decide what you like the best.

Ollie,

I think it's a mistake to think solely in terms of "should I shoot interlaced or progressive", and I'll try to explain why.

There are three main factors which define any given TV standard.

1/ Frame resolution - 1080 or 720 - the former has about twice as many pixels as the former.
2/ Frame rate. No of complete frames every second - 25 or 50 in European standards.
3/ Interlace or progressive.

And in isolation, it's reasonable to say that 1080 is better than 720, 50 frames is better than 25, and progressive is better than interlace.

From which, it seems that the obvious format to shoot is 1080p/50, the best of all worlds, yes? Unfortunately, no. The data rates are just too high for it to be viable with any commonly available equipment at a reasonable price. One of the factors has to be sacrified, so it becomes a case of choose two of the desirable factors out of the three,

Hence, the realistic choices become 1080p/25, 1080i/25, and 720p/50.

Next question is then likely to be "so which is best"? And the answer is (unfortunately) "it depends". IF you actively want film-look (or "jerky motion"), the obvious answer is 1080p/25. If you want smooth motion (for such as sport), both 1080i/25 and 720p/50 will give it, and they each have their pros and cons. For a sport only channel, there's a lot to be said for 720p/50, for a channel with a mix of sport and drama, 1080i/25 is a likely better choice, as it's easier to mix 1080i/25 and 1080p/25 than 720p/50 and 1080p/25 in such a case.

Either way, best to shoot at the desired final format and avoid conversions if possible.

When you refer to DVD, I'm assuming you mean a downconversion to SD? In which case, 720p/50 is best for smooth motion, 1080p/25 for "film-look".

Thanks both of you for your replies.

I believe the only available formats on the Z5 are 1080i50 and 1080p25. To achieve 720p50, would I put the 1080i50 footage on a 720p timeline in Premiere? As part of my A-Level Media coursework, I'm planning to make a short documentary about Skateboarding (Original I know haha, but i've got some cool ideas) - So I would have thought I'd be best shooting 1080i due to the movement of the skaters? (this links to my question about "converting" 1080i50 footage to 720p footage to eliminate interlacing artifacts?).

If what I said about going from 1080i to 720p was right, does this mean that I could shoot in interlaced, but if I wanted to export as progressive for the internet at a good quality, it'd be possible?

Another thing was, let's say that I decided to shoot in 1080p as I would be wanting to create bluray discs and upload to youtube, but was also asked for a DVD version... How would I go about downgrading the footage to be suitable for a DVD?

I'm just confusing myself!

Thanks a lot once again.

Ollie

In short, yes. Question then though is why do you then feel the need to go to 720p/50 at all? IF the camera shot 720p/50, it would be a different story, but I'm not sure I see why you'd want to convert to 720p for editing, then convert that to the final output format.

As far as cameras go, then I suppose there is no chance of the budget stretching to an EX, is there? Much better camera in so many ways than the others you mention, and has a good 720p mode as well as the 1080i/25 and 1080p/25 modes.

Hi David,

The EX1 is out of the question unfortunately :( I can get the Z5 for £3000 which is a struggle as i'm only a student - so the extra £1000 for the EX1 is just that step too far unfortunately.

I think i'll shoot 1080i for the documentary then, as am I right in saying that, DVD players/modern T.Vs, play back in progressive anyway to elimate any artifacts? (If this is correct, I believe I have to render the lower field first for DVDs?)

Thanks a lot,
Ollie

If the EX1 is impossible, I'd at least hang on until the 18th, Ollie. If you look in the "News" section, Sony are due to make an announcement at a Press Conference then. May turn out to be more suited to your needs than a Z5, whilst still being affordable! (Assuming it is a camera!)

See: Sony : Sony news from Inter BEE 2009 : United Kingdom

Sort of.

Remember that INTERLACED 1080 has less UPDATED pixels on the screen at a time (1440 x 1080 is actually halved to 1440 by 540 due to interlacing so 777600 per field; 1920 x 1080 is halved to 1920 x 540 for 1036800 per field. 1280 x 720 is 921600 pixels actively updated per frame (no fields in progressive)).

If you reread the original post, it deliberately splits the main attributes of an HD format into the three main parts, so in that context talking about frame resolution means exactly that - the number of pixels in each frame. No more, no less. And in that respect, a 1080 raster has pretty well twice as many pixels as a 720 raster on a per frame basis.

Framerate and interlace then become the other two main attributes.

The rest of the original post then goes on to address what you are referring to: "From which, it seems that the obvious format to shoot is 1080p/50, the best of all worlds, yes? Unfortunately, no. ..........
Hence, the realistic choices become 1080p/25, 1080i/25, and 720p/50.

In reality it's more complicated than you infer, owing to the necessity to avoid interline twitter. Scanning a chip for interlace means that lines have to be summed, but differently for different fields. Hence the lines of an even field may formed from chip lines 1+2, 3+4, 5+6 etc, the lines of an odd field from 2+3, 4+5, 6+7 etc. This reduces twitter, but also reduces vertical resolution compared to progressive scanning.

It's important to consider the three attributes separately. Too often, 1080 and interlace are just spoken of in the same breath, same with 720 and progressive. As said before, 1080p/50 would give the best of each attribute, unfortunately, it's normally necessary to compromise one of them for practical reasons.

I hope you're across this, Ollie? :-)

Hi David,

Thanks for the feedback.

So, I assume I'm just better off shooting in 1080i then rendered as 1080i and exporting a DVD from it?

My current cam is actually AVCHD, but it's a pain to edit (even though i'm using 3Ghz Quadcore, 2 GB DDR3 Ram etc)... That's one of the things that puts me off that new AVCHD cam...

True enough if you're talking about native editing of AVC-HD, but it is possible to transcode into the native format of the NLE. OK, that defeats a lot of the point of the speed advantages that solid state offers v tape, but it's worth a thought. The new camera does seem to offer a 720p/50 recording mode, and quite a few other goodies.