Frame rates and shutter speeds

[Vincent Oliver]

The trouble with many forums is that you are always going to get conflicting advice. It can be difficult to disgusting between the advice from a experienced user to that of a novice who may have the best intentions, but will possibly give you the wrong advice.

The best advice in this thread comes from Doug, "the best advice is to do your own testing and see what YOU like best". You will often learn and discover more about shooting video from your own mistakes, no footage will ever be wasted in the process of learning.

[Mark Watson]

Originally Posted by Vincent Oliver

No shoot at 30p or 60p, each frame will capture a complete image, wilth 60i you are capturing two frames to make up a complete frame (interlaced). Interlaced footage can display a tearing effect with fast moving subjects, due to the two frames that make up the one frame.If you intend selling the footage then 24p will be the preferred rate.

Actually you're capturing two "fields" to make up a complete frame.

FWIW in order to get 60P he'd have to drop down to 1280x720.
60i and 24P meet BluRay spec, 30P does not. The OP said he might want to go BR at some point.
If panning too quickly, he'll get jerky looking footage at 30P or 24P.

Two pertinent claims made in the XF300/305 manual:

"... the camcorder produces spectacular video with true-to-life color reproduction while reducing noise and "rolling shutter" artifacts thanks to twofold improvement (when the frame rate is 60i) over previous models in scanning speed."

"Autofocus takes longer to focus when the frame rate is set to [30P] or [24P] than when it is set to [60i]."


Mark Watson

[Doug Jensen]

As Vincent says, there's a lot of bad advice on forums like this.

The camera is not combining two fields to make up a single progressive frame. If it was, you'd see two overlapping ghost images on any progressive freeze-frame where motion occurred between the two fields. You don't see that with footage from this camera because it is capturing whole frames -- 30 or 24 times per second rather than 60 fields and stitching them together. In 30P and 24P the entire frame is being captured all at once and that is why 30P and 24P look different than 60i

If 24P and 30P will result in "jerky looking footage" on BluRay then why does every Hollywood feature film or big-budget documentary disc I've put into my BluRay player look just fine? They are all shot and edited with progressive frame rates, so how you can you explain the lack of jerkiness? And if they can do it, so can guys like us. 24P and 30P look just fine when done right. If someone's 24P or 30P footage looks jerky, then that person is doing something wrong in the camera or in post. Simple as that.

Finally, 30P is not part of the BluRay specifications because it is not needed. It would be redundant. If you take video that was shot as 30P and then convert it to 60i for delivery, it looks exactly the same. Let me say that again, there is no visual difference between 30P . . . and 30P converted to 60i. What happens during the conversion to 60i is that you get two fields, but both of those fields are identical so it still looks like a progressive frame. There is no temporal difference between them like you get when you shoot 60i with a camera. 30P converted 60i is a whole different animal that something that was captured as 60i in the first place. Therefore, having a 30P spec for BluRay isn't needed. This is the same reason network TV shows that are shot and edited as 30P or 24P (nothing excect sports and some local news is 60i anymore) and then broadcasted at 60i still retain the original progressive look. Furthermore, progressive also looks better for web video.

So there's really no justification for using interlaced in today's world. It is ancient, outdated technology that has no business being used today. Saying other people should shoot interlaced because you can't get good results with progressive is a little like saying you should go back to shooting B&W because you can't get your white balance right and you always get bad colors. If progressive doesn't look good, YOU are doing something wrong. And you better figure it out because soon cameras won't even offer an interlaced option anymore and you will eventually have no choice in the matter.

However, with all that said, I would not be surprised to see 60P become the norm sometime in the near future. But 60P and 60i are totally different things that have almost nothing in common. In today's world, 24P or 30P are king until 60P takes over. 60i should be put in the attic with other antiques.

MASTERING THE CANON XF305 & XF300 CAMCORDERS

Doug

[Mark Watson]

Appreciate the post Doug, but I don't plan to quit using 60i until I can upgrade to a camera that has an electronic shutter and can shoot full HD 60P.

I get most of my info of this forum. Not all has worked out for me, but mostly it's been a huge help.
There are posts on here that explains (to my satisfaction anyways), why big time movies are shot in progressive. (Hint: They ain't shooting them on $7,000 cameras.)

Here's two posts from May 8th I found helpful. (from the section on Sony AVCHD NEX-VG10 / NEX-VG20)
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Although I'm in 'PAL' land, I'm considering switching over to shoot 50i @ 50th or 100th shutter, rather than 50P. The reason for this is to reduce 'temporal' aliasing, ie: the slight jerkiness between 50p/60p frames. Although the absolute resolution of each 50i/60i frame may be slightly less than a 50p/60p frame, you may achieve a smoother pan and here's why: The best way to explain this technically, is to quote from an engineering friend of mine:

"This (ie: 50p/60p) is what gives it that tiny bit of jerkiness. It is tied up with shutter speeds and is apparent in all moderately priced electronic cameras. The higher end and thus more expensive ARRI Alexa and RED cameras apply an electronic shutter filter to the image. This has the effect of dissolving, if you will, between the original and the filtered image, resulting in a more smoother transition between the on/off shutter or exposure. This is done I believe around the 12Hz region.

One of the advantages of 50i/60i material is the fact that any movement of the frame through say panning is shared across 2 fields albeit half vertical resolution per field but the movement is smoother so I think you will get far better results using 50i/60i as your record format and less encoding artefacts during BD production. Temporal aliasing is not anywhere as noticeable using 50i/60i as well which is why broadcasters prefer it. Full resolution Progressive frames or Progressive Sequential Field recordings both exhibit the problem but interlacing results in a halving of the movement within a frame over 2 fields.

"...high frequency details (trees and leaves particularly) really pushes the ability of the sensor to charge and discharge at 50p/60p whereas halving this high frequency with 50i/60i recordings, minimises the aliasing requirements. 50P/60P recordings are wonderful, don't get me wrong but they really shine as static images rather than pans or where there is fast action contained within the frame. This is why the higher end cameras use shutter filtering circuits."

[Craig Marshall]
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At the same shutter speed the temporal motion for interlace 60i or progressive 60p is the same. One just takes a field the other a full frame. So motion blur is the same whether panning or zooming. That is governed by shutter speed, same shutter speed, same blur. I see no difference with either my CX700 or NX30 shooting in 60i or 60p with the same iris and shutter speeds.

60i and 60p take the same number of exposures. One records fields the other frames. On playback 60i also plays back 60 exposures as fields and the TV de interlaces to 60P for LCD or plasma and displays all 60 fields on a CRT .

There is a big difference shooting 30p and 60i as 60i is much smoother since there are twice as many exposures of the camera even if they are just fields. In my mind 60p is much better.

As far as sensor refresh is concerned I think most have been progressive for a while it was the rest of the processing that was the problem in encoding for recording or direct output encoding. Since earlier sensors were also not full 1920x1080 they also had to be interpolated to make full HD, more compute power or they had to be de Bayered from a single sensor. That compute power is what makes the camera hot !!! So yes it was easier to processes every other line as an interlace output. At least that is how I understand it. When you think about it the sensors have to be read out through a shift register so all the pixels get read ( progressive content) but not all need to be processed further depending on output needs. However, they probably are used for electronic image stabilization, noise reduction, face recognition, etc etc. With no deliver spec for 50P/60P at full 1920x1080 there was little incentive to provide output for Pro cameras ( most still do not have the frame rate) however for the consumer feeding their TV directly from the camera the progressive output is beneficial. TV shows what the camera took not the result of the TV de interlacing circuits. Smooth clear images and much better stills captured from the video if needed. Its why I shoot 60P for all my family stuff. You of course need to tell the TV that the input is progressive !!!

Ron Evans
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Is this some of that bad advice you're talking about?

The OP was asking about a specific situation; shooting video of bears in Alaska. If the bear is just going to sit there, then you could shoot that in progressive, but I would expect that he'd mostly want some clips of bears in action, swatting salmon out of a stream, scampering up trees, whatever bears do. So for a specific application I'm just guessing how I'd approach it. You make it sound like it's a sin to shoot interlaced, though it's been done for how many years? And why do I keep reading everywhere that it's the preferred mode for sports/action? You know the XF300 does not shoot full HD 60P. If it could, I would have recommended that.

If you go to the National Geographic site, there are 9 videos you can download. Eight of them are 60i. No idea why that is, but to claim 60i is antiquated....

Mark Watson

[Doug Jensen]

YES! This is exactly some of the bad advice I was talking about and I don't have time to address it point by point. I've said all I'm going to say and people can either take my advice or leave it, It makes no difference to me one way or the other. But the fact remains that no matter how much one person may love the look of interlaced, high-end clients, broadcasters, stock footage houses, and everyone who's opinion I value want no part of it. Interlaced is dead and people better be ready to do progressive properly or become a dinosaur. I honestly can't believe we are even having this discussion. Interlaced?? Really, in 2013? Am I being punked?

[Taky Cheung]

Agreed with Doug. DONT DO INTERLACE. All flat panel TV plus computer display are progressive. You will need to deinterlace output to web or playback on computer display. Just don't.

[Vincent Oliver]

Rather than read all the advice given here, take your camera outside and shoot some test footage, if 60i works for you, then it doesn't matter what people say or advise you with. I personally have no problems with shooting 25p or 24p, then again I don't do a lot of fast pans. However, I do do a lot of frame grabs and progressive frames always produce a better still image. Wipe the dust of your camera and take it outside for some test footage.

[Bob Safay]

Well I am back from Alaska. First I want to thank every one for their comments. A lot of good reading here. I shot about 145 GB of video with the XF300. My setting were 1920x1080 30P and a shutter speed of 60 fps. I must say that the video I got was stunning. This camcorder handled every type of lighting contitions I could through at it. Two of the photographers that were with me were using top of the line Nikon still cameras with 400 to 500 mm lenses. When they saw my footage on the built in monitor they were blown away. One said he could not believe how well the Canon XF300 handled the light. This camcorder continues to amaze me. As soon as I get to it I will be posting video clips on Vimeo. Take care and again thanks for your responces. Bob

[Vincent Oliver]

Thanks for the post Bob, glad it all worked out OK for you. We shall look forward to seeing your videos.

[Taky Cheung]

If you record 1080p30 the frame rate would be 30fps, not 60 fps. Shutter speed unit is second not frame per second. Or you mean you use a shutter speed of 1/60 ?

[Bob Safay]

Taky, your right. My shutter speed was 1/60..

[Vincent Oliver]

WE knew what you meant Bob