Progressive Scan question

[Hulk]

Could someone tell me a little bit about progressive scan dv cameras.

I suppose this means each frame is taken like a camera, the whole thing at once. Does that mean that non progressive scan cameras used an interlaced format when recording.

I have also read that the Sony TRV900 only does progressive scan at 15fps and is therefore useless for motion shots.

What is the advantage of progressive scan cameras?

If a camera supports progressive scan should you always use it?

What affordable cameras (under 2k) support progressive scan mode?

Thanks.

[Aryko]

Yes, non-progressive scan cameras use an interlaced format for recording. Dr. Mordrid could tell you better than I, but I _think_ a prog scan camera actually does 60 full frames per second but only records 30 to tape.

The advantage of prog scan cameras is that you can take a whole stream of video and select individual frames out for pictures. If it was interlaced the shot wouldn't look as good.

Also, with the shutter speed at 1/30 of a second, 30 fps prog scan goes a long way towards "film look".

I never use anything but progressive scan with my Canon Optura, which is also a great example of an affordable camera (US$639 at Worldwide Direct): (www.buydig.com)

Cheers
- Aryko

[This message has been edited by Aryko (edited 21 November 2000).]

[Patrick]

If I want to record still images with my TRV900, I don't use the Photo Mode. I just turn on the Progressive Scan Mode and shoot short bursts of video. Instead of having one still shot per picture (as with a "normal" camera), I'll have 15 per second to choose from. I love it!!!

[Aryko]

Heh, again Patrick, our paths meet.

If I want to record still images on my Optura, I have 30 per second to choose from.

However I think we could both agree that a picture at 720x480 sucks in comparison to a cheap megapixel digital still camera...

- Aryko

[Patrick]

Ah, but the 3 chips on the TRV900 really seem to be able to produce a fine looking still image (from the progressive scan mode). Even though it's only 640x480, it looks pretty good. Of course, I'm talking about how it looks on a monitor, not as an 8x10 enlargement.

Aryko, I'll be responding in the other thread shortly.

[Hulk]

Thanks for the reply's guys but the plot is only thickening. I have searched the forum archives here and still haven't found the answers I'm looking for. I'm going to state my questions as clearly as possible. Hopefully someone can clear this up for me.

Video cameras can either be interlaced or progressive.

From what I understand these cameras that are progressive can record in an interlaced or a progressive mode.

In the progressive mode they basically capture 30 (or 15 in the case of the TRV900) full frames per second. Kind of like a digital camera that can take pictures very quickly.

Some questions on this topic:
Why not always record in this mode? I read somewhere that the beginning sequence of "Saving Private Ryan" was shot in a manner similar to this to get that stop action film-like quality.
I also heard that this mode doesn't have much motion blurring (like interlaced video) and therefore doesn't look like what we're used to seeing. I'm thinking that all film cameras shoot in a "progressive mode" so why would this be good for digital cameras if the camera supports it?

How does the progressive digital camera convert the progressive video to interlaced video? Does it take each of the 30 frames in each second and split them into odd and even lines to create the 60 interlaced frames?

When a digital camera capable of progressive scan mode is used in the interlaced or "normal" mode how is the video recorded? More exactly, what is the difference from the above example where the camera shoots progressive and converts to interlaced? How does the CCD capture natively in an interlaced manner?

If a camera does not support progressive scan mode how does it capture? Does it do it the same way a progressive camera does when in the interlaced mode? If so then the picture quality (all else being equal) shouldn't really be any better with a progressive camera than with one that isn't, right?

Please help me out here. I'm getting very confused.

[Fred H]

Isn't there some similarity to Progressive and Realtime Streaming?
A good explanation of streaming could be found here: http://www.terran.com/CodecCentral/GenInfo.html

Apologize if I'm wrong in this comparation

Fred H

[Dr Mordrid]

PS gives you full frames without interlacing. With a device that can deliver 30 such frames/second, such as the Canon Elura, you have a large advantage when it comes to doing overlay effects and moving paths. Overlay and moving path effects often bring out the worst in interlaced video.

Fast action sequences filmed with non-interlaced frames (PS) are also easier to encode into MPEG or streaming formats.

Another advantage with *most* PS cams is that PS CCD's often come with advanced RGB filters. This can improve the image quality of a single CCD cam considerably.

Progressive scan also provides much higher quality stills for those cams capable of still frame photography. Again, the new Elura-2 comes to mind.

Dr. Mordrid


[This message has been edited by Dr Mordrid (edited 19 November 2000).]

[Patrick]

Fred, I'm afraid you've lost something in the translation!

Hulk, I'm guilty of skirting most of the issues raised in your last posts only because I don't know all the answers for sure. However...

Why not always record in this mode?
Except for only being able to shoot 15fps with the TRV900, I don't know what, if any disadvantage there might be.

Does it take each of the 30 frames in each second and split them into odd and even lines to create the 60 interlaced frames?
You've sort of got it backwards. Two fields make up a frame. With interlaced video, only one field at a time is recorded and/or displayed. In progressive scan mode, the two fields are combined into one frame during recording. These frames are displayed this same way during playback. With NTSC video you get a maximum 30 frames per second, whether it's interlaced or not. The TRV900 duplicates every second frame in it's progressive scan mode and therefore it displays 15 different frames per second even though 30 frames are being produced during recording and/or playback.

When a digital camera capable of progressive scan mode is used in the interlaced or "normal" mode how is the video recorded?
See my last answer.

More exactly, what is the difference from the above example where the camera shoots progressive and converts to interlaced?
Not sure what you mean. Camcorders with progressive scan capability do not convert from interlaced to non-interlaced or vice versa. They record video one way or the other depending on how you've set up the camcorder.

If a camera does not support progressive scan mode how does it capture? Does it do it the same way a progressive camera does when in the interlaced mode?
Yes.

If so then the picture quality (all else being equal) shouldn't really be any better with a progressive camera than with one that isn't, right?
Right, (if all else is equal).

The ability of the TRV900 to only shoot 15fps in progressive scan mode is not a real problem when the resulting video is going to be highly compressed. What's the one thing that usually gets sacrificed when video is optimized for small file sizes? Frame rate, right? If a video is going to have it's frame rate reduced to 15fps or less, having shot the video originally at 15 fps is hardly a disadvantage.

There's a good chance that some of my answers may not be absolutely correct, but I'm open to being brought up to speed!

[Aryko]

Patrick's right on the money, but to continue the analogy, I'll add my two cents...

I think it's a matter of personal taste as to whether you shoot in progressive scan or interlaced mode. I find that PS gives a "film-like" quality (I know, in technical points it doesn't come close, but it's a heck of a lot better than regular interlacing) - if you wanted to make it look like a television show, you'd want to shoot interlaced. It's all about style. Personally, I never shoot interlaced unless that's the effect I want the video to have on it.

Patrick also hits the 15fps limit on the TRV900 - if you need 30fps, you're out of luck there, but as he mentions, most distribution content in the future will be 15fps web-based, so go nuts.

About Saving Private Ryan, I'll just note that scenes from the movie (and Gladiator, for some scenes) were shot with a fast shutter speed to get that effect. By definition PS emulates the same shooting action as a film camera. I think it's nicely ironic that the actions sequences in Gladiator were shot with the same kind of high-speed shutter you'd see for pro sports events, where they want the shutter speed high so when they pause for replays, there's no motion blur.

- Aryko

[Fred H]

Patrick, sorry.

My intention was to compair Progressive Scan with Progressive Streaming.

Yes, I'm always missing something in "translation".

A little confession here: sometimes I need to translate even to swedish (and to/from other, odd languages). It's one of my "handicaps", so I am: and and

[Hulk]

Thanks to everybody for helping to clear this up for me.

It's so hard to express some of these questions in writing.

Let me try again.

Interlaced video - 60 field per second, right? A frame of odd lines followed by one of even lines (or vice versa).

Progressive video - Frame based. Let's say 30fps. For TV viewing the camera must then "take apart" each of these frames and create two fields for each frame.

Now the question that I'm having trouble explianing.

Does a interlaced camera (one that doesn't support PS) actually record 60 fields per second? One odd, one even and so forth? This would seem to imply that the CCD of such cameras is different than those of PS cameras.

Now. Does a PS camera when NOT in the movie mode (PS mode) record video like an interlaced camera described above or does it simply record PS and convert to interlaced format?

Put another way, do all video camera CCD's record in a frame based manner? If so then it seems that only software differentiates Interlaced vs. PS video cameras.

[Patrick]

Aryko, could you please delete that loooong link in your first post to make this thread easier to read without having to scroll left and right and left, etc. Thanks. Maybe the questions and answers would then make more sense to all of us.

[jeffw]

From page 108, Nov 2000, of DV magazine:
"Even the progressive scan systems use frame buffers and 'segmented field' recording to save and display a proscanned frame as two separate fields, making playback of all these formats work perfectly well with current equipment."

I interpret that to mean that the only difference is in the way that the image is captured by the CCD. Progressive scanning captures an entire frame at once (the two fields are captured at the same instant). Interlaced scanning captures a frame in two fields and those fields are not captured at the same instant - they are captured a 30th of a second apart, for instance.

The article quoted above was written by Adam Wilt and he has a great, informative website at:
http://www.adamwilt.com/DV.html

Another very relevant article which I haven't had time to read yet is at:
http://www.dv.com/magazine/2000/0900/wilt0900.html

Is the consensus that it's okay to capture in progressive scan mode even if the final medium is TV (VHS)? I was under the impression that for TV you should use interlaced mode, and that for computer-based viewing that you should use progressive. Is the only difference the "film-like feel" of progressive mode?
If it matters, I have an Optura Pi.

jeffw


[This message has been edited by jeffw (edited 21 November 2000).]

[Dr Mordrid]

PS generated video is simply frame mode video. No lacing, one solid pic/frame.

Once edited you would have to set up render options in the editor to provide a field order if desired. Once this signal is fed through a hardware device this video would be interlaced even if in frame mode.

I often use frame mode in my editor when using moving paths on video overlays to prevent interlace artifacts. This outputs perfectly as laced video once the proper setups are done.

Dr. Mordrid


[This message has been edited by Dr Mordrid (edited 21 November 2000).]