Why do we need progressive scan?
by brianluce
on
Jun 7, 2006 at 10:36:37 am
I know what progressive scan is by definition, and I've read how it gives a "smoother" image and better "temporal and spatial resolution" but I have no idea what any of those things actually mean in terms of what you get in the real world. Same camera in 30p and 60i, what will the actual difference be? motion signature? I wish I knew.
Re: Why do we need progressive scan? by Ed on Jun 7, 2006 at 2:44:16 pm
One thing you get with progressive is that it looks more like film, even 30P. We're used to 60i looking like video,
and we're used to the film look at 24P. 30P isn't quite the the look of 24P, but it's more like film than 60i is.
Ed
Re: Why do we need progressive scan? by brianluce on Jun 7, 2006 at 9:17:27 pm
Thanks ed, but saying progressive looks more like film takes me back to the beginning. What does it mean that something "Looks like film"? I still don't know why progressive is better and why people suggest progressive scanning improves image quality. Making something look like film doesn't make the pure quality any better.
Re: Why do we need progressive scan? by Ed on Jun 8, 2006 at 2:43:38 pm
It's not necessarily that it looks better, but our brains have been auto-smoothing out the 24P of film for so many years
that we've come to see 24P as film, so when you have a progressive format at or close to 24, your brain says "film". It's
only *one* factor, but it is a factor. The real question these days is "why do we need interlaced scan?". The original reason
for interlaced was because of limited bandwidth, not an issue these days.
Ed
[brianluce]"Thanks ed, but saying progressive looks more like film takes me back to the beginning. What does it mean that something "Looks like film"? I still don't know why progressive is better and why people suggest progressive scanning improves image quality. Making something look like film doesn't make the pure quality any better."
Re: Why do we need progressive scan? by SydneyS on Jun 8, 2006 at 4:25:26 pm
"Interlaced video can only be shown directly on CRT (cathode ray tube) displays. For all other display devices, some form of deinterlacing needs to be done to prevent the interlaced lines from becoming visible, which would be seen as saw tooth, edge distortion, mice teeth, combing or serrations."
With the advent of other television technologies like LCD and plasma televisions, it now becomes a real problem when watching interlaced video on the monitor. Editing, keying and compositing is more difficult with interlaced video, typically the fields are removed and/or interpolated/duplicated for many of these processes, which reduces the quality of the video. (60i referrs to 60 fields, two of which make up a frame.) When HD video came along, interlacing was still used, as it saved bandwidth, making the broadcast of 1080i possible. These days, it's more of a legacy process, and the major companies are finding ways of getting rid of interlacing entirely.
After the XL-H1 & the HD XDCAM....not entirely sure we do need it anymore.... by ShannonRawls on Jun 7, 2006 at 3:49:34 pm
Modern Day Progressive CCD vs. Modern Day Interlaced CCD for a final progressive recording. Can you "see" the difference? Well, some scientists claim they can see a difference under a microscope.
I don't agree.
And I beleive Canon & Sony is on my side with that assumption. In fact, since there is no HD equivalent camera to the Canon XL-H1 that uses progressive scan chips...there really is no way to make that claim or with 100% assurity say it is true.
But it can be (somewhat) tested in Standard Def....
Canon XL2 24P (2:3:3:2), progressive scan for a 24 fps SD recording to minidv tape.
vs.
Canon XL-H1 24F (2:3:3:2), interlaced scan for a 24 fps SD recording to minidv tape.
This is the closest test anybody can make today. It's still not entirely *fair* because the chip resolution is better on the XL-H1. But still, it's the best comparison in the world right now.
I have done it. However, my examination is visual only. I inspected it frame by frame. Image by Image. Blown up, shrunken down, compressed and recompressed, converted, burned to DVD, you name it...I checked it....the works!
And I am here to pronounce......that visually.....with my human eyeballs......they are identical.
*smile*
Now to put it under a microscope, you would need the expertise of a great man like Graeme Nattress (www.nattress.com) he could disect the two clips and check the DNA to see if they match. I don't have the tools or brains to do that like he does. I doubt he would come back with any negative results if he did. And even if he did....does it matter? We make movies for the public, don't we? *smile*
Shannon W. Rawls ~ Motion Picture Producer & owner of two Canon XL-H1's & a Sony Z1U, along with a bunch of other HD movie making gear.
Cinema Hill Motion Picture Company ~ Do you have a project in mind? Let's shoot it! *smile* We love making Dramas, True Stories, Horrors, Crime, Mysteries, Actions, & Urban Thrillers. Call anytime: 1-888-205-1700. If the script is good, we'll shoot it for free!
Hollywood DV/HD Festival ~ After you finish your HD project...Put it in a DEDICATED DV/HD festival!
Re: After the XL-H1 & the HD XDCAM....not entirely sure we do need it anymore.... by Postal Boy on Jun 7, 2006 at 8:14:49 pm
I guess it all boils down to what you are displaying it with. Interlaced footage looks fantastic on an interlaced display. Nice, smooth movement and so forth. However, when I put the same footage through a progressive projector display I can clearly see the interlacing between frames (the projector doesn't de-interlace by itself). Some displays deinterlace within the hardware so it takes the interlace lines out for you.
In the end, digital TVs are progressive, tubes are interlaced. Since digital is becoming more of the standard, the end users will be watching progressive screens - so the interlaced footage won't look as good on those displays unless it is de-interlaced first. Any time you de-interlace you are changing the original format so SOME loss is expected (although high end apps can do a very fine job of de-interlacing...I just can't afford one). If that small loss truly impacts your production then I think your production may be lacking somewhat, not the recording format. In other words, if it is a quality production then the small differences shouldn't be noticed except by die-hards that are picking the technology apart.
I think the interlaced/progressive thing will be dictated based on end displays rather than "which is better". The "which is better" argument is mostly opinion based with people saying "interlaced is more natural" and "progressive is more 'movie-like'"...until movie projections change to a faster rate, then the same people arguing for 24p now will say anything less than 60p is "dated" and looks "old".
Re: Why do we need progressive scan? by Thomas James on Jun 8, 2006 at 4:17:22 am
All of your flat panel televisions and all computers are natively progressive scan devices so progressive scan footage is going to be the most compatible with these new televisions. The problem with progressive scan HDV footage is that up until now the frame rate has been limited to 30 frames per second which resulted in motion that was not as smooth as 1080i. With the introduction of the JVC GY-HD200 you will have the ability to record 720p HDV footage at the unprecedented rate of 60 frames per second for ultra smooth motion perfect for the fast action sports. This new camera will effectively double the temporal resolution. Critics of the 720p60 format claim that it does not offer the resolution of 1080i. However the fact is that the 720p60 format displays more pixels per second than 1080i does so it offers more resolution than HDV 1080i and more resolution than HDV 1080p that is if you consider temporal resolution as equally valid as spatial resolution.
Re: Why do we need progressive scan? by Ken Hodson on Jun 11, 2006 at 5:51:09 am
I would say it depends on what your trying to show. Movies shot on film, which is a progressive medium, so to speak, look amazing on an interlaced TV. No surprise. Interlaced is superior for most run a gun type shooting where rules of camera motion can't be followed easily. Non tripod work or reality TV type stuff. If one can shoot 60p then of course interlaced has no advantage at all. Any progressive shot video can easily output as an interlaced format.
Re: Why do we need progressive scan? by David Newman on Jun 8, 2006 at 4:25:05 am
60i will be smoother in motion. 30p will have clear details in each frame but the motion is not as smooth. Comparing 60i to 30p is not easy to see the disavantages of interlaced. Comparing 60i to 60p,is clearer, as motion have the same motion characteristics. Yet 60i is a form of compression (2:1) over 60p, it halves the bandwidth by only sending half the information per frame. This was good idea before there was digital compression, now it is a pain. Compression is less efficient with interlaced, scaling is tricky with interlaced, lots of quality compromises.
Re: Why do we need progressive scan? by brianluce on Jun 8, 2006 at 7:44:07 am
" 60i will be smoother in motion. 30p will have clear details in each frame but the motion is not as smooth. Comparing 60i to 30p is not easy to see the disavantages of interlaced." -david newman
well then it sounds like 60i is better than 30 because you seem to be implying that the motion signature is more perceptible than the difference in detail. So why should anyone want 30p?
Re: Why do we need progressive scan? by David Newman on Jun 8, 2006 at 2:52:21 pm
You should have been clearer in your original question, I wouldn't have answered with the tech advantages to progressive. Here is the consumer advantages -- progressive sourced for DVD look MUCH when scaled up on HDTV -- that is worth it alone. The only reason to shoot 60i is for news gathering, reality TV, and consumers who can't how a camera steady. I think that is the type of over simplification that make the case for 30p over 60i.
Re: Why do we need progressive scan? by Mike_S on Jun 8, 2006 at 3:36:11 pm
From an audience perspective, it makes sense to originate your material as close to your final display format as you can afford, and then do all you can in post to keep that original quality.
If you're going to output to film, progressive scan is the natural choice.
If your primary target is people with displays that only handle an interlaced signal (TVs), then interlaced is better.
For HDTV, industry standards support both interlaced and progressive scan, and higher-end plasmas and LCDs will handle both well. Budget LCDs, and LCDs intended as computer displays and doubling up with an HD capability, will not - for these a progressive scan image will be better.
For sports, the ability to run higher frame rates on current progressive HD camcorders along with progressive scan images' better performance when slo-moed both make progressive a good choice.
For other types of footage, the richer detail of the 1080i image offsets the loss of smooth slo-mo, and many cameramen and producers then opt for 1080i.
From a camera perspective, a big factor on the 24 / 25 / 30 p formats (and film cameras) is that you have to handle pans, tracks and zooms more carefully than with an interlaced scan - the image starts to break up in the movement at slower pan / track rates. You can usually see it in the viewfinder, but it changes the rhythm of your moves a little: just slow enough not to "tear" or "strobe" is good, and fast can be great, but just too quick so the image starts to tear looks baaaaad ....
So it's really your choice: who's going to be watching, what will they be watching on, and what type of footage are you gooing to be showing them ..?
Re: Why do we need progressive scan? by Ken Hodson on Jun 8, 2006 at 3:45:06 pm
I would also like to add that the amount of post processing one plans on doing would affect the choice. If one plans an advanced compositing workflow some plug-ins will demand progressive footage or that it be deinterlaced first, if from an interlaced source. Blue-screening or chroma keying is on example where progressive footage is always prefered.
