Scaling 480p

kjohn · 2002-05-09

Can anyone tell me what is the benefit of a processor that can take 480p and scaling up to any other progressive resoultion such as 540p or 720p.

J

Jim Boden

· #2 · May 10, 2002

kjohn:

I don't think there are any scalers which will accept progressive input, although I could be wrong. The more common ones, such as the Faroudja NRS and Key Digital Leeza, only accept 480i for scaling. This is why you may see comments to the effect that DVD players should be set to interlaced output when being used with a scaler. They do a better job with 480i than the DVD player does with 480p.

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kjohn

Discussion Starter · #3 · May 10, 2002

The new Center Stage from Focus does take a 480p or 720p signal.

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Jim Boden

· #4 · May 10, 2002

KJ:

I've been reading the posts on this new scaler but guess I missed that feature. The documentation actually says it accepts 480/576P. Thanks for pointing it out.

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oferlaor

· #5 · May 10, 2002

What would be the purpose of scaling up 480p? With progressive signals, you would see marginal differences between different scaling algorithms. Except for the weekest scalers (e.g., pure line multipliers) you would not see signficant benefit using a fairly decent display.

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rbienstock

· #6 · May 10, 2002

Quote:

Originally posted by oferlaor
What would be the purpose of scaling up 480p? With progressive signals, you would see marginal differences between different scaling algorithms.

I can think of one thing: many scalers give aspect ratio control, which is useful if your 16:9 display locks into full mode whenever it receives a progressive signal. Without this, if you are starting with a 4:3 shaped 480p image it will be distorted (unless you zoom, in which case it is cut off). A scaler with aspect ratio control could insert the proper side bands. I have this issue with my ReplayTV units which look much better using their built-in 480p output than when scaling up the 480i output, but being stuck at a 4:3 stretched to 16:9 full is a real bummer. This is the BIGEST problem I have in my system. I'd even be perfectly happy with a device that didn't even scale but just inserted the side bands and output 480p.

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rbienstock

· #7 · May 10, 2002

Quote:

Originally posted by oferlaor
What would be the purpose of scaling up 480p? With progressive signals, you would see marginal differences between different scaling algorithms.

I can think of one thing: many scalers give aspect ratio control, which is useful if your 16:9 display locks into full mode whenever it receives a progressive signal, thus if you are starting with a 4:3 shaped 480p image it will be distorted (unless you zoom, in which case it is cut off). A scaler with aspect ratio control could insert the proper side bands. I have this issue with my ReplayTV which looks much better using its built-in 480p output than when scaling up the 480i output, but being stuck at a 4:3 stretched to 16:9 full is a real bummer. This is the one BIG problem in my system. I'd be perfectly happy with a device that didn't even scale but just inserted the side bands and output 480p.

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S Goff

· #8 · May 10, 2002

What would be the purpose of scaling up 480p? Many displays (chiefly CRTs) have only analog inputs, with no internal scaler. They need some sort of scaler to hit their sweet spot. It may be that a scaler using, say, the SIL504 for deinterlacing (such as the CS-1) does wonderfully deinterlacing film material, perhaps better that the Faroudja chip, but less well deinterlacing some video material. If you have a DVD player with the Faroudja DCDi chip, you might want to feed the scaler 480p while watching some video-based material, but 480i (from that or another DVD player) while watching film-based material. Since the 504 does not have full scaling built in, your scaler needs a separate scaling chip in any event. So a direct input to that scaling chip gives you the ability to scale progressive signals from the outside. Choice is good.

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Selden Ball

· #9 · May 10, 2002

To paraphrase what S Goff wrote:

If your display device can show more than 480 scanlines, then you should take advantage of it. The resulting image will look more "film like". 480 scanlines are easily distinguished on a large screen. Scalers upsample and interpolate between them to produce more scanlines, usually more than 1K. Digital display devices and most rear projection TVs include their own scalers, but often they don't produce as good an image as can be produced by a high quality external scaler.

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S Goff

· #10 · May 11, 2002

Yes, as Selden says, one goal of a scaler is scaling so that scan lines are not visible on the display device. Another may be matching the resolution of a fixed pixel device, although an internal scaler is often provided in such projectors and often works as well, given a good progressive-scan input signal. Another still may be deinterlacing, although there have been professional boxes out there that scale but don't deinterlace.

Again, if you have a scaler that takes either 480p from an external souce or 480i which it turns into 480p using an internal deinterlacing chip, you can choose whichever works better for you in the given instance.

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Ereiamjh

· #11 · May 11, 2002

So, if I want to be able to sit closer to the screen without seeing pixels/etc,

I could use a scaler to increase the fluid appearance of the picture? I was in the theater yesterday and estimated a 1:1 ratio of screen distance to width for the middle seating area. This is what I would like to create but at this ratio I see pixels. I use a pan rp56 with a nec lt 150. Would a scaler work?

Dan

P.S. Could I assume that as long as the above ratio is maintained, that ability to see more or less pixelation would remain constant as seating distance to screen changed?

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Selden Ball

· #12 · May 11, 2002

NEC's LT150 is a DLP projector with a fixed resolution of 1024x768. It has a builtin scaler which converts whatever signal it is fed to its native resolution.

An external scaler will not eliminate the pixels: they're caused by the design of the display chip in the projector. When the projector is sharply focused, the individual pixels of the display chip are imaged on the screen. Slightly defocussing the projector is one way to make them less objectionable.

A high quality external scaler can do several other things for you, however. For example, it should be able to do a better job of converting composite, s-video and component signals into RGB.

It can also do a better job of converting video signals that originated from film into appropriate progressive video signals. Presentation projectors normally don't include 3:2 pulldown logic. Also, external scalers usually can do a better job of that conversion than the relatively inexpensive progressive circutry in most DVD players.

Since the progressive signal coming directly from a DVD player only has 480 scanlines, the scaler in the projector still has to upconvert it to 768 scanlines. A good external scaler fed an interlaced signal and set to output 1024x768 (thus bypassing the projector's internal scaler) usually will generate a better final image.

I hope this clarifies things a little.

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Ereiamjh

· #13 · May 11, 2002

Thanks Selden,

Does that mean I will actually get a more defined pixellation with a scaler or HTPC? Not that this bad, it just means I have to sit farther back. In theaters, if you sit at the middle area the ratio of screen width to seating distance is roughly 1:1. I would like to recreate this in my set up to get that giant visual field effect. But it sounds like it is physically impossible due to projector specs. Though I would gladly give this up for a better picture quality .

Also, does a scaler only work with interlaced dvd signals? would I need to get an interlaced dvd to replace my progr. dvd if I use a scaler?

Dan

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Selden Ball

· #14 · May 11, 2002

Dan,

Please don't hesitate to defocus the projector slightly. Being able to see the individual pixels clearly can be quite distracting, as you've found. The image you're watching will actually benefit if the pixels are blurred enough so that their edges overlap slightly.

The apparent sharpness you see when the individual pixels are visible has nothing to do with the picture you're trying to watch. One way of considering it is that the incoming signal is comparable to 720x480 when you're watching a DVD, and significantly less when you're watching other standard resolution sources. The smallest feature you can resolve in the original signal occupies several projector pixels. Blurring the projector's pixels together isn't going to hurt it.

Using a scaler or HTPC won't have any effect on the visibility of individual projector pixels. Rather, they control how the incoming video signal is distributed among them.

The equivalent resolution of the film image in a high quality movie theater is greater than your digital projector can provide. It's more like 3k x 1.5k. (Of course, most theaters really aren't that good.) Unfortunately, this means your projector can't produce as good an image as film does when the image fills the same fraction of your visual field. An HDTV signal into a high resolution projector can come close, though.

Some of the newer scalers do work with progressive input signals. You'll have to check the specs of the ones you're interested in. All of the progressive DVD players I'm aware of can be set to produce an interlaced signal, too. Check the manual.

I hope this helps somewhat.

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Ereiamjh

· #15 · May 13, 2002

Thanks Selden,

You helped tremendously.

Best Regards,

Dan

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