HD>SD downconversion Mac/FCP only

[Mitchell Lewis]

Okay, I'm really nervous about making this post. It's shows how bizarre my logic is sometimes. Please go easy on flaming me. :)

Full-screen is full-screen, right? In other words, full-screen equals 100% in scale. If you're playing a video and it's full-screen, but then you shrink it by 20% it gets smaller and is no longer full-screen. Same thing if you increase the scale by 20%, it will get bigger and no longer fit on the screen.

If 1080 30P video is 1920 x 1080, any video with that pixel dimension will be full-screen on an HD television. If 480 30i video is 720 x 480, and video with that pixel dimension will be full-screen on an SD television. Further more, if you shrink a 1080 30P video (1920 x 1080) down to 480 30i (720 x 480) it will still be full-screen when viewed on an SD television.

So.....(here's where my mind get's really weird)

Text that was outlined with a 2 pixel wide outline in 1080 30P will still have a 2 pixel wide outline when shrunk to 480 30i, because it's still the same width when viewed full-screen on an SD television. KEY POINT: But there will be less pixels to describe the outline of the on screen text. It may not look as "crisp" as before.

There's probably a much better way to communicate this, but is there any truth to my "logic"? What am I missing here?

Sorry, maybe I partied a little too much last night. :)

[Perrone Ford]

No Mitchell, you're doing fine. The problem is that the rescalers don't know that your 2 pixel wide outline is an outline and not noise. So you need a rescaler that is smart enough to examine the patterns in the image and do their best to preserve the patterns and not just shrink everything down. When a rescaler scales down indiscriminately it's fast and it usually uses a method called "nearest neighbor". And this is what turns everything to mush.

Smarter rescale algorithms are able to look at patterns in the video and try to figure out what's going on before they rebuild a new image. It takes a LOT longer to run these routines and calculate for each frame, so generally you don't see these in realtime hardware or software. But they produce clean results.

Below is a frame grab comparison from a video I am currently working on. You one is native 1080p, the other is from a lanczos rescale down to SD. Look at the detail in both, the shadow quality behind the text, the edges of the letters. This is what I am talking about.

[Mitchell Lewis]

That looks great! I'm going to do some testing today on my Mac (I'm at work now)

[Perrone Ford]

Now you understand why I am always so mystified when people talk about how their rescales and how they can't get good results. That rescale was done with a FREE tool on the PC. HD -> SD can be done well, if you have decent tools.

[Dominik Seibold]

Originally Posted by Perrone Ford

There is no need to down-res the graphics as they are not "raster based" and as such are perfectly scalable up or down with no loss of quality.

If you downscale your video but let the vector-graphics render at the final resolution, then the edges of the downscaled video may have a different look than the edges of the rendered graphics. But if you first render the graphics at HD, overlay them to the video and then scale the flattened result down, the edges of the graphics and video-content will look more similar, which leads to a more consitent look.

Originally Posted by Barry J. Anwender

In any event, Apple engineers recommend to make the EX-XDCAM HD to SD translation in the FCP timeline and indeed this workflow provides excellent SD DVD results.

Doing the downconversion in FCP is faster but has worse quality than doing it in Compressor.

Originally Posted by Peter Kraft

Open that BPAV folder in XDCAM ClipBrowser and save video in DV format.

Sony has a legacy of offering very good downscales.

ClipBrowsers downconversion-quality isn't very good.

Originally Posted by Perrone Ford

So you need a rescaler that is smart enough to examine the patterns in the image and do their best to preserve the patterns and not just shrink everything down.
(...)
Smarter rescale algorithms are able to look at patterns in the video and try to figure out what's going on before they rebuild a new image.

I guess you overrate the intelligence of those rescalers. They don't work with any kind of pattern-recognition. They basically consists just of a lowpass-filter and and an interpolation-algorithm like a polynomial one like bicubic or sinc.

Originally Posted by Perrone Ford

, the other is from a lanczos rescale down to SD.

That example has perfect quality. :)

[Dominik Seibold]

I attached a downscaled version of Perrones 1080p-image to 720x405 with Compressor for comparison.

[Mitchell Lewis]

I've been doing some testing with actual footage.

I created 2 1080 30P movies. One rendered in XDCAM (20mb) and one rendered in ProRes HQ (120mb).

The problem I'm running into is that when I go from HD to SD it wants to make my progressive footage interlaced. That looks like crap when viewing as a QT movie. (too ugly to show you all) But for broadcast my video needs to be interlaced. I need to spend more time with this...

I did learn that it's important when viewing a QT movie for comparison, to make sure that High Quality is turned on. Everything looks bad if you forget to do this step.

I'm going to head to lunch and then do some more testing when I get back.

[Peter Kraft]

Originally Posted by Dominik Seibold

I attached a downscaled version of Perrones 1080p-image to 720x405 with Compressor for comparison.

Dominik, very impressive. Does the same apply to motion?

[Mitchell Lewis]

Yeah, I think compressing a still image isn't as big a deal as actual video (motion). Especially when you're dealing with interlacing issues.

Here's the HD movie clip I'm starting with.
http://www.ssscc.org/ftp/hd-sd/Test-...-1080-30P).mov

Now I just need to get it to look good in SD (720x480 letterbox)

[Mitchell Lewis]

Here's what I came up with (crap). I couldn't seem to get Compressor to transcode to SD without interlacing the footage. I went to the Encoder>Video>Settings and chose Scan Mode>Progressive, but it doesn't seem to make much difference.

http://www.ssscc.org/ftp/hd-sd/Test-...Anamorphic.mov

This is exactly what I predicted. The video in the background looks okay, but the graphics (red circle logo) look like crap.

This is harder than I thought!

[Dominik Seibold]

Originally Posted by Mitchell Lewis

The problem I'm running into is that when I go from HD to SD it wants to make my progressive footage interlaced. That looks like crap when viewing as a QT movie.

Your example has some strong reds. Are you sure that you don't confuse interlacing-artifacts with 4:2:0-artifacts?

[Dominik Seibold]

Originally Posted by Mitchell Lewis

http://www.ssscc.org/ftp/hd-sd/Test-...Anamorphic.mov

That confirms my suspicion: there's no interlacing going on, but 4:1:1-chroma-subsampling-artifacts of DV.

[Perrone Ford]

Originally Posted by Peter Kraft

Dominik, very impressive. Does the same apply to motion?

Send me a file to try, and we can see. I need a QT file that is compressed with something I can read on a PC. Like PNG Lossless, or QT uncompressed. Just send 3-5 seconds with high motion. It can be interlaced, and I'll try my de-interlacer as well.

I've done this for footage off the EX1 for myself, but would be interesting to try someone else's footage.

-P

[Mitchell Lewis]

Originally Posted by Perrone Ford

I need a QT file that is compressed with something I can read on a PC.

Hey! What's a PC guy doing on a Mac/FCP thread? hehehehehehe (just kidding)

[Perrone Ford]

Originally Posted by Mitchell Lewis

Hey! What's a PC guy doing on a Mac/FCP thread? hehehehehehe (just kidding)

LOL!

Trying to learn!

I have to work with Mac folks in this video editing world, so it behooves me (and other PC users) to learn as much as possible about BOTH systems.