Re: Converting 4:2:0 HDV to 4:4:4 letterboxed NTSC

[Mr. E. Trane] "On the color resolution analysis, I think I understand what you are saying here, but I’m not sure I quite understand the math... if you downscale the HD image to SD, you’ll end up with a 4:4:4 image and that this is possible because HDV has more chroma detail than SD 4:2:2. Maybe you could clarify this for me a bit..."

Sure. You've got the idea. Start with 1280x720 and downsize by some whole number amount to achieve the least loss possible during the resize. I'm advocating dividing by exactly 2 here in each dimension. Now we aren't ending up with a full 720x480 resolution, so there still is a sacrifice in resolution compared with a true high-end NTSC cam. But overall you end up with some danged great 640x360 30 or 60fps progressive video. Better than DVD quality since after the resize it ends up being 4:4:4 sampling. It has still gone through the MPEG2 compression process, so you will have slight macroblock artifacts in high-motion scenes, but it's quite bearable. It could be stretched in width from 640 to 720 pixels to accomodate the NTSC aspect ratio, and put on a DVD with excellent results. When you divide both the vertical and horizontal resolution exactly in half, the result is that every 2x2 block of pixels from the original becomes one pixel in the result. Lots less luma noise since you're averaging four values together. And since color is sampled precisely once in every 2x2 block of pixels, each pixel in the result also ends up with its very own chroma info.

For a fun experiment, try doing this with today's GR-HD1 cam. You're averaging luma down 4:1 in the process, so much less of that camera's grain in those low-lit scenes. As well the camera already has somewhat washed out color, so it won't be outstanding, but still usable. You can start to appreciate where this format can take us with this kind of experiment. I imagine if you do that with a good 3CCD HDV cam then you should be able to get similar results to a high-end NTSC cam, but without spending that much money. Okay, you'd still lack a black balance adjustment, and some depth of field, and you're limited to letterboxed 640x360, but it's 4:4:4, and better than pro DV for the same price. Video you release now in high-quality NTSC can later be re-released in 720p.

For upcoming cams that do 60fps, you can use NTSC's interlacing to your advantage by taking out every even-numbered scan line on odd numbered frames, and vice-versa for even-numbered frames. Weave sequential frames of this "bob'd" video together, and you have true 60 field per second interlaced NTSC with great quality. All this pixel shifting madness is fairly easy to accomplish in the PC world using the freeware AVISynth program. To feed AVISynth, use the version of VirtualDub that reads MPEG2, and set it up as a frame server. The output then gets cranked through the AVISynth script, and finally put through a lossless compression like HuffYUV. Stellar NTSC results on a $10K budget, and HD leftovers for later. Now we just need someone to release a 720/60p 3CCD HDV camera!

-Lorin