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Old November 16th, 2009, 12:35 PM   #1
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Blur aliasing with mask in post?

I'm wondering if anyone has tried to blur parts of footage that have aliasing in post? Maybe After Effects?

I know this would be time consuming but couldn't you make a mask to do this and be subtle about it, just enough to stop the strobe feeling, but not too much that it looks like you're editing out a logo on a tee shirt.

Has anyone attempted this?
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Old November 16th, 2009, 04:51 PM   #2
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If you have a pattern, like on the knit fabric of a polo shirt, filtering generally won't help. The high frequencies get turned into large, low frequency swaths.

On the other hand, aliased edges can be filtered. It helps reduce the jaggies, color errors, and dancing dots. If you can, mask the area to be filtered, feather the edge and filter to taste.

Best of luck.
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Old November 16th, 2009, 07:42 PM   #3
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Thanks for the idea Jon, I'll try that out. I want to believe there is a way to dull down the strobe dancing in areas effectively in post. But then again aliasing might not matter to the average viewer. I noticed the other night as I was flipping through channels an old episode of Entourage from 2007 season had a principle character with a white dress on with a bunch of diagonal grids as a pattern and she became an flashing disco floor on my HD TV from aliasing. This was happening for more then a moment as well.
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Old November 16th, 2009, 11:14 PM   #4
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Unless your HDTV is dot-by-dot, the aliasing you saw might have been in the TV.

Fox, ABC, and ESPN broadcast 720p. The others are typically 1080i. Many "720p" TVs really have 768 lines, and many 1080p TVs overscan, so they aren't dot-by-dot.

Sharp 1080p TVs (I work for Sharp Labs of America) all have a dot-by-dot mode. I'm not sure about other brands and models. Even with Sharp TVs, you need to select the correct display mode.

That's not to say that the Entourage content didn't alias. But there could be other factors...
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Old November 16th, 2009, 11:46 PM   #5
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You know I was wondering that actually Jon since I use an old Gateway FPD2185W as my TV and it only has 1680 x 1050 75 Hz max res native. But then I thought, wouldn't I see it all the time with HD footage from my direct TV? I do see it time-to-time but it's really rare especially from HD channels. I don't think I've ever see it from my blu-ray in to the monitor.

The other possibility is that I really notice it now that I'm constantly working with 5D footage so I used to not notice or accepted it beforehand. Just like I can't stand bad hand held/dolly/steadi footage now, hehehe.
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Old November 17th, 2009, 05:33 AM   #6
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You'll definitely get aliasing on the Gateway. But it's probably only noticeable on certain large patterns, or if you get up close and look at jaggy diagonal lines.

Regardless of brand, next time you shop for a TV, look for 1080p native and make sure it has dot-by-dot mode.

And always use a good dolly/steadicam. ;)
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Old November 19th, 2009, 06:34 PM   #7
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A while ago, I had to try and reduce twinklies on some computer-generated footage. Normal blurring didn't help much unless it was so extreme that it blurred all the detail in the clips. Eventually, the best compromise I found was a slight motion blur, which helped a lot because the problem is mainly due to the changes in fine details from frame to frame.

Doesn't help much with diagonal line stair steps though.

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Old November 30th, 2009, 09:01 PM   #8
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I've got a lot of experience with After Effects and Final Cut Pro. I wonder if the "flicker filter" that's normally used to fix interlace issues would help?
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