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Old April 26th, 2007, 12:20 PM   #1
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Red channel artifacts?

I'm loving my HV20, but I'm noticing quite a lot of jagged artifacts in the red channel. Anybody else getting this? Is it just part of HDV, or is it worse in this particular camera? Any advice on how to clean it up a little without destroying the rest of the picture?

I've attached a sample detail at 100% to illustrate the problem. This was shot 24p, and is from one of the full, non-interlaced frames.
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Red channel artifacts?-hv20-red.jpg  
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Old April 26th, 2007, 12:24 PM   #2
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Red never seems to do well with MPEG compression. It really stands out on my Dish Network channels. This has been an ongoing problem for years now.

-gb-
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Old April 26th, 2007, 12:52 PM   #3
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So hypothetically, would cooler colors yield a better picture?
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Old April 26th, 2007, 01:21 PM   #4
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Red is a huge no no in any video, especially DV and HDV. You can actually "clean" the red and blue color channels in HDV using filters in your NLE, After Effects or various plug-ins and it works quite well. Though if you re-export it back to DV or HDV you'll get the compression artifacts again. I usually capture my HDV from the HV20 and convert it to another codec/format as soon as possible and never look back.

Here's an example of how much of a difference cleaning just the Red channel can make...
Clean red channel
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Old April 26th, 2007, 01:42 PM   #5
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That is the Chroma upsampling error or CUE. This is due to how interlaced images are compressed with 4:2:0 color space. With 4:2:0 the color samples alternate every other line but so do fields in an interlaced image to the encoders split the chroma even more so that the chroma smaples alternate every other line in each field and not the whole image.

Reds are easier to notice the one line offset of the chroma samples. That is just the way 4:2:0 interlaced encoding works. I notice the same thing on PAL DV cameras because PAL also uses 4:2:0.

You really notice it on your computer screen because the video isn't playing back at one field at a time but showing you the whole frame all at once.
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Old April 26th, 2007, 04:27 PM   #6
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Ah, that makes sense. It never seemed quite so ugly when I was using DV. Wes, do you have any suggestions for filters I could use within FCP to achieve what you did in that screenshot? Thanks.
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Old April 26th, 2007, 04:48 PM   #7
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Quote:
Originally Posted by Wes Vasher View Post
Red is a huge no no in any video, especially DV and HDV. You can actually "clean" the red and blue color channels in HDV using filters in your NLE, After Effects or various plug-ins and it works quite well. Though if you re-export it back to DV or HDV you'll get the compression artifacts again. I usually capture my HDV from the HV20 and convert it to another codec/format as soon as possible and never look back.

Here's an example of how much of a difference cleaning just the Red channel can make...
Clean red channel
Thanks for this Wes - do you know if the Magic bullet de-artifactor would accomplish the same thing?
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Old April 26th, 2007, 05:07 PM   #8
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Fergus, you probably won't find a better HDV chroma cleaner than Magic Bullet Deartifactor IMHO... Nattress is supposed to work quite well also. The DV Rebel Guide details how to clean your chroma manually also.
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