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Old Nov 6, 2008, 4:03 AM   #1
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I have noticed that the 720 video that the AHD+ and Action HD makes are aliased ( have jaggies ) . The 1080 video does not exhibit this artifact.
I'm guessing that the 720 modes are sub sampling the sensors entire width and because the camera does not filter down the image, it has the problem.
For 1080p , they just use the center 1440 of the sensor and hence do not get the problem. This is why the 1080 mode gets a narrower view, BTW.

Q: Do the 720p only cams have the same jaggie video ?

I searched around here, and I didn't see any posts mentioning the aliasing issue, which is a bit surprising, considering all the scrutiny of these cams.

To see the issue: Shoot something like a fence with some nice high contrast straight lines. On video playback on a computer, zoom in and look at the edges.
720 will show jaggies, 1080 will be smooth.
This is not just a resolution issue. It's the throwing away of every other pixel in 720 mode that makes the artifact.

-Les
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Old Nov 6, 2008, 4:44 AM   #2
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welcome aboard lesdit.

a very observent post .

when I edit my vid and load 1440x1080 in, it is a 4:3 ratio. not 16:9, unless i modify the object properties.

When I laod in the 1280x720, it is 16:9 ratio..........

uncertain if that is the way to say what the actual ratio is.......... 1.333:1

I do not worry bout my video having Jaggies , so let others who are really concerned about footage, being perfect, on a low budget cm answer

thanks for the great question
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Old Nov 6, 2008, 9:17 AM   #3
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All of the hybrids...

1. DXG 720/30p mode;
2. Jazzcameras 720/30p mode;
3. Aiptek 720/30p mode.

...it doesn't matter which you buy.

They *all* constrain data rate on 720/30p to about 4 Mbps.

Some of the newer hybrids add the 720/60p mode, which has the advantage of lessening the "wobble" or "rolling shutter" artifact associated with CMOS sensors -- but -- the downside is that the 60 frames per second mode will result in *more* pixel artifacting because two frames are being processed in the same amount of time with only a modest increase in bit rate. At least, that's my opinion after quite a bit of experimentation with these clips.

The 1080/30p mode gets a higher bit rate, which helps -- but -- sometimes you only think you're seeing less artifacting because your computer's software player is -- in reality -- squeezing the 1440 x 1080 image into a smaller window for playback... resulting in what appears to be an image with fewer jaggies.
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Old Nov 7, 2008, 12:03 AM   #4
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Thanks for the replies and welcome!,

My issue/question has nothing to do with data rates. The Jaggies are from poor sub sampling ( pixel skipping instead of blending ) before compression.
I'm not concerned about macro blocking, or the h264 equivalent. I'm fine with that, it looks pretty good, in fact. In 1080 mode , looks great. But I like wide field of view and 60 fps.


I was thinking that the 720 only cams have better 720 modes.

-Les





Private Idaho wrote:
Quote:
All of the hybrids...

1. DXG 720/30p mode;
2. Jazzcameras 720/30p mode;
3. Aiptek 720/30p mode.

...it doesn't matter which you buy.

They *all* constrain data rate on 720/30p to about 4 Mbps.

Some of the newer hybrids add the 720/60p mode, which has the advantage of lessening the "wobble" or "rolling shutter" artifact associated with CMOS sensors -- but -- the downside is that the 60 frames per second mode will result in *more* pixel artifacting because two frames are being processed in the same amount of time with only a modest increase in bit rate. At least, that's my opinion after quite a bit of experimentation with these clips.

The 1080/30p mode gets a higher bit rate, which helps -- but -- sometimes you only think you're seeing less artifacting because your computer's software player is -- in reality -- squeezing the 1440 x 1080 image into a smaller window for playback... resulting in what appears to be an image with fewer jaggies.
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Old Nov 7, 2008, 7:43 PM   #5
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My mistake; I thought you were making reference to the artifacting caused by low data rates. Yes, I now understand you're making reference to things like diagonal edges of linear shapes, right?
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Old Nov 8, 2008, 12:16 AM   #6
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Yes, a slightly off vertical line or edge shows it clearly.
I was hoping that the 720 only cams use a different sensor and don't
have the problem.
I guess they don't have the processing power to filter down the image properly.
But hey, for $150 it's very good for now.
-Les

Private Idaho wrote:
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My mistake; I thought you were making reference to the artifacting caused by low data rates. Yes, I now understand you're making reference to things like diagonal edges of linear shapes, right?
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