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Old December 14th, 2011, 12:25 AM   #1
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Aliasing?

Looking at some 1080p footage from the VG20 online, I noticed what appear like interlacing artifacts whenever there is movement against a high contrast background. Is that the result of aliasing or is it something else?

For example, at about 0:18 in this video artifacts are clearly visible around the heads of the man and woman walking toward the ticket window. The same happens in the scene after when the girl wearing the maroon hat moves her head.
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Old December 14th, 2011, 05:27 AM   #2
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Re: Aliasing?

To be honest, here in Europe, 50i and 50p are really suffering from a very important aliasing and moire.

I was about to return my VG20, but I did some tests on 25p:
Good surprise: Aliasing and moire much less present, enhanced details,
and finally, an image quality quite good, in my opinion.
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Old December 14th, 2011, 10:02 AM   #3
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Re: Aliasing?

That is regular old interlacing. The person who uploaded the file was not
clever enough to deinterlace it before posting it. Not the fault of the camera.

The effect called aliasing is usually most visible with small amounts of motion on
subject matter that has lots of fine detail that repeats. It will show a Moire pattern
or the news-anchor's tie effect. I usually look for it on high-contrast transitions
between dark and light like a bright white edge. If the edge has lots of color-sparkle
it is a sign that the debayering algorithm can't deal with all the aliasing caused by
the sensor processing resolution/lens resolution mismatch.
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Old December 15th, 2011, 02:54 AM   #4
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Re: Aliasing?

Interesting, I didn't know the VG20 had interlace modes. So why does the 25p reduce the effects of aliasing present in 50p?

With standard definition 480i video, I'm used to the aliasing effect appearing on clothing or curtains that have closely packed stripes of contrasty fabric.

Are there any samples online of obvious aliasing artifacts appearing in high definition videos?
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Old December 15th, 2011, 03:19 AM   #5
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Re: Aliasing?

Here are some samples of my "torture tests"
Attached Thumbnails
Aliasing?-vg20-ext-50p.jpg   Aliasing?-vg20-ext-50p-detail.jpg  

Aliasing?-vg20-ext-25p.jpg   Aliasing?-vg20-ext-25p-detail.jpg  

Aliasing?-stores-50i.jpg   Aliasing?-stores-25p.jpg  

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Old December 16th, 2011, 10:03 PM   #6
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Re: Aliasing?

The venetian blind photos have the high-contrast edges and show
significant chroma aliasing. The debayering algorithm is slamming
between green and purple and neither is correct.

All of these s35 cameras other than the F3/FS100 are going to have
some degree of aliasing.

Quote:
Originally Posted by Adam Palomer View Post
Interesting, I didn't know the VG20 had interlace modes. So why does the 25p reduce the effects of aliasing present in 50p?
I am guessing here but with half the frames per second the processor has twice as much time to
process each frame. With more time, the processor can average together more pixels and do
a better anti-aliasing job. At 50P there just isn't enough time to properly process all the pixels
coming off that massive sensor.
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Old December 17th, 2011, 04:15 AM   #7
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Re: Aliasing?

A good Optical Anti Aliasing Filter would be a great Christmas gift !
is there someone from "Mosaic Engineering" who takes requests on "DVINFO"? ;-)
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