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Old January 19th, 2003, 03:11 AM   #1
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two fields not in sync?

Could someone please have a look at this image :

It is a jpeg picture the full bitmap image is also availible at 1.2Meg, captured it off a video file using premiere.

It seems to occure only when the camera (Canon xl1s) pans. I believe it is caused in the camera, but maybe it could be related to my pc.

Could anybody tell me the probabile cause.

Thank you

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Old January 19th, 2003, 05:19 AM   #2
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Did you de-interlace the frame before saving? You can do that either in Premiere before saving or with Photoshop after the frame has been extracted from the timeline.
Ed Frazier
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Old January 20th, 2003, 04:04 PM   #3
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That is known as interlacing artifacts. There have been very
lengthy discussion on this board regarding interlacing and I
suggest you use the search feature above to find those threads
(try searching for: interlaced, interlacing, progressive etc.).

The "problem" comes from a difference between your TV and
the computer screen. TV's are interlaced and computer monitors
are non-interlaced (also known as progressive).

What does interlaced mean? Interlaced means that your picture
gets divided in two. The first block contains all the even lines
(for example) and the second block all the odd lines. These are
recorded, transmitted and displayed very fast after eachother.
Your eye doesn't really see the difference and sees it as one
picture. Since the picture is basically being recorded AT TWO
DIFFERENT POINTS IN TIME (very small differences, but still) you
can SEE the difference on a computer monitor since it shows you
the whole image in one go. Therefor it is more or less incorrectly
showing you the two blocks of the image at the same time while
it should have been slightly after eachother.

This is not a real problem, why? Well, let me explain the methods
of distribution:

1) (S)VHS / SVCD / DVD
These can be encoded in interlaced and will play back fine on
any TV since they natively understand interlaced. If you playback
a DVD on your computer your DVD player software will de-interlace
the picture on the fly and try to make it look as good as possible

2) VCD / web
If you go with any of these formats the resolution will be lowered
and one of the blocks will dissapear. Therefor the time difference
is gone and you will not see any interlacing artificats.

3) Full resolution computer video
Here you might have a problem with viewability. See some
suggestions below.

If you don't want these interlacing artifacts there are two things
to do (depending on what camera you have). If you have a Canon
XL1(s) for example you can set it up to record in progressive/frame
mode so that it doesn't have the little time differences and therefor
those lines.

You might also de-interlace your footage after you transfer it
to your computer. Most editing applications support this (how
good it will turn out might differ greatly!) and there are some
special applications/plugins available just for this job.

I hope this has explained it a little bit. Some other people will
probably chime in to give you their explenations and opinions.

Good luck!

Rob Lohman,
DV Info Wrangler & RED Code Chef

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