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Triggerle
1st January 2002, 20:57
Hello,

As some of you living in central western Europe might know, some tv stations broadcast some of their shows in anamorphic encoding. With my Radeon AiW I get black bars at top and bottom and the picture is skewed.

Can anyone supply me with details on anamorphic tv broadcasts? How do I have to change the aspect ratio of my capture to get the original aspect ratio?

Many thanks,

Triggerle

rmatei
1st January 2002, 22:53
I don't think there's such a thing as anamorphic TV, you just mean letterboxed. Then the black bars are normal and you have to crop & resize to "make them go away" which is bad. (sorry if I insult your intelligence)

I don't know what you mean by skewed but if you mean that it has the wrong aspect ratio, then the theory is simple. To get correct aspect ratio for non-anamorphic signals (this includes all analog TV) you resize so that width/height = 4/3; for anamorphic signals width/height = 16/9.

Triggerle
2nd January 2002, 10:15
These broadcasts are not just letterboxed...the black bars contain (almost) invisible information of the original 16:9 source. Newer television sets can decode this extra information and display a better 16:9 picture. This broadcasting standard is called PALplus. It is only selected shows on some stations that are broadcasted in this format (ARD's 'Tatort' is such a show for example).

On an old 4:3 display i get a letterboxed image which is also off in the aspect ratio (the people look thinner than they are.) However, the aspect ratio is not off by much (still noticeable, I think) and a letterboxed->16:9 conversion would result in much too fat people :)

Triggerle

--edit--

I found something: http://tallyho.bc.nu/~steve/palplus.html

--/edit--