[vlc-devel] Re: VCD OGT subtitles and rescaling

R. Bernstein rocky at panix.com
Tue Dec 23 20:34:36 CET 2003

 > I don't understand what you mean by antialiasing here. 

Subtitles in SVCD OGT, CVD (and I think also DVD's) are pretty limited
in the number of colors that they can use. For SVCD, the palette is 4
colors. However one color, (usually color 0 which allows for a length
1-4 RLE), is transparent. So you have 3 colors: white, black and
something in between. The text bitmaps that you get appear
jagged. However the underlying chroma (I'm using YUV) doesn't suffer
such limitations. Hence antialiasing may be a win.

 > I also still don't
 > understand why you want to reuse the dvd rendering procedure. 

The state of developer documentation (and as I am learning, useful
support routines) are not to the stage where one (or at least not me)
would be able to do much than take existing working code, and read
that in order to infer how things work. In such an environment, one
may as well modify the code since one has to dig deeply in to it
anyway. No, it's not the way I prefer to work.

 > Why not write
 > a little function what does this directly, and not encode/decode an extra
 > time.

Antialiasing is a separable filter. Scaling is a separable filter. It
might be possible to interpret OGT and CVD-specific format, antialias
it, scale it and encode into the right chroma in one step. However for
me right now, it would be too complex to understand and difficult to

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