On Wednesday 23 May 2007 12:14, Herman Robak wrote:
> On Wed, 2007-05-23 at 11:24 +0200, Terje J. Hanssen wrote:
> > Herman Robak wrote on Tue, 22 May 2007
> >
> > >  The display has to be stretched by the player.  If Cinelerra is told
> > > that the resolution is 1440x1080 and the aspect ratio is 16:9, it will
> > > scale the image to fit the specified aspect ratio.
> >
> > Yes, but is this managed by filling out with more pixels horisontally on
> > the display?
> > If I'm right the display pixels are square i.e on a UWXGA LCD 1920x1200
> > in aspect ratio 16:10=1.6
> > I can't see how else the video frame can get the right 16:9 aspect ratio
> > geometry...
>  That is correct.  The player (here: Cinelerra) has to interpolate the
> 1440 "source" pixels into 1920 "screen" pixels.  And the player assumes
> square screen pixels, which _may_ be wrong, even for computer displays.
>  The important term here is "pixel aspect": the aspect ratio of the
> pixels.  1440:1080 = 12:9.  1920:1080 = 16:9.  So 12 source pixels
> need to be stretched to 16 screen pixels.  That gives you a pixel
> ratio of 16:12, or 4:3.  That's a fairly nice pair of numbers, compared
> to the oddball pixel ratios of NTSC and PAL.

Note that Cinelerra does two tasks: render and display.

To render, Cinelerra treats the 1440:1080 as square pixels. This is not 
optimal if something you render has both horizontal and vertical extent, but 
is driven by only one parameter, like the radius of the radial grandient, a 
radial blur, or the 'feather' radius of the masks. Such things will turn into 
ellipses because:

To display, Cinelerra simply stretches the available pixels to 16:9 ratio.

-- Hannes

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