[mythtv] automatic 14:9 or 4:3 zoom based on black bars detection?

Peter Schachte schachte at csse.unimelb.edu.au
Sun Jul 23 12:19:54 UTC 2006


[Sorry for resurrecting an old thread.  Just catching up on my
reading...]

On Sun, Jun 25, 2006 at 07:47:41PM +0200, Petr Stehlik wrote:
> Daniel Kristjansson pí?e v Ne 25. 06. 2006 v 11:41 -0400:
> > There are three distinct reasons
> > why people use the aspect ratio overrides.
> >  1/ For coping with material that misreports the aspect ratio;
> >     or does not report it at all and uses non-square pixels.
> >     This would never be a 14:9 aspect ratio BTW, as we are 
> >     refering to the aspect ration of the transmission including
> >     the black bars.
> >  2/ For zooming into material simply as you do ( and I do ).
> >     "Proper Zoom"
> >  3/ For filling the screen with video when the aspect ratio
> >     of the source material does not fit the display aspect ratio.
> >     This results in either lost portions of the image, or the
> >     improper aspect ratio; but this is the desired result.
> >     "Improper Zoom"

Maybe the user setting should be split into two separate settings:

	Override aspect ratio:
		o  no override (use program's reported aspect ratio)
		o  program is really 4:3 (whatever it reports)
		o  program is really 16:9 (whatever it reports)

and

	Adjust Fill:
		o  Whole image (Makes image is as large as possible
		   without clipping any, while maintaining aspect ratio)
		o  Fill (Zooms image to fill the screen, maintaining aspect 
		   ratio, clipping as little as possible)
		o  Stretch (Stretches image to exactly fill screen, 
		   distorting image to match display aspect ratio)

This, I believe, should cover the aspect ratio override options
currently in myth (except maybe fill?), and works equally for any
combination of programming and display aspect ratios.

I know we're trying to minimize the number of settings, but I think
this actually simplifies things, since you'd usually set the "adjust
fill" to suit your personal preference, and "override aspect ratio"
when the incoming signal reports the wrong aspect ratio.  And if an
effective real aspect ratio inference feature is added to the
comflagger as discussed elsewhere in this thread, it only affects the
"override aspect ratio" option; the user setting for "adjust fill"
would be unaffected, and myth would automatically do the right thing.
I think this is what the OP was after.

Now to the OP's idea of a 14:9 zoom.  This could be put in as a new
adjust fill option called 14:9, and would also work equally well in
letterbox and pillarbox situations.

But there's one more option that would be worth considering; I'll call
in "compromise."  This would zoom (and clip), stretch (distorting the
aspect ratio) and leave black bars in equal proportions.  This is what
my analog widescreen TV does by default for 4:3 programming, and it
works pretty well.  When stretching 4:3 programming to a 16:9 display,
it gives you black bands on the sides totalling about 11% of the width
of the screen, it clips about 11% of the height of the source image,
and it distorts the image by stretching it 11% horizontally.  In
practice, you can barely see the stretching, you don't really miss the
clipped part, and you hardly notice the narrow black bands on the
sides.  This approach should work equally well for displaying a 16:9
program on a 4:3 display, and would even extend to showing a
wider-screen DVD movie (maybe 2.something:1?) on a widescreen TV.

-- 
Peter Schachte              It is only with the heart that one can see
schachte at cs.mu.OZ.AU        rightly; what is essential is invisible to the
www.cs.mu.oz.au/~schachte/  eye.
Phone: +61 3 8344 1338          -- Antoine de Saint-Exupery 


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