#420 Aspect Ratio Correction Error

[Paulo Roberto]

I found a error in aspect ratio correctio in XBMP CVS 24
sep 2003. I have a 4:3 tv set and my full screen
calibration is 36,16 / -34,-14 .My real screen resolution
is 650x450.

Original resolution is 720x480 = Aspect Ratio ( 1.5 )
My final resolution is 650x450 = Aspect Ratio ( 1.44444 )
A 4:3 tv set Aspec Ratio is ( 1.33333 )

XBMP use a ARC ( Aspect Ratio Correctio ) but the
actual CVS do it wrong.

-- Actual CVS "ARC" calculation is :

Final Resolutio AR ( 1.44444 ) / Original Resolution AR
(1.5 )

Aspect Ratio Correctio (ARC) = 0,96296 ( This value
don't work for 4:3 tv sets )

>>> Take this example :

Original movie is 512x384 ( 1,33 ) and my final resolution
( after calibration ) is 650x450 (1.44444 )

1,33333 x ARC ( 0,96296 ) = 1.28 ( Final Aspect ratio )

My final movie resolution using Aspect Ratio (1.28) is
650x508 ( bigger then my screen ).

This error cause a strange 577x450 filme and don't fullfill
my screen.

-- The right "ARC" is :

Final Resolutio AR ( 1.44444 ) / TV set Aspect Ratio (
My case 4:3 = 1.33333 )

Aspect Ratio Correctio (ARC) = 1,0833327

>>> Using the same example :

Original movie is 512x384 ( 1,33 ) and my final resolution
( after calibration ) is 650x450 (1.44444 )

1,33333 x ARC ( 1,0833327 ) = 1.44444 ( Final Aspect
Ratio )

My final movie resolution using Aspect Ratio 1.44444 is
650x450 ( Perfect fullfill my screen ).

I hope that developers read this and fix the ARC ( using
the aspect ratio of tv sets 4:3 / 16:9 ) in the next CVS.

Congratulations for the good work and i really ( really )
tanks for this great program...

[Jonathan Marshall]

Logged In: YES
user_id=851643

This is a known problem - and your maths is correct, although
your ratios are not quite right. The problem is that your Final
Resolution (650x450 in your case) is not the frame size that
defines the 4:3 area in the PAL or NTSC standards. For PAL, the
4:3 frame is 702x576 pixels. For NTSC it's 702 (and a bit)x486
pixels.

I have coded this correctly in XBMC, and may get around to
porting it back to XBMP at some point, but I don't have a lot of
time.

2 things need to be done: First, the aspect ratio code has to
take the final pixel ratios into account, and second, the Aspect
Ratio Correction during calibration needs to be converted from
an additive constant to a multiplicative constant.