#PAR & S-VGA aspect ratio
8 messages in this thread
752/480 = 1.5666….
640/480 = 1.3333….
I'm very confused about the calculation of the PAR and the NTSC out rendering.
Now I'm setting the AR of 0.851 for 752×480 output. To minimize rendering time
& increased productivity, I decided to 3DS VIBCFG the rendering screen to only
640×480. I set the custom ratio of 640x408x.851 (just same as the 752×480) [So
far that AR is 640/408=1.568] However, when I use the 3DS's SAFE AREA feature,
I noticed that they don't match between the two! I JUST DON'T KNOW THE EXACT
FORMULA TO CALCULATE THE DISPARENCY. But I manage to eyeball and came w/ the
ratio of 0.72 . The calculation was [640x[/]408×0.72=1.129, not 1.333] Is this
corrrect or not? If it is, then how could it logically be? (The safe area
window matches w/ the AR @ 752x480x.851 .)
T-Spect,
There are two points to clarify about aspect ratios, Vibrant drivers and 3DS
that might be of some help.
1st, the formula for pixel aspect ratio is
1
pixel aspect = ——————–
(width/height)*0.75
Therefore, for 640×480 its "1", 720×486 its "0.9" and 752×480 its "0.85".
2nd, the way the vibrant drivers work is that they will set the absolute max
image size if you have it set. Therefore, if you Vibnrant setting for your VGA
card is set to 640×480 and you have Vibrant set during the rendering, the image
will still only be 640×480 even through the selected resolution is
752x480x0.85. Therefore, you need to make sure you have the renderer set to
NULL
.. that'll do it.
Ang, President Dynamic Technologies, Inc. An Autodesk Systems Center for
Multimedia in MD
Thanks for the consise formula & feedback.
>……the image will still only be 640×480 even through the selected
resolution is 752x480x0.85. Therefore, you need to make sure you have the
renderer set to NULL<
My point of configuring @ 640×480 and try to match that of the PAR's AR was
that I hate small dispay. I want everything to fill the screen as much as
possible. Another big important reason was the rendering time. After serveral
runs, I saved ~2-4 min./frame for just rendering at 640x408x0.72 then at
752x480x0.85 . [This applies to the initial design/preview stage. The final
rendering, of course, will be at full 752x480x.851 w/ NULL] The couple of
minutes might be insignificant, but it does add up the wait time.
– TSL
Lets start from the beginning as you are missing some basic understanding of
what is going on here:
The aspect ratio involves conversion of the horizontal pixel count for a
[non-square] pixel of different resolution NTSC. To fill the NTSC screen we
must also maintain an aspect ratio of 4 units wide by 3 units high. The
vertical pixel count works out nicely to 480 as the number of horizontal scan
lines in each video frame is approximately 480 in the active picture area ie.
525 less blanking and mask = approx. 480 to 492. Therefore computer hardware
manufacturers commonly choose the vertical pixel count of 480 as a matter of
economics and technical convenience in constructing the NTSC output device.
Given that the NTSC AR is 4/3 then 4/3 * 480 would conveniently give us 640.
Sound familiar? 640×480 VGA resolution. This is when the pixels are square.
But, what if the hardware mfg wants to sell a higher horizontal resolution? He
can without additional expense by keeping the vertical pixel count at 1 pixel
per scan line and more finely divide the scan line horizontally by more than
the 640 pixels. Now we have a problem as the pixels are no longer square. The
aspect ratio of the pixel must be defined. This is how it is done: eg. 640/480
* 1.0(AR)= 4/3 by the same method 752/480 * 0.851(AR) = 4/3
You can supply the algebra to do the conversion but replacing the pixel AR with
? you can solve for this by the equation ((4)(Vertical pixels)) /
((3)(Horizontal pixels)) = ? or pixel aspect ratio Doing this for the Targa+
resolution of 512X486 is ((486)(4)) / ((512)(3)) = 1.266 targa+ pixel aspect
ratio.
As for your safe frame issue: The NTSC video picture is further cropped by 10%
of the active picture area unlike computer screens which usually have a black
border. You do not need to account for this in computing the pixel aspect
ratio. However, do use it as this is a convenient tool to guage your graphics
placement to be sure all graphic elements are visible on most TV sets when
viewed.
Furthermore, please be sure you render to a "NULL device" when using these non
square pixel resolutions. This will enable an accurate safe frame display on
your square pixel computer monitor displaying the editor or keyframing screen
in 3DS.
First of all, thanks very much for the fast response to this technical issue.
The AR formula was very useful to clarify the confusions. It was very easy to
understand & I put it to action rightaway.
My point of config the Renderer @640×480 was to save precious rendering time &
fill the screen as much as possible. So I used your suggested formula for
640×408: ((408)(4)) / ((640)(3)) = .85 > PAR's aspect ratio!
[1632 / 1920 ]
By the way, I'm using the regular Trinitron monitor and planning to get the
XBR. I just can't afford $3-9K for the BVW series nor the PVV series. It had
needed features (overscan, blue, ect..) , but not important enough as RAM, hds,
ect.. Do you think the consumer XBR Trinitron is good enough?
To speed up test renderers I just do any small screen size that centers to half
the screen area, usually 320×240. It's usually to check the motion anyway.
Monitors are a personal thing. I don't favor the Sony XBR series but I do have
a PVE1344Q here and it is fine in component mode. Too much ringing in
composite though. So I'm not 100% on this monitor. The Panasonic 1350 is a
better quality picture overall but not as focused as the Sony. It's colors
seem warmer.
Thanks for the reply, continuing the related topic:
>Too much ringing in composite though.<
Speaking of ringing. I noticed that the PAR ntsc output had quite a few ringing
on virtually on all fine details of the image. My collegues have the same
problems and I think you do to. Do you know why it cause this?\ Any tips on
minimizing it?\ How come I don't see such problem on national broadcast TV?
– TSL
NTSC is 4/3 or 1.3333 ,640/480= 1.33333/1.333333 =1