Dan Byers wrote:
> ....is it normal to lose the edges of your video when making a DVD?  I put a
> couple of my animations on a test DVD, and when I view it on the TV, it
> looks like it's cropped part of the video on all four sides.  Nothing TOO
> catastrophic, but definitely noticable (to me, anyway).  Normal behavior,
> or did something go awry?  If you need more specifics, let me know...
> --
> Dan
> GoofyGraffix.com

It's called "overscanning", a hold-over from the bad-old-days of analog 
TV (oh wait, it's still the bad old days).  Long story short, it used to 
be hard to make TV's which would consistently project in the exact same 
way, and as such they could never be sure as to where the edges of the 
image would appear on the TV.  As such, overscanning was invented as a 
way around this - the image on the TV would be deliberately projected 
larger then the actual screen, thus ensuring the whole screen would 
always be filled.  TV shows were filmed with this in mind - action and 
detail was kept away from the edges, so nothing would be lost.

Today this standard has been kept, even though the technical issues have 
been resolved.  Even some HDTV TV's overscan; even though the standards 
were for no overscanning.  When it comes to video editing the following 
"rules" are usually followed, they work for povray animations as well:

1) Important action is not allowed within the outer 5% of the image. 
Meaning, if your image is 100 pixels wide you wouldn't allow the action 
to extend into the last 5 pixels on the left, right, top or bottom of 
the screen - i.e. you loose 10% of the image along each axis.

2) Important static images are kept out of the outer 10% of the screen. 
  This is because warping can occur near the overscan area.  This is 
hidden by moving images, but not by static images.

In video editing we use screen markers to keep things simple; see the 
"safe action and safe titles areas" on the following page for an example:

http://scanline.ca/overscan/

I actually have an overhead with these lines marked on (for a 720x480 
render) which I tape to my computer screen when setting up povray 
animations.  It makes this alignment easy.  Another, slightly slower 
method, is to render at a larger size (say 800x600) and a slightly wider 
camera angle, and then resize the image afterwards using video editing 
software to fit what you want into the safe image area.

One last point, which Warp already made, is that most computer DVD 
players will play back the whole image - not just the overscan part, so 
if you watch the DVD on your computer you'll probably see the whole thing.

Bryan

Post a reply to this message