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Probably a stupid question, but it wouldn't be the first time, so here
goes...
In the next month or two, I will finally be acquiring a DVD burner for my
poor little G3, and one of the first things I want to do after I get it is
put together a DVD with all the movies I've created to date. Some of my
movie's are shot at 16:9 aspect ratio, others at 4:3, all of them were
rendered with a width of 320 pixels. Obviously, this won't do for DVD --
therefore, I must re-render everthing.
My question for those who've created DVDs is what is the optimum image size
to render at? This is assuming NTSC settings, which I think are 720 x 480,
but that's a 3:2 aspect ratio, which will make my movies look stupid (well,
more so than they already are...). Of
course, I have no idea what I'm talking about, so if some kind soul could
possibly point my clueless brain in the right direction, I would greatly
appreciate it.
Thanks kindly in advance :)
--
Dan
GoofyGraffix.com
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Le 09/20/2006 03:51 AM, Dan Byers nous fit lire :
> Probably a stupid question, but it wouldn't be the first time, so here
> goes...
>
> In the next month or two, I will finally be acquiring a DVD burner for my
> poor little G3, and one of the first things I want to do after I get it is
> put together a DVD with all the movies I've created to date. Some of my
> movie's are shot at 16:9 aspect ratio, others at 4:3, all of them were
> rendered with a width of 320 pixels. Obviously, this won't do for DVD --
> therefore, I must re-render everthing.
>
> My question for those who've created DVDs is what is the optimum image size
> to render at? This is assuming NTSC settings, which I think are 720 x 480,
> but that's a 3:2 aspect ratio, which will make my movies look stupid (well,
> more so than they already are...). Of
> course, I have no idea what I'm talking about, so if some kind soul could
> possibly point my clueless brain in the right direction, I would greatly
> appreciate it.
720x480 NTSC (at ~30fps) is DVD... of course 720x480 is 3:2 with
square pixel, but the DVD pixels are not square!
The setting 16:9 or 4:3 is a field in the header of the movie.
Also, to make DVD, encoding must be Mpeg-2, with a limit bitrate of
10Mbps (sound included, if any).
Making the menu of the DVD is the hardest part: playing movie
streams is very easy!
--
The superior man understands what is right;
the inferior man understands what will sell.
-- Confucius
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Many thanks! :)
--
Dan
GoofyGraffix.com
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This is easy to do, but requires a bit of extra code to get right. DVD
(NTSC) has a resolution of 720x480 and an aspect ratio of 4:3. This
means that the image does not have square pixels. This means if you
render in povray without a little bit of extra code you'll end up with a
warped image (povray assumes square pixels and will render a 720x480 at
an aspect ratio of 3:2, not 4:3). So what you need to do is feed povray
the correct aspect ratio.
There are a number of ways to do this (most covered in the "Render HD
format", 4 threads above this one). My favorite way of doing this is
within the camera command:
camera {
location <0,0,0>
look_at <0,0,1>
up y
right x*(aspect ratio)
}
The important parts of this are the up and right commands - these two
commands set the aspect ratio of the image. You also need to render at
720x480 (i.e. by adding the relative code your resolution.ini file, or
setting it in the command line). Seems obvious, but I've screwed that
one up more then once.
As for the 16:9, you have two options. One is to render at 720x480, and
put black pars above/below the image. This is called "letterboxing" and
was quite common with older DVD's. The second option (which is how its
done on modern 16:9 DVD's) is to render at 720x480, but with 16:9 set
for the aspect ratio. You then need to tell the DVD that it is in
widescreen format. This is in the MPEG2 file header, under the DAR
(display aspect ratio) flag. This is something you set while authoring
the DVD, assuming you're software supports 16:9 resolution for DVD's (a
lot of the non-professional DVD encoders do not support 16:9).
Obviously the second option is the ideal one, as you do not loose image
resolution by rendering the black boxes. Downside is that many
non-commercial DVD encoders do not allow for wide-screen format, and
among those that do, few offer mixed-format DVD's. Adobe encore allows
for both 16:9 and mixed-ratio, but that's the only non-professional
software I know of which has that feature.
It's easiest to just pick one format and stick with that for the whole
disk. Plus it maximizes the computability with older DVD players, some
of which may not like mix-aspect disks.
Hope this helps, and makes sense.
Bryan
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Bryan Heit <bjh### [at] nospamucalgary ca> wrote:
> (povray assumes square pixels and will render a 720x480 at
> an aspect ratio of 3:2, not 4:3).
This is simply incorrect.
POV-Ray doesn't make any assumption on pixel aspect ratio whatsoever.
The only assumption it makes is the whole-image aspect ratio, which by
default is 4:3, but changeable with the 'right' keyword.
This means that if you render an image (without specifying any 'right'
in the camera) with an aspect ratio other than 4:3, the contents of the
image will not change (IOW the portion of the scene which the viewing area
covers will remain the same). In other words, the result will be "squeezed"
if viewed with square pixels.
If you want to render an image with an aspect ratio of 4:3 (regardless
of the shape of the pixels in the target media) then you don't have to
do anything to the scene. You just render it with the resolution of the
target media (eg. in this case DVD). If the target media stretches the
image so that it will cover a 4:3 area (IOW uses non-square pixels), then
the image will be correct.
Only if you want to change the aspect ratio of the image without
changing the aspect ratio of the pixels, then you have to use the
'right' keyword for that.
--
- Warp
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Warp wrote:
> Bryan Heit <bjh### [at] nospamucalgaryca> wrote:
>> (povray assumes square pixels and will render a 720x480 at
>> an aspect ratio of 3:2, not 4:3).
>
> If you want to render an image with an aspect ratio of 4:3 (regardless
> of the shape of the pixels in the target media) then you don't have to
> do anything to the scene. You just render it with the resolution of the
> target media (eg. in this case DVD). If the target media stretches the
> image so that it will cover a 4:3 area (IOW uses non-square pixels), then
> the image will be correct.
Although this is how it is implemented in the documentation, it is not
how it is implemented in the real world - at least in windows version
3.6.1c of povray. I've rendered over 30 hours of video (video time, not
rendering time), and if you do not manually enter the "right x*(4/3)"
command into the camera you get a distorted image on the DVD identical
to the distortion seen if you import a 720x480 square-pixel image. I've
seen this effect in multiple video-editing programs, so I doubt its a
software issue downstream of povray.
Bryan
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Bryan Heit <bjh### [at] nospamucalgaryca> wrote:
> and if you do not manually enter the "right x*(4/3)"
> command into the camera you get a distorted image on the DVD
That should be impossible because <1.33, 0, 0> is the default 'right'
for the camera setting when none is specified. Specifying it explicitly
doesn't change anything.
Could you post an example code which shows the behaviour you are
describing? (IOW a scene which rendered without "right x*4/3" and
with a non-4/3 resolution gives a *different* result than when the
'right' line is added.)
I can't think of any other camera parameters (except 'up') which would
affect its aspect ratio.
--
- Warp
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Warp wrote:
> Bryan Heit <bjh### [at] nospamucalgaryca> wrote:
>> and if you do not manually enter the "right x*(4/3)"
>> command into the camera you get a distorted image on the DVD
>
> That should be impossible because <1.33, 0, 0> is the default 'right'
> for the camera setting when none is specified. Specifying it explicitly
> doesn't change anything.
As I said, it's whats in the documentation, but it doesn't seem to work
out that way. I'll try and dig up some of my oldest animations I made
for DVD - there were a few I remember where the distortion was quite
strong. If I can't find it I'll just render a cube, burn it to disk,
and snap some photo's with my camera.
Another thing worth pointing out is that the images look fine on the
computer monitor - it is only after export that the distortion occurs.
It may be that povray is rendering it properly, but something is screwed
up in the file headers (or wherever aspect ratio would be written).
> Could you post an example code which shows the behaviour you are
> describing? (IOW a scene which rendered without "right x*4/3" and
> with a non-4/3 resolution gives a *different* result than when the
> 'right' line is added.)
I'll try and dig up a scene. But I can pretty much replicate the code
here - keep in mind I had these issues when I first started, before I
had learned the wonders of the 'right' and 'up' command...
I was using nothing more then:
camera {
location <x,y,z>
look_at <x,y,z>
angle ...
}
Rendered at 720x480 this looked fine on the computer screen, but when
exported to DVD had a noticeable distortion. Altering this to:
camera {
location <x,y,z>
look_at <x,y,z>
up y
right x*(4/3)
angle ...
}
Solved that issue. Image looks identical on the computer screen,
compared to the one rendered above, but does not get distorted when
exported to DVD.
> I can't think of any other camera parameters (except 'up') which would
> affect its aspect ratio.
Nor can I. I don't know a lot about file formats, but given that the
images look OK on computer, but wrong on the DVD, I suspect that povray
isn't putting some information into the header of the file outlining
aspect ratio, or something along those lines. Likewise, I have no idea
if this is a windows-only thing, or a general issue. I don't think it's
because of the video software I'm using, as I've used all of the
following programs for bmp -> avi conversion and seen the same thing:
ImageJ
AVISynth
Virtual Dub
Bryan
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Bryan Heit <bjh### [at] nospamucalgaryca> wrote:
> As I said, it's whats in the documentation, but it doesn't seem to work
> out that way.
Rest assured that if it didn't work that way, I would have noticed.
After all, I have written things like this:
http://tag.povray.org/povQandT/languageQandT.html#aspectratio
> Solved that issue. Image looks identical on the computer screen,
> compared to the one rendered above, but does not get distorted when
> exported to DVD.
Which image format did you use? OTOH, I don't understand why that
would make any difference.
--
- Warp
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Warp wrote:
> Which image format did you use? OTOH, I don't understand why that
> would make any difference.
BMP.
Bryan
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