I have been making a variety of animation which are being exported to 
video.  I've been exporting to both DVD (1.33:1) and HDTV (16:9) 
formats.  I've been using commands within the camera to set the aspect 
ratio; for example DVD aspect ratio is done as follows:

camera {
   location <0,12,-12>
   look_at <0,8,0.01>
   up <0,1,0>
   right <1.33,0,0>  //this would be 1.85 for HDTV
   angle 60
        }

Unfortunately, this means that I have to manually adjust both the aspect 
ratio (in the camera command) and the image resolution (in the drop-down 
menu for resolution.ini).  I'm a little forgetful, which means that I've 
rendered several animations where the aspect ratio and resolutions did 
not match.  Which means that I loose hours of time rendering videos 
which are totally distorted.

So is there some way I can add the aspect ratio into the resolution.ini 
file so that when I pick the resolution the appropriate aspect ratio is 
also picked?

Thanx

Bryan

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Bryan Heit <bjh### [at] NOSPAMucalgaryca> wrote:
>    right <1.33,0,0>  //this would be 1.85 for HDTV

right     x*image_width/image_height

where image_width and image_height are built in variables in which Pov
stores the width and height of the image as defined in the drop menu or ini
file.

JYR

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On Wed, 28 Dec 2005 21:34:48 -0500, JYR wrote:

> Bryan Heit <bjh### [at] NOSPAMucalgaryca> wrote:
>>    right <1.33,0,0>  //this would be 1.85 for HDTV
> 
> right     x*image_width/image_height
> 
> where image_width and image_height are built in variables in which Pov
> stores the width and height of the image as defined in the drop menu or ini
> file.
> 
> JYR

This will create an image with square pixels.  DVD needs non square
pixels, the image resolution could be 702*480,720*480,720*576,720*576
among others all at an aspect ratio of 4:3.

If you always set specific resolutions for standard or HDTV, you could
test for those and set the aspect ratio to 4/3 or 16/9 accordingly.

#if ( (image_width = 720) & (image_height = 576) )
  aspect = 4/3
#else
  aspect = 16/9
#end

Post a reply to this message

Or you could also declare your aspect ratio as a constant within the ini
file:
Declare = asp_rat = 1.33333
and then refer to that constant in the scene.
See the help section 3.1.2.5.1  Constant

Charles

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JYR <jyr### [at] hotmailcom> wrote:
> right     x*image_width/image_height

  Using that is not a good idea. There are several reasons:

  If the aspect ratio of the image is adjusted automatically like this,
it means that if someone renders the image with a resolution having a
different aspect ratio than what the author intended, the resulting image
will be either cropped or parts of the scene not seen in the original will
come into view. In many cases this is a bad thing because it affects (usually
negatively) the composition of the scene: Important parts of the scene may
get cropped out of view, or parts of the scene not intended to be seen
(eg. because of lack of modelling) suddenly come into view. If someone
does this he might often not even notice that there's something wrong with
the image.

  If the viewing angle is adjusted with the 'angle' keyword
(as is rather usual), it introduces a rather unwanted effect when
used in addition to the automatic aspect ratio setting with 'right':
The aspect ratio of the image will in this case always be done
in the vertical direction, either by cropping or extending the image in
the upper and lower sides. This means that if you try to eg. render a
"widescreen" version of the scene, you will only end up cropping the
image from the upper and lower sides (instead of adding new scenery
to the left and right sides). More often than not, scenes are designed
to be rather "panoramic" in nature, ie. the image can be expanded
horizontally. However using the automatic aspect ratio correction along
with a fixed 'angle' setting will not achieve this.

  The automatic aspect ratio correction given above assumes that pixels
are square. There are cases where one *wants* to render an image
for a resolution with non-square pixels (examples include the Windows98
startup screen, which uses a resolution of 320x400, and a DVD movie,
where the video has always an aspect ratio of 1.78:1 although it can then
be stretched to the intended aspect ratio, eg. 2.35:1 by the player). If
the automatic aspect ratio correction is used, it would not be possible
to render an image with non-square pixels without modifying the scene.

  The usage of the keywords image_width and image_height are due to change
in future versions of POV-Ray because they break the frontend-backend
boundary, which can cause problems when more complex ways of rendering
scenes are introduced to the program.

-- 
                                                          - Warp

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PoD wrote:
> #if ( (image_width = 720) & (image_height = 576) )
>   aspect = 4/3
> #else
>   aspect = 16/9
> #end


Thanx, that'll work perfectly (with a bit of modification).  I just need 
to adapt it so that it'll work properly with the lower-resolution "test" 
settings...

Bryan

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JYR wrote:
> Bryan Heit <bjh### [at] NOSPAMucalgaryca> wrote:
> 
>>   right <1.33,0,0>  //this would be 1.85 for HDTV
> 
> 
> right     x*image_width/image_height
> 
> where image_width and image_height are built in variables in which Pov
> stores the width and height of the image as defined in the drop menu or ini
> file.
> 
> JYR

Won't work.  The way you are calculating aspect ratio assumes square 
pixels (i.e. aspect of 1:1, or 1.0), whereas DVD/HDTV/TV use rectangular 
pixels.  In the case of DVD the aspect ratio of each pixel is 4:3 
(1.33), and for HDTV it is 16:9 (1.85).

If you work out the ratio you calculate you get 1.5 for DVD resolution 
images, quite a bit off of the 1.33 standard.  The HDTV is even more 
warped if you calculate the aspect ratio based on horizontal/vertical 
pixels.

It's irritating as hell - most computer media players don't play back 
the animation with non-square pixels, so it looks warped on the 
computer, but fine on the output...

Bryan

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On Thu, 29 Dec 2005 02:06:36 -0500, Charles C wrote:

> Or you could also declare your aspect ratio as a constant within the ini
> file:
> Declare = asp_rat = 1.33333
> and then refer to that constant in the scene.
> See the help section 3.1.2.5.1  Constant
> 
> Charles

Cool, I didn't know about that one. (Starts reading docs again)

Post a reply to this message

Bryan Heit wrote:
> pixels.  In the case of DVD the aspect ratio of each pixel is 4:3 
> (1.33), and for HDTV it is 16:9 (1.85).

sorry for my noobiness, but isn't 16:9 = 1.78? i often use the terms 
"1.33" and "1.85" when talking about my dvds, but i never before 
actually *calculated* what 16:9 equals. am i wrong?

bob

Post a reply to this message

bob <bob### [at] mailcom> wrote:
> sorry for my noobiness, but isn't 16:9 = 1.78? i often use the terms 
> "1.33" and "1.85" when talking about my dvds, but i never before 
> actually *calculated* what 16:9 equals. am i wrong?

  16:9 is 1.777...:1

  1.85:1 is the least wide format commonly used in movies nowadays
(from what I have seen it seems to be getting rarer, in favor of 2.35:1).

-- 
                                                          - Warp

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