scott <sco### [at] scottcom> wrote:
> >  What happens when you *want* to render the image for a resolution with
> > non-square pixels?

> You specify in some way that you want this, rather than it being the default 
> behaviour.

  I'd want it the other way: If you want to use a different camera aspect
ratio you have to specify it. By default the camera aspect ratio should be
preserved.

> >  (Yes, there are such situations, and they are pretty common. Search for
> > "anamorphic" if you don't believe me.)

> Whilst they may be pretty common, I can't believe they are as common 
> compared to people who change the aspect ratio for rendering as a desktop 
> wallpaper or printing out on certain sized paper.

  Have you taken into account that someone rendering someone else's scene
using an aspect ratio different than what the original author intended
might end up with an image which either clips out parts of the original
image or, worse, shows undermodeled parts which were not meant to be seen?

  Shouldn't the choice of how changing the aspect ratio of the camera
affects the composition of the image be left to the author of the image
rather than the person who renders the image (given that sometimes these
are two different people)?

-- 
                                                          - Warp

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>  Have you taken into account that someone rendering someone else's scene
> using an aspect ratio different than what the original author intended
> might end up with an image which either clips out parts of the original
> image or, worse, shows undermodeled parts which were not meant to be seen?
>
>  Shouldn't the choice of how changing the aspect ratio of the camera
> affects the composition of the image be left to the author of the image
> rather than the person who renders the image (given that sometimes these
> are two different people)?

If you read the rest of my post you'll see that I 100% agree with you, and 
this is what my proposed syntax allows, albeit with more flexibility than 
the existing one.

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scott <sco### [at] scottcom> wrote:
> If you read the rest of my post you'll see that I 100% agree with you, and 
> this is what my proposed syntax allows, albeit with more flexibility than 
> the existing one.

  It is currently possible to make a camera which always assumes square
pixels. Doing so in a way that changing aspect ratio affects the composition
of the image vertically (ie. the image is clipped or extended on the upper
and lower sides) is easy. The horizontal equivalent requires a bit more
work, but is also perfectly possible.

  (Personally I don't really recommend doing so, for the stated reasons.
I'd say the principal reason is that rendering for an anamorphic resolution
with non-square pixels cannot be done without modifying the scene file.)

-- 
                                                          - Warp

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scott wrote:
> camera{
> hfov 90
> }

What's wrong with the "angle" keyword?

-- 
Chambers

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"scott" <sco### [at] scottcom> wrote:
> Then, of course you could specify both "hfov" *and* "vfov" if you really
> wanted both directions to be fixed, this would allow for non-square pixels.

Not the ideal solution, as getting from the desired image & pixel aspect ratios
(which I expect to be *the* known values in such cases) to the angles requires
some messing around with trigonometrics.

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Chambers <Ben### [at] gmailcom_no_underscores> wrote:
> scott wrote:
> > camera{
> > hfov 90
> > }

> What's wrong with the "angle" keyword?

  It sets the horizontal field of view (regardless of what the camera
aspect ratio is). Making it set the vertical field of view instead requires
something more complicated.

-- 
                                                          - Warp

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Warp <war### [at] tagpovrayorg> wrote:
> > You specify in some way that you want this, rather than it being the default
> > behaviour.
>
>   I'd want it the other way: If you want to use a different camera aspect
> ratio you have to specify it. By default the camera aspect ratio should be
> preserved.

Me, I cast my vote for the default-to-square-pixels approach.

>   Have you taken into account that someone rendering someone else's scene
> using an aspect ratio different than what the original author intended
> might end up with an image which either clips out parts of the original
> image or, worse, shows undermodeled parts which were not meant to be seen?

This argument is a bit short-sighted: The same could be said about rendering an
image at a much higher resolution than originally intended by the author -
which may get you "undermodeled" parts *everywhere*.

Furthermore, an author cannot pass on his scene's source code and at the same
hide those undermodeled parts from curious eyes - just a few changes to the
camera block will reveal them anyway.


Even so, as some previous poster mentioned, a possible solution to this issue
would be to allow the scene author to specify (in the camera settings) how to
deal with non-matching aspect ratios, by choosing between (e.g.)

  a) adjust horizontal field of view to fit
  b) adjust vertical field of view to fit
  c) enlarge field of view to fit
  d) reduce field of view to fit
  e) distort to fit
  f) enforce aspect ratio

(Option f) could pick a resolution with about the same total number of pixels as
specified on the command-line / ini file, but the ratio chosen by the scene
author.)

If complemented with command-line / ini options to explicitly specify a pixel
aspect ratio, I guess we'd have all aspect ratio issues solved.

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clipka <nomail@nomail> wrote:
> Me, I cast my vote for the default-to-square-pixels approach.

  Why? You can *already* do that with the current POV-Ray. There's no need
to add anything new to get the behavior.

> >   Have you taken into account that someone rendering someone else's scene
> > using an aspect ratio different than what the original author intended
> > might end up with an image which either clips out parts of the original
> > image or, worse, shows undermodeled parts which were not meant to be seen?

> This argument is a bit short-sighted: The same could be said about rendering an
> image at a much higher resolution than originally intended by the author -
> which may get you "undermodeled" parts *everywhere*.

  There is a big difference between rendering at higher resolution and
outright clipping big parts of the image out, or adding big parts which
weren't intended to be seen.

> Furthermore, an author cannot pass on his scene's source code and at the same
> hide those undermodeled parts from curious eyes - just a few changes to the
> camera block will reveal them anyway.

  You would have to intentionally tamper with the scene file in order to
destroy the image composition. With an automatic square-pixel assumption
the tampering would be inadverted.

> Even so, as some previous poster mentioned, a possible solution to this issue
> would be to allow the scene author to specify (in the camera settings) how to
> deal with non-matching aspect ratios, by choosing between (e.g.)

>   a) adjust horizontal field of view to fit
>   b) adjust vertical field of view to fit
>   c) enlarge field of view to fit
>   d) reduce field of view to fit
>   e) distort to fit
>   f) enforce aspect ratio

  All of those can be already done with the current version of POV-Ray.

> If complemented with command-line / ini options to explicitly specify a pixel
> aspect ratio, I guess we'd have all aspect ratio issues solved.

  In fact, that can also be done currently, albeit indirectly. You can use
the 'Declare' command-line option to pass values to the scene file. You
can create a camera definition which sets its aspect ratio according to
such an identifier.

-- 
                                                          - Warp

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Warp wrote:
>   All of those can be already done with the current version of POV-Ray.

In fact, I fail to see a need for changing the camera at all.  Of 
course, I'm one of the people who simply "got it" when reading (gasp!) 
the docs.

-- 
Chambers

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>>   a) adjust horizontal field of view to fit
>>   b) adjust vertical field of view to fit
>>   c) enlarge field of view to fit
>>   d) reduce field of view to fit
>>   e) distort to fit
>>   f) enforce aspect ratio
>
>  All of those can be already done with the current version of POV-Ray.

I think the point of the request is to make easier to choose from the above 
options without needing to resort to some carefully figured out statements.

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