>> Of course you can, but it's usually by some contrived method
>
>  I wouldn't consider cropping an image "contrived", but whatever.

How do you work out what to type in for +w and +h to start with?  YOu need 
to go and find the correct camera block for the render, which is often not 
trivial for complex scenes due to multiple cameras being defined in 
different files.  Then you need to wait for the render, and start up a 
separate image editing program.  Is all that really necessary when you just 
want to put the image on your desktop?  It certainly seems unnecessary to 
me.

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Warp <war### [at] tagpovrayorg> wrote:
>   I'm sorry, but I just disagree with you. The original image composition
> should be preferred over anything else, unless the author *specifically*
> allows other aspect ratios to be used (which he can in the current POV-Ray).

To the contrary, I think that the default behavior should fit an "out of the
box" approach.

To this end, the default would have to fit scenes where *no* thought whatsoever
has been put into aspect ratio - neither from the author, nor from the person
rendering the scene. (Unfortunately, this is not the case.)

If an author has put enough thought into the aspect ratio issue to favor a
particular one, I think it is reasonable to expect from him to *explicitly*
specify this in the scene file in some way or the other.

Therefore, I advocate the original composition should be preferred *only* if the
author specifically *disallows* (or shall we rather say, disocurages) other
aspect ratios. Which, in current POV-Ray, he can do - though I'd agree that a
simpler mechanism to do so would be helpful.

The biggest issue in this area, however, is IMHO the fact that current POV-Ray
has no mechanism whatsoever to detect the difference between a mismatching
screen aspect ratio and a non-square pixel aspect ratio.

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Warp <war### [at] tagpovrayorg> wrote:
> > No wonder POV is so slow to develop if you have to debate whether
> > using more meaningful keywords is a good thing or not :-(  Oh well.
>
>   Have you ever thought that adding new keywords can potentially break
> existing scenes? The SDL namespace is already heavily cluttered as it is.

Have you checked lately where we're discussing?

I guess POV 4 will break quite a lot of existing scenes anyway. Well, at least I
hope so, because I hope for a better SDL.

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>   If you have a 4:3 photograph and you want to fill your 16:9 screen with it,
> what do you do?
>
>   Why can't the same answer be applied to a 4:3 povray-generated image?

Yes, that's probably a sensible answer to the question for a default behavior:

- assume 1:1 pixel aspect ratio
- use a "virtual" field of view as specified in the scene file
- render only a subset of the image, so that it fits the specified output
resolution

Or, alternatively:

- assume 1:1 pixel aspect ratio
- reduce the field of view as needed to fit the specified output resolution


Note that the second approach is probably a bit easier to implement, but the
first one would be superior when it comes to preserving exact scene content, in
case the field of view is used as parameter to scene content creation.

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Chambers <Ben### [at] gmailcom_no_underscores> wrote:
> Perhaps a sensible compromise would be that if only the width or height
> of the file is set, and not the other, POV will assume square pixels and
> adjust the other according to the camera aspect ratio.  That is, if you
> set +w1600, and don't set height, POV will check the camera aspect ratio
> (up and right vectors) and, in the case of the default 4:3, set +h1200
> on its own (and other values according to other ratios).  This would
> certainly make scaling images easier.

I'm repeating myself here, but I think what POV-Ray *really* lacks is a separate
option to explicitly specify the output image pixel aspect ratio.

From there on, the door would be wide open to all sorts of "automatic fixing" of
the residual aspect ratio issues.


Even your suggestion would not catch cases where a user may want to preserve the
original image's aspect ratio, but render for a different pixel aspect ratio.

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"scott" <sco### [at] scottcom> wrote:
> IMO the default behaviour should be to preserve the horizontal FOV, as this
> is usually where the detail is modelled - more or less vertical FOV tends
> just to be more or less sky or emtpy ground.  So in your example the 3:4
> rendering would show more sky and ground (or whatever is in the image) than
> the original rendered at 4:3.

As a matter of fact, I recently did a submission to the TC-RTC where this
approach would fail if the aspect ratio was significantly narrower than my
design: It includes grass "planted" all over the visible section of the ground,
with the algorithm requiring that the top edge of the shot is still below the
horizon.

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scott wrote:
>>> Of course you can, but it's usually by some contrived method
>>
>>  I wouldn't consider cropping an image "contrived", but whatever.
> 
> How do you work out what to type in for +w and +h to start with?  YOu 
> need to go and find the correct camera block for the render, which is 
> often not trivial for complex scenes due to multiple cameras being 
> defined in different files.  Then you need to wait for the render, and 
> start up a separate image editing program.  Is all that really necessary 
> when you just want to put the image on your desktop?  It certainly seems 
> unnecessary to me.

It is unnecessary.  If you just want to put the image on your desktop, 
all you have to do is right-click, and choose "Use as desktop."  Problem 
solved, POV isn't even necessary.

-- 
Chambers

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scott wrote:
> Assuming the scene file author has specifically written in the camera 
> block that the aspect ratio should not be changed, then POV should give 
> the person starting the render the choice of what to do from your choice 
> - and an additional choice of changing the actual image resolution to 
> match the aspect ratio fixed in the scene file.

First, POV is highly automated.  That is, it is perfectly possible to 
start a render, walk away, and get the finished result.  Interrupting 
this process to ask a question would be a change in style (not 
necessarily bad, just needs to be pointed out).

As far as "specifically [writing] in the camera block" goes, scene 
authors already do that.  They use the "up" and "right" vectors, as well 
as the "angle" keyword, to define very specific viewports into their scenes.

Omitting these parameters is not the same as saying you don't care; it 
is still saying that you want a very specific set of parameters, just 
that these parameters happen to be the default ones.

-- 
Chambers

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> with the algorithm requiring that the top edge of the shot is still below 
> the
> horizon.

In that case it seems ok to require that the author add some command in the 
camera block fixing or limiting the aspect ratio (or in this case the 
vertical FOV).  For the default behaviour though...

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> It is unnecessary.  If you just want to put the image on your desktop, all 
> you have to do is right-click, and choose "Use as desktop."  Problem 
> solved, POV isn't even necessary.

You're right, rescaling existing images has nothing to with POV.  Shall we 
get back to rendering with POV now?

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