>  If you have a 4:3 photograph and you want to fill your 16:9 screen with 
> it,
> what do you do?

Well not what POV does by default, that's for sure, unless I want everyone 
to look fat :-)

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scott <sco### [at] scottcom> wrote:
> >  If you have a 4:3 photograph and you want to fill your 16:9 screen with 
> > it,
> > what do you do?

> Well not what POV does by default, that's for sure, unless I want everyone 
> to look fat :-)

  So my question stands: Why can't you do the exact same thing with a
povray-generated image as you would do with a photo?

-- 
                                                          - Warp

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>  So my question stands: Why can't you do the exact same thing with a
> povray-generated image as you would do with a photo?

Of course you can, but it's usually by some contrived method (either within 
POV or with some external tool).  If the default POV camera behaviour 
matched what most people want to do when showing a 4:3 image on a 16:9 
device then it would be a lot simpler (ie you just type in +w1920 +h1200 or 
whatever and hit render).

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scott <sco### [at] scottcom> wrote:
> Of course you can, but it's usually by some contrived method

  I wouldn't consider cropping an image "contrived", but whatever.

-- 
                                                          - Warp

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scott wrote:
>>  I somehow get the feeling that you are making the assumption that all
>> scenes are designed for a 4:3 aspect ratio because that's the default,
>> and that you are arguing what happens when you want to render it for a
>> 16:9 (or sometimes 16:10) monitor.
> 
> Yes, that is my assumption for the default behaviour, that the author 
> just uses the default aspect ratio without a second thought for anyone 
> else who might want to render it.  This is quite typical of the images 
> you see posted on this server, which often then people then want to 
> render as a desktop wallpaper.

Alright then, let's ask this:

What should the behavior be, when a scene is composed "without a second 
thought for anyone else," and originally rendered in the default 4:3 
aspect ratio... and you want to render it in a 3:4 aspect ratio for a 
vertical poster?

How should POV handle this?

The way it currently works (and which I approve of), is that aspect 
ratio is set in the scene file, and resolution is completely independent 
of it.  That is, every time you render a scene file, the picture will 
fill exactly the same shape, with all the output pixels squished into 
that shape.  If you want square pixels, then you need to make sure that 
your file aspect ratio matches the camera aspect ratio; if you have (for 
some reason) non-square pixels, then you can adjust your file ratio 
appropriately.

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.

-- 
Chambers

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scott wrote:
> within POV or with some external tool).  If the default POV camera 
> behaviour matched what most people want to do when showing a 4:3 image 
> on a 16:9 device

What do most people want to do in this situation?

Some (myself) approve of letterboxing.  Others prefer pan&scan.  What 
should POV do, that appeases both groups?

-- 
Chambers

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Warp <war### [at] tagpovrayorg> wrote:
>
>   So my question stands: Why can't you do the exact same thing with a
> povray-generated image as you would do with a photo?
>


I have published products at zazzle.com where I have povray generate the white
border around the image. Some of these are 1:1, some are 2:1.  It soon becomes
a labor-saving device when you generate 100 of these products. Before you call
me petty, I've sold about a dozen of them.

If the docs were to empower someone to understand the camera, none of this
discussion would be necessary-- it wouldn't have been started by me! :)  The
docs fail because they don't teach someone how to create an object that
precisely covers the screen, regardless of pixel aspect ratio or camera angle.
Once I figured out how to do it, I wondered if it were a cleanly written
algorithm. 4:3 is the tripping point.

Again, I'd say let's step back from the issue of forcing the developers to go
rewrite povray.  One thing that troubles me in this discussion is the concept
that there are petty uses of povray, that povray is only for certain noble
tasks. Don't worry about anything that could also be done by mouse-dragging in
photoshop (like cropping to get certain aspect ratios-- imagine doing THAT for
a 2000-frame animation!!!)  Suppose I were able to find an animation contest
(didn't in 5 m of googling) that required non 4:3 aspect ratio.  Would you say
povray is not for professional animation contests?  When you critique a
critique of the current system, think BIG, not small.

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gregjohn wrote:
> Warp <war### [at] tagpovrayorg> wrote:
>>   So my question stands: Why can't you do the exact same thing with a
>> povray-generated image as you would do with a photo?
>>
> 
> 
> I have published products at zazzle.com where I have povray generate the white
> border around the image. Some of these are 1:1, some are 2:1.  It soon becomes
> a labor-saving device when you generate 100 of these products. Before you call
> me petty, I've sold about a dozen of them.
> 
> If the docs were to empower someone to understand the camera, none of this
> discussion would be necessary-- it wouldn't have been started by me! :)  The
> docs fail because they don't teach someone how to create an object that
> precisely covers the screen, regardless of pixel aspect ratio or camera angle.
> Once I figured out how to do it, I wondered if it were a cleanly written
> algorithm. 4:3 is the tripping point.
> 
> One thing that troubles me in this discussion is the concept
> that there are petty uses of povray, that povray is only for certain noble
> tasks.

That has nothing to do with it.  It's not about the ultimate intended 
purpose of the image; its about making the image display correctly.

Changing the aspect ratio of an image can cause serious problems because 
of either cutting out portions of the image, or displaying objects / 
textures that weren't meant to be "on camera."

> Don't worry about anything that could also be done by mouse-dragging in
> photoshop (like cropping to get certain aspect ratios-- imagine doing THAT for
> a 2000-frame animation!!!)

It's not about what's easy to do in Photoshop; it's about what's easy to 
do, period.  In this case, adjusting an image for different aspect 
ratios has two possible solutions: Letterbox it (ie just leave it 
alone), or crop it (which is a solved problem when you use other tools 
like Photoshop or the GIMP).

-- 
Chambers

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> Alright then, let's ask this:
>
> What should the behavior be, when a scene is composed "without a second 
> thought for anyone else," and originally rendered in the default 4:3 
> aspect ratio... and you want to render it in a 3:4 aspect ratio for a 
> vertical poster?
>
> How should POV handle this?

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.

> 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.

So explain how you render a 3:4 version for a poster with your compromise?

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>> within POV or with some external tool).  If the default POV camera 
>> behaviour matched what most people want to do when showing a 4:3 image on 
>> a 16:9 device
>
> What do most people want to do in this situation?
>
> Some (myself) approve of letterboxing.  Others prefer pan&scan.  What 
> should POV do, that appeases both groups?

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.

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