You know far more than I. Maybe I'm confused, but
this camera statement does give a wider field of view
if you change the width to more pixels. If you render
at 800x400 you see more on the sides than if
you render at 600x400. I find it to be convenient
for changing the aspect ratio. Such as rendering
for slide film (1.5:1) 3000x2000 or computer
screen (1.33:1) 800x600.

 camera {location <0,-0.5, -5.5>
        right x*image_width/image_height
        look_at <0,0,1> }

Harold

"Warp" <war### [at] tagpovrayorg> wrote in message
news:416edac8@news.povray.org...
> Slime <fak### [at] emailaddress> wrote:
> > right image_width/image_height
>
>   You mean "right x*image_width/image_height"?
>
> > though many (including myself) consider this bad style when used for
> > anything but quick test scenes, since it makes the image difficult to
render
> > with a non-1:1 pixel aspect ratio, which is useful and necessary in some
> > cases.
>
>   Using the automatic aspect ratio (to always get 1:1 pixels) like above
> sounds tempting at first, but as you said, it's actually not necessarily
> a good idea with most scenes.
>
>   What one does not immediately realize (before making actual tests) is
> that adjusting the aspect ratio of the camera with the 'right' or the 'up'
> keywords always adjusts it vertically (regardless of which one of them is
> used, which comes as a surprise to most). That is, if you change the
> aspect ratio of the camera, part of the scene will go out of the image
> or additional scenery will appear in the upper and lower sides of the
> image. The horizontal range of view will keep constant (it can't be
> adjusted with 'right' nor 'up').
>
>   More often than not, if a scene is designed to be viewed at different
> aspect ratios, it's usually designed so that the viewing range can be
> freely modified horizontally. This is very typical in eg. outdoor scenes.
> That is, if you render a wider image, more scenery appears at the sides
> of the image. It's quite rare that scenery is designed so that interesting
> new parts can come to view if the image is enlarged vertically.
>   In these types of scenes having an automatic aspect ratio correction
> in the camera would not be helpful at all: Changing the aspect ratio will
> not change the horizontal viewing area.
>
>   However, this is actually not the main problem: The main problem is
> that it's not at all unusual that only visible parts of the scene are
> modelled, while the parts of the scene outside the viewing area are
> modelled with less accuracy or not at all. For example, someone could
> model a brick wall just up to the altitude that it covers the intended
> image.
>   This means that if the scene had automatic aspect ratio correction and
> someone happens to render an image with a different aspect ratio, some
> parts of the scenery may become visible (at the top and bottom of the
> image) which were never intended to be shown.
>   Moreover, if this someone renders a scene with the aspect ratio set
> to the other direction, parts of the original scene will end up out of
> the image, perhaps even clipping something important in the original
> image.
>   I assume this is seldom what the original author had in mind.
>
>   This phenomenon is also bad in that if someone rendered an image like
> this with a different aspect ratio, chances are big that he would not
> notice there is something wrong with the image. If due to the clipping
> or extra unwanted scenery coming to view the overall quality of the
> image suffers, this person could just think the author sucks.
>   On the other hand, if the scene had no automatic correction, what
> the user would get is a squeezed image which has a higher probability
> of alerting him that something has gone wrong. (Even though the modern
> convert-4:3-tv-image-to-16:9-tv-by-squeezing generation might actually
> not see anything wrong, but that's a different story.)
>
>   Also, as you said, if someone *wants* to render the image with
> non-square pixels (one example being the Windows startup image),
> the automatic aspect ratio correction would only cause trouble.
>
>   Now, what if someone really wants an automatic aspect ratio correction
> which does it *horizontally* instead of vertically (which might be quite
> feasible with some scenes)?
>   This is a much less trivial thing to do. In order to do this one would
> have to change both 'right' and 'angle' values of the camera in such way
> that the vertical visual range would not change but only the horizontal.
> The correct formula to do this is something I have yet to see.
>
>   (Hmm... Would this subject make a good entry in the povQ&T site?)
>
> -- 
> #macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb
M()}}
> N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
> N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  -
Warp -

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