Gilles Tran wrote:
> 
> The confusing part is that this not true when the rendered image starts at
> +SCx.x with x>0.
> The starting x position is apparently saved in the BMP while the starting y
> is not. When I render +sc0.8 +ec0.9 +sr0.5, all the viewers I have return an
> image with a strip of rendered bits at +sc0.8 +ec0.9 but at y=0. The
> consequence is that it's not possible to layer directly the re-rendered part
> on the original render and that it has to be repositioned by hand (I make
> the pixels half transparent to make sure that the superposition is precise).
> It's not a major issue for most people, but it still makes things a little
> more difficult for the few who make composite POV-Ray images.
> Ditto for TGA images, btw, with the difference that the lines below the last
> one repeat it (they're interepreted as black in a BMP).

This is exactly as it should be, notwithstanding Warp's suggestion for 
an additional feature.  You have to bear in mind a few things:

- a lot of file formats do not support any information about the image 
geometry except width and height.
- for those file formats that support additional information (for TGA 
for example POV-Ray stores more than just width and height) nearly no 
imaging program reads it.
- while the height of the image is not necessary to know for reading 
most file formats (you can conclude it from the file size) the width is 
required to correctly display the image.  Therefore POV-Ray has to use 
the width of the actual render size.  For the height it uses the 
complete image height (which is necessary for a continued trace) 
although a lot of imaging programs blindly rely on height information 
and actual size being identical (what you see below the actual image 
data in your imaging program completely depends on that program).
- adding a 'black rim' around the render would be possible but at the 
cost of much larger images, slower renders, increased network traffic 
for render farms, ...

Christoph

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