Nicolas Alvarez wrote:
> Bryan Heit <bjh### [at] NOSPAMucalgaryca> wrote:
>> Any how, I've been playing around with this and I think I know what it
>> going on.  It appears to be a problem with how povray is writing (or not
>> writing) the aspect ratio to the BMP's header, plus how my video editing
>> software seems to handle BMPs.
>>
>> Bryan
> As far as I know, BMPs don't have an 'aspect ratio' field on their headers.
> Only image size in pixels.


They don't have a specific aspect ratio entry per se.  Rather, they have 
4 "size" entries - 2 which are the x and y size in pixels, and 2 which 
are the x and y size in units of measure (mm, inches, cm, or something). 
  You can calculate the aspect ratio from the second set of "size" 
measures.

Unfortunately, I haven't found a good reader for the header, so I 
haven't been able to determine exactly what's going on - there is a 
difference if you use povray's default aspect ration compared to 
assigning it yourself [as right x*(4/3)].  Assuming I counted the bytes 
right, this difference is in the second set of size measures for the 
image.  If I had to guess, povray probably assigns integer values (i.e. 
x = 4 units, y = 3 units) when you use the default aspect ratio, but 
stores the decimal values (i.e. x = 1.33333 units, y = 1 unit) when you 
enter the aspect ratio manually.

As far as I can tell the problem I was having was due entirely to the 
program I was using for converting the bmp's to avi (VirtualDub).  Using 
other image formats (i.e. PNG) solved the problem, and updating to the 
newest version of virtualdub also fixed the problem; regardless of how I 
assigned the aspect ratio to the images.

Bryan

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