POV-Ray : Newsgroups : povray.newusers : sphere proportions : Re: sphere proportions Server Time
19 Jun 2021 20:10:12 EDT (-0400)
  Re: sphere proportions  
From: clipka
Date: 2 Jun 2021 09:47:51
Message: <60b78c07$1@news.povray.org>
Am 01.06.2021 um 19:37 schrieb Psnarf:

> Why does the radius of the sphere change if the render window is not 1:1.333?

For some background information:

POV-Ray's historic roots date back as far as 30 years. The earliest 
pieces of code were developed for the Commodore Amiga series of computers.

When the earlier versions of the current scene description language were 
designed, square pixels were still a novelty, while screen aspect ratio 
was pretty much standardized: Virtually all personal computers of that 
era used standard PAL or NTSC analog TV sets as a displays, which had a 
designed aspect ratio of 4:3, and even computers that came with their 
own display followed that convention. (It was customary to have a small 
border around the image, so that the edges of the image wouldn't be 
hidden in the somewhat rounded corners of the TV set, but that usually 
didn't affect the aspect ratio too much.)

When it came to pixel resolution though, those early systems had a wide 
variety of standards: 320x200 was quite common, especially in NTSC 
dominated regions (note the 8:5 = 16:10 aspect ratio!), but the pixels 
would have been slightly taller than wide; 320x240 (genuine 4:3) was 
occasionally seen in computers specifically targeted at PAL-dominated 
regions, but e.g. the Amiga 500 in PAL mode would have used 320x256 
(5:4), using slightly squashed pixels.

And then there were those computers that used different modes to get 
more colours out of the same amount of video buffer memory (and memory 
read timing) at the cost of horizontal resolution, or vice versa, giving 
image resolutions as odd as e.g. 160x200 (4:5) or 640x200 (16:5). Not 
anywhere close to square pixels there.


TL;DR: Back in those days, it was anything but a given that the "storage 
aspect ratio" (the aspect ratio in pixels) of an image would match the 
"display aspect ratio" (the aspect ratio in cm or inch as displayed on 
screen), because pixels were rarely square back then.


That still holds true in some professional applications, e.g. HDV or 
DVCPRO HD - though the details of those formats tend to rarely be 
exposed to end users anymore.

Also, POV-Ray allows to render formats where the display aspect ratio is 
fixed in some other ways while the storage aspect ratio could be adapted 
depending on requirements; e.g. 360 degrees panoramic images (the 
standard 2:1 ratio there is sub-optimal unless your main focus of 
interest is near the "equator").


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