Aspect Ratio

A legend first:

~ ~ ~

Frame width: w
Frame height: h
Frame width ratio: fW
Frame height ratio: fH
Pixel width: pW (aspX in Blender)
Pixel height: pH (aspY in Blender)

~ ~ ~

An example.

Take a PAL DV scene. The frame width (w) is 720 and frame height (h) is 576.


Now decide if it's a full-frame 4:3 (fW:fH) image or a 16:9 (fW:fH) image.

To calculate the pixel width and heights (pW and pH) do as follows.

1.) Divide: w by fW
2.) Divide: h by fH

Divide the answer from step 2 by step 1 and you get the pixel aspect ratio.

So...

720 divided by 16 (for widescreen) = 45
576 divided by 9 (for widescreen) = 64

64 divided by 45 = 1.422...

So the pixel aspect ratio for a PAL DV frame, 720x576 in 16:9 widescreen is 1.422...

Try another....

NTSC DV frame, 720 wide (w), 480 high (h)
Full-frame 4:3 (fW:fH)

720 divided by 4 = 180
480 divided by 3 = 160

160 divided by 180 = 0.88...

So the pixel aspect ratio for an NTSC DV frame, 720x480 in 4:3 full-frame is 0.88... (Often just rounded to 0.9)


With these two examples, here's how to enter it IN blender for use in the aspX and aspY fields.

Example 1: The result was 1.422... to 1

Blender won't take the decimal so you have to get rid of it. So 1.422
becomes 1422 and 1 becomes 1000. But blender won't take that either.
Only values between 1 and 200. Since we can't factor 1422 and 1000 down
beyond 711 and 500, we have to backtrack and do some rounding instead.

If we work with 1.42:1, we can see that it would then become 142:100
(or even 71:50 after factoring it down). Now either of these set of
values WILL work in aspX and aspY.


Of interest:

"16:9 1280x720 (720i)
16:9 1920x1080 (1080i)"

It's interesting to note that in these two cases of HD material, the pixel aspect ratio is exactly 1:1.

1280 / 16 = 80
720 / 9 = 80

80 / 80 = 1. So that's aspX 1 and aspY 1.

I think this is why HD will be so much better because it seems to deal
entirely with a square pixel ratio which requires no stretching of
images. Who knows, just my thoughts.



Let me know if I got any of this wrong and I'll gladly delete

The term aspect commonly refers to the DAR value (display aspect ratio) which indicates the shape of the replicated image. In the television world the most common values are 4:3 (1,33:1) and 16:9 (1,78:1). Yet the resolution of a video conforming to the PAL standard stands at 720×576 pixels which, based on a simple mathematical equation, does not correspond with either of the mentioned values but instead with 5:4 (1,25:1). This ratio of vertical and horizontal pixels derived from the resolution is knows as SAR (storage aspect ratio). Hence, for the image to be replicated correctly, a third variable known as PAR (pixel aspect ratio) is needed to tell the appliance which shape of pixels are involved. In the computer world it has become the norm for pixels to be as wide as they are tall (square pixels) but in the PAL world the pixels are just a little bit wider: the pixels of a traditional 4:3 video have a ratio of 1,066:1 and the anamorphic 16:9 image has the pixel ratio of 1,422:1. The total ratio between these three variables can be demonstrated as the equation DAR = PAR X SAR á 16:9 = 1,422 x 5:4.





The European television sets, digital receivers, and DVD players conform to the PAL standard which means that the video image will be replicated in them correctly as long as the right aspect ratio
(DAR) has been selected or the appliance can detect it automatically.
However, as computer and mobile appliance screens make use of
different, square shaped pixels (square pixels), and the media players remain at times unable to do the appropriate conversion, the image is usually interpolated for these purposes with the result that the end resolution will be either 768×576 (4:3), 1024×576 (16:9), or of another derived size, and so the image gets replicated correctly without being flattened.


On the note of aspect ratio, the using of a mobile camera in the Neo Arena productions posed a challenge of its own. The image produced by a mobile camera (Nokia N92) was quite unexpectedly CIF sized (325×288) which as square pixels would have equaled a DAR value of 11:8, and such a ratio
does not fit well with audiovisual production. What happened was that
we had to crop the materials in postproduction in order to create a 4:3
image (CIF has a somewhat greater vertical height). The other
alternative would have been to scale the image in such a way which
would not have resulted in any information loss but the borders would
have been taken over by unused space shown as black blocks. Newer
mobile models record VGA sized video so the aspect ratio problem does not exist there.