PAL aspect ratio: 720 x 576 is not 4:3

I "think" I understand what you are aking though I don'y work in the PAL format. I don't know what "native" PAL DV pivel count is so I'll talk NTSC and see if this applies to you stuation.

NTSC DV is recorded at 720x480. iMovie displays it on screen as 640x480. This is accomplished by using non-square pixels, taller and narrower than "square". I know...wierd. When NTSC is exported full quality DV the resulting picture looks s-t-r-e-t-c-h-e-d because it is displayed in its native 720x480 resolution. If you are importing into iDVD then there is no problem because iDVD understands and takes care of this. I however you plan on just using the Full Quality DV for something, though the resulting file size and data rates can be problematic, you have to do something to bring the ratio back to 4:3.

In iMovie go to share and select expert settings, not full quality DV. Click the Share button. Another screen opens. In the export drop down select DV Stream. Select the Options button to the right. Click n PAL and the aspect ratio. It looks like PAL is also 4:3 or 16:9. This should take care of the aspect ratio being out of wack. You can also deinterlace from this window and select the output type.

Hope that helps.

Read all about this nasty aspect ratio stuff from "A Quick Guide to Digital Video Resolution and Aspect Ratio Conversions":

http://www.iki.fi/znark/video/conversion/

"Not a single one of the commonly used digital video resolutions exactly represents the actual 4:3 or 16:9 image frame.

Shocking, isn't it? 768×576, 720×576, 704×576, 720×480, 704×480, 640×480... none of them is exactly 4:3 or 16:9; not even the ones you may conventionally think as "square-pixel" resolutions."

"720x540 is an oddball compromise format. Better to avoid unless you really know what you are doing. [...] the original interlaced field structure (if any) will go haywire as you mess around scaling in the vertical direction."

http://www.uwasa.fi/~f76998/video/conversion/#4.7

So:

To convert rectangular pixel PAL 720x576 DV to square pixel image you should scale to 788x576, then optionally crop it with 10 pixels from both sides so that the final image is 768x576.

To convert rectangular pixel NTSC 720x480 DV to square pixel image you should scale to 656x480, then optionally crop it with 8 pixels from both sides so that the final image is 640x480.

And to the other direction:

To convert a 4:3 (2048x1536, 768x576 etc) square pixel still image to PAL 720x576 rectangular pixel video, you should resample to 702x576, then pad with 9 black pixels to the sides so that the final image is 720x576.

To convert a 4:3 (2048x1536, 640x480 etc) square pixel still image to NTSC 720x480 rectangular pixel video, you should resample to 702x480, then pad with 9 black pixels to the sides so that the final image is 720x480.

I hadn't spotted the expert settings (Apple probably wants to keep us amateurs out of it!)

Notice that in iMovie HD 5.0.2 exporting via the expert settings as a DV stream or .avi deinterlaces video and loses the timestamp. Other codecs may not suffer from this unexpected behaviour. iMovie 4 has a related bug, too.

http://www.sjoki.uta.fi/~shmhav/iMovieHD_bugs.html#expertsettings

http://www.sjoki.uta.fi/~shmhav/iMovie4bugs.html#PAL-DVCPRO

Notice also that the 4:3 and 16:9 and Interlaced vs Progressive options there just flag the exported file accordingly. Setting those options does nothing else to the output. It just sets a flag. It doesn't scale the image nor does it deinterlace it. It just sets the flag so you must do scaling or deinterlacing elsewhere (unless you take advantage of that deinterlacing bug in the expert settings 😉

Matti,

Shocking, isn't it? 768×576, 720×576, 704×576, 720×480, 704×480, 640×480... none of them is exactly 4:3 or 16:9; not even the ones you may conventionally think as "square-pixel" resolutions."

It sure seems to me that the old NTSC square pixel 640x480 and PAL square 768x576 formats are in a 4:3 ratio - that's what my calculator tells me.

It's when you throw non-square pixel DV into the mix that things get a little confusing.

To convert rectangular pixel PAL 720x576 DV to square pixel image you should scale to 788x576, then optionally crop it with 10 pixels from both sides so that the final image is 768x576.

To convert rectangular pixel NTSC 720x480 DV to square pixel image you should scale to 656x480, then optionally crop it with 8 pixels from both sides so that the final image is 640x480.

This means that when you start with a square-pixel still digital camera image of 4:3 aspect ratio, it doesn't exactly fix into what an iMovie/iDVD DV frame expects to see.

It sure seems to me that the old NTSC square pixel 640x480 and PAL square 768x576 formats are in a 4:3 ratio - that's what my calculator tells me.

I think the page stresses the word exactly with those particular resolutions. That nit-picking page seems to indicate that not all square pixels are exactly square...

For PAL: "Industry standard" 625/50 square-pixel video's sampling matrix is 768x576 but its actual active picture size is 767x576 and the pixel aspect ratio is 768/767, so the pixels are almost square. ("True" computer square-pixel aspect ratio is listed as 1/1 in those charts, though).

For NTSC: "industry standard" 525/59.94 square-pixel video's sampling matrix is 640x480 but its actual active picture size is 646+5/22 x 486 and the pixel aspect ratio is 4752/4739.

(For NTSC the "True" computer square-pixel resolution (all 486 active scanlines) video's sampling matrix and actual active picture size is 648x486 (there we have the 4:3) and the pixel aspect ratio is 1/1.)

This means that when you start with a square-pixel still digital camera image of 4:3 aspect ratio, it doesn't exactly fix into what an iMovie/iDVD DV frame expects to see.

Yes. Compared to iMovie 4, iMovie HD uses new routines when importing a still image and when saving as a still frame. The new routines follow almost the nit-picking page I mentioned earlier in this thread.

So now the aspect ratios are better preserved but the math is more difficult to grasp and many people may think there is something wrong.

For example:

If you want no black borders to the imported still images in 4:3 video projects, their aspect ratio must be NTSC 720x528 or PAL 788x576 or some larger multiple of those figures (NTSC 1024x751, 2048x1502, 2095x1536 etc, or PAL 1024x749, 2048x1497, 2101x1536 etc). No neat 4:3 figures anymore...

If you want no black borders to the imported still images in 16:9 video projects, their aspect ratio must be NTSC 874x480 or PAL 1050x576 or some larger multiple of those figures.

http://www.sjoki.uta.fi/~shmhav/iMovieHDbugs.html#stills

guys just like to join in the discussion of the 4:3 16:9 ratio discussion.

as previously discussed .........the commonly used digital video resolutions exactly representing the actual 4:3 or 16:9 image frame.

A note on this.. for PAL

You actually use 576 as the multiplying factor for 4:3 or 16:9

ie 576 *4/3 = 768 as a computer sq pixel then as a tv pixel aspect ratio of 1.066 divided by to get 720

therefore widescreen
576*16/9 = 1024 as computer sq pixels then divide by 1.422 for the anamorphic pixel ratio you get 720...

cheers matthew

I know what you mean about abusing the system! Right now I'm compressing and burning in iDVD while I'm compressing 3 mp4s! Things get a little skow...

I hadn't spotted the expert settings (Apple probably wants to keep us amateurs out of it!)

It might have been better if they had labelled them advanced settings or additional settings.