Non-Square Pixel Rendering

[montepix]

Can someone give me the definitive answer for this one? (MSP 7.0)

I have DV footage to be rendered for viewing on a TV screen. Should I have non-square pixel rendering turned on or off? From my review of the help screens - I think it should be on. However, when I did this, my titles were no longer centered, and seemed to ignore the "title safe" area. A little expert explanation would help clear this up.

Thanks

[Hulk]

If you are working with 16:9 (widescreen) footage then it should be on. Otherwise it should be off.

Mark

[Maggi]

depends on your project settings and the capabilities of your video interface:

PAL:
768x576 -> square pixels
720x576 -> full D1 resolution non-square pixels

NTSC:
720x486 -> full D1 resolution non-square pixels

to be honest, I'm sort of lost, what picture resolution would be used if doing NTSC in square pixels, but I would guess it's 640x480.

[montepix]

Non-Square Pixels

I'm inclined to agree with Maggi. I always thought NTSC DV at 720x480 was "non-square" - whereas video captured with analog cards is usually 640x480 and therefore "square". The MSP help files seem to indicate that you should use non-square rendering when outputting for display on a TV, and "square rendering" for PC output (regardless of aspect ratio). But I would really like to understand what it is doing in the process.

[Brian Ellis]

I don't think you're right, guys. Read the manual p. 121:
In the Project Options dialog box, you can set the size for the display and output screen to 4:3 (for traditional letterbox TVs, computer monitors or some DV camcorders) or 16:9 (widescreen used in HDTV, theaters, or some DV camcorders). To use the 16:9 display, select Perform non-square pixel rendering on the Video Editor tab first and choose 16:9 as the display aspect ratio on the General tab.

This implies that non-square is used ONLY for 16:9, as I read it.

[Maggi]

to find out on your own, you'd just need to think about it and do a bit of calculations:

physical TV screen dimension ratio is (was) usually 4:3
video footage fullres in PAL is 720x576, which is a ratio of 5:4
to compensate the difference, so that you'll get "round circles" on TV, you need a pixel aspect of 4:3/5:4, ie. 16:15 which is obviously not 1:1

...

video footage in PAL is 720x486 which is a ratio of 40:27

for compensation you'd need a pixel aspect of 4:3/40:27, ie. 9:10.

...

you might ask yourself: WTF, are those numbers telling me and what am I supposed to use'em for ???

Eg. you want to create some graphics in Photoshop and you want to ensure that it will look correctly (not distorted in proportions) on your tele.
Your main problem will be that PS generates picture in squarepixels.

Now the math ...

PAL square pixels:
width: 720 x 16 : 15 = 768
height: stays at 576
so that your PS doc should be done in 768x576 (square pixels) and at the final stage, ie. before saving to disk for importing it into a video programm, unproportionally scaled down to 720x576.

NTSC is basically the same, but I'd recommend to keep full horizontal res at 720 and use an altered vertical res instead, for retaining maximum quality
width stays at 720
height: 486 x 10 : 9 = 540
accordingly your PS doc should be setup in 720x540 and at the final stage squashed down to 720x486.

Btw, 768:576=4:3 and 720:540=4:3

Finally, all above rules also apply for working in anamorphotic 16:9, ie. you'd have to recalculate the picture dimensions when working in PS (or the like), or simply choose oversize in 1600x900 and squash it down, at the final stage, to either 720x576 or 720x486 respectively.

Hope that sheds some light on these issues ...

[edit]
some typos
[/edit]

[SpiralDragon]

http://www.adamwilt.com/index.html

excelent source of DV related info..... but i hate the way he writes... (but then again who am i to complain... )

[Brian Ellis]

Maggi

Great explanation but, sorry, irrelevant to the thread! I quote from the first post:
"I have DV footage". Nowhere does the guy mention importing stills from PS or anywhere else. He's asking when should he check the box "Perform non-square pixel rendering" and I believe that this is only when the AR is 16:9.

[Maggi]

sure thing, Brian, but he also said that he wanted to understand what would be behind all this ...

[SpiralDragon]

the corect question would be to ask WHO is behind this.... ..... sory OT but i am watching Pinky and the Brain... hence the lame replay

[montepix]

OK guys - let me quote the actual help screens that appear when this option is available:

From the Template Options help ... "Select to perform non-square pixel rendering when previewing your video. Non square pixel support helps avoid distortion and keeps the real resolution of DV and MPEG2 content. Generally, the square pixel is suited for the aspect raio of computer monitors, while the non-square pixel is best used for viewing on a TV screen. Remember to take into account which medium will be your primary mode of display."

From the Video Save Options help .... the same as above.

Neither section mention 16:9 or 4:3. However, we know that DV does not use square pixels - otherwise its aspect ratio would equal 1.5 instead of 1.3333. I know the Ulead site mentions selecting non-square pixel rendering when setting up fo 16:9 but it could well be unrelated to the aspect ratio inasmuch as it is required for DV files in general.

So, in tha absence of a definitive answer from anyone, I have selected non-square rendering when creating AVI files for output to DV, for display on a TV screen (4:3). The picture looks fine - but you have to make sure any titles are added or edited while this option is set, otherwise they will not be centered (so it seems).