720x480 -- SD and Widescreen not 4:3 or 16:9

[Sengstack]

Hi,

This is one of those topics that I've not seen answered definitively.

NTSC DV is 720x480 square pixels.

If it's NTSC SD, the final display is 640x480 -- a 4:3 "frame" or screen aspect ratio. The pixels are squished (taller than wide) such that the pixel aspect ratio is .9091. But if you multiply 720 by .9091 you get 654.552. What happens to those extra 14.552 pixels?

If it's NTSC widescreen, the final display is 853.333x480 -- a 16:9 "frame" or screen aspect ratio. In this case the pixels are stretched (wider than tall) such that the pixel aspect ratio is 1.2121. But if you multiply 720 by 1.2121 you get 872.712. What happens to those extra 19.37867 pixels?

Thanks to whomever clears this up or points me to a definitive answer.

Jeff S

[Harm_Millaard]

Instead of 720, start with 704. The rest is to compensate for overscan.

[Sengstack]

But overscan applies to regions at the top, bottom and sides an NTSC screen. And it's a variable value depending on the TV set.

[Ann Bens]

NTSC DV is 720x480 square pixels.

No its not.

The DV NTSC pixels have a pixel aspect ratio of 0.91 (nonsquare). DV pixels, which are always rectangular, are vertically oriented in systems producing NTSC video and horizontally oriented in systems producing PAL video.

[Sengstack]

The DV NTSC pixels have a pixel aspect ratio of 0.91 (nonsquare). DV pixels, which are always rectangular, are vertically oriented in systems producing NTSC video ...

Ann,

I should have worded my initial statement differently. But, it is essentially correct. It should say:

NTSC DV starts its life as 720x480 square pixels.

NTSC displays those pixels at a frame ratio of 4:3 (SD) or 16:9 (Widescreen). Those pixels are altered -- stretched wider or narrower -- to accomodate those frame ratios. But, those pixels taken on their own -- when they are just pixels and not displayed as NTSC signals -- are square.

A nifty way to see this, is to use the Export Frame feature in the P Pro Program Monitor. Use it on an NTSC SD clip (in an SD sequence) and on an NTSC Widescreen clip (in a widescreen sequence). In both cases the resulting image will be 720x480 square pixels.

Jeff

[Jim_Simon]

NTSC DV starts its life as 720x480 square pixels.

That's not correct either.  NTSC DV is never square pixels, not at any point whatsoever.  They are always, from start to finish, .9 or 1.2.  They are never anything but .9 or 1.2.

In both cases the resulting image will be 720x480 square pixels.

In image is not DV.  PNG, TIFF and the other image options are not constrained to the DV specifications.  So even if correct, this is a moot point.

DV is NEVER square pixels.

Having said all that, your calculations are using the incorrect figure.  PP is using the outmoded Clean Aperture concept form the days of analog.  Instead of the entire 720 raster, it uses only 704 pixels in it's calcultaions of PAR.  Try working with those numbers instead.

[Sengstack]

I stand corrected about NTSC pixels. They are not square. Thank you for the clarification.

What I am still looking for are answers to the original questions.

[Jim_Simon]

PP is using the outmoded Clean Aperture concept form the days of analog.  Instead of the entire 720 raster, it uses only 704 pixels in it's calcultaions of PAR.  Try working with those numbers instead.

[Sengstack]

Jim Simon wrote:

PP is using the outmoded Clean Aperture concept form the days of analog.  Instead of the entire 720 raster, it uses only 704 pixels in it's calcultaions of PAR.  Try working with those numbers instead.

Jim,

If this is the case, why is it that an exported frame from any P Pro NTSC sequence, be it SD or widescreen, is 720x480?

Jeff

[Ann Bens]

Premiere squishes everything into 720x480 with square pixels: looks distorted.

If you un squish the frame it still would be 720x480 but with rectangular pixels (stretched vertically): looks normal.

It does the same with PAL dv and HDV.

Draw a circle and export that it wont be perfectly round in ntsc standard it will look squased. Widescreen looks like an egg.

[Jim_Simon]

why is it that an exported frame from any P Pro NTSC sequence, be it SD or widescreen, is 720x480?

Because those are the DV and DVD legal dimensions for NTSC video.  The PAR (which is calculated based on 704) is what causes the frame to look square or wide.  But the file itself is always 720 x 480.

(Well, 720 x 486 is sometimes used as well, but not nearly as often these days.)

[Stan Jones]

A nifty way to see this, is to use the Export Frame feature in the P Pro Program Monitor. Use it on an NTSC SD clip (in an SD sequence) and on an NTSC Widescreen clip (in a widescreen sequence). In both cases the resulting image will be 720x480 square pixels.

As Jim says, moot, but I was curious about Encore.

Export of a frame from an SD 4:3 clip from Encore is a regular DV sized/par'ed frame: 720x480 PAR .91.

[Roboberto]

So glad I found this, 9 years later. I was transcoding a film using Handbrake and when I set the pixels to 704 x 480 the aspect came out right. One day I'll dive into all the theory.

Robert

[Stan Jones]

I always found this chart interesting....

http://lipas.uwasa.fi/~f76998/video/conversion/#conversion_table

[Sengstack]

The chart is interesting but I don't see how it addresses or, more directly, answers my questions.

For example, the chart states that in DV (and D1), a sampling size of 720x480 has an actual picture size of 710.85x486. It doesn't explain why this is the case, but I'll accept it for discussion purposes.

Multiply 710.85 times .9091 and you get 646.23, not 640. Why is the height 486? Finally, 646.23:486 is not a 4:3 frame aspect ratio.

Same thinking holds true for widescreen: 710.85 times 1.2121 = 861.62, not 853.33. 861.62:486 is not a 16:9 frame aspect ratio.

If 486 is the actual picture height, then 4:3 SD should be 648x486 and 16:9 widescreen should be 864x486.

Jeff

[Stan Jones]

The chart is interesting but I don't see how it addresses or, more directly, answers my questions.

Jim and Harm have answered your direct question. The chart (and all the narrative above and below) illustrates how complex the larger scenario is.

I can do the simple calculations, but everytime I try to look at the bigger picture, I realize how complicated it is.

This was one of my favorite articles, which includes discussion of production and clean apertures etc.

http://provideocoalition.com/index.php/cmg_keyframes/story/par_for_the_course/

[Ann Bens]

The square pixel equivalent for ntsc 4:3 is 720x534 and 872x486 for widescreen (pal is 788x576 and 1050x576)

If you export a frame from Premiere and load that into Photoshop, set it to the correct aspect ratio it would look normal, i think Encore does the same.