Respectfully, Terry, I have to disagree.
When sampling non-square pixels for NTSC, it implies you have a higher
sampling frequency in the horizontal direction than if you were sampling
square pixels.
Imagine you have a sensor that is 1 inch wide. You sample it one line
at a time from top to bottom, to get your 480 lines -- that part doesn't
change between square and non-square pixels. For each individual line,
if you take 720 samples, each sample will be 1/720th of an inch apart
horizontally. If you take 640 samples, they will be more widely spaced
-- each 1/640th of an inch apart -- you will be sampling that line of
the sensor at a lower resolution horizontally.
So in this example, which I have made up to make the math easy, the
following is true:
In the case of square pixels, the distance between horizontal
samples is identical to the distance between vertical lines - 1/640th of
an inch in both directions.
In the case of non-square pixels, the distance between samples will
be 1/720th horizontally, but 1/640th between vertical lines.
Regards,
--Michael
On 12-01-25 9:01 PM, Terence Curren wrote:
>
> You folks don't seem to grok square pixels vs. non square pixels.
>
> http://en.wikipedia.org/wiki/Pixel_aspect_ratio
>
> And here you can see the ATSC standards for SD, both square and non
> square:
>
> http://en.wikipedia.org/wiki/ATSC_standards
>
> --- In Avid-L2@yahoogroups.com <mailto:Avid-L2%40yahoogroups.com>,
> Michael Brockington <brocking@...> wrote:
> >
> > I'm with Steve on this one.
> >
> > 720x486 = 349,920 pixels
> > 640x480 = 307,200 pixels
> >
> > They might both be SD technically, but the first one has about 14% more
> > resolution.
> >
> > Cheers,
> > --Michael
> >
> > On 12-01-25 3:14 PM, Mark Spano wrote:
> > >
> > > Steve,
> > >
> > > 480 lines of resolution is SD. The math there is that .9 ratio
> times 720
> > > equals 648 but that is representative over 486 lines. 640 is the
> best math
> > > for 4x3 to get 480. (640 *3 / 4 = 480). And we're talking about square
> > > pixels, so that math works out perfectly.
> > >
> > > The artful look of the square is the best reason I've ever heard why
> > > anyone
> > > would shoot this way. But possibly the fear of downconversion
> softness is
> > > why they shot SD for an SD spot.
> > >
> > > good luck...
> > > -Mark
> > >
> > > On Wed, Jan 25, 2012 at 6:08 PM, Steve Hullfish
> > > <steve4lists@... <mailto:steve4lists%40veralith.com>>wrote:
> > >
> > > > I don't buy that. I mean I know it's CLOSE to real SD, but...
> > > >
> > > > The difference between square pixels and 601 pixels is .9 right?
> The
> > > math
> > > > (720x.9) works out to slighly more than 640. And 480 is a little
> shy
> > > of 486.
> > > >
> > > > Avid used to claim 640x 480 was broadcast SD, but it's really
> 720x486.
> > > > With 720x480 being DV and DVD.
> > > >
> > > > So it's CLOSE to SD, but I say it's NOT SD. The bigger question
> is WHY
> > > > shoot 4:3 SD when you have a 16:9 camera? For the artful look of the
> > > > square? :-)
> > > >
> > > > Steve Hullfish
> > > > contributor: www.provideocoalition.com
> > > > author: "The Art and Technique of Digital Color Correction"
> > > >
> > > > On Jan 25, 2012, at 4:38 PM, Terence Curren wrote:
> > > >
> > > > >
> > > > >
> > > > > --- In Avid-L2@yahoogroups.com
> <mailto:Avid-L2%40yahoogroups.com> <mailto:Avid-L2%40yahoogroups.com>,
> > > Steve Hullfish <steve4lists@> wrote:
> > > > >
> > > > > <<it has a 640x480 setting. So that's actually LESS than SD.>>
> > > > >
> > > > > Not actually. If it's square pixels that is SD.
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > [Non-text portions of this message have been removed]
> > > >
> > > >
> > > >
> > > > ------------------------------------
> > > >
> > > > Search the official Complete Avid-L archives at:
> > > > http://archives.bengrosser.com/avid/
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> > >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
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