Re: Determining the Shape of Pixels and Frames
- From: "Bob [MVP]" <bob@xxxxxxxxxx>
- Date: Mon, 15 Aug 2005 17:01:06 -0400
The DV standard (originally known as DVC for Digital Video Cassette) specifies the resolution for converting analog NTSC and PAL television video to digital video.
Using NTSC as an example, that standard specifies a frame aspect ratio of 4:3. The DV standard specifies a resolution of 720:480. I'd tell you to do the math, but I've already done that. ;-)
We have been talking about the *standard* DV format used by Movie Maker -- not some arbitrary non-standard digital video camera format, as you described in your example below. Right?
It seems that while I have been referring to resolutions and aspect ratios specified in the NTSC and DV standards, you seem to be referring to DV more generically as a video encoding algorithm.
I think we both "get it"... :-)
-- -Bob _______________________________ Microsoft MVP Windows XP Media Center Edition http://www.microsoft.com/ehome
"Al Stu - MVP" <NOYB@xxxxxxxx> wrote in message news:eOu7uHdoFHA.2472@xxxxxxxxxxxxxxxxxxxxxxx
It is not a difficult concept understand. What is difficult to understand is that some people think DV-AVI pixel aspect ratio is specified and is always non-square, when in fact (so far as I have been able to determine) DV-AVI pixel aspect ratio is neither specified nor required to always be non-square. They are just pixels.
For example if I have a digital video camera with a field aspect ratio of 1.5 (3:2) and captures 720x480 pixels (3:2) and import that into a DV-AVI file, what is the pixel aspect ratio going to be? Are they square or non-square?
--
Al Stu - MVP If your world is flat, be careful not to step over the edge.
Copyright © 2005, Al Stu (2348410). All Rights Reserved.
"Bob [MVP]" <bob@xxxxxxxxxx> wrote in message news:unCSomcoFHA.2904@xxxxxxxxxxxxxxxxxxxxxxxYes, been to that page several times in my search for DV-AVI pixel aspect ratio specification.
"... AVI files do not contain pixel aspect ratio information,..."
You're right. The file itself doesn't contain that information. But the standard for converting from analog 4:3 NTSC to 720x480 DV results in a specific nonsquare pixel aspect ratio.
Sorry, but I just don't understand why this is such a difficult concept to understand. It's a matter of simple geometry and simple arithmetic.
The aspect ratio of a pixel is equal to the frame's aspect ratio divided by the digital resolution (expressed as a ratio of the number of horizontal pixels divided by the number of vertical pixels) of the frame.
For NTSC DV-AVI the frame's aspect ratio is 4:3. The digital resolution of the frame is 720x480. This results in a pixel aspect ratio of:
(4/3) / (720/480) = 0.8888... = 1:1.125
So each pixel is slightly taller than it is wide. HTH...
-- -Bob _______________________________ Microsoft MVP Windows XP Media Center Edition http://www.microsoft.com/ehome
"Al Stu - MVP" <NOYB@xxxxxxxx> wrote in message news:uZQ4RPcoFHA.2156@xxxxxxxxxxxxxxxxxxxxxxxYes, been to that page several times in my search for DV-AVI pixel aspect ratio specification.
"... AVI files do not contain pixel aspect ratio information,..."
"Bob [MVP]" <bob@xxxxxxxxxx> wrote in message news:egE$crboFHA.3380@xxxxxxxxxxxxxxxxxxxxxxxhttp://www.microsoft.com/windows/windowsmedia/howto/articles/PixelFrames.aspx
"The CCIR-601 (Consultative Committee for International Radio) standard uses pixels of different shapes (nonsquare pixels) to standardize conversion from the various international analog video standards to digital video."
-- -Bob _______________________________ Microsoft MVP Windows XP Media Center Edition http://www.microsoft.com/ehome
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