Aspect ratio question at DVinfo.net

Jeff Yin · September 13th, 2007, 06:49 PM

Another newbie question.

What is the relationship betweem 1.333 and 16:9? What I mean is although I know 16:9 is an SD format, is 1.333 similar? When I am seeing a DVD in letterbox format, has that been converted to 16:9, or is it some other ratio?

Daniel Browning · September 13th, 2007, 07:57 PM

There is no relationship. 16:9 is an aspect ratio, a common one. 1.333 is a *pixel* aspect ratio used by some formats (e.g. HDV 1080).

An aspect ratio describes the shape of the entire frame. A *pixel* aspect ratio describes the shape of individual pixels.

A widescreen DVD contains an image with 720x480 pixels (3:2 ratio) but they are stretched by a factor of 1.2 (the pixel aspect ratio) during playback to make the frame appear in 16:9 aspect ratio (864x480).

Pete Bauer · September 14th, 2007, 12:29 AM

In addition to Daniel's correct comments, 4:3 DV is also 720x480 (NTSC), but with a pixel aspect ratio (PAR) of 0.9. Then 1.2 / 0.9 = 1.33. So the 1.33 is the difference in PAR between 4:3 and 16:9 and also the difference in image aspect ratio since they contain the same number of pixels. If you make the shape of the pixels of either one of them square instead of "stretched" or "squashed," the pictures will have, just as Daniel said, a picture W:H ratio of 3:2.

Just for clarification, the 864x480 is what a 16:9 image would be if you resampled it to square pixels, rather than 1.2 PAR, which some software programs and add-in cards do.

September 13th, 2007, 06:49 PM	#1
Jeff Yin Regular Crew Join Date: Aug 2007 Location: Fremont California Posts: 27	Aspect ratio question Another newbie question. What is the relationship betweem 1.333 and 16:9? What I mean is although I know 16:9 is an SD format, is 1.333 similar? When I am seeing a DVD in letterbox format, has that been converted to 16:9, or is it some other ratio?

September 14th, 2007, 12:29 AM	#3
Pete Bauer Wrangler Join Date: May 2003 Location: Eagle River, AK Posts: 4,100	In addition to Daniel's correct comments, 4:3 DV is also 720x480 (NTSC), but with a pixel aspect ratio (PAR) of 0.9. Then 1.2 / 0.9 = 1.33. So the 1.33 is the difference in PAR between 4:3 and 16:9 and also the difference in image aspect ratio since they contain the same number of pixels. If you make the shape of the pixels of either one of them square instead of "stretched" or "squashed," the pictures will have, just as Daniel said, a picture W:H ratio of 3:2. Just for clarification, the 864x480 is what a 16:9 image would be if you resampled it to square pixels, rather than 1.2 PAR, which some software programs and add-in cards do. __________________ Pete Bauer The most beautiful thing we can experience is the mysterious. It is the source of all true art and science. Albert Einstein Trying to solve a DV mystery? You may find the answer behind the SEARCH function ... or be able to join a discussion already in progress!

September 13th, 2007, 07:57 PM	#2
Daniel Browning Major Player Join Date: Jan 2007 Location: Portland, OR Posts: 949	There is no relationship. 16:9 is an aspect ratio, a common one. 1.333 is a pixel aspect ratio used by some formats (e.g. HDV 1080). An aspect ratio describes the shape of the entire frame. A pixel aspect ratio describes the shape of individual pixels. A widescreen DVD contains an image with 720x480 pixels (3:2 ratio) but they are stretched by a factor of 1.2 (the pixel aspect ratio) during playback to make the frame appear in 16:9 aspect ratio (864x480).