Resolution info vs. aspect ratio -- I'm confused!

[fastartcee]

I have some analog 8mm vacation videos that I have copied to DVC-R discs. I have then ripped an mpeg from one of the discs to do some editing.

When I used to show the videos directly from the camcorder, on our (older) TV, the frame size ratio was 4 to 3; but when I now project the DVD it looks like 3 to 2.

(The data for the mpeg file states a frame size ration 4 to 3, but a resolution of 720 by 480, which is 3 to 2.)

Question: Is the frame aspect ratio on the original Sony analog 8mm *actually* 3 to 2, so my DVD copies contain more video data, ie, a wider image?

Thanks.

[JohnnyMalaria]

I have some analog 8mm vacation videos that I have copied to DVC-R discs. I have then ripped an mpeg from one of the discs to do some editing.

When I used to show the videos directly from the camcorder, on our (older) TV, the frame size ratio was 4 to 3; but when I now project the DVD it looks like 3 to 2.

(The data for the mpeg file states a frame size ration 4 to 3, but a resolution of 720 by 480, which is 3 to 2.)

Question: Is the frame aspect ratio on the original Sony analog 8mm *actually* 3 to 2, so my DVD copies contain more video data, ie, a wider image?

Thanks.

4:3 is the "physical" aspect ratio - i.e., the width of your TV display to its height.

720 x 480 is the size of the video frame. Your TV will take the 720 pixels per line and make them fit the width of the screen. It will do that 480 times. The output will still be 4:3.

Even widescreen video is 720 x 480 - the 720 pixels are displayed across the full width of a widescreen TV (when told to do so, either by a manual setting on the TV or by a flag sent with the video cable).

[fastartcee]

Thanks for the reply, JohnnyMalaria.

I'm used to working with digital stills. If you show an image that has a resolution of 720 by 480, you will get an image with a 3 to 2 aspect ratio.

It seems to me that if you 'squeeze' 720 pixels into a 4 to 3 frame, you would get horizontal compression, and people would look 'skinny'.

Isn't it more likely that a 4/3 TV simply shows the middle portion of the frame? IE, the sides of the 720 by 480 image are trimmed to get a 640 by 480 image ...which fits the old TV frame.

So maybe I'm *still* confused.

[JohnnyMalaria]

Isn't it more likely that a 4/3 TV simply shows the middle portion of the frame? IE, the sides of the 720 by 480 image are trimmed to get a 640 by 480 image ...which fits the old TV frame.

No. Although the TV will overscan the image - that will be proportionate in both directions, though.

For PAL, the equivalent dimensions are 720 x 576 - but the image is still displayed as 4:3 on the TV.

To convince yourself, get some footage that has a perfect circle that has been created at 720 x 480. On a computer, it will look slightly fat - unless the media player is savvy enough to correct it. On a TV, the circle will appear correct.

For DV, the specification states that the video shall be sampled at 720 pixels per scan line.

[edDV]

Forget the idea of square pixels for CCIR-601 based digital video.

How did you capture again? DVC-R ???? Your typos put me off guessing - answering.

DVC is digital tape.

[jagabo]

No, with video in general, the display aspect ratio (the shape of the picture you see on TV) is independent of the frame dimensions.

A 720x480 image displayed as 4:3 doesn't give you tall skinny people because the image in the file has been "stretched" before saving the frame. I put stretched in parenthesis because I don't mean the image was literally stretched from 640x480 to 720x480, it was captured as 720x480 to start with.

[edDV]

...

Question: Is the frame aspect ratio on the original Sony analog 8mm *actually* 3 to 2, so my DVD copies contain more video data, ie, a wider image?

Thanks.

NO
8mm analog tape dosen't have pixels. It only has 480 lines (486 as analog broadacst actually).

[jagabo]

And the analog signal can be digitized with any number of samples per scan line.

[JohnnyMalaria]

Have a look here: http://www.microsoft.com/windows/windowsmedia/howto/articles/NonSquarePixel.aspx

To quote:

"Each set of test files below contains source AVI files that are specifically created with visual elements that demonstrate square and nonsquare pixels."

You can download a small (1.71MB) file that contains a lot of examples.

I've capture a single frame from the 720x480 4:3 example. You can clearly see that the circles aren't circular. But on a TV, they would be. Also, if you play the .WMV file, Windows Media Player *is* savvy enough to compensate for the computer vs. TV mismatch.

[fastartcee]

Thanks for all the info ...I think it's actually sinking in!

I knew that analog tape doesn't have 'pixels', and I now know that when I copied it to a DVD it was converted to 4 by 3 frame, with 720 x 480 resolution.

What threw me off was I was working with a few frames that I had captured from the mpeg, and those jpeg images are 720 x 480, and show up on my computer screen -- with square pixels -- as images with a 3 by 2 aspect ratio.

When I look at them carefully now, I can see that object are, in fact, vertically compressed. On screen, I set a captured jpeg beside a video player displaying the exact same frame. When I adjusted the width of both images to 7.5 inches, the jpeg image was 5 inches high, but the video image was about 5.7 inches high, so people in the jpeg image appeared artificially shorter.

But in the video images, I now understand a 720 x 480 resolution image is presented accurately in a 4 x 3 frame.

Again, thanks for the education!

[edDV]

Next concept to master is 16:9 DVD is also 720x480. Digital SDTV is 704x480. The only difference is the pixel aspect ratio.

HDTV 1280x720p and 1920x1080i use square pixels.

That is unless they are HDV in which case 1440x1080 non square is used for 16:9.