Deleting Distortion

[GParent]

Input File = 4:3, 'dvsd' Interlaced Video, 720x480 DV Camcorder:


Problem: About 8 pixels from the bottom, there is distortion that I do not want in the final DVD I am encoding.

I have played with the FILL filter and it draws a black bar across the distorted area. This works and I get to keep the 720x480 AR.

A couple of scenarios I'd like to postulate:

(1) When I mask the distortion at the bottom with 8 pixels in height of black, I have 472 lines of good video information. Now I would like to center that. Have 4 pixels of black at the top and 4 pixels of black at the bottom. Its a kind of pseudo letterbox of the original 4:3 when done.

Possible?

Please give details how?

(2) Is it possible or even worth while to render the 472 lines of good information into 480 lines throough resizing. This may create its own kind of distortion by causing the video to lose sharpness. Any comments on doing this or how its done?

Thanks,

GParent

[Leuf]

Remember that when you watch a dvd on a tv there is overscan, ie the edges of the video aren't visible. Your bottom 8 rows of pixels aren't going to show up. So just masking it out like you have is probably the best solution.

If you did want to center it, the way to do this would be to crop the bottom 8 pixels, then resize but keep the dimensions at 720x472, and check expand frame and set that to 720x480.

Resizing the cropped frame to 720x480 would give you a full frame, but if you are keeping the video as interlaced you definitely don't want to do that.

[GParent]

Are you sure about the 480 lines not all showing up on a TV? A standard TV has 525 lines interlaced frames, and a DVD has a frame size of 480 lines, called the ACTIVE AREA. Meaning viewable area. I guess it depends on how many of those 525 lines get chewed up by your TV, but any modern large screen or digital TV set will probably show any junk at the bottom of the 480 line acive area of the DVD. Right?

[GParent]

FROM DVD DEMYSTIFIED:

Don't confuse lines of horizontal resolution (resolution along the x axis) with scan lines (resolution along the y axis). DVD produces 480 scan lines of active picture for NTSC and 576 for PAL. The NTSC standard has 525 total scan lines, but only 480 to 483 or so are visible. (The extra lines are black. They contain sync pulses and other information, such as the Closed Captions that are encoded into line # 21). PAL has 625 total scan lines, but only about 576 to 580 are visible. Since all video formats (VHS, LD, broadcast, etc.) have the same number of scan lines, it's the horizontal resolution that makes the big difference in picture quality.

[Leuf]

How much there is varies from tv set to tv set, you can't count on a specific amount of overscan to be there. But at the top of the picture you have closed captioning info, at the bottom you've got things like vhs audio. When they produce a program they use what's called the safe area to fit things like titles to be sure they aren't cut off in the overscan, which is supposed to be no more than 10% on each side. If you do the math on that, for NTSC that's 72 on the sides and 48 on the top/bottom. Obviously no modern tv has that much overscan, but I would suspect that even an hdtv has at least some.

What I did for my tv was make an svcd with test pattern that consisted of 8 pixel wide bands of color, then I could see how much was cut off. So for my 27" which is about 8 years old it was about 25 on the sides, 12-16 on the top/bottom.

[GParent]

Yes, good points on making test discs. But 720x480 DVD specfically addresses overscan and 480 lines (out of 525 for NTSC)is supposed to be the sweet spot where most sets can display the full number.

[dvd_master]

If you want to even it out, just use the Fill filter 4 times, adding the black bar on all sides. Really, if you just leave it at the bottom of the video, no one will notice. It isn't that bad. Or you can crop it off, and then resize it back to 720:x480, but it will be stretched a tad. (very little)