Stretching a video and keeping the correct aspect ratio.

[jmsrickland]

I had to cut some of the video clip at the top to remove a damaged area. The cut part was approx. 60 lines. But this left a thick black bar at the top. So, to remove that black bar I stretched the part that I kept so that it would fill up the black area. This however, results in a slight distortion of the video. So, if I want to get it back to the correct aspect ratio I figure that I need to also stretch it horizontaly.

My question is if I stretch vertically 60 lines should I also stretch 60 horizontal lines? The true aspect ratio is 4:3 or standard screen.

[TJohns]

can't tell from what you've given ... did you chop 60 pixels from a total of 600 (requiring a 10% "stretch") or 60 from 6000 (only a 1% stretch)

Just divide the original width by its height to get your starting ratio, then calculate what NEW width/height you need to get the same number.

[jmsrickland]

OK, thanks. I see what you are getting at. I will fnd out what the width - height is on the original and do that calculation. I believe, however, you answered my question that stretching it horizontaly has to be a slight more than stretching it vertically.

[guns1inger]

Personally, I would add 30 lines to the top and bottom, and leave the image as is. Resizing always risks quality loss - softness, jaggy edges etc. A 30 line bar top and bottom will be almost un-noticed on most TVs due to overscan anyway.

[jmsrickland]

Personally, I would add 30 lines to the top and bottom, and leave the image as is. Resizing always risks quality loss - softness, jaggy edges etc. A 30 line bar top and bottom will be almost un-noticed on most TVs due to overscan anyway.

I know how to remove lines (or pixel lines if that is what they are called) but how do you add lines?

I use Video Studio to remove lines off the top. Here's how I do it. I insert the damaged clip into the overlay track and make it original size. I then use the up arrow on the keyboard which cause the clip to advance upward until the damage area is above the screen border. This then actually leave the same height black bar at the bottom of the clip. I then drag the bottom down to the bottom border which makes the video now fill the screen area. I can drag the clip horizontally to a point where the video now appears to have the correct aspect ratio.

I see no way, at least using Video Studio, to add lines.

Also you say leave the image as is. How then would that hide the damaged area if left as is?

[guns1inger]

I would add 30 lines to the top and bottom, and leave the image as is

I meant after the crop.

I don't use Video Studio, but I would be looking for a way to crop then shift the position of the clip. Usually this if referred to as track motion or similar. Another alternative would be to move the image up only 30 lines, then overlay a black border across the top 30 lines.

[jmsrickland]

Yeah, I relized what you meant after I posted.

Your method would work however there are two things about doing it that way that I don't want to do.

1) 60 pixel lines removed is a very obvious amount. I went back to the clip and centered it after cropping thus putting 30-pixel lines at the top and bottom. The results were similar to a wide screen video of about 1:178. This wouldn't be too bad except for one thing.

2) The damaged part of the video is only about a 30-second segment of a 2 hour video. To do it this way would mean I would have to do it to the entire 2 hour video and that wouldn't be acceptable. Clipping 60 pixel lines off the top would be removing way too much stuff that is important to the rest of the video so I can only do this crop in the area where it is damaged and then stretch it back so that it blends in with the rest of the video.

[guns1inger]

Actually, it is exactly half the size of NTSC 16:9 (1.78) black bars.

Using my trusty Photoshop NTSC template, a uniform scale reduction in height of 60 pixels (crop) requires a matching reduction in width of 90 pixels. After that, you should be able to do a uniform scale up to fill the frame without distorting the image.

[Cornucopia]

Personally, I don't like the resize this-resize that business. Then every pixel is an average of some sort-losing quality.

You should go back to the original and use "delogo", "blur", "temporal noise reducer" filters, etc. to cover/mask/clone over the offending area. Then, nothing else needs to be messed with.

Scott

[jmsrickland]

Good advise but you are not telling me how to do those things