Learning about Compression

[Dan Achatz]

It’s pretty simple really. A compression scheme is a method of making a large file smaller while trying to retain the best file quality. One method may be to narrow the contrast a bit. Another might mix color differently. all of which will make the file size smaller for any given still image.

Now the typical 8 megapixel camera shoots a JPEG file in it’s native size which is about 3Megs. It takes pictures to make one second of video. 30 x 3Megs = 90 Megs. DVD’s max out at 8 Megs/second. So you can see if we are going to show real time video, we are going to have to compress the heck out of it to make it happen.

Moving image compression schemes like Motion JPEG, MPEG and others actually use frame buffering in the compression and decompression process. This allows them to not use up to much memory space on areas of the picture that are mot moving. This help reduce the file sizes.

I hope that helps.

[Allen Zagel]

When I’m using stills in a video, I just size them and put them on the timeline. Don’t forget to de-interlace them. When you render your project, all the compression is taken care of.

I use the Canon Rebel XT which does 8mp photos. If I’m not going to do any pan/crop to those, Vegas likes 655 X 480. If I’m going for the Ken Burns effect, then I generally leave them in their original size.

Allen

ASX Media Productions
https://www.asxvideo.com

[Jsteinamite]

You wrote: “Don’t forget to de-interlace them.”
What exactly does that mean and how and why should I do it?

You also wrote: “Vegas likes 655 X 480”.
I’ve seen this written before, and knowing that 720 X 480 is a norm, why do we say that Vegas “likes” 655 X 480?

Finally, you wrote: “If I’m going for the Ken Burns effect, then I generally leave them in their original size.”
I’ve heard about this Ken Burns effect also. What is it? And why would you keep images in their original size?

Jonathan Stein

[Allen Zagel]

>You wrote: “Don’t forget to de-interlace them.”
>What exactly does that mean and how and why should I do it?

De-interlacing removes that flicker you normally get on stills in a DVD movie. Right click on the photo, select “switches” and click on de-interlace.

>You also wrote: “Vegas likes 655 X 480”.
>I’ve seen this written before, and knowing that 720 X 480 is a norm, why >do we say that Vegas “likes” 655 X 480?

I don’t know the technical answer but I first head it here when I originally joined the forum. If you set a photo at the 720 x 480 it just doesn’t come out right. By using the 655 x 480 the photo lines up better in the timeline and you keep your aspect ratio.

>Finally, you wrote: “If I’m going for the Ken Burns effect, then I >generally leave them in their original size.”
>I’ve heard about this Ken Burns effect also. What is it? And why would you >keep images in their original size?

I have a powerful enough computer to keep them large. It helps greatly if you’re going to pan/crop (pan n scan) or use track motion and especially zoom in. You get a much clearer picture.

Ken Burns effect is using motion on stills to create a movie. Every or most every photo has some kind of panning or zooming to keep it interesting, rather than just static shots in a slide show. 1 photo I’ll zoom in and the next zoom out. Next set I’ll pan right on the 1st photo and left on the 2nd an so on.

I dont know if there’s a sample available. I think there is somewhere. I know theres some words about it here or on another site. Search the forum for “Ken Burns Effect”. Maybe Ed or someone can jump in here and tell you.

Hope this helps
Allen

ASX Media Productions
https://www.asxvideo.com

[Edward Troxel]

I talk about the Ken Burns effect in Vol 1 #8 of the newsletters. The Video Scrapbook sample video demonstrating the effect (automatically created by Excalibur) at https://www.jetdv.com/excalibur which you can watch.

Edward Troxel