I've tried to replace the bg of a video by using diffrence masking, I've followed this guide Difference Masking-Unmasked in Sony Vegas Software
I've done this once before and it worked but not this time for some reason, I've exacly as they did in the guide. Here's a pic of the result ImageShack - Hosting :: fail2ky1.jpg

What I wanted to do was make it look like the car was flying but the bg didn't change, But a little bit of the car changed some how (The bluer part in the middle).

I found when tried this that the background and fore ground lighting made a lot of difference the final image.

I think I know what the problem might be, I did some editing on the clips, for exampel I cut away some pieces from the bg footage that I cudlnt work with, so when I rendered the new bg clip there might have been some changes so it wasn't identicle with the bg from the subject clip. I'm trying again now with the unedited clips.

Sorry about the bad spelling but you'll just have to live with that

Okey, so I've tried once again but got the same result. But I was right, there was a huge diffrence in the lightning and shadow in the bg and the subject footages
see for yourself ImageShack - Hosting :: fail3sc5.jpg

Not sure how it's possible tho, all we did was move the car when we did the bg footage

To repeat and underline what Cheema said - Lighting!

The "emptied" - no car - BG has very low light levels; the car is being shot in FULL Sun!! I can see the glints. That is a massive difference! Can't you see that?

No, sorry, difference masking has to rely heavily on the difference from before and then after. If you have such major lighting/lumin difference to start with, then THAT is what will be "differenced" - do you see? Vegas is doing exactly what it should. Do have any shot of the FULL Sun without the car?

I would never do/attempt a difference procedure in a non-controllable environment, which is basically what you are gallantly trying to attempt.

Grazie

Yeah I know that now. well you learn from you misstakes, So next time I'll chose a better place to shoot at

Learn and have fun. That's what it's all about, isn't it? (OK speaking from a hobbyist's point of view)
Key thing is - you had a go

__________________
Tim