How do I produce ghosted images of people?

[Rudgey]

Can any of you clever chaps tell me how to produce ghosted images of people?
I have a good example of what I’m trying to achieve here: http://vimeo.com/15834358. He is using a DSLR camera to shoot it.
Any help would be great.

[jagabo]

You use two pictures or videos from the exact same position, one with the people, one without. Then you overlay one onto the other with ~50 percent transparency. If you don't have a shot of the scene without people you can create one by pasting from several frames of the video (assuming the people are moving and you can get all parts of the frame people-free). You can make the people disappear using a cross fade.

[Rudgey]

Thanks Jagabo, I understand now, would you have a problem to correctly expose the scene as you be adding + 50% to it? ie making the background scene + 50% darker. Or do you have to overexpose it by 50% so when you add the other layer you come back to the correct exposure?
Does that make sense?

[poisondeathray]

The exposure and lighting setup should be the same for both shots (so you would have to shoot at the same time if shooting outdoors, otherwise things like shadows won't match). The key is to lock off the shot. Even the smallest vibration will make the shot unusable

The background plate is the layer and footage without people

The forground plate is the layer and footage with people (you would put this on top in your editor or composition application)

If you use ~30-50% opacity (or transparency on the top layer, it will show similar to that video - only things that differ between the layers will show through as "ghosting"). If you use other transfer modes, then there will be funky additive effects. But using "normal" transfer modes you will get the ghost effect. Everything else that overlaps will look normal. The transfer modes are similiar to those in photoshop (e.g. add, subtract, lighten, multiply etc...)

[Rudgey]

Thank you Poisondeathray, top man or women?

Thank goodness you don't have to work out the exposure for each layer!
Looks simple enough to do, I will give it a go over the next few days, thank you again.

[poisondeathray]

Thank you Poisondeathray, top man or women?

Thank goodness you don't have to work out the exposure for each layer!
Looks simple enough to do, I will give it a go over the next few days, thank you again.

women on top or bottom , I'm ok with either

By the way you don't need expensive software either, most NLE's like vegas, premiere can do this easily. You should be able to do it for free with avisynth and overlay() as well

[jagabo]

Here's a sample AviSynth script:

v1=AviSource("video.avi").ConvertToYV12()
v2=ImageSource("frame.png").ConvertToYV12()

Overlay(v1, v2, opacity=0.5)

I used the first frame of the video as the image to blend with. Sample Xvid AVI attached.

[jagabo]

Here's another sample where I blended with the same video delayed by 1 second.

v1=AviSource("video.avi")
v2=Trim(v1, 30, 0)

Overlay(v1, v2, opacity=0.5)

[guns1inger]

Another option, which can give you more flexibility, is to film your "ghost" in front of a black background. Just make sure the subject are well lit. Black is easier to work with in this case than blue or green screens. It also gives oyu much more flexibility as you can move your ghost around in your editor without the masking problems caused by filming them on location.