Stepping through the Portal with the Portal effect?

HeySiri
HeySiri Website User Posts: 382 Just Starting Out*

I have a scene in an upcoming short film where the main character shoots a portal onto the wall in front of him, then steps through the portal, and the cameraman "follows him through" the portal, and they both emerge outside. The room itself is completely CGI—the actor is going to be in front of a green screen. I am good with green screening and I can place markers on the green screen to track, moving the background with the camera if you get what I mean. But, how can I have him step through and be outside? I could do it with clever masking, but when he steps outside the lighting needs to be realistic to outside as opposed to the dull, more mood-lighted room he was in (which will be a CGI room composited in place of the green screen). How can I achieve this stepping through effect? How can the cameraman "step through" the portal with the actor, since it'll be in front of a green screen, then need to be outside? I wanted to do it in one continuous shot, but if I can't I can use two shots and do some editing to make it look like they just walking through.

Comments

  • CleverTagline
    CleverTagline Moderator Las Vegas, NVModerator, Website User, Ambassador, HitFilm Beta Tester Posts: 3,238 Ambassador

    If you're okay with masking and chroma-keying, I suggest that you actually shoot it outside (including the greenscreen) to solve your lighting issue.  Set up some flags (or equivalent gear) out of frame to block the light on the actor for the part when he's supposed to be indoors. When he steps past the area these flags are affecting, he will naturally emerge into daylight. You can color correct the earlier part so that it appears to be indoor lighting, then dial back that color correction as he passes through the portal.

  • HeySiri
    HeySiri Website User Posts: 382 Just Starting Out*

    @jsbarrett What about when he steps through the green screen?  How does he step through it? If there’s a green screen in front of him outside, how does he “step through it”? I was thinking if someone behind the green screen moved it as he walked near, it might work, but then the transition wouldn’t be “going through a portal” it’d be just the background changing. How do I get this going through effect?

  • CleverTagline
    CleverTagline Moderator Las Vegas, NVModerator, Website User, Ambassador, HitFilm Beta Tester Posts: 3,238 Ambassador

    @HeySiri You didn't say the actor would be stepping through the green screen. You specifically said he would be in front of it. Also, my recollection of most portal effects is that you see the target environment through the portal, so there isn't really a feeling of a person going through a layer of anything that they need to push aside/through. It's just a hole in space between two places. This is the kind of portal I'm picturing:

    If you want the talent to push through something, you could perhaps animate a mask around them to make it look like they're going through some substance.

  • HeySiri
    HeySiri Website User Posts: 382 Just Starting Out*

    @jsbarrett I apologize I didn't say that well. It's not like they're going THROUGH a substance, they're just physically walking through a portal. There's nothing they're pushing through. They're essentially stepping through a hole in the wall. The thing I can't figure out is how to get it so that they are in front of the green screen, then they "step through the wall/portal", and emerge outside. The hard thing is I want to get one continuous shot of them walking outside because it'd look really cool cinematically. However, the lighting in a dull room and the lighting outside are VASTLY different, so I don't know how to make this continuous shot from a greenscreen scene to outside. Does this make any more sense?

  • CleverTagline
    CleverTagline Moderator Las Vegas, NVModerator, Website User, Ambassador, HitFilm Beta Tester Posts: 3,238 Ambassador

    Yeah, that makes sense. It's just a really tough setup, but sometimes VFX is tough.

    Here's what I would do: ditch the greenscreen, and shoot it all outside. Instead of a greenscreen, put some tracking markers on stands to represent the wall where the portal is going to end up, and place those on either side of the path where the talent is going to be walking as he goes through the portal. As I said before, set up your shooting area so you can block the light falling on the talent so that he starts in an area that's much darker to represent the "room," and then walks into sunlight as he passes those stands with the tracking markers. Your room and the portal will be all CG, and you'll use the tracking markers you added earlier to add those elements so they track properly as the camera moves through them.  You can use the portal shape to cut out the hole you'll need in the wall to show through to the outside area. The rest will be rotoscoping your talent until he's through the portal and fully outside.

    Admittedly I've never shot anything this complex (and have never shot with a greenscreen, either), so this is just how I would approach it after some quick brainstorming. I'd love to hear others' ideas as well.

  • tddavis
    tddavis Moderator, Website User Posts: 4,721 Moderator

    @HeySiri @jsbarrett a lot will depend on the camera angle you envision showing the character step through.  If a side view or slight angle, you could still use the method as described but the character would  not face the green screen.   I think the easiest way to approach it is with a shot of the back of the character  pantomiming step through in front of the green screen then unblock the sun have him turn around and finish the pantomime of stepping through into the full light.  The effect of the portal in front and behind will hide a lot of mismatch and masking will help too.  But that's just the way I would try it.  May not be the best way.

  • Triem23
    Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 19,361 Ambassador

    Also look at the Film Riot and FXHOME playlists for Portal Combat. They have BTS videos that will help show how they approached the problem. There's also "Portal Trick Shots" by Corridor Digital, and its making of/VFX breakdowns.

    The bottom line is to do a continuous take moving between different lighting conditions, you have almost no choice but to control your shoot location to create different lighting conditions. @jsbarrett gives great advice. 

  • Palacono
    Palacono Website User, HitFilm Beta Tester Posts: 3,448 Enthusiast

    This might give you some ideas as well.

  • tddavis
    tddavis Moderator, Website User Posts: 4,721 Moderator

    I went looking for this and found Triem23 had already  mentioned it, but here's a link anyway.

  • Palacono
    Palacono Website User, HitFilm Beta Tester Posts: 3,448 Enthusiast

    And this, plus some free downloadable assets to use. Easily converted to Hitfilm Express.

     

  • HeySiri
    HeySiri Website User Posts: 382 Just Starting Out*

    @Palacono that video is sweet! How did they do the portal gun, though? I can get that it's just tracked but it rotates and stuff... how is that done?

  • Palacono
    Palacono Website User, HitFilm Beta Tester Posts: 3,448 Enthusiast

    @HeySiri a 3D model tracked using the various blobs on it and composited over the top.

    Could perhaps be done in Blender as that can both track and do the 3D, but there are other ways it could be done: Cinema 4D and AE, Element 3D and AE.

    Tricky in Hitfilm as not sure how mocha would turn those blobs into something you could track in 3D, as it's more about giving you a 3D camera on an entire scene.

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