Effect? i dont know what it's called

[upper]

How does one put fake 3D object in real motion picture?
For Example, Jurassic park used a 3D dinosaur in a real picture.

[Supreme2k]

You're talking about blue (green) screen, superimpose, or a combo of both.

[poisondeathray]

chroma keying

http://en.wikipedia.org/wiki/Chroma_key

[jagabo]

Or overlay with alpha channel. And matting, if you want parts of the video/film to appear in front of the 3d object and parts behind.

[upper]

for example, i shoot 2 people running from nothing at my front yard, then i go to 3d program to make a monster and how do i put that monster in the movie that i just shot chasing the 2 people running away from nothing. kinda like jurassic park.

[guns1inger]

You have a number of choices.

1. Shoot the background plates first, with no-one in them. Shoot the green screen plates of the people running next. You will have to use the same camera settings, and if the camera moves, you will have to also make the same movements in each shot. Finally, create the 3D material, probably as several different passes so you can match it to the live material. Now you can layer all of these in a compositing tool such as after effects or combustion (or fusion or, if you have money, inferno)

2. Shoot the live plate with the background and foreground (people) elements, then shoot just the background again as a second pass. Create your 3d elements as before. Using a mixture of rotomasking and other tricks, insert your 3d elements in behind the people.

3. Shoot just a single background/foreground pass, then use rotoscoping/masking tools to carefully extract the people from the plates. Insert your 3d elements, then layer the people back over the top.

If done well, the order of best results would be method 2, method 1, method 3. Method 3 is the cheapest for a one man show, but most manually intensive and will give the worst results.

If you want to keep it really simple, frame the shot so you have enough space to the side of the people running so the monster never crosses behind them, and so they never interact. Then you can use method 3 with better results.

[CogoSWSDS]

OK I've always wondered a little about the green screen thing. Why couldn't you shoot the background with the people running, then "film" the T-rex or whatever on a green screen (for example, if you've done a CGI of the T-rex, CGI a green screen in behind the T-rex) then use the chroma keying to put the people and background in? (I'm assuming the people are running across the frame, not toward or away from the camera)

Seems that CGI'ing a green screen in behind the CGI monster would be easier than putting all three together...

Beuller? Beuller? Anyone?

CogoSWSDS

[guns1inger]

You don't need to green screen the CG because it is rendered with alpha masks ready for compositing. The reason you would green screen the people is so you can have the creature/CG effect pass behind them. If you watch the example given (Jurassic Park) you will see scenes where the T-Rex is in the background behind characters. it is far easier to do this if you can film the characters separate to the background plate.

If the two don't have to cross paths at all then you don't even need a green screen. It depends on the requirement of the shot.

[CogoSWSDS]

OK that makes sense. Thanks Guns1inger

CogoSWSDS

[upper]

how about like iron man

[guns1inger]

The descriptions of techniques above are very simplified and based on what a single person might be able to achieve on a desktop computer with consumer software.

When you start talking about feature films like Iron Man, or even Jurassic Park in serious terms then you need to think in terms of a team of 100+ people, all skilled in different areas of vfx production, farms of CPUs for processing power, and mixture of shrink wrap and custom written software, huge quantities of custom written shaders, particle effects generators etc. and huge numbers of person hours in effort.

Iron Man is a huge mix of live and computer generated characters, hand painting, digital painting, blue and green screen work, composites that are several hundred layers deep with hundreds of separate elements, and (did I mention this ?) lots of trained people at the wheel.

If you really want to learn about how this type of thing is done, there are magazines, both real and virtual, vfx sites where pros discuss how certain effects are done, and lots of other places to play.

If you want to see some of the basics and what can be accomplished by the man on the street, I would start with Video Co-Pilot ( http://www.videocopilot.net/ ), which is a huge (and growing) library of After Effects tutorials that covers a wide range of topics. If nothing else, it will give you an idea of the effort and preparation required in order to do this type of thing, and whether or not you are up the challenge.

Edit : Added Video Co-Pilot link

[greymalkin]

after watching the Transformers HD DVD I checked out all the extra features where they talk about rendering the transformers themselves and then the actual transformations...etc. They didn't really get too deep into it at all because it would just make your head explode...I do remember that each of the more complicated frames would take something like 96 hours to render...and this is with a dedicated render farm

[guns1inger]

Some of the Transformers had thousands of modeled components totaling hundreds of thousands of polygons. Add to that the HDRI (High Dynamic Range Imaging) based photorealistic lighting, detailed and complex shaders, and 96 hours isn't surprising. And remember - that isn't for a completed frame as you see it on the screen. That is just for the CG component of a single transformer. Multiple transformers means multiple renders per frame, then compositing, then colour matching, then colour grading . . . . .

[edDV]

Start here:
http://en.wikipedia.org/wiki/Alpha_compositing
http://rmagick.rubyforge.org/src_over.html
http://rmagick.rubyforge.org/web2/web2.html

[guns1inger]

If you want to watch something a little more realistic, dig out the double disc set of a little Australian horror film from a couple of years ago called Undead. The effects in this were done on a consumer rig (for the most part) and most of them are pretty effective.