Just imagine the first image to be a live-action shot. I didn’t have my digicam around to make a real one, so I had to improvise a bit using a virtual scene (including shadows/shading for a bit of realism)
One thing that works really well is to set the world as an alpha image file. I just made a 10 x 10 pixel alpha .png and set to to world settings. I found in previous versions that this way I wouldn’t get that annoying shade halo around objects with a transparent background. I have not tried with the new version yet so I don’t know if this is the case.
To be honest I haven’t really gotten in to using blenders compositing nodes yet, but the way it is generally done is with garbage mattes. What you do is a roughly mask out objects that you dont want to be visible before you use the cromakey to remove the green. This mask can be done in blender with a black bezier plane or two in the 3d-view while leaving the background (=what sould remain visible in the end composite) white.
I confess… I love my Macintosh, and the tools that are available for that. You can do “very good” video editing strictly within Blender, of course, but there are advantages to using it simply to produce footage that you can then integrate into the other (live) material using the tool that you’re already using for that live material.
You’re probably going to need to concentrate first upon taking your live-footage and cleaning it up. In other words, apply the chroma-keying filters so that you are looking strictly at “the live footage with the background subtracted out.” Study that footage carefully, by hand for “artifacts,” and clean them up. If there are extraneous objects, matte them out. A pro-grade video editor can do that easily enough.
Be especially careful of cases where a reflection of the chroma background has “splashed” onto an object you want to keep. It can easily render such a thing “translucent.” Likewise, similarly-colored objects, on clothing and such, can pop up as “holes.”
Ideally, you would do all of the “chroma” processing first, replacing that with a pure alpha-channel mask, before proceeding. I like to preview all that stuff against several garish, brightly-colored background planes in the video editor, playing it slowly forward (or, to help break my eyes from “watching it,” slowly backwards) until the whole piece has been visually inspected. The garish backgrounds help to point out the holes and such. It’s time-consuming, exasperating work, but it must be done and done well, because the client sees all. :rolleyes:
Obviously, when you are shooting … when you are setting up the live shots, working out camera angles and so-forth … is the best time to catch these “issues,” i.e. before you start to roll, but you can’t always control what happens next.
I look forward to writing a How to Use section, Werner, once you get it worked out Check outt he garbage matte technique video from I think Siggraph, I think the post is on BlenderNation. He integrates a blue screen shot of a spaceship model over an earth that is perfect. Garbage matte is used to block out what isnt blue screened.
Btw, I think you want the shadows to be there, so that when you alpha over, the shadow comes with it. That’s why the lighting in the blue screen shots and the real background has to be the same; so that there is no mismatch. That is the purpose of shooting the chrome ball with the live action.
I’ve re-added the deleted text for the matte-nodes to the wiki-page.
I wont have much time to dig far into the new nodes (yet), but a (simple) tutorial or example woudl get me started faster for sure … do you stil have the link, i can’t seem to find the news entry you are referring to. :-/
I’ve seen quite some examples where the shadow was re-added after bluescreening by using OnlyShadow planes and other geometry as well. Whatever works best i assume
Yeah, that is a good idea … but why don’t we just make a pratical example fro the new matte nodes (especially the chroma key node)? They where added for exactly this purpose. I’ll try to come up with some nice example.
On a related note: Did anybody try the “Chroma Key” node in the recent CVS builds? I can’t get it to work at all. Feeding it a bluescreened image and tweaking the options doesn’t affect the output at all (output=white matte output and original image). :-/
The “Difference Key” node seems to work (at least in some cases … i need to play with it a bit to check this)
I wrote the chroma key nodes and I’m curious as to the problem your having. If you can, send me the image to bob_holcomb ‘at’ hotmail.com. I’ll be happy to help you out and try to make those nodes better.