Greenscreen spill suppresion.

Discussion in 'Fan Films, Fan Audio & SciFi 3D' started by PixelMagic, Jun 4, 2002.

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  1. Neszis Jedi Padawan

    Member Since:
    May 23, 2001
    star 4
    I would like more info.

    Spikey and long...sounds like a mullet.

    Do you have a mullet?

    ~Neszis~
  2. Neszis Jedi Padawan

    Member Since:
    May 23, 2001
    star 4
    Here ya go, i made an attempt at it. I simply keyed out the green, and used the AE spill supressor. I also messed with the brightness/contrast. The only thing noticeable is a faint line on ur face...

    [image=http://jediacademy0.tripod.com//sitebuildercontent/sitebuilderpictures/pixel.jpg]

    [link=http://jediacademy0.tripod.com//sitebuildercontent/sitebuilderpictures/pixel.jpg]clikcie[/link]

    actual URL
    http://jediacademy0.tripod.com//sitebuildercontent/sitebuilderpictures/pixel.jpg

    ~Neszis~
  3. t-toe Jedi Youngling

    Member Since:
    May 27, 2002
    star 1
    Haha, no, spikey and kinda long on the top. Short in the back... Mullets... you see a lot of them down here in the south... :::shudders:::
  4. Lord_Rive TFN Fan Films Staff

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    Member Since:
    Jun 29, 2000
    star 4
    Any clue as to how I might fix this?

    Well, the first thing that you should know is that keying hair (from miniDV footage) is typically a pretty problematic endeavor, and the success that people are getting with Pixel's shot isn't really indicative of how it usually goes (this shot is one of the easiest ones I've come across when it comes to keying the hair). You can take some valuable information away from looking at the shot, though:

    The primary thing that makes this shot relatively easy to key is the luminescence variation between the hair and the greenscreen. Unadjusted, the luma value of the wispy hair near his part is pretty dark, ranging in value from 50 to 95, while the greenscreen is pretty bright -- near 120, plus or minus (with 0 being black, and 255 being white). This provides a pretty big difference with which to perform a levels call -- which is basically what all keying software is doing: a series of levels calls to various channels. The situation becomes more difficult when the luma values are closer... without a lot of room to push the hair to one end of the spectrum and the screen to the other, things get chunky pretty easily. Think of it like this: you grab some pizza dough that's sitting on the counter, already formed but not baked. If you take it by the edges and pull, it will stretch wider without breaking apart. If you grab it in the middle, though, it won't have enough material to fill in the area that's being stretched, and you'll get holes.

    As an example, if you take Pixel's shot and look at just the luma information, and then perform a levels call where you push the green to white and the hair to black and then invert the information, you've [link=http://www.crewoftwo.com/dave/bwpixel.jpg]already got the beginnings of a pretty good looking alpha[/link]. From this you can derive the following strategy: when filming people with dark hair, try to film them on a bright screen (like Pixel's got). If you've got someone with light hair, film them on a blue screen (which will typically have a significantly darker luma value than green). A levels call on footage of that variety will push the blue to black, and the light hair to white -- giving you the alpha you're after... or at least the part that pertains to the hair. Screening the resulting footage over a normally derived alpha will help to fill out all that data you need to have a good key. Part of the importance of all of this lies in the fact that luminescence is uncompressed in miniDV footage, so it's your best source for trying to get fine details like hair.

    Regarding chokers: I only use them as a last resort. They're bad things, I tell you! The problem is that they rob detail from edges (like hair), and play havoc with things like motion blur...
  5. PixelMagic Jedi Master

    Member Since:
    Oct 8, 2001
    star 5
    You made me look freaky in that black and white image, Dave. But then again, I always look freaky. And yeah, I was suprised how easy it was to key the hair. This is only my 3 or 4th try at keying Mini-DV video. Gosh, I'll be so glad when they come out with a format that is easier than Mini Dv with bluescreening.

    And get it straight, Dave, it's an OCCLUSION PASS. And I wrote that tutorial when I didn't know what I was doing. I only use occlusion passes for reflective objects now. (like your terminator head) :p
  6. Obi-Timbo Jedi Youngling

    Member Since:
    Dec 29, 2001
    star 1
    Rive[/], you guys are coming to Canada...cool. Any chance you guys are gonna come to Edmonton, Alberta??? :D

    Tim
  7. t-toe Jedi Youngling

    Member Since:
    May 27, 2002
    star 1
    Aha, thank you, Lord Rive! I see now what my problem is: I have light hair, and was shooting on a green screen with pretty light green values. I'm gonna try to construct a blue screen now too. ^_^

    One more quick question: Are there any tutorials around that relate to lighting a green/blue screen? That's my second biggest problem. The cheaper the solution, the better. (Us college students don't have an excess amount of money lying around. Hehe.)

    --t.toe
  8. lokmer Jedi Padawan

    Member Since:
    Mar 15, 2000
    star 4
    To light a screen cheap:
    Go to home Depot. Get some floor shop lamps.

    Go to an Art store and get some Vellum.

    Stretch the vellum over the lights, being sure to leave enough room for circulation so you don't start a fire.

    Point lights at greenscreen. at 45 degree angle or less.
    -Lokmer
  9. Shadoe42 Jedi Youngling

    Member Since:
    Aug 30, 2001
    star 3
    I have been messing with this a bit. Anyone know any good methods for spill supression in Media Studio Pro?

    http://home.swbell.net/miller42/composite.jpg

    That is what I have so far. The one time I got rid of the green the thing came out in monochrome.

    Oh and the tutorials in the CTK from dvgarage...do those apply only to AE or are they techniques that could be applied across programs? Thanks
  10. Lord_Rive TFN Fan Films Staff

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    Jun 29, 2000
    star 4
    And get it straight, Dave, it's an OCCLUSION PASS. And I wrote that tutorial when I didn't know what I was doing. I only use occlusion passes for reflective objects now.

    Ah, see? I knew that was going to come back and bite me. I don't have the tutorial you wrote bookmarked, and I only looked at it the one time when you first posted it a couple of months ago. I did get it straight from the standpoint that it is a technique that produces subtle results with respect to reflections, though... An ATTENUATION PASS, as I'm sure you know, is a technique for replicating the "Fresnel Effect" -- another subtle occurrence in reflections wherein the amount of reflectance you see on an object increases as the surface of the object reaches a more acute viewing angle... And of course (like the occlusion pass) it's only really useful with reflective objects -- and even then, in a subtle way.

    The point is, I don't see how one (subtlety in 2D) is different from the other (subtlety in 3D).

    Shadoe42: That's a good start! There's a little loss of detail in the hair, though -- without being a Media Studio user, it's hard for me to say what you might consider doing differently, except to suggest that maybe you approach keying the hair separately (on a different footage layer)...

    With respect to the spill, does Media Studio have the option of adjusting the hue/saturation of a particular color spectrum? If you can desaturate just the greens and yellows, it shouldn't come out too monochrome, and you'll get rid of most of the spill...

    Oh and the tutorials in the CTK from dvgarage...do those apply only to AE or are they techniques that could be applied across programs? Thanks

    Yes, for the most part they do... Pretty much everything is based in AE, but it covers concepts like multi-pass keying, shadow generation, light wrap... I think you'll find in the final version that there will be a lot more stuff that will be program-unspecific as well, like the "build your own CDK".
  11. DRProducer Jedi Youngling

    Member Since:
    Mar 23, 2002
    star 1
    Lord Rive,what did you see wrong with the keying of the Lord of the Rings?I could tell in the shot where Frodo and Sam walk down twoards Mordor at the end of the movie,that they used a bluescreen for that.And when they are in the mines of Moria,that they shot all the actors separatley in front of the bluescreen,and scaled them down to different sizes.They did not use a ratio for that shot.They just sized the actors guessing what the sizes of the hobbits would be.

  12. Lord_Rive TFN Fan Films Staff

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    Jun 29, 2000
    star 4
    It wasn't the keying that I stood out to me, but more the compositing. There were a number of shots in the film where the matte had been achieved rather well, but I kind of winced as I watched it, because the characters looked pasted on -- the edges didn't seem to blend properly into the background. Now, don't get me wrongo. ;) I thought that they did an excellent job on the film, and that the effects were great -- inspiring, even. The point of the post was that, despite Pixel's assertion that 3D is harder to do realistically than 2D, it seems that it's the 2D compositing issues that betray the visual effects going on in the shot most often -- at least for me...
  13. DRProducer Jedi Youngling

    Member Since:
    Mar 23, 2002
    star 1
    They only shot that was not done well at all in compositing,waswhen it was pitch black,and Gandalf lit his staff.They actually rotoscoped the light.They could have done a much better job.Maybe I am just dissing WETA Digital because they are relativly new.And because I like ILMs method of doing the effects much more than I do WETAs.
  14. PixelMagic Jedi Master

    Member Since:
    Oct 8, 2001
    star 5
    In my opinion, Weta Digital does better in SOME areas than ILM. ILM is getting to the point where they rely too much on computer graphics. Weta Digital enhances effects digitally, but doesn't go over board with it. Some of ILM's shots in Episode II, although very impressive, we unmistakingly poorly done CG shots. Now, I know this is due to the fact that they are working on SEVERAL films at once, and have a limited time frame. But Weta just has done some much better shots in Lord of the Rings. Like, ILM uses their water simulation software WAY too much. It would look much better if they used real water in some shots. Like in Episode II, there is a beauty shot of the water city on Kamino where the ocean splashes against a colunm. It is very good as far as simulation and movement and dynamics, but it just looks really fake. However, if you noticed in LOTR when the squid creature (don't know the name, I hate LOTR) splashs around the splashes are done with practical elements. Much more impressive. Oh, and so this stays on topic, I'm working on a third attempt at keying my shot using MULTIPASS KEYING...ha ha. And Dave, I'm not sure how to do an Attenuition Pass, I'd be interested in knowing this.
  15. Neszis Jedi Padawan

    Member Since:
    May 23, 2001
    star 4
    Pixel...what about my try?

    ~Neszis~
  16. Lord_Rive TFN Fan Films Staff

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    Jun 29, 2000
    star 4
    And Dave, I'm not sure how to do an Attenuition Pass, I'd be interested in knowing this.

    The process is pretty simple: with the object textured white and with no reflectivity, place a single light source in the same position as the camera. The resulting image will be brightest on faces that are directed at the camera, and will fall off on faces that are pointing away from the camera. Take this image, and invert it (so that it's now brightest on the the faces that have a more acute angle), and use it to darken the reflections. Fairly straightforward...

    An [link=http://www.opengl.org/developers/code/sig99/shading99/course_slides/ShadingComputations/sld077.htm]example.[/link]

    You can see the effect in more detail [link=http://www.dvgarage.com/garage/a2d/tut/tutpast/tutpast_1_20.php]here[/link] (check out the two tutorials with the aluminum twist-top -- a tutorial Alex wrote on multipass rendering -- hard-core multipass rendering... ;) ).
  17. Lord_Rive TFN Fan Films Staff

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    Member Since:
    Jun 29, 2000
    star 4
    Neszis: I haven't been able to get your link to work... I just get that "Image Hosted by Tripod" logo... :(
  18. PixelMagic Jedi Master

    Member Since:
    Oct 8, 2001
    star 5
    Neszis: it looks as through yours has the best spill suppression. Some work still needs to be done the matte though. The hair strands don't look natural (although, I couldn't do any better using After Effects) But it appears as though After Effects's spill suppressor is better than the Composite Wizard spill suppressor. And you gave me a nice saber! Gool idea. I think I will do that in my next example.

    Dave: So does that mean I use set the Frensel effect's layer to Multiply in After Effects? Or Darken?
  19. Shadoe42 Jedi Youngling

    Member Since:
    Aug 30, 2001
    star 3
    woot! thanks Rive. Went back and toyed with the hue/saturation a touch then fiddled with the monochrome filter used to make the matte...and this is the result

    http://home.swbell.net/miller42/composite2.jpg

    still some slight spillage but the hair is much more distinct.
  20. Lord_Rive TFN Fan Films Staff

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    Jun 29, 2000
    star 4
    Pixel: I'd take it on a case by case basis, depending on the shot, and employ the method that looks the best to you... Another option might be to use it as a luma-matte to actually subtract from your reflection pass...

    Shadoe: Wow! That's a big improvement. Losing a little color in the collar though (it's kind of turning brown int he back)... You might consider increasing the blue saturation a touch to make up for it. Hair's much better this time around, too. :)
  21. Macho Jedi Padawan

    Member Since:
    Sep 21, 2001
    star 4
    pixel i think ILM has done a better job than weta digital in many instances. the best effects/compositing job I have ever seen is by Mill Film for blackhawk down. I was reading through the 3dworld and was surprised some shots that were cg that I thought were completly real! Their copters looked exceptionally good espically considering they couldn't get any real textures from the copters
  22. Shadoe42 Jedi Youngling

    Member Since:
    Aug 30, 2001
    star 3
    hehe hey cut me some slack...I am supposed to be working here(peers out for boss) :) :) hehehe but seriously I didn't notice the collar. Was just trying to get rid of the spill. hehe guess I need to learn how that multipass keying thing works :) seems like that would probably help in this case.

    hmm...the hue&saturation filter I am using is not real robust it seems...pretty much just the main RGB channels... blue you say? sweet I will try that. Thanks again.


    Shadoe
  23. Shadoe42 Jedi Youngling

    Member Since:
    Aug 30, 2001
    star 3
    oo blue worked really nice. :) got a pretty good composite out of it.. heh I will quit fiddling with pixel's pictures(try saying that three times fast) now :) :)

    http://home.swbell.net/miller42/composite3.jpg
  24. Lord_Rive TFN Fan Films Staff

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    Jun 29, 2000
    star 4
    Awesome, Shadoe. Much better! :)
  25. PadawanNick Jedi Master

    Member Since:
    Jun 6, 2001
    star 4
    Great job Shadoe!!
    Always fun to see such nice results from another MSP user!!!

    Have fun!
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