Home Forums Open Forums Soft Keys in Mistika


This topic contains 4 replies, has 3 voices, and was last updated by  walger 10 months, 3 weeks ago.

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  • #18417

    Patrick Hirlehey

    I’m working with a large variety of greenscreen comps that were shot on a greenscreen that doesn’t seem to have as good separation between red/blue and green on the screen itself (its more of a teal screen). The source greenscreen has an RGB value of R13 G27 B14, I’m using a ColorGrade to select the greenscreen and push it towards R12 G44 B10, to better work with the Greenscreen Keyer and incorporate the Background Build for a difference key. There are some motion blur edges and some very fine tufts of white fur that I’m having trouble with. Any strategies for dealing with those kinds of soft keys?


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  • #18419



    I’m not the best compositor in the world (David Cox would probably be the best on Mistika) but I’ve done a fair few green screens and I quite like Mistika for doing this sort of thing – mostly because I can get flexible how I approach each particular key.

    Firstly, do you realize that the GreenScreen effect can take up to 3 Inputs? The 2nd works as a reference for what’s being keyed. I end up using the effect twice usually – the 1st time I use a solid (set to the same colour as the average of the majority of the screen that you’re keying). Get your best key using that and then use ExternalKey & EdgeBuild to create an improved version of what you did with a Solid on your 1st pass.

    Before I did any of that though I would grade the screen to best work for keying it. Personally (and this is just me – make up your own mind) I wouldn’t use a Key at this point. I would use Primaries and then bands to maximize the contrast between screen and subject, as well as trying to get the screen’s colour as consistent as possible. At this point using something like a Medium Blur or Denoise can also be useful for getting closer to that average.


    Fixed Vectors is the really useful one though. Using HUE and SAT to maximize the difference between the screen and the subject can be quite easy with Fixed Vectors, as opposed to a key – which could mess up your final key in the end.


    Obviously working in multiple passes is usually essential. Getting as large a core key and then working on the fiddly sections (hair detail) in passes the only other advice that I really have.

    If you attach a single frame, or a small section, I’d be happy to have a go at it. If I can’t make it work then I should probably work out why 🙂



    Patrick Hirlehey

    Here’s a Greenscreen and Comp – I’m having trouble with the motion blur on the hand with the Greenscreen effect
    GREENSCREEN – http://imgur.com/u67Hqm7
    COMP – http://imgur.com/oelVGD7



    Sorry for the late reply – my Mistika license ran out and I was waiting for a new one. I’ll give you what advice I have though, hopefully it makes sense. I would have just sent an .RND if I could.

    What effects are you using to get this key? Just the GreenScreen effect? If so I would recommend using some others with it. As I said earlier – the GreenScreen effect has more than 1 input. You can use either a Colour SOLID or the ScreenBuild effects for the 2nd input. They will improve how well the GreenScreen effect works.

    I would usually both pre-process and post-process the image with ColourGrade as well. You’ve already got quite good contrast and colour separation between the subject and the GreenScreen. Part of the problem that you’ve got is that motion blur is effectively working like a transparency – so you’ve something like 50% green bleeding though. You could erode the key of course, but then you just risk losing all the other detail that you want to keep (like hair fringe detail).

    I would use FixedVectors first to accentuate the differences between the Greenscreen and the subject. You can do that by doing things like increasing Green Saturation, or Hue Shifting colours like Red away from Green to further excentuate the difference. If you have a clean plate of the greenscreen (assuming that it’s a locked off shot) then I would use the Difference blending mode to further add to the key (you’ll normally at least get the edge detail that way). I’ve also built myself an Edge Detect effect using the Grow & Shrink Blur effects. Increase the amount of Shrink to get an edge that keys inwards, i<span style=”line-height: 1.5;”>ncrease the amount of Shrink to get an edge that keys outward, and use Grow & Shrink with equal values to have the key run along the edge both inside & outside equally. Here’s an example.

    Seeing as your main problem is with the hand you could also use a Shape and use different values for inside the Shape (the hand) than for outside. The EdgeBuild effect could also help you (although I believe that EdgeBuild is included within the GreenScreen effect)

    Sorry for the late reply – I don’t look at the forums on weekends. I’ll see if I can dig up a preset that I used to use for Greenscreen (all of the effects that I would use in 1 FXPreset). I’m on sam@silverscreenpictures.co.uk if you need an answer quickly and don’t have time to wait for a forums reply.</span>



    The best is to rotate the hue until the background reach the green peak. Just hue with no secondaries, just the entire image.

    Later you can add your screen plate (the background greenscreen plate without figure), or you can use also a hard key of the character (made with a fast keying with the same greenscreen, but cancelling the supression) and to use the Background Build. BG Bluid makes a clean version of your key background, by using color average of the borders of your fast key. You need to adjust the 2 simple parameters of the BgBluid. Aplly the same hue shift that you use in the original shot.

    Now you are ready to use Greenscreen FX with 2 inputs. The 1st is the original shot and the 2nd is the “screen plate”. When you use the keyerwith the 2nd input, you willl see the difference during the tolerance and softness adjustments… THe 2nd input in the Greenscreen effect works like a “gain map” of the key, by adjusting per pixel the tolerance of the pulling.

    This mode is like the Ultimatte algorithm… similar as Image Based Keyer (IBK) in Nuke. BgBuild works linke IBKColor in Nuke too.

    Just use a new grade to revert the hue shifting, or maybe the best is just take the alpha of the FX and use that for a copy of the original one and make the color supression with a secondary grading by adjusting a qualifier to catch the spill.


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