çhroma keying with FF

[Alfredo Luis Mateus <almateus@globalsite.com.br>]

> Dear FFDG
> 
> Am new to filter factory and would be most grateful if you guys could
> give
> me any suggestions on filters that can mimic travelling Matte / Chroma
> key.
> Blue and green.
> 
> I know there are several proprietary  plug  ins on the market, but I
> am interested in seeing what  can be achieved  in ff.
> 
> If I want to lift foreground  objects  off blue  or green screen
> backgrounds. To composite onto  different scenes. .
> In ideal circumstances  such backgrounds  would  have  good density
>  and the minimum  of red green contamination.
> 
> The  only  image  in Photoshop 5 (samples) that is at all indicative,
> is the CMYK balloons. This exhibits  too much variation to be an ideal
> subject; but as a point of discussion. I have experimented with  some code, trying  to remove the sky area without  effecting the foreground.
> As follows.
> 
> R:
> ( r>40&& r<80) ? (b>100? R-90: r-0) : (b<70?  r-0 : r )
> G:
> g>140?(b>145 ? g-150:g-20 ) :g
> B:
> b.140?(g>80?b-200:b-0):b
> 
> Werner Streidt gave me some valuable  input  on this.
> It works quite well within a limited range, but when the range is
> extended
> red tears through in the foreground.  Can I improve on this?
> 
> Also is it possible  to remove blue /green information  and leave
>  this area
> as RGB 255 white  / instead of black.
> 
> Werner also  suggested  that I might try working with the hue chroma.
>  and he indicated that there   had been some  previous  discussion this
> topic  on the FFDGG.
> So far I havent been able to locate this. any  ideas where  this
> might live.
> 
> Also any  books / literature this topic/ chroma key .
> 
> Many thanks.
> 
> David Joe Bruton.
> London UK