Halftone 3 meaning & how to encrust?

Hello.

Short questions: what is the effect/behaviour of a halftone 3 filter? How does it impact a “screen” blend mode?

Long Story, if have some time to help me understand what happens: I want to encrust a semi transparent layer (forest) in a frame that is filled with fire, the blend mode “screen” seems fit to the job, and it works nicely when I simulate it on 2 images (png exports).

expected result:

Nevertheless when I replace the picture of a fire by the real (animated) synfig layers the result is not exactly the same:
failed “screen” on the real synfig object:

I guess this problem is due to the black on top of the fire not being completely black… as can be seen in the next screenshot:

So, while trying to “filter out” the remaining noise from the black on top of the fire, by cutting away some color info, I tried to add a “Halftone 3” layer and it allowed for a nice “screen” blend. No other change was brought but adding this Halftone 3 with its default settings.

It turns out the noise in black effectively removed by halftone 3… but i still don’t understand the effect of this layer and its link to “screen” blend mode. I’m happy to get the wanted result… but would definitely like to know how it works!

By the way, as I was looking for a green-screen like effect I tried Luma Key filter… but it turns out I cannot pick the color to be excluded (only parameters of the Luma Key layer are z-depth, amount and blend. Is this a bug in 0.62.0? Is there any other option for encrusting material in a given color of another layer?

Thanks in advance for any tip / pointer… and feel free to have a look at the attached .sifz if it helps you figuring what I mean.
Berteh.

PS: ah ah, some wood will definitely burn soon!
forest_on_fire_2.sifz (2.1 KB)

Luma key works with the luminance of the picture - i.e. black becomes transparent. Akhil did write a greenscreen module, but he isn’t quite ready to release it as part of the standard package yet.

I figured the use of Haltone 2 (Black & White) and Halftone 3 (Cyan, Magenta & Yellow) thanks to the explanations and illustrations at en.wikipedia.org/wiki/Halftone, have a look if you wonder how to use these interesting filters.

@pixelgeek: thanks for the info on Luma Key. I was mislead by the documentation at synfig.org/wiki/Layers#Luma_Key that mentions a “color”.

Regarding my problem described above I ended up filtering the black noise with a Clamp [0,-] instead of Halftone 3, and adding a Luma Key to get transparent black. A solution easier to use than screen mode in my case.

Thanks to the developers for the nice effects in Synfig.
B.