DotScreenPass with original colors. Mask from black-white texture

I’m trying to achieve a DotScreenPass effect but instead of black and white I want to use scene colors from before applying this effect.

So I have first composer doing the colorful scene:
let composer = new EffectComposer(this.renderer);
composer.renderToScreen = false;

then I have a second composer for the effect:
let composer2 = new EffectComposer(this.renderer, renderTarget2);
let texturePass = new TexturePass(this.composer.renderTarget2.texture);
// Here I would need to use current output as a mask (black=0, white=1).
composer2.addPass(texturePass); //And here adding a colorful texture.

So I think the question comes down to: how do I add a MaskPass based on previous effect outputting BW?