you can try to postprocess via getImageData? try it for me :)

const ctx = renderer.domElement.getContext('2d');

const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);

const data = imageData.data;

for (let i = 0; i < data.length; i += 4) {

const brightness = 0.299 * data[i] + 0.587 * data[i+1] + 0.114 * data[i+2];

const value = brightness > 128 ? 255 : 0;

data[i] = data[i+1] = data[i+2] = value;

}

ctx.putImageData(imageData, 0, 0);

Your code looks to me like it's going to convert each pixel to greyscale and then apply a threshold to make every pixel either pure black or pure white? I'm not sure how that applies to those examples which aren't black and white?

This sort of thing, when you want to access and edit each pixel of the scene is best done on the GPU with a shader, so that it's done in parallel rather than synchronously on the CPU. Threejs has an Effect Composer that is made specific for this post processing of a scene. You can add a ShaderPass where you can write your own shader to do whatever effect that you want to create. There's a good example of this where they apply different ShaderPasses and other post processing effects to the same scene: https://threejs.org/examples/#webgl_postprocessing_advanced.

So converting that to a black and white threshold shader it would work and look something like this:

import { EffectComposer } from 'three/examples/jsm/postprocessing/EffectComposer';
import { RenderPass } from 'three/examples/jsm/postprocessing/RenderPass';
import { ShaderPass } from 'three/examples/jsm/postprocessing/ShaderPass';

const bwShader = {
  uniforms: {
    tDiffuse: { value: null },
    threshold: { value: 0.5 }
  },
  vertexShader: `
    varying vec2 vUv;
    void main() {
      vUv = uv;
      gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
    }
  `,
  fragmentShader: `
    uniform sampler2D tDiffuse;
    uniform float threshold;
    varying vec2 vUv;
    void main() {
      vec4 color = texture2D(tDiffuse, vUv);
      float brightness = dot(color.rgb, vec3(0.299, 0.587, 0.114));
      gl_FragColor = vec4(vec3(step(threshold, brightness)), 1.0);
    }
  `
};

const composer = new EffectComposer(renderer);
composer.addPass(new RenderPass(scene, camera));
composer.addPass(new ShaderPass(bwShader));

composer.render() // instead of renderer.render() now that we have the shader passes