title: How to use toon shader to convert 3D models to patent drawings
body: <p>USPTO requires patent drawings to be black and white lines images.</p>
  
  <p>I'm using blender to make 3D models. At first I got this:
  <img src="https://i.stack.imgur.com/q6Cu2.png" alt="enter image description here"></p>
  
  <p>The problem is it's grayscale with no black lines.There's a answer to suggest using toon shader. <a href="https://stackoverflow.com/questions/30016838/convert-3d-models-to-patent-digrams">Convert 3D models to patent digrams</a></p>
  
  <p>I checked "Edge" and set "Threshold" to max 255 in "Render" tab, I got:
  <img src="https://i.stack.imgur.com/DrfD3.png" alt="enter image description here"></p>
  
  <p>It's getting better but need more edges to be drawn. I searched and found a tutorial <a href="http://www.minimaexpresion.es/?p=1070&amp;lang=en" rel="nofollow noreferrer">http://www.minimaexpresion.es/?p=1070&amp;lang=en</a> , then I got:
  <img src="https://i.stack.imgur.com/2OAPg.png" alt="enter image description here"></p>
  
  <p>It's too complicated for me and I don't know how to use render layers. So I tried another tutorial <a href="http://download.blender.org/documentation/oldsite/oldsite.blender3d.org/80_Blender%20tutorial%20Toon%20Shading.html" rel="nofollow noreferrer">http://download.blender.org/documentation/oldsite/oldsite.blender3d.org/80_Blender%20tutorial%20Toon%20Shading.html</a> , which says I should assign different materials with different colors to different objects, so I tried and got this:
  <img src="https://i.stack.imgur.com/iPSQT.png" alt="enter image description here"></p>
  
  <p>It leaves only one way to give a shot: render layers. Is there any simple methods to make it work? I only want this and convert it to indexed colors with black and white palette:
  <img src="https://i.stack.imgur.com/6sveG.jpg" alt="enter image description here"></p>
  
  <p>And the "Freestyle" only has one option about line thickness:
  <img src="https://i.stack.imgur.com/KDmmp.png" alt="enter image description here"></p>