Case Study: 9to3Animation Non Photoreal Rendering

We were approached by 9to3Animation in Holland to see if we could achieve a very custom non photoreal sketch look, all in a 3d render, that was inspired the work of the great illustrator Carl Hollander and Helen van Vliet, with custom shaders and plugins in Pixar's RenderMan renderer.

The Netherlands has a long tradition of children’s illustrators who provide atmosphere without limiting children’s imagination. Our goal is to do the same in our animations. Therefore, the visual art style of the film, which we developed after extensive experimentation, was made for RenderMan rendering software in co-operation with LollipopShaders from Vancouver, Canada. The style was inspired by a number of Dutch illustrators.
-- Ernst Janssen Groesbeek, owner 9to3 Animation Studios

Reference Artwork by Carl Hollander

Reference Artwork by 9to3Animatioin

Helen van Vliet has a dynamic style in which all the elements are integrated to form a whole. Her work is unforced, not strictly inside the lines realistic but credible all the same. -- Ernst

These art references were quite extreme with the squiggly lines going off the geometry, we knew we wouldn't go that extreme in 3d but it was a great example to look at even though ultimetaly the lines going off the gemetry would be much more subdued.

Challenge: Creating hand-drawn looking lines

Given 3d geometry, the goal was to have multiple techniques to create lines on features of the geometry.

The typical approach is to:

1) Sample “curvature”, where the surface normal of the geometry is evaluated to see how much it changes over a certain patch

2) “facing ratio” which gets us an outline around the edges that are facing away from the camera (typically used for fake lighting and a velvet look), but is camera dependent.

We found that these techniques worked well in certain cases, but weren’t providing enough information of certain parts of geometry to creates drawn lines around all features of the geometry, so we developed a few more techniques for edge detection which ultimately provided regions to draw lines in.

The additional techniques utilized random id assignments on different pieces of geometry, assigned by a custom shelf button in Maya that looped through all geo in a scene. Then the difference between the random assignments was automatically examined to draw “cel lines” around all features of the geometry.

Also, a further technique utilizing components of the surface normal combined with camera z-depth information was developed to pull more lines off the geometry.

Having this extensive tool set for detecting edges gave 9to3animation many options in different scenarios and on different geometry to get really nice and detailed sketch outlines in 3d.

Edge detection to create cel lines, animated for slight vibration to make it dynamic
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Challenge: Going off the geometry with brush strokes

The big challenge was going off the geometry with brush strokes and sketch lines, as depicted in the reference artwork we were looking at. There are a lot of non photoreal rendering (NPR) examples and approaches, but most of them stay on the geometry so you end up with just painted textures and procedurals. We’re happy to have achieved multiple different styles that go off the 3d geometry all in a 3d render.

Challenge: Dynamic Hatching

Dynamic Hatching with "Screen" Projection, and animated outlines off-geometry
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Dynamic Hatching with "UV" Projection, and animated outlines off-geometry
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Dynamic Hatching responding to light intensity, with multiple edge-detection techniques to create outlines along all parts of geometry
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Dynamic Hatching responding to light intensity
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NPR Techniques applied to "RenderMan Kitchen Challenge" scene

Alternate variation

Experimental: "Painterly"

Cornell Box with Painterly shader - all rendered in 3d in RenderMan

Painterly animation - all rendered in RenderMan!
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Experimental: NPR mixed with Physically Based
Experimental approach where we mix in our toon sketch shading in a physically-based environment, all in a single pass 3d render! Note the reflections and refreactions of the toon character in the physically-based render, you can't do this in a post pass all has to be done in the render.
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Art Reference with Final Renders


Ernst Janssen Groesbeek
Pauline Quast
Christos Obretenov
Brandon Onstott

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