[C4D] Ambient Occlusion with Cinema4D CE version

[stefan]

Cinema4D is a nice modeling, rendering and animation application. An older version was re-released for free with some magazines and user forums. This is the version CE. It is fully functional, but lacks some of the recent improvements, such as the SLA-shaders and Radiosity (amongst others).

To have quite a similar effect, it is possible to use "Ambient Occlusion", which samples the amount of occlusion around points, to see how much light they might receive from the surroundings. A good explanation can be found on http://www-viz.tamu.edu/students/bmoyer/617/ambocc

This is far from real radiosity, but has been used in many film projects to speed up radiosity-like renderings. On http://www.stewreo.de/cinema/ao.html you can find a free COFFEE-shader, which implements this algorithm for Cinema4D (release 6 and higher) and which is thus usable in the older version CE too.

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Render a regular image from your scene and call it "rendering01".

Create a new material, call it "Amb.Occ", disable all channels. Activate Transparency and set its brightness to 0% (this forces C4D to use raytracing, which is required). Activate the Luminance channel and add the "Ambient Occlusion" shader to the texture field.

Duplicate all geometry, remove the material tags and add the newly created material to it. Disable all transparant objects, such as glass.

Render the scene again and call it "rendering02".

Open Photoshop or similar, open "rendering01" and place "rendering02" as a new layer above it and set the layer blending mode to "Multiply".

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To improve the quality, split the rendering further up.

1 - Create a shadow-catching material, by using the Shadow Catcher shader from http://savards.fuzehost.com/shad_detail.php?ArticleID=3 in the Luminance channel (disable all other channels). Use it instead of the Ambient Occlusion shader on the copied geometry.
---> Render this pass as "Shadow-only"

2 - Create an ambient-only light, 100% white, enabling the "Ambient Illumination" and "No Specular" options. Hide the copied geometry and show the regular geometry.
---> Render this pass as "Colour-only"

3 - Reuse the "Ambient occlusion" pass.

4 - In photo-editor:
---> place the Shadow pass on top, multiply, 45%
---> place the Ambient Occlusion underneath, multiply, 70%
---> place the Colour-only at the bottom, normal, 100%.

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Voila, you can still tweak the balance in realtime, without re-rendering.

[stefan]

And a tweaked rendering