This tutorial will cover how to light, shade, and render a CAD model of a Lego technic rally car. It will show you how to light the car model using Arnold area lights (quad_light). It covers how to realistically shade the Lego model using the standard_surface with round_corners and how to use the clip_geo shader to create a cross-section animation effect. Once shading and lighting of the scene are complete we will cover how to create a stylized look using the Arnold toon shader that could be used in an instruction booklet. Finally, we will tweak some of the Arnold render settings to improve the quality of the final render. More examples of Lego renders using Arnold can be found here.The Lego technic rally car model can be downloaded here.
A studio lighting scene can be downloaded here. |
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Importing the CAD Data
- Start off by downloading the CAD model (link above).
- Extract the contents and import this step file: LEGO Technic - Rally Car (42077).stp
- Position and rotate the car so that it sits flat on the grid as in the above animation.
- Create a floor plane (or use the cyclorama from the studio lighting scene in the above link).
- Assign a standard_surface shader (from the Slate Editor) to it. Reduce the specular_weight to 0 (we don't want any distracting specular reflections from the cyclorama to distract from the car model).
Lighting
We will add an Arnold quad_light to the scene. This light will mimic a softbox studio lighting setup as can be seen in this tutorial. Alternatively, you can download a pre-made lighting studio from the link at the top of the page.
- Go to Arnold -> Lights. Select Area Light (quad_light by default). Position, orient and scale it so that it is slightly larger than the car as in the image below.
Scene lit with quad_light (exposure: 16)
Exposure is an f-stop value that multiplies the intensity by 2 to the power of the f-stop. Increasing the exposure by 1 results in double the amount of light.
Realistic Shading using Standard Surface
Scene Converter
We will now convert the shaders (Phong, etc) to Arnold standard_surface shaders.
- Go to Arnold -> Shaders -> Convert Shaders to Arnold.
- It will display a dialog window asking to convert all shaders or selected shaders. Choose All. You should see that all of the scene materials are now standard_surface.
Standard Surface
We now want to create a set of realistic plastic shader parameters that can be replicated across all of the standard_surface shaders. Change the following parameters for each standard_surface shader so that the bricks appear more like plastic:
Lego plastic shader settings
Round Corners
This shader modifies the shading normals near edges to give the appearance of a round corner. It can be used with hard surface models where bevels have not been modeled to simulate a round beveled edge, thus saving valuable modeling time.
Rollover image to view without round_corners
round_corners -> standard_surface.normal_camera
Clip Geo shader
clip_geo does not currently work with GPU. We can use the clip_geo shader to create a cut-away shading effect in the camera model.
To avoid clipping the floor plane:
- Create a trace set by entering a name in the shader Trace Sets text box (for example, "objects_not_to_clip").
- Clear the Inclusive checkbox.
- Put the objects in that trace set (by entering the same trace set name for those shapes).
- All objects not in the trace set will be clipped.
Cube with clip_geo assigned to it. The plane is not clipped because it has a Trace Set that matches the clip_geo Trace Set. Inclusive is disabled.
Stylized Shading using Toon
To view the toon edge, you must change the filter type (sampling settings) to contour. Note that increasing the contour filter width (sampling settings) value will increase render times.
Contour filter_width: 1. Rollover for contour filter_width: 2 (default).
toon shader parameters
Final Render Settings
When rendering with the CYC background geometry (scene link at top of page) the scene appears quite dark with the default diffuse_ray_depth of 1. Increasing this value will allow more light to bounce around the CYC and car geometry (at the expense of increased render time).
diffuse_ray_depth: 1 (default). Rollover image to view diffuse_ray_depth: 4. For final frame rendering, we will need to increase some of the sampling settings.
quad_light.samples: 1 (default). Rollover image to view 4. There is some noise apparent in the interior and underneath the car. Increasing the number of diffuse_samples should clean this up. Remember to check your AOVs if you are unsure where the noise is coming from. e.g. shadow (light_samples) or indirect light (diffuse_samples).
diffuse_samples: 2 (default). Rollover image to view diffuse_samples: 10.
Camera (AA) samples: 3 (default). Rollover image to view Camera (AA) samples: 5.Ray Depth
Reducing Noise
Quad Light Samples
Diffuse Samples (Interior Noise)
Camera (AA) Samples
That's it. You have reached the end of the tutorial. Well done! We encourage you to spend some more time with the MtoA user guide where you can find other tutorials such as this.