This tutorial will cover how to light, shade, and render a CAD model of a DSLR camera. It covers various styles including a product shot and illustrative styles that could be used in a product brochure. These styles include wireframe, facing ratio (x-ray), and a toon edge. We will also cover how the utility shader can be used to create render passes for use within a compositing package and can also be useful for debugging scenes.

A DSLR camera model can be downloaded here.

Importing the CAD Data

• Start off by downloading the CAD model (link above).
• You should see the following parts in the .zip file. Unzip the data to your hard disk.

• Select the files and drag them from your file explorer onto the Maya viewport. Maya will then convert the CAD geometry for you. You should see the model appear in your Maya scene (see below).

• Ensure that you have the ATFPlugin.mll plugin loaded in the plug-in manager otherwise the camera geometry will not import.

• The model has originated from a CAD package that works the in Z-up axis, whereas Maya defaults to the Y-up axis. Go to Preferences -> Settings -> World Coordinate System and change it to Z.

_{The CAD files imported in Maya. World Coordinate System: Z}

Lighting

The scene is simply lit using a studio HDRI connected to the skydome light color.

• Choose Arnold under the Create tab and click on Arnold Light. Click in the viewport to create the skydome light.
• Rotate the skydome light 90 degrees in X as the scene is set to Z-up.
• Reduce the camera visibility of the skydome light to 0. We will add a separate white background later.
• Connect a file texture to the color attribute of the skydome light and choose a suitable HDRI. An example of a studio HDRI that could be used with this scene can be downloaded here.

_{Choose a bitmap (HDRI) for the Texture of the skydome light}

To test the lighting, we can quickly assign a standard surface shader to the camera.

• In the Hypershade window create and assign a standard surface shader to the camera.
• Change its base color to black.

• Render the scene using the default Arnold sample settings. These settings are fine for IPR test rendering the scene. Do not worry about any noise in the scene at the moment. We will change the sample settings once we are happy with the lighting and shading at the end of production.

_{Render Settings -> Diagnostics -> Feature Overrides}

_{Debug shading: wireframe}

Background

Next, we need to change the background environment color to white.

• Go to Render Settings -> Environment -> Background and create a ray switch shader.
• Change the camera ray type to white.

_{Environment -> Background -> ray switch camera: white}

Realistic Shading

We want to create a plastic shader that can be copied and used for the main body, the leather style grip, and lens. We will also create an anisotropic metal shader for the adapter ring and glass shaders for the lens and flash.

Body

Create a standand surface shader and assign it to the main body and lens of the camera. Change the following parameters:

• base color: black.
• specular roughness: 0.467.
• specular IOR: 1.55 (plastic).
• coat weight: 0.1
• coat roughness: 0.3
• coat IOR: 1.55 (plastic).

Leather Syle Bump

We can use the cell noise shader to create a convincing leather style texture to the camera grip shader.

• Duplicate the plastic shader and assign it to the leather grip object.
• Connect a bump3d to the normal parameter of the standard surface.
• Connect a cell noise to the bump map parameter of the bump3d. Using a bump 3d as opposed to bump 2d means we do not have to be concerned about the UVs of the model as it will render it in 3d object space.
• Change the pattern of the cell noise to alligator. This will give the leather style look.
• Increase the number of octaves to 8.
• You may need to increase the scale depending on the size of your camera model. In this case, a value of 6 was used.
• Reduce the density to around 0.5.

_{cell noise -> bump3d -> standard surface}

Camera Lens Adapter Ring

We will create an anisotropic metal material that could be used for an adapter ring of a camera.

• Assign another standard surface shader. Assign it to the metal adapter ring on the camera body and rename it to 'Metal Ring'.
• Change the base color to a mid-gray color.
• Increase the metalness to 1.
• Increase the specular roughness to around 0.7. Lower amounts will appear shinier.

To create the anisotropic metal effect, we will use ramp rgb -> specular anisotropy. We will project it using a uv projection shader to avoid any UV issues from the CAD geometry.

• Create a ramp RGB shader and change the type to radial. Insert around five black and four white knots. Ensure that their interpolation is set to catmull-rom (smooth).
• Connect it to a uv projection shader. This is to planar project the ramp RGB onto the metal ring.
• Connect the uv projection to the specular anisotropy of the standard surface shader.

You may notice faceting appears in highlights when using specular anisotropy. It is possible to remove the faceted appearance by enabling smooth subdivision tangents (via Arnold subdiv smooth derivs parameter. Take into account this requires a subdivision iteration of at least one in the polymesh to work.

_{ramp rgb -> uv projection -> standard surface}

Glass Lens

• To reveal the lens first hide the lens cap (cache.1, cache2.1 and Symmetry of cache2.1.1 in the Scene Explorer window).
• Assign another standard surface shader to the glass lens geometry (Body.8) and call it 'Lens Glass'.
• Reduce the specular roughness to 0.
• Change the specular IOR to 1.5 (glass).
• Increase the transmission weight to 1.
• Under thin film, increase the thickness to around 450 and the thin film ior to around 1.28.

Stylized Shading

Now we will look at a variety of shading methods to create stylized renderings such as wireframe, orthographic line-art (toon), x-ray (facing ratio) and cut away renders (clip geo).

Wireframe shader

• To create a wireframe/semi-shaded look we can use the wireframe shader connected to the opacity of the black plastic shader we created earlier.
• Change the edge type to polygons. Adust the line width to a low amount. In this case, a value of 0.02 was used.

_{wireframe -> opacity of standard surface}

Toon shader

• Assign a toon shader to all of the camera geometry. Change the following parameters:

• Reduce the angle threshold to around 10. This will give more detailed edges around the geometry.

• Reduce the base weight to 0. We are only going to use emission.

• Ensure that specular weight is 0.

• Increase the emission weight to 1.

• The toon shader does not currently work with GPU. This is planned to be fixed in a future release.

• 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.

• Another variation would be to connect a utility (color mode: geometric normal (ng)) shader to the edge color of the toon shader (emission weight: 0).

_{utility -> toon edge color}

Facing Ratio shader

We can create an x-ray shading effect by using the facing ratio shader.

• Assign a standard surface shader and reduce all of the weights to 0.
• Create a facing ratio shader and connect it to the opacity of the standard surface shader.
• Reduce the bias to around 0.1.
• To further refine the effect, connect a color correct shader in-between the facing ratio and the standand surface shader.

_{facing ratio -> color correct -> standard surface}

Clip Geo shader

We can use the clip geo shader to create a cut-away shading effect in the camera model.

• Create a Box (geometry to be used for clipping and position it where you want to clip the geometry (in this case it is cutting into the lens).
• Assign a clip geo shader to the box.

AOVs

AOVs are Arnold's method of rendering render passes. They provide a way to render any arbitrary shading network component into different images. For example, an artist might find it convenient to separate direct and indirect lighting contributions and later recombine them during compositing. Arnold provides built-in AOVs for outputting depth, position, and motion vectors.

Some example sets of additive AOVs for the full beauty AOV are:

• direct, indirect, emission, background.
• diffuse, specular, coat, transmission, sss, volume, emission, background.
• diffuse_direct, diffuse_indirect, specular_direct, specular_indirect, coat, transmission, sss, volume, emission, background.

Simply adding together such AOVs is all that is needed for the beauty AOV. The albedo AOVs are not needed to reconstruct the beauty AOV but may be used for example to get just the lighting without the surface texture, by dividing diffuse by diffuse_albedo, or for denoising just the lighting while keeping the texture detail intact.

• To access AOVs go to the AOVs tab in the Arnold Render Settings window.

_{Arbitrary Output Variables (AOVs) Manager. Create diffuse, specular, specular indirect, transmission, and background AOVs.}

• Choose the file Type. The default EXR is normally recommended, however, for this example we will use Png as we will simply be rebuilding the RGBA beauty in Photoshop.
• Render out the AOVs to disk either from the Render View window or via Render -> Batch Render.

Compositing in Photoshop

• Open the AOVs that we saved to disk in Photoshop.
• Drag and drop the layers from each Png onto the Background image layer as indicated in the image below.
• Change the blending layer mode to Linear Dodge (Add) for each layer. You should see the final beauty layer.

_{AOVs opened in Photoshop and layered together using Linear Dodge (Add)}

_{The various color modes used by the utility shader}

Final Render Settings

For final frame rendering, we will need to increase some sample settings.

• Select the skydome light and increase the number of samples to 3 or 4. This should clean up a lot of the noise in the shadows.

• Increase the number of Camera (AA) to around 5. This will improve the general image quality.
• Even, though we have increased the Camera (AA) samples there is still some noise on the lens (visible in the specular AOV). We can reduce this further by increasing the number of specular samples to 4. Note that your render times will be longer when increasing this value.

That's it. You have reached the end of the tutorial. Well done!