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
- 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 color of a skydome_light.
- 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.
Feature Overrides
This group of switches allows you to disable a number of important rendering features. By selectively disabling some features, you can get a feel for where the renderer is spending most of the time, which helps optimizing scenes. Lighting or look-dev could be sped up by enabling ignore_textures or ignore_shaders for example. This is also useful for isolating errors and artifacts when debugging. Note that not all of these options are interactive - some of them may require the entire scene to be refreshed/exported.
Render Settings → Diagnostics → Feature Overrides
Debug Shading
This temporarily replaces the shading applied to all objects with a variety of debugging shading modes. This is used for interactive rendering purposes only and won’t change anything in the Maya scene.
Debug shading: wireframe
A studio lighting scene can be downloaded here.
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
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Background: Color: Black (default)
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Background: Color: White
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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. Create a standand_surface shader and assign it to the main body and lens of the camera. Change the following parameters: We can use the cell_noise shader to create a convincing leather style texture to the camera grip shader.Body (boitier2.1)
Leather Syle Bump (boitier2.1 - Body.18)
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. 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. 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. anisotropic_rotation can be used to change the location of the specular_anisotropy highlight.
ramp_rgb → uv_projection → standard_surface
Glass Lens
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
wireframe → opacity of standard_surface
Toon shader
utility → edge_color of toon
Facing Ratio shader
We can create an x-ray shading effect by using the facing_ratio 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. clip_geo does not currently work with GPU. This is planned to be fixed in a future release.
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. The RGBA beauty AOV can be split into smaller AOVs where each contains part of the lighting. In compositing, these AOVs can then be individually modified and added together to get the full beauty AOV. More AOVs give more control in compositing, but also extra work to handle, and they take up more memory and disk space, especially combined with light groups. Some example sets of additive AOVs for the full beauty AOV are: 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.Composing the Beauty AOV
- 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.
Cryptomatte
Crytomatte AOVs can also be used to create ID mattes for compositing later on. Cryptomatte creates ID mattes automatically with support for motion blur, transparency, and depth of field. Names, object namespaces, and material names can be used to organize ID mattes in the scene.
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crypto_asset
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crypto_object
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crypto_material
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Compositing in Photoshop
To create a correct rebuild of the RGBA beauty AOV you must use add/plus operations in the composite. If you use screen or multiply you will get an incorrect result. AOVs opened in Photoshop and layered together using Linear Dodge (Add) The utility shader is a general 'all-purpose' utility node shader that can also be used to create passes for use within a compositing package. It can also be useful for debugging scenes. For example, the geometric_normal position could be used to re-light the model in post-production.
The various color modes used by the utility shaderUtility Color Modes
Final Render Settings
For final frame rendering, we will need to increase some sample settings. Remember to check your AOVs if you are unsure where the noise is coming from. That's it. You have reached the end of the tutorial. Well done!