Lighting & Rendering 2: Arnold Part 2

 This segment of Toolkit 2 explores the assets within Maya that can benefit rendering in Arnold. from lighting to 

Physical Sky Light

Physical Sky is an Arnold light setting setup like a dome, allowing us to position the sun on an axis to create different times of the day. Colour manipulation can enhance a lighting structure by suggesting real-time midday, sunset or sunrise. Shadows can also be manipulated. The Physical Sky lighting system has its limitations; it's a standard technique and therefore noticeable, it's unable to achieve night time lighting. 

In Maya's Node Editor, we can see that the Physical Sky light setup consists of two lights.

Physical Sky Attribute Settings

Turblitily – matter in the atmosphere (haze)

Ground Albedo – bounce light from the earth/ground.

Elevation – The height of the sun in the scene's sky.

Azimuth – 360 degree rotation of the sun in the scene. Shadows are altered.

Intensity – the intensity of the sun

Sun size – the size of the physical sun mass in the scene. In some cases, we might not want the sun visible in a scene.

Renders

Physical Sky Render 1 – natural and clean. The sun is visible in the scene. Standard.

Physical Sky Render 2 – the sun has been rotated. Sunlight is now hitting the front of the building. Midday atmosphere.

Mesh Lights

Mesh lights are lights derived from geometry. This scene uses polygon spheres to create lighting. Polygons are the only types of geometry that can be used to create mesh lights. In Maya's outliner window, we can see that 3d nodes work by projecting images onto a parented object. Fundamentally, Ramps are being projected onto the spheres in this scene. These lights create a high amount of noise and require lots of clean-up and work poorly when in close proximity in another object. 

Projections/ Ramps on a graph network shown within the hypershade window. 

Mesh Lights Render Outcome

Ambient Occlusion

Add ambient occlusion pass to a render to add more realism to something that is CG perfect. ambient occlusion is the decay of light based upon the distance of two object's. Typically, You'll always need an ambient occlusion pass if you aim to create realism.

Above, an Ambient Occlusion Render. Realism is added by the decay of light in darker areas of detail. 

An ambient occlusion pass can be composited onto a beauty pass in Photoshop, before getting exported as an 8 bit Jpeg. This can be seen above. 

Photometric Lights

This tutorial demonstrated how you can use real IES files from lighting manufacturers to help create realistic and specific lighting by changing the qualities and characteristics of the light source/ bulb. This information can be downloaded from manufacturer websites and viewed within IES viewers. 

An example of an IES viewer. The visual diagram  represents light decay over distance. Maya is able to use the information within IES files and replicate the specifications within its 3D environment.  

The final render shows A good general illumination of the scene that includes architectural realism. Pools of light on the wall are believable and accurate, these would be hard to replicate without an IES file. 

Depth of Field

Depth of Field is the amount of blurring that would happen in-camera. This tutorial demonstrates how realistic blurring and depth can be created within Maya and Arnold renders. 

Render 1 – too crisp and CG perfect, which is inaccurate. Realistically, we would have blurring based upon focusing and camera characteristics.

Render 2 - successful depth of field. This should always be composited onto a clean, non-blurred image in an editing software, as the blur is destructive to the composition. Therefore, it can’t be removed from a rendered image. 

Camera settings and render settings for the second image render. 

Filtermap uses ramps to create light gradients on the edge of an image, a vignette.

Rolling shutter is the way in which a camera scans an image. This setting mimics the stylisation we would find in digital camera technology.

Display > heads up display > object details - here, we can find information about an object in the scene, including an objects distance from camera. This can be used for the focus distance setting to create an accurate background blur and object focus.

Bokeh - A high degree of blur that turns light into distinct shapes.

Fog (Legacy) & Atmosphere

Atmosphere can be created in two ways using Arnold; Ai Fog (legacy system) and Volumetric (newer system). 

AiFog appears as a gradient or ramp, which can be moved around a scene and made more or less opaque. In this render, colour has also been manipulated to create a heavily stylised/ atmospheric image. 

You will always see the light source when using volumetric fog. Adding a gobo (2D texture Fractal) can help break up a light source and introduces light rays. The example above has variation due to the light rays, creating a realistic light source. 

Displacement

Displacement maps are created using Autodesk Mudbox and then imported into Maya. Displacement maps are plugged into Maya using shaders. When previewing the Maya model, its important to look for seams or tears, these would indicate an exporting issue that would have happened in Mudbox. 

The image above is an example of a standard displacement map being created in Mudbox. A standard displacement map. It directly pushes and pulls a surface based upon a black-to-white gradient.

Above, a Maya render revealing all the detail from Mudbox that has been transferred over. 

Above, an example of a vector displacement map. These use coloured maps to create bends, undercuts and angled surfaces to produce more dynamic models. Vector displacement maps have very few limitations, unlike standard displacement maps. 

Above, a successful displacement render.

Sub Surface Scattering

This tutorial outlines how to create a realistic skin shader using Sub Surface Scattering and Arnold.

Above is a final render that reflects how multiple maps can be manipulated into a realistic skin shader. 

Maps within this render:

Diffuse - the outer layer of skin holding shading and blemishes.

Scatter - The inner layer of skin, flesh and blood.

Weight - The amount of sub surface in different areas of the model.

Specular - highlights across the surface of the model.

Normal - The subtle details, such as pores. 

Displacement - A black to white ramp that pushes and pulls the models surface to create folds in the skin. 

Above, the render settings used to produce the final image. 

AOV's

The term AOV stands for arbitrary output value, it allows us to break a render into separate and isolated elements, which can be manipulated in after effects. 

Above, the different types of render passes. A longer list indicates more control, but this also indicates a longer render time. 

This outcome uses a mixture of Maya, After Effects and Photoshop. The separate AOV passes are exported out of Maya as an EXR file. These are imported onto a composition in AE where they are layered and composited. Next, the outcome is saved and opened as a photoshop file, where it wan be saved out as a JPEG or other image format. 

Stand-Ins

This tutorial Solves a common problem with lowering view port memory to create more ambitious modelling. The solution is Arnold Stand-ins/ Proxy objects. Stand-ins use bounding boxes, these are representative of the volume of the object exported out. To create a stand-in:

• Highlight all geometry on a model
• Arnold > Stand-in > Export Stand-in (settings)
• Arnold > Stand-in > Create Stand-in (Settings)

Stand-ins are only a representation of an object, its entirety can only be seen in an Arnold render. 

Working with a large volume of bounding boxes is less stressful for the viewport, reducing lag. 

Motion Blur

Motion Blur helps to add realism and reduce the appearance of a CG perfect Arnold render. However, using motion blur drastically increases render times. Similarly to depth of field, Motion blur is also destructive to the render image. Therefore, we cant remove the blur once the video/ image has been exported. 

Above, the same frame before and after the addition of motion blur in Maya. 

Above, three options that create motion blur to an animation. 

Above, an example of Post Effects motion blur. Instead of applying motion blur within Maya, Post Effects applies the effect after the render and within after effects. This limits the adjustments that can be made. 

Caustics

Caustics is the light being refracted by water onto a surface below, often seen in an area of shallow water in high sunlight. 

In this instance, a caustic image sequence was adjusted in After Effects and then exported as a new image sequence. Within Maya, the caustic image is imported into a gobo spotlight.

  

The use of a spotlight has helped create rays of light that cut through the water/ atmosphere. An underwater illusion with convincing caustics that heavily amplifies the atmosphere of the scene.