#KBF00001 - Render Passes
Instructor : Pradeep Mamgain
Composting is the art of combining multiple images into a unified final scene. All professional productions are rendered in multiple layers or passes and finished though compositing.When you render in passes, you render different attribute of an image separately such as color, shadow, specularity, reflection, contact shadows and depth. It gives you precise control over the different aspects of your scene. Once you render the passes in given 3D application, you can bring them into the composting software like Fusion, Shake or After Effects and generate a quite nice result after fine tuning the passes.
#Passes
When you render Diffuse Pass only diffuse shading is performed. This pass is the full color rendering of your image. It includes diffuse illumination, color and texture and excludes highlights, shadow or reflection. To render Diffuse Pass in Maya, you can use its diffuse preset. You can also set this pass manually or infect any pass. What you can do is apply a preset and then reverse engineer it. To manually set diffuse pass you can turn off the specularity of the lights. Turn the shadows off and modify the material and turn off any specularity or reflectiveness.
An Ambient Pass is a simple pass also known as color pass shows the texture and color information on your surface. It does not include any diffuse shading, specular highlights, shadows, or reflections. In this pass object appears flat as you can see in the image left. In Maya, you can turn off all the lights and then add an ambient light and set ambient shade parameter to 0.
Shadow Pass, produces only the shadow component of the image in the alpha channel. No color information is produced. If you have scenes with overlapping shadows, it is better to keep the shadows separate in different shadow passes so that you compositor can handle those shadows differently.
Normal Pass is a nice pass for catching the highlights off the pre-rendered geometry. You can relight your render image in comp software. 3D application renders a tangent space normal map from the renderable camera.Based on the amount of red, green or blue, this map defines the rendered image's normal direction per-pixel within the color channels’ output.
Occlusion Pass is also known as Dirt Pass. It gives you nice effects for contact shadows or soft fill lighting. This pass is a costly pass and takes loads of time to render. However you can produce fake occlusion using lighting techniques.
Reflection Pass lets you fine tune the reflection information inside of your comp. A reflection pass can include self-reflections, reflections of other objects, or reflections of the surrounding environment. You can turn off the primary visibility of the object but make it visible in reflections.
Specular pass is also known as highlight pass. No mask or Alpha channel is produced when you render the Specular Pass. Only specular shading is performed. It is also dependent on the type of material (Phong, PhongE, Blinn, and Anisotropic) you have choosen. To render this pass, turn off any ambient light if any and make diffuse shading and color pure black.
Luminance Depth pass, which is grayscale render based upon the distance from the camera, is used to determine the Z depth when you compose it inside comp software. Brighter shades of gray represent parts of the scene that are closer to the camera. This pass is often used with the Deep Pixel categories of the tools, like Depth Blur, 3D Fog and Shaders tool inside Fusion. You can also use this pass for atmospheric perspective color shift. Distant objects will look dull in color.
Geometry Mask Pass is a black and white version of geometry's alpha. Some artist also call it cut matte. This pass does not respect the transparency settings of the materials.
These are the common type of passes used to fine tune the scene. We are in process of making a special tut on how to render passes in Maya, where we will look into deep in the process.
#Other Info
# eyeon Fusion KB # Adobe After Effects KB # Autodesk Maya KB # Composting Passes Inside Fusion