LEARN HOW TO RENDER LIKE PIXAR
Unlock the secrets of Pixar's Renderman with VFX artist Rusty Hazelden
For over 30 years, Pixar's Renderman has been used in the film industry to render movies featuring groundbreaking animation and visual effects.
In this four-part tutorial series, we're going to discover how to harness the power of Renderman by taking an animated shot from start to finish, and learn all of the techniques required to create a photorealistic animation using Pixar's Renderman for Maya.
Creating photorealistic images with Renderman has never been easier. In this series we begin with untextured objects in Maya, and learn how to create surface materials, set up lights, adjust camera attributes, and batch render the final animation to disk using Local Queue as a series of EXR images.
By the end of the project, you will have a solid understanding of
the workflow used to light and render a dramatic night-time scene using Renderman for Maya. Along the way, you will learn numerous tips and tricks that will come in handy on your next Renderman project!
In part four of this tutorial series, we're going to finish the work light scene by adding depth of field and motion blur. Then we will review the Renderman render settings and launch Local Queue to render out the final animation to a series of EXR files. We're also going to learn how the Renderman denoiser can be used to slash render times!
01 OPEN THE MAYA SCENE
Let's continue from where we left off in part 3 of the tutorial series. Go ahead and open your Maya scene from the end of part 3. The cameras used in Maya to render computer-generated scenes provide many of the same controls found on real photographic cameras. Let's take a closer look at the camera called Render_cam. Expand the Render_cam_group in the Outliner, and select the Render_cam object. Then click on the shape tab in the Attribute Editor in order to display the Camera Attributes.
02 MANY CAMERA OPTIONS
The Camera Attributes section lists all sorts of camera controls including Focal Length, Angle of View, Near Clipping Plane, and Far Clipping Plane. These controls are changed frequently as new shots are set up and virtual lenses are adjusted. Changing the lens on a camera in Maya is done by adjusting the Focal Length (in mm) or Angle of View (in degrees). Scrolling down further in the Attribute Editor will also reveal the Film Back settings where the size of the image sensor used by the camera can be entered. Scroll down to the Depth of Field section and expand it.
03 THE DOF CONTROLS
Let's start an IPR render using the Renderman Shelf. Rightclick on the IPR Clapboard icon and select Render_cam. The Depth of Field camera controls are used to accurately simulate the physical properties of a real camera lens that relate to focus.
Depth of field is also known as DOF, and is a powerful artistic tool used by photographers to draw the audience's attention to certain parts of the image by controlling the region that is in focus. Depth of field is controlled using the F-stop setting and Focus Distance.
04 MEASURE FOCUS DISTANCE
Focus is set by measuring the distance from the camera to an object in the scene. From the Display menu, select Heads Up Display>object Details. Then select the Bent_nails group in the Outliner to determine the distance between the Bent_nails and the Render_cam. The ‘Distance From Camera’ value is now displayed as text in the Maya Viewport. This text is called a HUD, which is short for Heads Up Display. The HUD indicates how far away the selected object is from the camera. At the beginning of the animation, on frame 0, the Bent_nails are 51 units away from the camera.
05 PULLING FOCUS
If we jump to frame 56 in the timeline, the camera has moved closer to the Bent _Nails object, and now the Distance From Camera HUD reads 34 units.
Pulling focus is a film industry term for setting focus in a moving shot. If you want to keep an object in focus when Depth of Field is enabled, you will have to measure the distance between the object and the camera at several points in the animation, and set keyframes on the camera's Focus Distance attribute.
06 ENABLE DEPTH OF FIELD
Select the Render_cam object in the Outliner. Then click on the shape tab in the Attribute Editor to display the Camera Attributes and scroll down to the Depth of Field section. Let's turn on the Depth of Field checkbox to activate this camera feature. Since the IPR is active in the Maya Render View, it will update the rendered image. Now the nails in the background are slightly blurred while the nails in front of the work light are in focus. This is the depth of field effect.
07 REVIEW THE KEYFRAMES
As you can see in the time slider, there are several red keyframe ticks. These keys have already been set in the scene and they are used to control the lens Focus Distance in the shot. As we move along in the time slider between keyframes, the camera translates in the scene and the Focus Distance field updates in the Attribute Editor. The red square behind the Focus Distance field indicates that it is a keyframed value.
08 SET THE F-STOP
The next step is to decide on the F-stop setting for this shot. F-stop refers to the size of the aperture, or opening, in a photographic lens. The aperture on a traditional lens is used to control the depth of field and it also has an effect on the exposure or brightness in the final image. In Renderman, the F-stop value is only used to control the depth of field and it doesn't affect the brightness of the image. Set the current time to frame 56. With the F-stop set to a value of F5.6 the bent nails in the foreground are in focus and the background behind the nails is blurry.
09 INCREASE THE F-STOP
Depth of field is useful for drawing the viewer's attention to a particular object in a shot. In this case, it highlights the R-shaped nail on the floor. Let's try setting the F-stop to a value of F16. With a higher F-stop value, more of the scene is in focus. Using a high F-stop value like F16 is useful when several objects in a shot need to be in focus.
10 REDUCE THE F-STOP
Type in an F-stop value of F1.4 for a shallow depth of field. The term ‘shallow depth of field’ refers to images where a very small percentage of the image is in focus. The rest of the image is heavily blurred to the point where it is difficult to make out individual objects in the background. For artistic purposes, this can be useful, but for this scene let's dial it back a little bit so more of the work light is in focus.
11 FIND THE RIGHT BALANCE
Let's set the F-stop back to F5.6, as this provides just the right amount of blur for the shot. In shots with moving cameras, the process of maintaining focus as the camera moves can become quite challenging. In these cases, it is often a good idea to select an F-stop that is a bit more forgiving if the focus distance varies. There is less room for error when pulling focus in a scene with shallow depth of field.
12 ENABLE MOTION BLUR
Another feature that adds realism is called motion blur. When you take a photograph of a moving object in the real world, the object will appear blurred. The faster the object moves in the frame, the more pronounced the blur will be in the resulting image. Let's open the Render Settings window and take a look at the Motion Blur feature. Switch to the Renderman tab, then click on the Features tab to display the Motion Blur controls. To enable motion blur, select 3D Motion Blur and then turn on the Camera Blur checkbox.
13 COMMON RENDER SETTINGS
In this shot, the effect of motion blur is most visible on the R-shaped nail that falls down in the scene and lands on the wooden floor in front of the work light. To really appreciate motion blur, we need to render out the entire animated sequence. Let's take a quick look at the render settings and then render out the animation. Let's begin on the Common tab. Rendering at 1,920 by 800 will produce a beautiful animation, but if you're short on time you can always scale this down to a smaller size and it will render faster.
14 RENDERMAN SPECIFIC SETTINGS
Let's switch to the Renderman Sampling tab. This is where you'll find all sorts of controls that can be used to fine-tune how Renderman works. Right now the settings displayed in the tab are a pretty good starting point for this scene as they produce a nice balance between image quality and render
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time. The classic dilemma is that you can render noisy images quickly but high-quality images will take longer. Depending on what stage of rendering you are at, you will have to decide if this is a preview render or a final render, and then you can adjust the settings accordingly.
15 SAVE TIME WITH PRESETS
For artists just getting started with Renderman, I would suggest using one of the presets available in the render settings window. To use a preset, go to the Presets menu, select Import Render Settings, and look at the presets found in the User menu. These presets are easy to use and produce beautiful images. For this project, I used the ‘Renderman_ Denoiser’ preset, which is fairly fast compared to the slower presets like ‘Renderman_
Production’ and ‘Renderman_ Production_high’.
16 SAMPLES DEFINE IMAGE QUALITY
The Min and Max sample values act as the overall quality knobs for the Renderman renderer. They limit the minimum number of samples calculated per pixel when a render starts up, and the maximum number of samples allowed as it reaches the end of the rendering phase. Raising these values will produce a cleaner image, but it will also take longer to render. The current sample values are rather low but they work well when the denoiser is active.
17 RENDERMAN INTEGRATOR SETTINGS
Renderman ships with a variety of ‘Integrators’. You can think of these as ‘rendering algorithms’ that are tuned for a specific type of lighting transport. The default integrator is called Pxrpathtracer and it's a unidirectional path tracer well suited for exterior scenes. More complex interior lighting situations often produce cleaner images with less noise when the PXRVCM integrator is used. There is also a new experimental integrator called Pxrunified that is in development and also features helpful performance enhancements for rendering caustics.
18 THE BEAUTY AOV
Click on the AOVS tab and select the Beauty AOV. The AOVS tab is used to create extra render passes that can be utilised by compositors to isolate objects with mattes, render individual lights, and denoise images. Render passes are also known as AOVS, which stand for ‘Arbitrary Output Variables’. The left column lists all of the available channels that can be added to your renders. The right column lists the active AOVS in the scene. As you can see, we're using an AOV in this scene called Beauty.
19 RENDER TO EXR FILES
The ‘displaytype’ menu is set to ‘d_openexr’ which renders an EXR image to disk. The EXR image format has become the official 19 20 standard used in the feature film industry. It's a great format for rendering image sequences since it supports high dynamic range data and extra render channels. EXR images can be easily used in many compositing applications. In order to use the Renderman denoiser, the EXR image format is utilised so it can hold several AOVS with render data for denoising.
20 ENABLE THE RENDERMAN DENOISER
Scroll down to the Denoise section. Make sure the Denoise checkbox is enabled and set the Mode to Single Frame. This mode denoises one image at a time in the animation. If you have a more complex animation, the Crossframe mode comes in handy as it takes into consideration several frames at once and can produce cleaner results. The denoiser helps to slash render times and produce
cleaner images. The denoiser only works with batch rendered images; this means we won't see the result of the denoiser in the Maya Render View, so we're going to batch render our animation to create a denoised sequence.
21 LAUNCH THE BATCH RENDER
This animation will look best when rendered at 1,920 x 800.
Depending on how powerful your computer is this will probably take a little while to render. One way to speed things up is to change the Resolution to a smaller frame size like 960 x 400, and it will render a lot faster.
Let's close the Render Settings window. From the Renderman menu, select Batch Render.
On a normal workstation, the Renderman batch render command will queue the job in Local Queue and render it on your local computer. In larger facilities, a batch rendering job can be network distributed using a render farm and Pixar's render manager called Tractor.
22 WRITE RIB FILES TO DISK
When a batch render starts, the Maya current frame indicator will step through the time slider one frame at a time and export the Maya scene to RIB files on disk. These RIB files encapsulate all of the scene information required to batch render the scene with Renderman. These RIB files are then handed to Local Queue which renders them, one image after another, using Renderman until the entire animated sequence is complete.
23 LOCAL QUEUE MANAGES JOBS
Local Queue is a render manager provided by Renderman for running batch renders on a single workstation ‘locally’. This is a handy way to queue up several shots and let them render in the background while you work on other tasks. Each render job is shown in Local Queue with a progress bar, along with detailed status messages. If a job runs into problems all you have to do is look at the logs to find out what happened, and then you can restart the job to finish the render.
When the batch rendering job completes you will have the work light animation saved to disk as a series of EXR images. The Pixar ‘it’ image tool can be used to easily review EXR renders and playback sequences.
24 MAKE IT GLOW
You can add a little bit of colour correction and glow using a compositing program to make the final images really shine. The glow effect is a common image processing filter that looks for super-bright pixels in an image. Then the filter applies a glow effect to them. Adding glow makes the light sources in the scene appear even more realistic. In the final animation, the glow effect is visible primarily on the light bulb, and on the shiny metal surfaces.
Well, there we have it, the work light scene is now complete! This four-part, step-by-step tutorial series has covered a wide range of Renderman techniques that you will be able to apply to your next project! •