Photorealistic Stills
I’ve spent a lot of time working on nonphotorealistic rendering, so I wanted to try building some photorealistic scenes. I also wanted to try out Renderman. The pots were an exercise in building up wear and tear on different materials; the window was mainly my experimentation with using lighting to convey a mood.
Goals
Wear and tear
One of the key parts of material building is wear and tear. To show age on an object requires carefully observing the material, identifying the different layers of age (dust, scratches, etc), and replicating each of those layers in a shader. I wanted to work on my wear and tear skills while experimenting with Renderman.
Light to convey a mood
Lighting can change the entire interpretation of a scene. The color, the intensity, and the focus of the lighting can all help craft a mood. I was interested in using Renderman’s advanced lighting capabilities to add depth and emotion to a scene.
Wear and Tear
For this scene, I was inspired by matkas, traditional Indian clay pots used for cooking and collecting water. I wanted to focus more on designing different materials that showed wear and tear. The metal pots are dull and dented, the clay pots are rough and dirty.
All modeling was done in Maya and shading and rendering was done with Renderman.
After modeling, I focused on the materials. I built the clay pot texture with a PxrLayerSurface- the base layer is entirely diffuse and carries most of the terra-cotta color and the bump texture. The bump texture is from an image of paintbrush strokes, meant to mimic the rough, hand-shaped texture of a terra-cotta pot.
The next 3 layers of the shader are various patterns of dust. These dust layers were made with PxrFractal and Mountain nodes, with varying shades of brown. This helps mimic the build up of dust and dirt with darker and lighter shades. A slight bump was also added to give the dirt some depth.
The black clay pot was a simple variation on the clay pot. I added another layer to the clay pot shader for the black paint. I used another mountain node to manipulate the transparency of this layer- if you look closely you’ll see some red poking through the black. The parameters for the dust noise textures were changed, so the dust patterns don’t look exactly the same as the clay pot.
I then focused on the metal shaders which were fairly simply to create. Again, these two pots used PxrLayerShaders. I used a bump texture with a perlin noise image for the dent in the aluminium pot. The gold-colored pot was just a simple layering with more noise textures to look like dirt.
For this exercise, I mainly focused on the materials of the pots so the background and lighting is relatively simple. The background wall is simply an image texture- nothing developed procedurally. I added some bump mapping to the ground and to the wall behind, to add more realism to the scene. The lighting is a simple PxrDomeLight.
Light to convey a mood
For this scene, I wanted to craft an atmosphere of calm and peace. This scene is based off my childhood bedroom window, and how the late afternoon light would filter into my room through the trees.
I spent some time shading the windowsill, but the majority of my time was focused on how the light would filter through a dusty window. I wanted to age my childhood bedroom window, and used many of the techniques I learned with the pots scene. As such, the windowsill’s paint is worn, showing the wood beneath in certain places. The windowpanes are scratched and dull, showing dust where the light hits.
All modeling was done in Maya, and all shading and rendering were done with Renderman.
At first, I experimented with making a dusty window screen. However, with the image I had picked was too repetitive and looked too low-poly and sparse. For the purposes of completing the shading, this shot has an extra spot light pointed at the window. This will not remain in the final shot.
Here is the shot with the shading fully complete and only a PxrDomeLight for lighting. The shot is mostly evenly lit, with some shadows around the edges of the window. The trees outside are simply an image on a semi-plane. This allows the light to look like it’s coming through the white parts of the photo more. Note that there is no dust on the window (yet).
In the previous shot, the lighting is entirely white. However, to evoke a peaceful mood, an afternoon light, I needed a warm glow. I added a PxrRectLight directly outside the window, which creates the yellow sunlight lighting the windowsill. I also started experimenting with some noise textures on the glass to use as dust. I added a gobo so the shadow of branches appear on the windowsill.
The dust in the previous photo was too aggressive. I changed the frequency and density of the dust.
I added some lights within the room and changed the angle of the spot light outside the window. Adding lights within the room helps simulate light bouncing around the room and lighting the wall behind the window.
I experimented more with the dust placement and color. The dust in previous shots was too brown- this is more grey. I also adjusted the spot light to be at more of an angle so the light filters into the room more. I lowered intensity of lights within the room as well.
I did a high-res render so that I could better critique my lighting. In the previous shots, the light was too yellow to be considered realistic. Here, the lighting is much whiter, with a yellow tint. I like the angle of the main light source and how it hits the right edge of the windowsill. The light directs the eye down the right edge of the window and across the windowsill. The dust looks a little too thick for how uneven it is.
The left hand corner of the windowsill in previous shots was entirely in shadow. This isn’t realistic since the light would bleed and bounce around the room and still light the corner of the windowsill, to some degree. I added another PxrRectLight opposite the main light, at a much lower intensity. This light hits that corner and lightens the shadows.
The final render. The spotlight within the room was turned up slightly, to make the wall surrounding the window a little lighter. This helps direct the eye more towards the center of the window and helps make the wall look more realistic.
Reflections
Looking Back
Ultimately, I think my two exercises were a good introduction into Renderman and how it works. I’m really happy with the window shot- I think it effectively conveys the calm, peaceful mood I was looking for. There is obviously much, much more that I could learn. I think I could’ve spent more time on the metal shaders with the pots and spent more time with the clay layer on the pots. All this being said, Renderman might be a little too powerful for my lowly MacBook Pro- the final render for both shots took about ~18 hours (each). It wouldn’t be effective for me to attempt any sort of long-form animation with Renderman.
Moving Forward
Renderman is a powerful tool. While this was an exercise in photorealistic materials and lighting, I’m curious to see how it could be used in NPR shots. I’m also curious about volumetric lighting with Renderman- how would the window shot look if I added dust in the air? How would subsurface scattering work with Renderman? There are countless opportunities to explore both stylized and photoreal shots with Renderman.