Reading Notes

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 What is Sampling

  • Producing realistic looking scenes require lighting and camera work
  • Sampling means to collect information from the geometry, lighting, and shader which then which then creates light transport paths that connects it to the pixel through the light sources
  • Quality of the pixel depends on how many paths it has
  • Arnold sends out numerous amount of rays at a scene to determine things like color of the pixel
  • Increasing the number of samples result in less noise
  • The camera value controls the pixel sampling rate
  • It is important to identify the source of the noise so that those specific rays are increased
  • Light sampling is using rays to that deal with light
  • It is more difficult to identify the source of noise for light especially if the light is large
  • Noise from direct light sources appear in specular highlights and in soft shadows
  • Indirect diffuse rays interact with objects and their shaders
  • Direct diffuse rays are random
  • When dealing with specular rays, turning the specular depth and the diffuse depth to zero can isolate the noise
  • Sampling volumes takes longer to do than surfaces
  • Ray marching, direct and indirect lighting is important to consider when dealing with volume
  • Step size can determine how volume is rendered
  • Low step size increases render time
  • If increasing sample doesn't work then reducing step size is an option

Understanding Physically based rendering in Arnold

  • Understanding physical laws of materials can help in simplifying shading and lighting
  • How photons interact with the object determines the material it will be
  • A material is energy conserving if it has less or equal the amount of photons leaving the surface compared to coming in
  • The weight and color of the material should not exceed 1
  • If the photons scatter more there is a softer render of the scene, if it scatters less then it is harder and when the photons go through the object then is will look more thin
  • Color is determined by what color wavelength is scattered back
  • Low roughness mean that it has less variation as well as more sharp reflection
  • IOR stands for the index of refraction
  • The underlying diffuse interior will be visible the more refractive the specular layer is
  • The Fresnel effect is how photons are reflected or refracted based on the view
  • Opacity can determine where photons can pass straight through

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