# photography

# fundamental model

light source
* pose
  * position
  * orientation
* support geometry
  * size
  * shape
* magnitude: total source strength
* spatial profile: emission distribution across the source surface
* angular profile: emission distribution by direction
* spectrum: wavelength distribution; approximately temperature + tint when sufficient

lighting system
* source count: number of independently controlled sources
* layering: superposition and spatial arrangement of source contributions

scene
* geometry: surfaces, orientation, distances, occlusion, visibility
* material transport
  * diffuse reflection
  * specular reflection
  * transmission
  * subsurface transport

camera
* viewpoint and projection
* focus / depth response
* exposure integration
* spectral response
* spatial transfer
  * diffraction
  * diffusion
  * bloom
  * halation
  * flare
* recording / tone response

conditional
* temporal profile: flash duration, flicker, synchronization
* polarization: when source, material, or camera is polarization-sensitive

# derived lighting properties

* apparent extent: angular size and shape of the emitting field as seen from the subject
* incidence angle: source direction relative to a surface
* softness: shadow-transition character produced mainly by apparent extent and geometry
* coverage: illuminated region produced by pose, angular profile, and scene geometry
* feathering: placement of the target within a nonuniform angular profile
* spatial falloff: change in illumination across space
* exposure contribution: result of source magnitude, geometry, distribution, spectrum, and receiving surface
* rim / outline: source-scene-camera configuration producing visible edge illumination
* glow: appearance produced by transmission, scattering, broad highlights, diffusion, bloom, halation, flare, or local contrast

# principal relations

* source distance changes apparent extent, exposure, and spatial exposure gradients
* source orientation changes illumination without changing source position
* physical source size != apparent source extent
* source magnitude != received exposure
* same exposure != same lighting
* support geometry != spatial profile
* apparent extent != angular profile
* softness is derived, not a source property
* layering is a relation among sources, not a light property
* scene material can radically change the photographed result without changing the source
* camera spatial transfer can create glow-like structure absent from the scene illumination

inverse-square behavior
* irradiance approaches `1 / distance²` for a sufficiently small source in free space
* extended nearby sources require geometric treatment rather than simple point-source approximation

# optics and capture

focal length
* controls projection scale and angle of view for a given sensor format
* does not by itself determine perspective; viewpoint does
* longer focal length + greater camera distance can produce narrower framing with compressed apparent depth relations

focus
* correct focus maps a scene depth sharply onto the image plane
* defocus produces blur circles whose size depends on aperture, focus distance, subject distance, focal length, and sensor geometry

aperture
* controls admitted light and contributes to depth of field, diffraction, and blur geometry

viewpoint
* determines perspective and relative geometric projection
* lens choice determines how much of that projected field is recorded

# lighting practice

natural light
* sunlight: very distant, small apparent angular source, strongly directional unless modified by atmosphere or environment
* window light: extended source whose apparent extent depends strongly on subject distance and window geometry
* environment can add reflected and transmitted contributions while one source remains dominant
* spectrum varies with time, weather, surroundings, and transmitted/reflected surfaces

studio light
* begin with one motivated dominant source
* control independently:
  * pose
  * apparent extent
  * magnitude
  * angular profile
  * spectrum
* add sources only when an additional independently controlled contribution is required
* avoid accidental conflicts in direction, spectrum, shadow structure, or visual motivation

background
* control independently from the subject when necessary
* gradients arise from source pose, distribution, distance, and background geometry
* black backgrounds emphasize separation, edge structure, and local contrast
* white backgrounds require sufficient illumination and spill control to remain clean
* seamless surfaces and regular edges reduce unintended geometric structure

reference practice
* study photography, film stills, paintings, and CGI by reconstructing:
  * source count
  * source pose
  * apparent extent
  * angular profile
  * relative magnitude
  * spectrum
  * material response
  * camera response