35.0 COMPUTATIONAL ILLUMINATION⧉
Most of this book optimizes the camera: the lens, the sensor, the sampling, the processing that turns light into a picture. This part optimizes the other side of the imaging equation: the light itself. The measurement a photosite makes is illumination × reflectance × geometry integrated over the pixel, and if you are allowed to control the illumination, you gain a new handle: shoot the same scene under two or more known, different lightings and the differences between the shots provide constraints on terms entangled in a single exposure, under a model of the scene and light transport. Turn a flash on and off and subtract, and you isolate the added flash response in aligned, linear, exposure-matched images. It favors the foreground when the background receives little flash light. Time a strobe to the microsecond and you freeze a bullet. Flicker a projector through a sequence of patterns and you can pry apart the light that bounced once from the light that bounced many times, or read the depth of every point, or even swap the roles of the camera and the projector entirely. In each case the light is an input we code, and the picture we want falls out of inverting how the scene transformed that coded light.
That reframing, illumination as a designed active input, runs through the part along several axes: timing (flash and high-speed strobing freeze and reveal motion the eye cannot hold), pattern (projected codes matte foregrounds, scan geometry, and separate direct from global transport), direction (a dome of lights, or a light flown into place, measures or sculpts how a surface responds to every incoming ray), and reciprocity (dual photography and coherent imaging exploit symmetries between where the light comes from and where it is measured). The recurring lesson applies the field's core move to the source rather than the sensor: you can recover what a passive snapshot cannot by modeling and inverting a transformation you deliberately imposed. Here, that transformation is how a scene turns your light into your measurement.
Chapter 35.1, Flash photography is the everyday entry point: fill flash, flash/no-flash pairs, red-eye, and why on-camera flash looks the way it does. Chapter 35.2, High-speed and stroboscopic photography, codes light in time: Edgerton's strobes and the ultrafast regime that freezes the unfreezable. Chapter 35.3, Illumination-based matting and Chapter 35.4, Separation of Direct and Global Illumination code light in pattern: routing foregrounds out of backgrounds, and peeling the once-bounced light apart from the multiply-scattered glow. Chapter 35.5, Light domes and Chapter 35.6, Automatic aesthetic lighting control light by direction and position: measuring a surface's full reflectance field, or driving a physical light source (a bounce head, a drone) to a target look. And Chapter 35.7, Dual photography and Chapter 35.8, Coherent imaging exploit the deep reciprocity and wave structure of light transport: imaging from the projector's point of view, and using coherence itself as the probe.
Contents of this part
- 35.1 Flash photography
- 35.1.1 Flash / no flash
- 35.1.2 Ramesh's multiflash
- 35.1.3 Removing flash artifacts
- 35.1.4 Dark flash and covert infrared photography
- 35.2 High-speed and stroboscopic photography
- 35.3 Illumination-based matting
- 35.4 Separation of direct and global illumination
- 35.5 Light domes
- 35.6 Automatic aesthetic lighting
- 35.7 Dual photography
- 35.8 Coherent imaging