As anyone with a little background science knowledge will know, light can be measured as discrete quanta called photons. These particles behave as both a wave AND a particle, (as an aside, the wave-like behaviour of light is responsible for diffraction, which softens photographs taken at small apertures). For now, I shall focus on the particle side of things.

Photons of different wavelengths from a light source bounce off various objects in a scene before eventually being captured and counted in a pixel on a camera sensor. The number of red, green, and blue photons that make it onto the corresponding coloured pixels on the sensor determine the brightness of those pixels. There are many, many trillions of these photons bouncing around, and the overwhelming majority of these never make it anywhere near the sensor of a camera that is trying to capture a scene. What is important to note, though, is that while the number of photons bouncing around is very large, it is also finite. read more