Our eyes are not taking a single still photo, they’re taking in real life in real time. Our eyes constantly adapt to changing conditions as we look around a roo

Our eyes are not taking a single still photo, they’re taking in real life in real time. Our eyes constantly adapt to changing conditions as we look around a room. This capability is finite though, as anyone who has walked out of a dark room into the midday sun has experienced. The limitation in all photographic technologies has to do with the fundamental light gathering mechanism. In the case of photographic film, it is grains of photosensitive chemicals such as silver halides. In the case of digital cameras it is photosensitive semiconductors called CCDs or CMOS sensors. These sensors (chemical and digital) operate by collecting photons during the exposure. In either case, and with our eyes too, they can only collect so many photons before they “fill up.” In the case of film, this meant enough photons had arrived at the grain of silver halide to provide it with the energy needed to cause the reaction to take place. This reaction causes an irreversible change in the colour of the grain. In the case of digital sensors, when enough photons arrive the device stores its maximum possible charge which is then read out and converted to a number (usually the maximum number for that integer type). So then why can’t we make photographic technology that can gather a larger number of photons before “filling up”? It’s a tradeoff. The larger we make the (sensors or film grains) the more capacity for light gathering (called dynamic range) they have, but the lower the resolution they have. Unfortunately, in the world of consumer devices, resolution (megapixels) is king. The fundamental problem we’re dealing with in nature is that the dynamic range of real life is many orders of magnitude. Outdoor midday sunlight can be something like a hundred million photons per second per pixel whereas night time under starlight that falls to less than one photon per second per pixel.