The primary element for light capture in photography is the silver halide crystal. In color photography, the oxidized developer is used to create a colored image in register with the developed silver. Although the structure of the AgBr and AgCl lattice is face-centered cubic, an enormous variety of crystal shapes can be obtained, depending on the number and orientation of twin planes and the conditions during growth. To add to this complexity, the crystals in commercial emulsions usually contain mixed halide phases. Films suitable for a hand-held camera generally contain silver bromoiodide, in which iodide ions are incorporated into the AgBr lattice during crystal growth.
Practical photography is possible from conditions of bright sunlight to night street lighting.
Sensitivity to light, or photographic speed, is one of the most important attributes of the emulsion. Different layers in a color film contain emulsions that have been dyed to respond selectively to blue, green, and red light, thus making color photography possible. The perennial challenge to Kodak s emulsion scientists is to increase film speed while maintaining image quality and keeping performance.