In contrast to the conventional two-step method, which involves the generation of reactive functional groups followed by incubation in a dye solution (a wet developing process), the "precursor approach" enables the rapid and cost-effective generation of patterned images in one step, without the need for an additional wet process. By using the "precursor approach", the fluorescence of precursor molecules in polymer fibres can be effectively manipulated by: (1) photoinduced removal of transient protecting groups; (2) photoinduced protonation or intramolecular proton transfer; (3) photochromism; (4) photoinduced formation of fluorophores; (5) photoinduced oxidative degradation or molecular orientation.