The full form of STTP is Short Term Training Program.
In the processing of photographic films, plates or papers, the photographic developer (or just developer) is a chemical that makes the latent image Latent_imageonthe film or print visible. It does this by reducing the silver halides that have been exposed to light to elemental silver in the gelatin matrix. As a generalisation, the longer a developer is allowed to work, the greater the degree of reduction of the silver halide crystals to silver and therefore the darker the image.