"fringe projection" is a highly technical term from the science of interferometry. To understand it you would have to read scientific texts.
If you have the necessary scientific background I suggest you google the term. If you do not then we cannot explain it here.
_______________________________________________________________________________________________________ monochromatic fringes in a Michelson interferometer: (a) White light fringes where the two beams differ in the number of phase inversions; http://en.wikipedia.org/wiki/Interferometry
Perhaps the simplest way of describing it is to say that it is a method for measuring small irregularities in a surface. Thus it can be used to measure wrinkles on someone's skin.
Here it is contrasted with an older method.
The quantitative determination of the skin’s surface topology, both skin roughness and macrostructures such as wrinkles or cellulite, is one of the most important and probably most frequently performed investigations in the field of cosmetics, and increasingly in dermatological research as well. A still very common method of evaluating skin roughness involves the use of silicon replica as used in dentistry.
Read More: http://informahealthcare.com/doi/abs/10.3109/9781420005516.010