A software module that extends the functionality of Adobe Photoshop and compatible programs.
Several different types of Photoshop plug-ins exist. Probably the most common are filter plug-ins, which filter an image, producing some kind of special effect, or correcting some defect or imperfection in the image.
Another common type of Photoshop plug-ins allows the host program (i.e., Photoshop and compatibles) to read and write different image file formats.
The filter plug-ins can be created by using special tools, such as Filter Factory, or programmed directly by using a programming language. C and C++ are the languages most often used, though not the only ones. For example, the filter plug-ins by Red Prince are written in assembly language for greater speed and small memory requirements.