The Programmer's Imaging Kernel System (PIKS) is an application program interface (API) for image processing. It is one of three parts of a standard for Image Processing and Interchange being developed by the International Standards Organization (ISO) and the International Electrotechnical Commission (IEC). This paper presents an overview of the API; companion papers discuss the imaging architecture and image interchange parts of the standard. PIKS contains a rich set of operators, tools, and utilities. PIKS operators are functional elements that perform manipulations of images or of data objects extracted from images in order to enhance, restore, or assist in the extraction of information from images. These operators range from primitive operators such as convolution and histogram generation to complex, higher level operators such as adaptive histogram equalization and texture feature extraction. PIKS tools are elements that create data objects to be used by PIKS operators, e.g., the generation of filter transfer functions. PIKS utilities are elements that perform basic mechanical implementation tasks such as extracting pixels from an image. PIKS provides a fundamental operator model that supports match point translation of images prior to processing, image-related region-of-interest processing control, image/operator coordinate index assignment, and the ability to define reusable chains of operators.