A digital slide scanning apparatus that includes a scanning stage, a focusing sensor, an imaging sensor, and at least two processors. A main processor is configured to control the scanning stage to move a sample relative to the focusing sensor and the imaging sensor. The main processor controls the secondary processor to process focus buffers generated by the focusing sensor and image buffers generated by the imaging sensor. The secondary processor access each buffer and processes the data in the buffer to generate an average contrast vector for the buffer. The average contrast vectors for the focus and image buffers are then provided to the main processor for further processing in connection with autofocus and/or generation of a digital slide image.