Abstract: A document processing system directs documents at a high rate of speed past an optical scanner which captures written information on the documents as video image data. The video image data is directed over a data channel to a host computer system where the data is stored on a mass data storage device for subsequent retrieval. A buffer is provided between the scanner and the data channel, which receives data a rate which varies in relation to the amount of information present on the documents. Data is extracted from the buffer at a rate which is limited by the host computer's channel transfer rate. A control means is associated with the buffer and is operable for controlling a hierarchy of actions ranging from slowing down the incoming data stream to stopping the data stream altogether in order to prevent any loss of video image data due to overfilling of the buffer.