An image processing apparatus has a line memory for writing and reading image data of one line. A write/read controller controls writing and reading the image data of one line in and from the line memory. A white line determiner determines whether an image corresponding to image data of one line being written in the line memory is a white line. An image processor performs specified image processing on the image data of one line read from the line memory by the write/read controller. An image processing controller generates an operation clock used in the image processor and causes the image processor to perform the specified image processing for the image data of one line determined not to be a white line and stops generating the operation clock and reads white data from a white data storage for the image data of one line determined to be a white line.