A general image processing apparatus that converts an image calculates a converted pixel value of a converted pixel located at a converted coordinate in a converted image by referring to a unconverted pixel value of a unconverted pixel located at an unconverted coordinate corresponding to the converted coordinate of unconverted coordinates in an unconverted image before a conversion.
A conventional image processing apparatus is connected to an external memory and includes a cache memory. Image data is stored in the external memory. The image processing apparatus refers to the unconverted pixel in the external memory, calculates the converted pixel value, and writes the calculated converted pixel into the external memory. In order to decrease the number of access times to the external memory, the image processing apparatus confirms whether the unconverted pixel is stored in the cache memory when referring to the unconverted pixel value. When the unconverted pixel is stored in the cache memory, the image processing apparatus calculates the converted pixel value using the unconverted pixel value of the unconverted pixel stored in the cache memory. When the unconverted pixel is not stored in the cache memory, the image processing apparatus reads the unconverted image from the external memory. The read unconverted image includes the unconverted pixel to be referred and the peripheral pixel located around the unconverted pixel.
However, depending on an image conversion pattern, only part of the unconverted pixel stored in the cache memory is referred to in calculating the converted pixel value, which reduces use efficiency of the cache memory.
On the other hand, when the unconverted pixel necessary to calculate the converted pixel value is not stored in the cache memory, a fetch request to transfer the unconverted pixel stored in the external memory to the cache memory is issued, which results in a problem in that latency of access to the external memory increases.