1. An image processing apparatus performing image processing on image data stored in a temporary storage area, comprising: a size-reducing unit that reduces a size of original image data, wherein the size of the original image data is reduced according to a parameter of the original image data such that a size-reduction ratio of a chroma component is greater than a size-reduction ratio of a luminance component, to perform the image processing; and a storage control unit that stores size-reduced image data in the temporary storage area to perform the image processing.