1. An image processing apparatus, comprising: a temporary storage area; a processor; and a memory configured to store computer readable instructions that, when executed by the processor, instruct the processor to perform processes comprising: generating, if a size of the temporary storage area is less than a size of original image data, size-reduced image data by reducing the size of the original image data, the size of the original image data being reduced such that a size-reduction ratio of a chroma component is greater than a size-reduction ratio of a luminance component, and the reducing comprising: reducing the size of the chroma component without reducing the size of the luminance component if a size of the temporary storage area is less than the size of original image data and greater than a predetermined data size, the predetermined data size being related to and less than the size of original image data, and reducing both the size of the chroma component and the size of the luminance component if the size of the temporary storage area is less than the predetermined data size; storing the size-reduced image data in the temporary storage area if the size of the temporary storage area is less than the size of the original image data; and storing the original image data in the temporary storage area if the size of the temporary storage area is greater than the size of the original image data.