1. An image processing apparatus comprising: expansion means for expanding coded image data; storage means for storing data indicative of characteristics of an image obtained at the time of the expansion processing performed by said expansion means; first conversion means for performing resolution conversion on the image data, expanded by said expansion means, in accordance with the data indicative of the characteristics; and second conversion means for quantizing the image data, on which the resolution conversion is performed, in accordance with the data indicative of the characteristics.