1. An image processing apparatus comprising: an image compression conversion unit to quantize an image having attribute data for each pixel; and a memory to save the image quantized by the image compression conversion unit, wherein when a region of the image has the attribute data of a photographic image, the image compression conversion unit quantizes the region by a BTC method, and saves a quantized image in the memory, wherein when a region of the image having the attribute data of other than the photographic image is a halftone region, the image compression conversion unit quantizes the region by the BTC method, and saves the quantized image in the memory, and wherein when the region of the image having the attribute data of other than the photographic image is a high resolution region, the image compression conversion unit generates a density pattern for the region, quantizes the region according to the generated density pattern, and saves the quantized image in the memory.