1. An image processing apparatus comprising: an image compression conversion unit that, in an event of quantizing an image having attribute data for each pixel, creates a density pattern in which pixel values of plural pixels composing a region as a quantization target are binarized, quantizes the region based on the density pattern, and binarizes, for each pixel, the attribute data individually owned by the plural pixels composing the region; and an image extension conversion unit that, in an event of decoding the image of the region quantized based on the density pattern by the image compression conversion unit, decides a density pattern of the region before the quantization in response to an attribute pattern that is based on the binarized attribute data of each of the plural pixels composing the region, and decodes the region in response to the decided density pattern.