1. An image processing method of processing image portrayal information used for rendering by attaching textures, the method comprising: separating an image into a texture area to which the texture is attached and a non-texture area to which the texture is not attached, in a coordinate system of a rendering-completed image represented by the image portrayal information, wherein pixels of a part other than the non-texture area are interpolated by a predetermined interpolating process such that a pixel value is gradually changed from a boundary of the non-texture area; compressing the image portrayal information of the non-texture area by a first compression method, wherein the image portrayal information after the interpolation is compressed by a JPEG compression method that is the first compression method; compressing the image portrayal information of the texture area by a second compression method different from the first compression method, wherein the image portrayal information of the texture area is compressed by a lossless compression method that is the second compression method; and rendering by attaching a predetermined pattern with different grayscale values set for each coordinate to a 3-dimensional model as textures, wherein correspondence of coordinates of the rendering-completed image and coordinates of textures is set by analyzing a rendering-completed image obtained as a bitmap image by the rendering, and is stored as the image portrayal information, and further wherein a desired texture is disposed on the rendering-completed image on the basis of the stored image portrayal information at the time of displaying the desired texture as an image.