1. A method for controlling an immersive head mounted display (HMD) configured to provide a virtual space to a user, the method comprising: generating and storing virtual space image data having a first image quality, wherein the virtual space image data is usable for forming a virtual space viewable by the user; generating a virtual space image, wherein generating the virtual space image comprises reading the previously stored virtual space image data; determining a reference line of sight; determining a field-of-view region of the virtual space based on the reference line of sight; and generating, using a computer, in the field-of-view region, a field-of-view image having a second image quality higher than the first image quality, wherein generating the virtual space image further comprises reducing a 3D polygon count as compared to the field-of-view image, and wherein generating the field-of-view image comprises increasing the 3D polygon count of the virtual space image, wherein the field-of-view image corresponds in size to the field-of-view region, wherein the virtual space image outside of the field-of-view region is not visible to the user, and wherein the virtual space image is generated outside the field-of-view region simultaneously with the generating of the field-of-view image.