An image signal outputted from a CCD is converted into a digital signal by an AD converter via a sampling hold circuit. While 3D content looks of good quality, the quality of any co-existing 2D content in windowed mode on the same screen looks poor. Suggested internal core functions include facilities, budget and contracts. At least a radially inner side of the rear surface inclines rearward in the rotative direction from the radially inner side to a radially outer side. Holes, running the length of the preform, collapse during the drawing, causing the core to have an elliptical cross section. The process includes adding water to a reactor, adding a copolymerization agent, adding thioglycolic acid and allowing to react, adjusting pH, mixing a powdered extract of a plant or tannin to a desired concentration, raising the temperature, adding sodium bisulfite, and keeping the reaction heated and at pressure for about 4 hours.