1. A method for image-based rendering of light in a virtual volume comprising the steps of: (i) dividing light sources into two groups, in which a first group is behind a three-dimensional object, and a second group is in front of the three-dimensional object; (ii) arranging a sequence of forming a two-dimensional image for the first group of light sources; (iii) forming a two-dimensional image for an illuminating effect of each light source in the first group of light sources; (iv) selecting a merging mode to merge the two-dimensional images for the illuminating effects of the first group of light sources and storing the merged image in the first buffer; (v) determining whether or not each of the two-dimensional images for the illuminating effect of each light source in the first group of light sources are merged into the merged image stored in the first buffer, if yes go to the next step, otherwise go to step (iii); (vi) blending the merged image stored in the first buffer and the image of the three-dimensional object to obtain a blending image and storing the blending image in the second buffer; (vii) arranging the sequence of forming two-dimensional images for illuminating effects of the second group of light sources; (viii) forming a two-dimensional image for the illuminating effect of a light source in the second group of light sources; (ix) providing a special effect to the two-dimensional image for the illuminating effect of the light source in the second group of light sources by calculation with a special function and storing the image having a special effect in the third buffer; (x) selecting a merging mode to merge the image stored in the third buffer and the blending image stored in the second buffer; and (xi) determining whether all of the two-dimensional images for the illuminating effect of each light source in the second group of light sources have been merged, if yes go to the end, otherwise go to (viii).