Figure 4

Blob-ELLR format. In the blob (the radius a = 2), a projected pixel X_j contributes to four neighbour projection rays (L1, L2, L3 and L4) using only one view (left). The nonzeroes of W are stored in a 2D array A of dimension (4B) × N in blob-ELLR without symmetric techniques (middle). The symmetric optimization techniques are exploited to reduce the storage space of A to almost 1/16 of original size (right).