FIGURE 4. (Left) Principle of backprojection for one 2 x 3 sinogram. Value in each pixel is sum of values of bins that, given angle of detector, can receive photons from that pixel and is divided by number of rows of sinogram. (Right) Example: f₁ = (g₃ + g₄)/2 = (7 + 6)/2 = 6.5. Compare this slice with that of Figure 3, and note that after 1 projection and 1 backprojection, initial slice is not retrieved.

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