Figure 1

Cross artefact caused by image boundary discontinuities. Transfer functions displayed: (a) true; (b) reconstructed using the Welch window function and \(\sigma \to 0\); (c) reconstructed without windowing and the same σ; (d) reconstructed without windowing and large σ—even with σ so large that the TTF becomes smeared, the cross-like anisotropy is still clearly present. Note that the colour scale in part (c) is adapted to the full value range—the smooth central bump corresponds to TTFs in the other three parts.