Figure 1.

Sketch of two steps of calibrations: irradiation A, the center of the EPID at the coordinates $(\mathrm{x},\mathrm{y})=(0,0)$, and irradiation B, at $(\mathrm{x},\mathrm{y})=(1,0)$, respectively. The gray pixel is the reference pixel and its coordinates (linked to the EPID (i,j) system) are in both A and B configurations $(\mathrm{i},\mathrm{j})=(1,1)$.