Figure 4: (a) In the uniformity flood images, a frame-shaped pattern is seen, superimposed on the main image, which is shifted to the upper right corner, the characteristic pattern of this artifact or “picture-in-picture artifact.” As it can be seen, the results of integral uniformity and differential uniformity are far higher than the acceptable levels. (b) After replacing with a new properly functioning board, the results of uniformity tests (visual and quantitative) are acceptable