According to Microsoft Paint, the luminescence values of the two pixels diagonal to the "white" pixel in the vertical stem of the E are 68 and 98. Interpolation of these values gives (68 + 98) / 2 = 83. The luminescence value of the "white" pixel is 202, and the maximum potential value is 240. ((202 - 83) / 240) * 100 = 50. The bottom pixel on the stem of the E has a luminescence value of 143, while the pixel diagonal to it has one of 75. ((143 - 75) / 240) * 100 = 28. As 50 - 28 = 22, it is to be concluded there is approximately a 22% difference in luminescence, relative to the diagonal background patterns, between the "white" pixel and the pixel at the bottom, both from the stem of the E.
Visual depiction, represented by the blue lines.