Panel a: intensity contrast at the continuum of the Fe I 6173 Å line in the annotated intervals of B. We binned the intensity contrast measurements within each B interval by μ in bins of 0.05. The filled circles and error bars correspond to the mean and standard deviation within each μ bin. The standard error of the mean is given by the quotient of the standard deviation and the square root of the number of measurements in the bin. Each bin contains 10⁵ measurements, such that the standard error is too small to be represented in this plot. The solid curves follow the bivariate polynomial in the μ and B fit to the measured intensity contrast (Eq. (2) and Table 1). The dashed curves represent the result from the similar analysis in Yea13 at the original spatial resolution of HMI, which are largely hidden because they agree so closely. Panel b: the same, except for the intensity contrast at the core of the Fe I 6173 Å line (red) and 1700 Å (blue). The Fe I 6173 Å line core values are scaled by a factor of 10 to facilitate the comparison.