Limiting, T_b,lim (top row of datapoints) and minimum, T_b,min (bottom row of datapoints), brightness temperature estimated directly from visibility data for 3C 345 (top panel) and NGC 1052 (bottom panel), plotted against the spatial frequency q (uv radius). The estimated values are compared with the brightness temperatures of the Gaussian model fit components (dotted lines for the jet components, thick dashed line for the core component) used to describe the source structure as shown in Fig. 2. Running stairs show the respective rows of the brightness temperature averaged within radial bins of 10 Mλ in extent. Both the original and the averaged rows of the brightness temperature indicate that at q ≳ 150 Mλ, the interval [T_b,min,T_b,lim] provides a good bracketing for the maximum brightness temperature in each of the two objects. Braces indicate the conservative ranges of spatial frequency q identified as ranges dominated by the most compact part of the source structure. Averages of T_b,min and T_b,lim made over these ranges constrain the respective T_b,mod estimates well.