Examples of discarded fits for the four cases given in Sect. 5, represented as white-line ellipses. (a): Filaments and/or diffuse emission at 610 MHz. (b): Strong or large sources that are ill represented by a combination of fits at 325 MHz. (c): Reduction artifacts at 325 MHz. (d): Fits of emission similar to the noise at 610 MHz; in this last case, the fits accepted as good fits are shown with black-line ellipses.