Reconstructed images of the granulation at three opacity levels in the 630.15 nm Fe i line. The geometrical scale is in arcseconds. Left panel: image at continuum level. Middle panel: image at line-center level. Right panel: image at line cord index 6 (close to the contrast inversion layer). Color code: the mean image intensity, I_m is coded in black. The intensity range in each image is coded on 4 colors, showing respectively the levels  [I_m + (I_max − I_m)/2;I_max] : red,  [I_m;I_m + (I_max − I_m)/2] : magenta,  [I_m − (I_m − I_min)/2;I_m] : cyan,  [I_m − (I_m − I_min)/2;I_min] : blue. I_max and I_min denote respectively the maximum and minimum intensity in the image. The white circles show examples of structures exhibiting contrast inversion in the upper photosphere.