Assessing the quality of the reconstructed flux contrast field. The quality is checked for the different values of S/N and two different configurations, corresponding to the resolution of R = 1000 and the reconstruction scale of L_T = 4 Mpc (configuration C1, left column) and the resolution of R = 2000 and the reconstruction scale of L_T = 2.5 Mpc (configuration C2, middle column). Right column: 3 additional flavors of the C2 configuration (see Sect. 2.1.4 for details), with a constant exposure time and at least S/N = 4 on all spectra (S/N = 4,CT), with no noise on spectra (No noise) and with a spatially uniform background sources distribution (No noise, uniform). Upper row: distributions of the pixel-by-pixel differences between the smoothed original and reconstructed flux contrast fields. Note that the distributions are normalized in a way that the peak of the narrowest distribution equals 1. Bottom row: scatter plots of the original flux contrast field (for S/N = 4) against the reconstructed one. The original field has been smoothed with the same L_T scale as the corresponding reconstructed one. Black line shows δ_rec = δ_orig relation. Overplotted contours of number counts (computed at a level of 10 counts and smoothed afterwards) show the change of the 2D distribution for reconstruction for different S/N values of the spectra.