Background intensity computed from the MPS-ATLAS solar model atmosphere (solid), the standard solar Model S (dashed), and from the observations (dots). Left: Limb darkening (I_c(μ)/I_c(μ = 1)) in the continuum around the HMI line compared with the observations from Neckel & Labs (1994). Right: Synthesized FeI spectral line background intensity ($\stackrel{\sim }{I}(\lambda ,\mu )/I_c(\mu =1)$) compared with the observations from the IAG spectral atlas (Ellwarth et al. 2023) at μ = 1 (blue) and μ = 0.5 (red). The wavelength offset is with respect to the center of the HMI line λ_HMI = 6173.33 Å. The black dashed curves represent the six HMI filtergrams.