Hardness-intensity diagram computed from the unabsorbed fluxes of the NICER dataset of Cygnus X-1. The hardness ratio in x axis is defined as the ratio of the unabsorbed flux in the 2 − 12 keV band to that in 0.3 − 2 keV band, while the y axis is the unabsorbed flux in the 0.3 − 12 keV band. The fluxes were obtained from the fitting each 128 s segment with a model consisting of disc black body plus a power-law component, both affected by interstellar absorption. The different colours indicate the 10 distinct regions we use in this paper, parametrized by the increasing spectral index, Γ, of the power-law component (see legend). The grey error bars in the main panel indicate the 1σ errors of the fluxes and hardness ratios. Top-right inset panel: HID of Cygnus X-1 computed from the observed count rates in the same energy bands as in the main panel; the black points correspond to the segments we used in this work, whereas the grey points are the segments that we discarded in our analysis (see text for details).