Evolution of the IPCA with ARDI estimate through the iterations, using the same dataset as in Fig. 3. The blue curve relates to the left y-axis and displays the value of the SSIM for each estimate. The orange curve relates to the right y-axis and represents the gradient computed over the full frame, as described in Eq. (4). The g_tol has been set to 10⁻² and is represented on the figure by the two gray lines. The black dot indicates the iteration where the gradient curve reaches the g_tol and does not exceed it in further steps. The x-axis represents each iteration, where the minor ticks represent a single iteration, and the major ticks represent a rank update.