Signal processing apparatus for deblurring a digital input signal (6, I ( x i)), - the signal processing apparatus being configured - to compute a plurality of local length scales (l k, l ( x i)) based on at least one of a Fourier Ring Correlation (FRC k) and a local signal-to-noise ratio (SNR k), wherein for a larger signal-to-noise ratio a smaller length scale is selected than for a smaller signal-to-noise ratio, and to compute each local length scale of the plurality of local length scales at a different location ( I k ( x i)) of the digital input signal, each different location comprising at least one sample point ( x i) of the input signal; - to determine a set of different constant local length scales (l n) based on the plurality of local length scales ( l k,l ( x i)), the constant local length scales (l n) having the same value at all sample points (x i); - to compute a plurality of baseline estimates (44, f n ( x i, l n)) of the digital input signal (6, I(x i)) each based on a different constant local length scale of the set of different constant local length scales (l n), wherein each baseline estimate is computed using a polynomial fit or spline fit to the input signal, wherein a least-square minimization criterion, which is to be minimized for the fit, is used for computing each baseline estimate, wherein said different constant local length scale is contained in a penalty term of the least-square minimization criterion, wherein the penalty term comprises a derivative of the respective baseline estimate; and - to compute a digital output signal (36, O(x i)) based on one of (a) the plurality of baseline estimates and (b) the digital input signal and the plurality of baseline estimates. - the signal processing apparatus being configured - to compute a plurality of local length scales (l k, l ( x i)) based on at least one of a Fourier Ring Correlation (FRC k) and a local signal-to-noise ratio (SNR k), wherein for a larger signal-to-noise ratio a smaller length scale is selected than for a smaller signal-to-noise ratio, and to compute each local length scale of the plurality of local length scales at a different location ( I k ( x i)) of the digital input signal, each different location comprising at least one sample point ( x i) of the input signal; - to determine a set of different constant local length scales (l n) based on the plurality of local length scales ( l k,l ( x i)), the constant local length scales (l n) having the same value at all sample points (x i); - to compute a plurality of baseline estimates (44, f n ( x i, l n)) of the digital input signal (6, I(x i)) each based on a different constant local length scale of the set of different constant local length scales (l n), wherein each baseline estimate is computed using a polynomial fit or spline fit to the input signal, wherein a least-square minimization criterion, which is to be minimized for the fit, is used for computing each baseline estimate, wherein said different constant local length scale is contained in a penalty term of the least-square minimization criterion, wherein the penalty term comprises a derivative of the respective baseline estimate; and - to compute a digital output signal (36, O(x i)) based on one of (a) the plurality of baseline estimates and (b) the digital input signal and the plurality of baseline estimates.