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. <EOS>