Abstract
Background: In this paper, a method for adaptive Pure Interpolation (PI) in the frequency
domain, with gradient auto-regularization, is proposed.
Methods: The input image is transformed into the frequency domain and convolved with the Fourier
Transform (FT) of a 2D sampling array (interpolation kernel) of initial size L × M. The Inverse
Fourier Transform (IFT) is applied to the output coefficients and the edges are detected and counted.
To get a denser kernel, the sampling array is interpolated in the frequency domain and convolved
again with the transform coefficients of the original image of low resolution and transformed
back into the spatial domain. The process is repeated until a maximum number of edges is
reached in the output image, indicating that a locally optimal magnification factor has been attained.
Finally, a maximum ascend–descend gradient auto-regularization method is designed and
the edges are sharpened.
Results: For the gradient management, a new strategy is proposed, referred to as the Natural bi-
Directional Gradient Field (NBGF). It uses a natural following of a pair of directional and orthogonal
gradient fields.
Conclusion: The proposed procedure is comparable to novel algorithms reported in the state of the
art with good results for high scales of amplification.
Keywords:
Gradient management, optimal scales of amplification, high frequency conservation, NBGF, novel algorithms, SR.
Graphical Abstract
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