Image enhancing device, image enhancing method, image enhancing program and signal processing device

An image enhancing method for sharpening an image represented by an input signal, comprising:

• a filtering step of generating a first signal by removing, from an input signal which represents an image, at least a DC component of frequency components contained in the input signal;
• a nonlinear processing step of generating a second signal by performing a nonlinear process to the first signal;
• and
• an adding step of adding the second signal to the input signal;
• wherein the nonlinear processing step includes
• generation of a third signal based on the first signal, the third signal making monotonic increase in a broad sense, nonlinearly or in positive-negative symmetry with respect to the first signal at least in the neighborhood of zero, and
• generation of the second signal based on the third signal so that positive and negative signs in the first signal are substantially preserved in the second signal while the second signal does not contain a DC component.

A non-transitory computer-readable recording medium containing the image enhancing program for sharpening an image represented by an input signal, the program causing a computer to execute:

• a filtering step of generating a first signal by removing, from an input signal which represents an image, at least a DC component of frequency components contained in the input signal;
• a nonlinear processing step of generating a second signal by performing a nonlinear process to the first signal;
• and
• an adding step of adding the second signal to the input signal;
• wherein the nonlinear processing step includes
• generation of a third signal based on the first signal, the third signal making monotonic increase in a broad sense, nonlinearly or in positive-negative symmetry with respect to the first signal at least in the neighborhood of zero, and
• generation of the second signal based on the third signal so that positive and negative signs in the first signal are substantially preserved in the second signal while the second signal does not contain a DC component.

A signal processing device for improving a quality of an input signal, comprising:

• a filter section for generating a first signal by removing from an input signal at least a DC component of frequency components contained in the input signal;
• a nonlinear processor for generating a second signal by performing a nonlinear process to the first signal;
• and
• an adder section for adding the second signal to the input signal;
• wherein the nonlinear processor
• generates a third signal based on the first signal, the third signal making monotonic increase in a broad sense, nonlinearly or in positive-negative symmetry with respect to the first signal at least in the neighborhood of zero, and
• generates the second signal based on the third signal so that positive and negative signs in the first signal are substantially preserved in the second signal while the second signal does not contain a DC component.