Signal Processing Device, Control Method For Signal Processing Device, Control Program, And Computer-Readable Storage Medium Having The Control Program Recorded Therein

A signal processing device which carries out a process for sharpening an image with respect to an input signal representing the image, so as to output an output signal representing the image which has been sharpened,

• said signal processing device comprising:
• frequency component decomposition means for decomposing the input signal into a plurality of frequency components in different frequency ranges;
• higher harmonic wave generating means for generating a higher harmonic wave for each of a part or all of frequency components obtained by removing a frequency component in the lowest frequency range from frequency components into which the frequency component decomposition means has decomposed;
• and
• output signal generating means for composing (i) the higher harmonic wave generated by the higher harmonic wave generating means and (ii) a frequency component for which no higher harmonic wave has been generated by the higher harmonic wave generating means of the frequency components into which the frequency component decomposition means has decomposed, so as to generate the output signal,
• the higher harmonic wave generating means including:
• nonlinear process means for generating a nonlinear process signal (i) in which positive and negative signs of a frequency component for which the higher harmonic wave is to be generated are retained and (ii) which broadly monotonically increases nonlinearly with respect to the frequency component when the frequency component is located at least in the vicinity of 0 (zero);
• and
• addition means for adding the nonlinear process signal to the frequency component, so as to generate the higher harmonic wave.