Image processing apparatus, method, and computer-readable recording medium having image processing program recorded thereon

A non-transitory computer-readable recording medium having recorded thereon an image processing program which is executable to control a computer to perform functions comprising:

• image-capturing-mode selecting processing for selecting one image-capturing mode from a plurality of image-capturing modes;
• signal-value-region setting processing for setting a predetermined signal-value region on image signals input from an image-acquisition element;
• noise-level calculating processing for calculating noise levels;
• noise-reduction processing for performing noise reduction processing on input image signals based on the calculated noise levels;
• and
• reference-noise-model storing processing for storing a plurality of reference noise models determined in accordance with properties of the image-acquisition element;
• wherein:
• each reference noise model indicates a relationship between signal value and noise level, and has a characteristic such that the noise level increases with an increase in the signal value;
• the signal-value-region setting processing sets a signal-value region as the predetermined signal-value region, signal values of the signal-value region being at or below a threshold from among a plurality of thresholds determined in association with the image-capturing modes, when the image-capturing mode selected by the image-capturing-mode selecting processing is a specific image-capturing mode;
• the noise-level calculating processing calculates (i) a noise level of a signal-value region other than the predetermined signal-value region, based on a reference noise model, and (ii) a noise level of the predetermined signal-value region, based on an applied noise model, the applied noise model being modified so that the noise level of the predetermined signal-value region is higher than the noise level of the reference noise model which corresponds to the image-capturing mode selected by the image-capturing-mode selecting processing, when the predetermined signal-value region is set by the signal-value-region setting processing;
• and
• the noise-level calculating processing calculates a noise level of an entire region of the input image signals based on the reference noise model, when the predetermined signal-value region is not set by the signal-value-region setting processing.

An image processing method comprising:

• selecting one image-capturing mode from a plurality of image-capturing modes;
• setting a predetermined signal-value region on image signals input from an image-acquisition element;
• calculating noise levels;
• performing noise reduction processing on input image signals based on the calculated noise levels;
• and
• storing a plurality of reference noise models determined in accordance with properties of the image-acquisition element;
• wherein:
• each reference noise model indicates a relationship between signal value and noise level, and has a characteristic such that the noise level increases with an increase in the signal value;
• the setting the predetermined signal-value region comprises setting a signal-value region as the predetermined signal-value region, signal values of the signal-value region being at or below a threshold from among a plurality of thresholds determined in association with the image-capturing modes, when the image-capturing mode selected by the selecting is a specific image-capturing mode;
• the calculating the noise levels comprises calculating (i) a noise level of a signal-value region other than the predetermined signal-value region, based on a reference noise model, and (ii) a noise level of the predetermined signal-value region, based on an applied noise model, the applied noise model being modified so that the noise level of the predetermined signal-value region is higher than the noise level of the reference noise model which corresponds to the image-capturing mode selected by the selecting, when the predetermined signal-value region is set by the setting;
• and
• the calculating the noise levels comprises calculating a noise level of an entire region of the input image signals based on the reference noise model, when the predetermined signal-value region is not set by the setting.