Biometric image processing apparatus, biometric image acquisition method, and biometric authentication program

An image acquisition method that acquires an image picked up with the optimum exposure value with respect to an object to be picked up, the method comprising the steps of:

• a first step of setting up exposure values of a plurality of stages for image pickup element;
• a second step of extracting the contour of an object in image signals output from the image pickup element;
• a third step of generating first histograms for image signals before extraction and second histograms for image signals after extraction for the respective stages with the broadening of the distribution in the histograms set constant;
• a fourth step of calculating the amount of change between the kurtosis of the first histograms and the kurtosis of the second histograms for the respective stages;
• and
• a fifth step of selecting, of the image signals after the extraction corresponding to the respective stages, an image signal after the extraction corresponding to one of the stages in which the amount of change is larger than a predetermined amount as an optimum image for an object to be picked up.

A non-transitory memory comprising a program comprising the steps of:

• setting up exposure values of a plurality of stages for image pickup element;
• making control element for controlling the image pickup element extract the contour of an object in image signals output from the image pickup element;
• making the control element generate first histograms for image signals before extraction and second histograms for image signals after extraction for the respective stages with the broadening of the distribution in the histograms set constant;
• making the control element calculate the amount of change between the kurtosis of the first histograms and the kurtosis of the second histograms for the respective stages;
• and
• making the control element select, of the image signals after the extraction corresponding to the respective stages, an image signal after the extraction corresponding to one of the stages in which the amount of change is larger than a predetermined amount as an optimum image for an object to be picked up.

An image processing apparatus comprising:

• a processor, and
• a memory coupled to the processor,
• wherein the memory is encoded with one or more instructions that, when executed by the processor, define
• a setup unit that sets up exposure values of a plurality of stages for the image pickup unit;
• an extraction unit that extracts the contour of an object in image signals output from the image pickup unit;
• a generation unit that generates first histograms for image signals before extraction and second histograms for image signals after extraction for the respective stages with the broadening of the distribution in the histograms set constant;
• a calculation unit that calculates the amount of change between the kurtosis of the first histograms and the kurtosis of the second histograms for the respective stages;
• and
• a selection unit that selects, of the image signals after the extraction corresponding to the respective stages, an image signal after the extraction corresponding to one of the stages in which the amount of change is larger than a predetermined amount as an optimum image for an object to be picked up.