Optical image detector and method for controlling illumination of the same

An optical image detector comprising:

• a light source for controlling illumination in response to an illumination control signal and irradiating light having the controlled illumination onto a subject;
• an image sensor for generating and outputting an photo-current proportional to a quantity of light reflected from the subject;
• an electronic shutter for accumulating the photo-current transmitted from the image sensor in response to a shutter control signal when a shutter-on time arrives and generating and outputting image signals corresponding to the accumulated photo-current;
• and
• an image processor for calculating an average value of the image signals, comparing the calculated average value of the image signals with at least one of maximum and minimum values of the average value, and generating and outputting the illumination control signal and the shutter control signal for maintaining former illumination and shutter-on time when the calculated average value of the image signals is less than the maximum value of the average values and greater than the minimum value of the average values, decreasing the former illumination and shutter-on time when the calculated average value of the image signals is greater than the maximum value of the average value, and increasing the former illumination and shutter-on time when the calculated average value of the image signals is less than the minimum value of the average value;
• wherein the illumination control signal is a pulse signal whose width is modulated according to the compared results.

A method for controlling illumination at an optical image detector, the method comprising the steps of:

• calculating a shutter-on time using image signals and comparing the calculated shutter-on time with at least one of preset maximum and minimum shutter-on times;
• maintaining a present illumination of a light source when the calculated shutter-on time is less than the maximum shutter-on time and greater than the minimum shutter-on time;
• increasing the present illumination of the light source when the calculated shutter-on time is greater than the maximum shutter-on time;
• and
• decreasing the present illumination of the light source when the calculated shutter-on time is less than the minimum shutter-on time.

A method for controlling illumination at an optical image detector, the method comprising the steps of:

• calculating an average value of image signals and comparing the calculated average value of image signals with at least one of preset maximum and minimum values of the average value of the image signals;
• maintaining former illumination and shutter on time when the calculated average value of the image signals is less than the maximum value and greater than the minimum value;
• decreasing the former illumination and shutter on time when the calculated average value of the image signals is greater than the maximum value;
• and
• increasing the former illumination and shutter on time when the calculated average value of the image signals is less than the minimum value.