Background subtraction method, image module, and optical fingerprint identification system

An image module, comprising:

• an image capturing unit, configured to capture at least one first image of a first object, at least one second image of a second object and a target image, wherein the first object has a uniform color and has a first reflectivity, the second object has a uniform color and has a second reflectivity, and the first reflectivity and the second reflectivity are different;
• a background subtraction unit, configured to perform the following steps:
• obtaining a first background image according to the at least one first image, and obtaining a second background image according to the at least one second image;
• calculating a plurality of relative values of the first background image relative to the second background image to obtain a mask image;
• subtracting the second background image from the target image to obtain a first background-removed image;
• and
• calculating and outputting a second background-removed image according to the first background image, the second background image, the first background-removed image and the mask image.

An optical fingerprint identification system, disposed in an electronic device, wherein the optical fingerprint identification system comprises:

• a fingerprint identification module;
• and
• an image module, disposed under a touch screen of the electronic device and coupled to the fingerprint identification module, wherein the image module is an image module comprises:
• an image capturing unit, configured to capture at least one first image of a first object, at least one second image of a second object and a target image, wherein the first object has a uniform color and has a first reflectivity, the second object has a uniform color and has a second reflectivity, and the first reflectivity and the second reflectivity are different;
• a background subtraction unit, configured to obtaining a first background image and a second background image according to the at least one first image and the at least one second image respectively, calculate a plurality of relative values of the first background image relative to the second background image to obtain a mask image, subtract the second background image from the target image to obtain a first background-removed image, and calculate a second background-removed image according to the first background image, the second background image, the first background-removed image and the mask image;
• wherein the fingerprint identification module receives the second background-removed image to implement fingerprint identification according to the second background-removed image.