An image processing method for a fluorescence reaction region of teeth, comprising: emitting blue light from a light source to illuminate the teeth in a mouth, so that the teeth generate fluorescence; capturing a first teeth image of the teeth by an image capturing unit; separating the first teeth image into a first red-value image, a first green-value image, and a first blue-value image by a processing unit; characterized in that the method further comprises transforming the first red value image into a second red value image by the processing unit using a pixel value transforming function, wherein in the step of transforming the first red-value image into the second red-value image, further decreasing the red pixel value of the first red-value image that is smaller than a predetermined value, and increasing the red pixel value that is greater than the predetermined value, wherein an upper limit of the increased red pixel value of the first red-value image is 2 n -1, and a lower limit of the decreased red pixel value of the first red-value image is 0, where n is a positive integer; and combining the second red-value image, the first green-value image, and the first blue-value image into a second teeth image by the processing unit, wherein the step of reducing the red pixel value that is smaller than the predetermined value is to subtract a first transformed red pixel value from the red pixel value that is smaller than the predetermined value, wherein the first transformed red pixel value is obtained by substituting the red pixel value that is smaller than the predetermined value into a first elliptic function; and wherein the step of increasing the red pixel value that is greater than the predetermined value is to add a second transformed red pixel value to the red pixel value that is greater than the predetermined value plus, wherein the second transformed red pixel value is obtained by substituting the red pixel value that is greater than the predetermined value into a second elliptic function. emitting blue light from a light source to illuminate the teeth in a mouth, so that the teeth generate fluorescence; capturing a first teeth image of the teeth by an image capturing unit; separating the first teeth image into a first red-value image, a first green-value image, and a first blue-value image by a processing unit; characterized in that the method further comprises transforming the first red value image into a second red value image by the processing unit using a pixel value transforming function, wherein in the step of transforming the first red-value image into the second red-value image, further decreasing the red pixel value of the first red-value image that is smaller than a predetermined value, and increasing the red pixel value that is greater than the predetermined value, wherein an upper limit of the increased red pixel value of the first red-value image is 2 n -1, and a lower limit of the decreased red pixel value of the first red-value image is 0, where n is a positive integer; and combining the second red-value image, the first green-value image, and the first blue-value image into a second teeth image by the processing unit, wherein the step of reducing the red pixel value that is smaller than the predetermined value is to subtract a first transformed red pixel value from the red pixel value that is smaller than the predetermined value, wherein the first transformed red pixel value is obtained by substituting the red pixel value that is smaller than the predetermined value into a first elliptic function; and wherein the step of increasing the red pixel value that is greater than the predetermined value is to add a second transformed red pixel value to the red pixel value that is greater than the predetermined value plus, wherein the second transformed red pixel value is obtained by substituting the red pixel value that is greater than the predetermined value into a second elliptic function.