1. An image processing apparatus, comprising: a storage unit, being configured to store an image and a piece of intensity statistical information of the image, wherein the piece of intensity statistical information records that the image has a first number of pixels having a first intensity value, a second number of pixels having a second intensity value, and a third number of pixels having a third intensity value, the first intensity value is smaller than the second intensity value, the third intensity value is greater than the second intensity value, and the second number is greater than zero; and a micro-processing unit, being configured to calculate a centralization degree of the second intensity value in the image according to the first number, the second number, and the third number, wherein the micro-processing unit determines that the centralization degree is greater than a threshold, then calculates an adjustment value for a pixel having the second intensity value in the image according to the second intensity value and an intensity value of at least one neighboring pixel of the pixel, and adjusts the second intensity value of the pixel to a fourth intensity value according to the adjustment value.