An image processing circuit and method thereof for enhancing text displaying of an image are provided. The image processing circuit performs the method. Firstly, at least a first illumination area and at least a second illumination, which is located adjacent to the first illumination area in the image are defined according to luminance values of a plurality of pixels of the image. Next, a luminance regulation value of at least one of the pixels in the first illumination area is calculated, and the luminance value of the corresponding pixel in the first illumination area is adjusted according to the luminance regulation value. During processing of the image, the luminance values of all of the pixels in the second illumination area are restricted from any adjustment.