1. A method of gathering statistics of gray distribution of an image in an image processing device, comprising: determining gray information of a plurality of data of an input image by a comparing unit in the image processing device, wherein each piece of gray information corresponds to a count value; sequentially adding a fixed value to the corresponding count value according to the gray information of each of the data by a plurality of counters in a count unit in the image processing device; and resetting the count value and updating the gray distribution of the image when the count value exceeds a predetermined value by a data allotment unit in the image processing device.