1. An image processing apparatus, comprising: an image determination unit for determining an image attribute of each pixel of an inputted image; and a screen processor for determining each pixel value of a screen processing application unit region composed of a plurality of pixels to which a threshold matrix is applied in the inputted image, wherein the screen processor carries out a screen processing by applying one threshold matrix among a plurality of threshold matrices in which applied positions of threshold values are different from each other to the plurality of pixels in the screen processing application unit region based on the determined attribute and each determined pixel value, wherein the screen processor compares each determined pixel value with each threshold value of the threshold matrix, and selects one threshold matrix from among the plurality of threshold matrices based on a comparison result to apply the selected threshold matrix to the screen processing, and wherein the screen processor selects a threshold matrix in which each threshold value is applied in an ascending order of the threshold values to the pixels in a descending order of the determined pixel values, based on the comparison result.