Patent ID: 8189936

Claim:
An image processing apparatus comprising: a feature index calculator configured to calculate feature indices of each partial image area of an inputted image; a criteria setter configured to set selection criteria based on the relation between the feature indices calculated by the feature index calculator and a cumulative number of partial image areas; an intensity selector configured to select, on the basis of the selection criteria set by the criteria setter, one of a plurality of quantization intensities for each partial image area of the inputted image; a quantizer configured to quantize image information on each partial image area with the quantization intensity selected by the intensity selector; and a processor programmed to control at least one of the feature index calculator, the criteria setter, the intensity selector and the quantizer, wherein the quantizer comprises: a one-tone grader configured to replace each pixel value of a plurality of pixel values for the partial image area with an average pixel value of the partial image area; and a two-tone grader configured to identify a maximum pixel value and a minimum pixel value of the partial image area, classify each of the pixel values in the partial image area having values above an average of the maximum pixel value and the minimum pixel value into a first group, classify each of the pixel values in the partial image area having values below the average of the maximum pixel value and the minimum pixel value into a second group, replace each pixel in the first group with an average pixel value of the first group, and replace each pixel in the second group with an average pixel value of the second group.