Patent ID: 7746501
Filing Date: 2010-06-29
Classification: H04N

Abstract:
1. A method performed in a computer for compressing image data having a gradation property, the method comprising the following steps: a first step for dividing the image data into predetermined areas, so as to determine a representative value of densities of pixels in each area; a second step for determining a density of each pixel included in the area using the representative value of the area and an interpolation rule; a third step for testing reproducibility of an image obtained on the basis of the density of each pixel determined in the second step, by using the image data and a dither pattern that is used for a pseudo gradation step performed on the image data; and a fourth step for performing an encoding process on the basis of the representative value determined in the first step for areas where the reproducibility was good in the test of the third step, wherein the representative value is a value between a minimum value K of a threshold value in the case where a threshold value of the dither pattern is larger than a density value of the image data and a maximum value J of a threshold value in the case where a threshold value of the dither pattern is smaller than a density value of the image data, Wherein each step is performed by said computer.