Patent ID: 8254672
Filing Date: 2012-08-28
Classification: H04N

Abstract:
1. An image compressing method for compressing a color image, comprising steps of: generating, on the basis of the color image, a foreground mask representing pixels of a foreground corresponding to a text and/or a line drawing included in the color image; generating, on the basis of the generated foreground mask and the color image, a foreground layer by replacing color information of respective pixels of the foreground with N (wherein N is a natural number) kinds of foreground identifiers for identifying color information included in the foreground and by replacing color information of each pixel of a background with a background identifier indicating the background; generating a table in which color information included in the foreground, a foreground identifier for identifying the color information and the number of pixels having the foreground identifier are correlated and stored with one another; reducing, when the number of kinds of foreground identifiers is to be reduced to be smaller than N, the number of kinds of foreground identifiers to M (wherein M is a natural number smaller than N) by replacing one kind or a plurality of kinds of foreground identifiers included in the table with the background identifier on the basis of the numbers of pixels stored in the table; correcting, on the basis of the table in which the foreground identifier has been replaced with the background identifier, the foreground layer to a corrected foreground layer by replacing the foreground identifier included in the generated foreground layer with the background identifier; generating, on the basis of the corrected foreground layer, M binary images, each of which is obtained by binarizing a pixel value of one kind of foreground identifier and pixel values of the other kinds of foreground identifiers, respectively corresponding to the M kinds of foreground identifiers; performing lossless compression on the generated M binary images; generating a background layer on the basis of the corrected foreground layer and the color image; and performing lossy compression on the generated background layer.