Patent ID: 7532762

Claim:
An image coding/decoding method in which an image coding apparatus sends coded information which is obtained by coding an original image to an image decoding apparatus and said image decoding apparatus decodes said coded information to obtain a reproduced image, said method comprising the steps of: extracting edge information which is binary information representing an edge part of said original image; obtaining density information of an edge unsharpened image from said original image by unsharpening said edge part using said edge information, unsharpening the edge part includes obtaining density information x′ of a pixel of said edge part of said edge unsharpened image according to a first equation x′=(1−λ)x+λC, wherein λ is a positive constant, x is density information of said pixel of said original image, and C is surrounding density information representing density state of a surrounding region of said pixel; obtaining coded edge information by coding said edge information according to a first coding algorithm; obtaining coded density information by coding said density information of said edge unsharpened image according to a second coding algorithm; sending said coded edge information and said coded density information as said coded information to said image decoding apparatus; and said image decoding apparatus performing the steps of: obtaining said edge information by decoding said coded edge information according to a first decoding algorithm corresponding to said first coding algorithm; obtaining said density information of said edge unsharpened image by decoding said coded density information according to a second decoding algorithm corresponding to said second coding algorithm; obtaining said reproduced image from said density information of said edge unsharpened image by restoring said edge part of said edge unsharpened image by using said edge information and using a predetermined equation according to a steepest-descent method, said predetermined equation being defined on the basis of a relationship between said density information x′ formulated by said first equation and restored density information; wherein said second coding algorithm and said second decoding algorithm are based on a standard coding method using a discrete cosine transform, and wherein all the above steps are performed using one or more processors.