Patent ID: 7558441

Claim:
A decoding method of decoding encoded image data which has been hierarchically encoded in advance by a discrete wavelet transform method, comprising: using a processor to perform the following: determining a size of an image to be output; judging a minimum number of layer/layers of hierarchy needed to obtain a decoded image of size equal to or exceed the determined size; determining whether the minimum number of layer/layers of hierarchy corresponds to all the layers of hierarchy of the encoded image data; decoding, if the determination proves true, all the layers of hierarchy of the encoded image data, and otherwise decoding the encoded image data up to a layer of hierarchy which is one or more layers higher than the minimum number of layer/layers of hierarchy; and reducing the size of the decoded image to the determined size, wherein, in said judging step, the number n satisfies a condition of 1/2 n >S out/ S in>1/2 (n+1) where Sout is an output image size, and Sin is the input image size, n is an integer equal to or greater than 1, and is judged as the minimum number of layer/layers of hierarchy, and in said decoding step, image data is decoded up to a hierarchy until an input-output ratio of image size becomes 1/2 (n−1) .