Quantization is an essential step which leads to compression in discrete cosine transform (DCT) domain. In this paper, we show how a statistically non-optimal uniform quantizer can be improved by employing an efficient reconstruction method. For this purpose, we estimate the probability distribution function (PDF) of original DCT coefficients in a decoder. By applying the estimated PDF into the reconstruction process, the dequantization distortion can be reduced. The proposed method can be used practically in any applications where uniform quantizers are used. In particular, it can be used for the quantization scheme of the JPEG and MPEG coding standards.

Digital watermarking schemes have been discussed to solve the problem associated with copyright enforcement. Previously, we proposed a method using inter-block correlation of DCT coefficients. It has the features that the embedded watermark can be extracted without the original image nor the parameters used in embedding process and that the amount of modification, the strength of embedded watermark, depends on the local feature of an image. This feature makes it difficult for pirate to predict the position in which the watermark signal is embedded. In this paper, we propose a method which can embed/extract watermark with high speed by utilizing this watermarking method for JPEG file format.

We proposed a method for embedding binary data into JPEG bitstreams and extracting embedded data from JPEG bitstreams using the standard JPEG decoder. In the proposed method, we can decode the image from JPEG bitstreams into which the binary data is embedded first using the traditional standard JPEG decoder, and then we can extract the embedded binary data perfectly by the post-processing from the decoded JPEG image. For the post-processing, we use only the decoded image data to extract the embedded binary data. Namely, we do not need any kind of particular parameters, which are used for JPEG decoding, such as quantization table value. Thus, we can use the traditional standard JPEG decoder for the pre-processing of extracting binary data. Furthermore, we address the effect of the calculation bit accuracy of discrete cosine transform (DCT) and inverse discrete cosine transform (IDCT) for extracting embedded binary data perfectly as post-processing. Simulations using extracting embedded binary data as post-processing are presented to quantify some performance factors concerned. And we confirmed that the proposed method could be of practical use.

A new lossless scalable coding based on a lossless wavelet transform (LWT) and a lossless multi-channel prediction (LMP) is proposed. A rough image can be expanded from a part of the bit stream for the use of progressive transmission. The LMP, a non-separable 2D filter bank, is optimized for an arbitrary input image signal so that remaining correlation of the band signals of the LWT can be utilized. Filter coefficients are optimized for each of input images under the lossless coding gain.

This paper discusses a method of designing linear phase two-channel filter banks for integer wavelet transform. We show that the designed filter banks are easily structed as the lifting form by leading relationship between designed filters and lifting structure. The designed integer wavelets are applied to image compression to verify the efficiency of our method.

A novel image improving algorithm for compressed image sequence by merging a reference image is presented. A high quality still image of the same scene is used as a reference image. The degraded images are improved by merging reference image with them. Merging amount is controlled by the resemblance between the reference image and compressed image after applying motion compensation. Experiments conducted on sequences of JPEG images are given. This technique does not need a prior knowledge of compression technique so it can be applied to other techniques as well.

Intending to contribute to constructing better multimedia network systems, we propose a new concept of image database system of which form of storage is featuring exponential or graceful oblivion and abrupt recollection like the human memory property. By virtue of this property of database storages that is realized by employing hierarchical or pyramidal image coding, the database memory and transmission costs can be significantly reduced. In this paper we will describe the details of the concept, the results of theoretical analysis based on a simplified model which reveals the effectiveness of the proposed system, the structure of an experimental prototype system and the result of an experimental image retrieval service carried out by implementing it over ATM high speed channels.