Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1997-08-28
2001-05-01
Garber, Wendy (Department: 2715)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C348S405100
Reexamination Certificate
active
06226445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a device which compresses still image data in accordance with a JPEG (Joint Photographic Expert Group) algorithm and records the compressed image data in a recording medium and, also, to a device which reads the compressed image data from the recording medium and expands the compressed image data to reproduce the still image.
2. Description of the Related Art
A standard algorithm, for the encoding of high resolution images and the transfer of that information through telecommunication transmission channels, has been recommended by the JPEG. In order to enable a large-scale data compression, the baseline process of the JPEG algorithm breaks down the original image data into components on a spatial frequency axis using a two-dimensional DCT process. Thereafter, the data expressed on the spatial frequency axis is quantized by using a quantization table. The quantized data is then encoded using a Huffman table.
The encoded (or compressed) image data can be expanded by carrying out a process, which is the inverse of the compression process described above, so that the original image data can be reproduced. Namely, the compressed image data is decoded, subjected to a dequantization process, using a quantization table, and finally, subjected to a two dimensional inverse discrete transformation, so that the original image data is reproduced.
At the moment, however, even if there is a copyright on the original image, for example, the compressed image data of the original image, which is recorded in the recording medium, is still, fully, reproduced if an image expansion is carried out using a conventional image expansion device.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image compression device which can compress and record, in a recording medium, the original image data, so that, when the original image should not be reproduced in a coherent form from the compressed image data recorded in the recording medium, an image having a lower quality than the original image is recreated.
According to the present invention, there is provided an image compression device, by which compressed image data is recorded in a recording medium, having a compressed image data recording area, in which said compressed image data is stored, and a first table recording area, which is accessed in a usual expansion process. The image compression device comprises a two-dimensional discrete cosine transformation (two-dimensional DCT) processor, a quantization processor, an encoding processor, a compressed image recording processor and a first table recording processor.
The two-dimensional DCT processor processes original image data to obtain a DCT coefficient for each spatial frequency. The quantization processor quantizes the DCT coefficients by a normal mode quantization table, which is used in the usual expansion process, to obtain quantized DCT coefficients. The encoding processor encodes the quantized DCT coefficients to obtain compressed image data. The compressed image recording processor records the compressed image data in the compressed image data recording area. The first table recording processor records a security mode quantization table, which is used in a security mode for reproducing an image having a lower quality than the original image, in the first table recording area.
Another object of the present invention is to provide an image expansion device which can cancel the security mode, in which an image having a lower quality than the original image is reproduced from the compressed image data recorded by the image compression device, so that an image having a normal quality is reproduced.
According to the present invention, there is provided an image expansion device which reads and expands compressed image data from a recording medium, the recording medium having a first table recording area, in which a security mode quantization table, which is used in a security mode for reproducing an image having a lower quality than the original image, is stored, a second table recording area, in which a normal mode quantization table, which is used in a usual expansion process, is stored and an information recording area, in which security information is stored. The device comprises a decoding processor, a table selecting processor, a dequantization processor and a two dimensional inverse discrete cosine transformation (two-dimensional IDCT) processor.
The decoding processor decodes the compressed image data to obtain quantized DCT coefficients. The table selecting processor selects the security mode quantization table from the security mode quantization table and the normal mode quantization table, if a password, corresponding to the security information, is not inputted to the image expansion device. The dequantization processor dequantizes the quantized DCT coefficients, using the quantization tables selected by the table selecting processor, to obtain DCT coefficients. The two-dimensional IDCT processor processes the DCT coefficients to reproduce original image data corresponding to the compressed image data.
REFERENCES:
patent: 5068744 (1991-11-01), Ito
patent: 5497246 (1996-03-01), Abe
patent: 5666209 (1997-09-01), Abe
patent: 5802210 (1998-09-01), Kurata et al.
patent: 7135568 (1994-11-01), None
Asahi Kogaku Kogyo Kabushiki Kaisha
Garber Wendy
Greenblum & Bernstein P.L.C.
Onuaku Christopher
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