Image analysis – Image compression or coding
Reexamination Certificate
1998-10-02
2004-02-24
Tran, Phuoc (Department: 2621)
Image analysis
Image compression or coding
C382S250000, C382S248000, C382S251000, C382S244000, C382S246000
Reexamination Certificate
active
06697525
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The invention is related generally to a system for building data compression devices and more particularly, to a system for building a data compression device for coding of images.
B. Description of the Prior Art
With the advent of high speed low cost microprocessors, there has been a rapid growth in the development of digital. communication devices for the transmission of print, voice and video. The rapid growth and demand for such devices has quickly out paced the ability of the present communications hardware infrastructure to provide communications bandwidth to meet the digital communication demands. In the field of digital communications systems, the amount of data capable of being transmitted through a given media over time is referred to as bandwidth.
One solution to expand available bandwidth is through the implementation of data compression techniques to reduce the amount of digital data needed to represent the information transmitted. Digital compression techniques currently represent the most common solution for increasing the throughput of digital communications hardware. Given the variations in hardware technology and digital computer platforms that exist in various industries and internationally, standards have been established to provide certain data compression techniques that may be implemented universally.
In field of image information systems where images or pictures are represented in a digital form by data, numerous commercially accepted standards have been developed for compressing such digital images. One such standard was developed by the Joint Photographic Experts Group (JPEG), an international body formed to establish an international standard for the compression of grayscale and color images. This compression standard has come to be known as the JPEG standard in which digital images are compressed through an encoder and represented in a compressed form known as JPEG format. Images stored in the JPEG format have a file size which is significantly smaller than the file size of the same digital image stored in an uncompressed form. The JPEG standard was recommended by the International Telegraph and Telephone Consultative Committee (CCITT) as recommendation T.81 on Sep. 18, 1992 and was published by the International Standards Organization and International Electrotechnical Commission (ISO/IEC) as standard ISO 10918:1 entitled, “INFORMATION TECHNOLOGY—DIGITAL COMPRESSION AND CODING OF CONTINUOUS-TONE STILL IMAGES—REQUIREMENTS AND GUIDELINES ITU-T Rec. T.81 | ISO 10918:1”.
The JPEG standard actually comprises two classes of compression processes, namely, lossy and lossless compression techniques. In lossy compression, substantial compression is achieved while some loss of the image data occurs when the image is subsequently decompressed. However, such losses in image quality may be so minimal that they are generally not considered discernable when viewed by the naked eye. Those processes that are based upon the discrete cosine transform (DCT) are considered lossy. An encoder
20
(
FIG. 1
) using lossy compression generally includes a DCT engine
21
, a quantizer
22
and an entropy coder
26
. These functions are defined in the JPEG standard. In the second class, lossless compression is achieved using an alternative technique to DCT in which no loss in image quality occurs when the image is decompressed. However, lossless compression does not achieve compression ratios as large as lossy compression. Thus, digital images when compressed under a lossless compression will have a greater file size and will take more time to transfer through a communications line than the same image when compressed over the lossy standard. Except in fields where image accuracy is desired, such as, in medical imaging where any change in the representation of an image containing human tissue may affect the diagnosis of an illness by a medical professional, most image applications can utilize the lossy compression standard for digital transmission.
In some real time applications, such as, transmitting digital images between facsimile machines, the JPEG standard for compressing digital images is more than capable of simultaneously compressing the data in conjunction with the transmission of the images. This is due to the fact that the narrow bandwidth of conventional analog phone lines for digital data transmission is inherently slower than other digital communications methods and provides more than adequate time for the simultaneous JPEG compression processes to occur in real time. However, in other hardware communications systems that have improved digital throughput or have been designed for digital transmission, such as computer buses and networks as well as digital television systems, the availability and need for even greater throughput and speed is in demand. In communications systems such as digital television transmission, it will be realized by those skilled in the art that the Moving Pictures Experts Group (MPEG) standard for compressing and transmitting moving picture images which is based upon the JPEG standard is also limited by this time constraint. Moreover, faster methods are needed for compressing and storing JPEG images prior to when image data is transferred, for example, to personal computers (PCs) from peripheral devices or for use with the storing of images in digital cameras and the like. When conventional JPEG compression processes are used in such environments in real time, the compression time needed to convert digital images into the JPEG standard using conventional JPEG compression methods can slow down the overall transmission rate of such high speed communications systems.
Thus, it may be appreciated that the time saved in transferring such compressed files has been reduced in part by the time needed by conventional compression techniques to encode a digital image into the JPEG file format. Such time constraints limit the effectiveness of the JPEG file format in applications that require the compression and transmission to occur quickly, simultaneously and/or in real time.
Thus, the need exists for encoding and decoding devices and processes that can convert digital images between an uncompressed and compressed file standard, such as JPEG or MPEG, in real time and without delay while operating with high speed communications systems.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image compression device and process that improves the conversion rates for encoding digital images between an uncompressed and compressed data standard.
It is another object of the present invention to provide an image compression device and process that improves conversion rates for digital transmission of compressed images using a lossy compression process.
It is yet another object of the present invention to provide an image compression device and process that reduces the time required for the discrete cosine transform (DCT) in the lossy compression process used to produce a compressed image under the JPEG standard.
An advantage of the present invention is the ability to provide a good quality image from a lossy compression process having improved compression rates.
Another advantage of the present invention is improved timing by eliminating DCT cycles not needed, but performed during conventional lossy compression.
A further advantage of the present invention is that it can be manufactured on an economical basis and has portability between various communication platforms.
A further advantage of the present invention is the capability to discriminate between types of uncompressed digital image data and to provide a lossy coding stage for a first set of image data and to perform conventional DCT on the second set of image data, thereby eliminating the need for use of the DCT on the first set of data.
It is a feature of the present invention to provide a compression device and process that substantially improves the transmission of data across communications link and
Alavi Amir
Eitan, Pearl, Latzer & Cohen Zedek LLP.
Parthusceva Ltd.
Tran Phuoc
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