II. Background Information

1.  Introduction

2.  Background Information

3.  Comparison between JPEG and JPEG 2000

4.  How does JPEG 2000 work?

5.  Applications of JPEG 2000

6.  Conclusion

7.  References

 


 

            Digital images are compressed using a compression standard to reduce the amount of memory each image uses.  To illustrate the need for compression, consider a color picture measuring three inches by four inches that one wants to digitize at a resolution of 500 dots per inch (dpi), a common resolution.  Resolution is a measure of the quality of the image; as the resolution increases, the quality of the image increases.  Since the image is 12 in2, and each in2 has 500x500=250,000 dots (pixels), the image will contain a total of 3,000,000 pixels.  Each pixel requires 3 bytes of data (24 bits) in order to store the different colors in the picture.  Therefore, the image would require 9,000,000 bytes or about 9 MB of memory.  In comparison, a floppy disk only contains about 1.4 MB; this single image would require seven floppy disks.  In order to store many digital images without compression, a huge amount of memory would be needed.  Also, these images would require large transfer times when sent electronically via modem or some other means, especially for those with slow connection speeds. 

            Data compression was developed to make storing and transmitting digital images much more practical.  Compression techniques today enable images to be compressed to several times less than their original size, allowing for easier storage and transmission.  There are two main types of data compression: lossy and lossless.  In lossy compression, some of the data is lost during the compression process, resulting in a final image that is of a lower quality than the original image.  Very high compression rates can be achieved with lossy compression.  In contrast, lossless compression regains the original image after compression so that the quality of the image is not sacrificed.  However, lossless compression rates are lower than that obtained by lossy compression.  Various applications may require one type of compression or the other.

Currently, the most common form of image compression is known as JPEG.  This standard was developed by the Joint Photographic Expert Group (hence the name JPEG) in the late 1980’s, and since then has been the most successful and widely used compression technique.  About 80% of all web images today are JPEG encoded7.  However, in 1997 the JPEG committee decided that the needs and requirements of imagery applications in today’s world point to the need for a new standard.  At this time JPEG 2000 began to be developed.

            The JPEG 2000 standard has been mostly completed, and some software is currently available which utilizes the JPEG 2000 technology.  Over the next several years, JPEG 2000 will likely become the standard used in most image compression because of its many features and advantages over other types of encoding.  However, most popular software does not currently support JPEG 2000 files, which have the extension “.j2k”.  For example, neither Microsoft Internet Explorer nor Netscape Navigator, two popular Internet browsers, currently support JPEG 2000 file formats.  As JPEG 2000 becomes more widely known and its superior features recognized, it will take its place as the main player in the image compression industry.

 

 

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