What is JPEG2000
Robert Han
University of Wisconsin – Madison, College of Engineering
ECE533 Final Project report
1. Introduction
In the digital image processing area, there are many different methods to
compress images. Each compression method has different aspects and different
characteristics. Among those methods, the compression standard developed by Joint
Photographic Expert Group (JPEG) is currently the most widely used in many
applications such as web applications. It is because that JPEG compression method
can compress large amount of image data into relatively small amount of data size.
About ten years later when JPEG image standard was developed, the new
compression standard for image compression was developed in year 2000 and it was
named JPEG2000. JPEG2000 is new image compression standard from JPEG and it
adapts different algorithm from previous JPEG standard. With this new algorithm,
JPEG2000 can perform much improved image compression with higher quality.
However, JPEG2000 is not yet widely used in both commercial and non-commercial
applications and most of general image application users do not know about this new
image compression standard.
Therefore, in this report, I will explore features and characteristics of
JPEG2000 compression standard. First, I will explain the basic features of JPEG2000
image standard and make technical comparisons between JPEG2000 and JPEG
technology. And introduce the Kakadu software which is developed to implement
JPEG2000 images. And implement some JPEG2000 image samples with the Kakadu
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software and demonstrate results. Finally, I will perform the actual experiments with
JPEG and JPEG2000 image and determine how JPEG2000 is improved over previous
JPEG standard.
2. Background information of JPEG2000
In digital image processing area, there was a need for a standard image
compression method to enable interoperation among applications and equipments
from different manufacturer. Therefore, the Joint Photographic Expert group (JPEG)
was established with specialists from CCITT and ISO, and developed the first
international digital image compression standard for continuous-tone images in late
1980s. Currently, JPEG images are the most widely used compressed image. In year
2000, about ten years after the JPEG standard was developed, the Joint photographic
expert group developed new standard for JPEG image with different algorithm and
this standard was named JPEG2000.
JPEG2000 is a new image-encoding standard that provides a feature set vital
to many high-end and emerging imaging applications. JPEG2000 provides high
compression with image quality superior to all existing standard encoding techniques.
This high compression and quality performance is due to the adaptation of wavelet
transforms. Wavelet transforms are mathematical formulas that represent complex
structures in the image, thereby compressing an extremely large amount of image data
into a relatively small amount of compressed data. This compression technique allows
applications to save compressed images with higher compression ratio and better
image quality as compared to any other software currently in production. And due to
the wavelet based compression algorithm, JPEG2000 image can store the image data
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in a hierarchical format which contains several stored resolutions of the image in the
same file without duplication. For this reason, a compressed with JPEG2000 standard
image can then be sent to a device in the resolution that best fits without additional
storage overhead. And the file structure of the image becomes very flexible, so that it
can be used for a variety of applications such as internet images, digital photography,
medical images, and wireless images. However, JPEG2000 images are not yet
currently widely used in current commercial or non-commercial applications.
Figure 1. JPEG2000 compression algorithm
Although JPEG and JPEG2000 standard adapt different algorithm for image
data compression, they share same basic architecture of standard. As shown in figure 2,
source image data is quantized after the forward transform. And after the quantization,
the data set is encoded through entropy encoding and transformed in to compressed
image data.
Source
Forward
image data
Transform
Quantization
Entropy
Compressed
Encoding
image data
Figure 2. Basic Architecture of standard for JPEG/JPEG2000 image compression
This basic structure is applicable to both discrete cosine transform for JPEG standard
and discrete wavelet transform for JPEG2000 standard.
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3. The KAKADU software
The Kakadu software is a complete implementation of the JPEG2000
standard, Part 1. This new image compression standard is substantially more complex
than the existing JPEG standard, both from a computational and a conceptual
perspective. The Kakadu software also provides a comprehensive implementation for
several of the most useful features from Part 2 of the JPEG2000 standard, including
general multi-component transforms and arbitrary wavelet transform kernels.
The Kakadu software framework provides a solid foundation for a range of
commercial and non-commercial applications. The objective of Kakadu software is to
encourage the widespread adoption of JPEG2000 image standard by making a
consistent and efficient implementation of the standard widely available for both
academic and commercial applications.
The Kakadu software has been written specifically with a variety of different
types of applications in mind. These include:

Image and volume compression

Image and volume decompression/rendering

Trans-coding between related representations

Interactive rendering applications

Client-server applications

Digital Cinema applications
For the experimental purpose, I actually performed implementations of JPEG2000
images with some basic functions of the Kakadu software and demonstrated results in
this report.
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Figure 3. Basic figure of the Kakadu software
4. Kakadu implementation examples
JPEG2000 image may contain multiple embedded image structure, which
form the foundation of quality progressive remote image browsing. By default, local
files are opened at maximum quality in the Kakadu software. With the Kakadu
software, it is possible to reduce the number of layers of the image and to compare the
visual quality associated with each compressed quality layer.
Original Image
JPEG2000 Image
JPEG2000 Image
With 5 layers
With 1 layer
Figure 4. The Kakadu software implementation – Layer reducing examples
The format of the original image is in the png format which stands for Portable
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Network Graphics. The png compression method is known to be able to compress the
image without losing the image information. As seen in figure 4, JPEG2000 image
with all of its layers shows almost as same quality as the quality of original png image.
And after reducing its layer to one, then the quality of the image decreased
dramatically.
Along with layer reducing function, the Kakadu software supports single
component mode which can extract only one compositing layer of the JPEG2000
image.
Original Image
First component of image
Last component of image
Figure 5. The Kakadu software implementation – Extracting image component examples
Each Image components typically correspond to color channels such as red, green,
blue, or luminance, and chrominance channels, and represented as gray scale image.
An image component may also correspond to alpha blending channels, palette indices,
or anything else.
Since JPEG2000 image is composed with layered code-streams, users can
add metadata to edit the JPEG2000 image of the selected region. When the codestream is added to the image, then the image is edited and the visual differences after
editing are shown in figure 6.
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Adding code-stream
Adding code-stream
Adding code-stream
Figure 6. The Kakadu software implementation – Adding metadata examples
Just as other imaging software applications, the Kakadu software also has
basic image editing functions such as flipping, cropping, rotating, and zooming. These
operations for JPEG2000 images are not yet supported in most of commercial image
editing applications. Therefore, the Kakadu software is currently most suitable
application in editing JPEG2000 images.
Original Image
Horizontal flip
Vertical flip
Figure 7. The Kakadu software implementation – Flipping examples
Currently the Kakadu software is the most suitable and widely used imaging software
for JPEG2000 images. And the Kakadu is freely distributed to people who want to
have experiments with JPEG2000 images.
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5. Visual performance comparison between JPEG and JPEG2000
JPEG2000 standard was developed in order to improve previous JPEG
standard. With the adaptation of Discrete Wavelet Transform (DWT) algorithm, much
more image data can be compressed into much smaller data set with improved image
quality. However, this quality improvement is often very hard to see with human
visual system even though there is an actual improvement in image quality. Therefore,
in this report, I focused on demonstration of the quality difference between JPEG
image and JPEG2000 image which can be distinguishable with human visual system
respect to different compression ratio. I used four different kinds of image in the
experiments, regular color image, gray scale image, scanned document image, and
computer generated animation image. Each type of image was generated from original
png format image. Therefore, file size of compressed image could be the comparison
criteria of two compression standard other than visual image quality difference.
The regular color image used in the experiment was 439kb png format image.
I transformed this image into three JPEG2000 and three JPEG images.
JPEG2000, 10:1 76.8kb
JPEG 100% quality 247kb
JPEG2000, 50:1 15.4kb
JPEG2000, 100:1 7.78kb
JPEG 50% quality 34.7kb
JPEG 0% quality
Figure 8. Visual performance comparison – Color image
23.4kb
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As mentioned above, the actual quality difference in regular size images were very
difficult to distinguish with human eye. Therefore, I enlarged the certain region of the
images in order to make it easier to compare the actual quality differences of images.
Regularly, the file sizes of JPEG2000 images were much smaller than JPEG images
respect to similar compression ratio. Especially in 10:1 compression ratio, the file size
of JPEG2000 image was four times smaller than JPEG image. And the file size of the
most compressed JPEG image was even larger than the file size of the JPEG2000
image with 50:1 compression ratio which has better image quality.
The gray scale image used in the experiment was png format image with
168kb file size. Generated images were compressed as same ratio as previous regular
color image experiment.
Jpeg2000, 100:1
File size : 4.54kb
Jpeg2000, 50:1
File size : 24.5kb
Jpeg2000, 10:1
File size : 156kb
Jpeg, 0% quality
File size : 41.7kb
Jpeg, 50% quality
File size : 79.1kb
Jpeg, 100% quality
File size : 193kb
Figure 9. Visual performance comparison – Gray scale image
For the gray scale image, the noticeable result was that the image sizes for the
compressed images with best quality were not much reduced from the original image
for both JPEG2000 and JPEG image. The size of JPEG image was even larger than
the size original image. And, unlike the color image, the quality difference was not
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easy to distinguish even in the enlarged images. That is probably because the gray
scale images do not contain as much data information as regular color images.
Therefore, it might be recommended to use highly compressed gray scale image in
some applications if smaller file size of the image is preferable, since the file size
decreased dramatically with higher compression ratio with relatively small changes in
image quality.
One of most dramatic improvement of JPEG2000 standard over JPEG
standard could be found in scanned document. JPEG2000 image could represent
much more details in characters in this experiment, and I think this improvement can
be the most useful application of JPEG2000 standard.
JPEG2000 format
JPEG format
Figure 10. Visual performance comparison – Scanned document
As seen in figure 10, JPEG2000 image represented the details of each character much
more correctly than JPEG image. And as with all other experiments, the file size of
the scanned document was also smaller in JPEG2000 image. Therefore, with this
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improvement, JPEG2000 image standard can be used in applications such as fax
machine and wireless document transfer with higher quality and reduced transmission
cost.
For the experiment in cartoon image, I actually created a png format cartoon
image with the Adobe Photoshop and converted this image into three JPEG2000
images and three JPEG images.
Jpeg2000, 100:1
File size : 54.6kb
Jpeg2000, 50:1
File size : 114kb
Jpeg2000, 10:1
File size : 243kb
Jpeg, 0% quality
File size : 77.8kb
Jpeg, 50% quality
File size : 109kb
Jpeg, 100% quality
File size : 278kb
Figure 11. Visual performance comparison – Cartoon image
JPEG2000 image
JPEG image
Figure 12. Visual performance comparison – Cartoon image
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In this experiment, the result was somewhat different from previous experiments.
JPEG2000 images still showed better performance than JPEG images, but the file size
of the compressed images were larger than the original png format image in certain
compression ratio. JPEG2000 images represented perfect color information of the
original image regardless of the compression ratio, but a JPEG image with the highest
compression ratio failed to represent the exact color information of the original image.
As seen in the figure 12, the green color of the JPEG image was darker than the
original image and the JPEG2000 image. The representation of details of the image
was also poor in JPEG image than JPEG2000 image.
6. Conclusion
JPEG2000 standard showed improved performance over JPEG standard
throughout my experiment. It reduced the image size while enhanced the image
quality. Then why JPEG2000 images are not currently widely used in practical
applications? Since JPEG2000 standard has past only about five years from its
development and most of applications in current digital image processing area were
developed to apply the compression standard that were developed earlier than
JPEG2000 standard. And those standards are already adapted in various applications.
However, there is more public attention to JPEG2000 in these days, and many
application developers began to apply JPEG2000 standard to their application
software. Therefore, it is clear that JPEG2000 standard will become the one of most
widely used image compression standard in very near future, and with this new
powerful standard the area of digital image processing will generate more powerful
applications to the practical usage.
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7. Reference
1. Requirements ad hoc group, JPEG2000 requirements and profiles version 6.3, July
2000
2. ISO/IEC JTC1/SC29/WG1, Call for contributions for JPEG2000 image coding
system, March 1997
3. Takahiro Fukuhara, David Singer, Motion JPEG2000 Final Committee draft,
March 2001
4. JPEG2000 Part VI FCD, JPEG2000 Image coding system: Compound image file
format, November 2001
5. http://www.jpeg.org , The official JPEG committee homepage
6. David Taubman , User Manual for Kakadu’s “kdu_show” Tool, March 2005