volume38-number3(1).pdf

A forum for the exchange of circuits, systems, and software for real-world signal processing

Volume 38, Number 3, 2004

JPEG 2000 Image Compression ... see page 3

In This Issue

Editors’ Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

JPEG 2000 Image Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

All About Direct Digital Synthesis (Ask The Application Engineer—33) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Adjustable Cable Equalizer Combines Wideband Differential Receiver with Analog Switches . . . . . . . . . . . . . . . . . 13

A Reader Notes—Reactant Flow Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Application Brief—Measuring Air Flow Using a Self-Balancing Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Recent Product Introductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Editors’ Notes

THE HARMONY OF ANALOG AND DIGITAL

It’s interesting to observe that the three feature

articles in this issue are highly representative

of the currents that are basic to our businesses.

Each illustrates a facet of what real-world

signal processing (and Analog Devices) is

all about—digital, analog, and the interface.

They exemplify our long-held conviction that,

although we live in an analog physical world,

analog and digital must cooperate to solve

each other’s problems.

Take, for example, JPEG 2000 Image Compression (page 3). The JPEG

2000 standard deines a new image-coding scheme that uses state-

of-the-art compression techniques based on wavelet technology.

Its architecture is useful for many applications, including Internet

image distribution, security systems, digital photography, and medical

imaging. The article highlights some of its beneits.

The technology involves applying the highly sophisticated wavelet

transformation in a purely digital interpretation scheme for encoding,

transmitting, receiving, storing, and selectively using pictorial

material. Yet it starts with electrical samples that depend on light

intensity (an analog quantity), and is intended for ultimate display in

some form by modiications of light from a source to produce pixels

of light whose intensity (an analog quantity) correspond more-or-less

faithfully to an intended relationship to the original.

Consider now, if you will, Adjustable Cable Equalizer Combines

Wideband Differential Receiver with Analog Switches (page 13).

Category-5 unshielded twisted-pair cable , like any transmission medium,

suffers from dispersion and high-frequency signal loss. This article

presents an equalizer design that compensates Cat-5 cable at

frequencies to 100 MHz and lengths to 1000 feet, making it suitable

for KVM networking and high-resolution video transmission.

The subject of this article is, quite evidently, preserving the integrity

of analog signals. But what do the initials, KVM, stand for? Keyboard,

video, mouse ! What could be more digital? Again, we have a scheme for

preserving information, but this time, the purpose of the design is to

preserve digital information—subjected to the tender mercies of the

analog world in the cable. Since KVM suggests computer , the source

and destination of the information could both be totally digital in

nature—starting with symbols and ending with symbols.

Finally, we have: All About Direct Digital Synthesis —Ask the

Applications Engineer—33 (page 8). Direct digital synthesis (DDS) is

a method of producing an analog waveform—usually a sine wave—by

generating a time-varying signal in digital form and then performing a

digital-to-analog conversion. Because operations within DDS devices

are primarily digital, they can offer fast switching between output

frequencies, ine frequency resolution, and operation over a broad

spectrum of frequencies.

The operation speaks for itself! The properties of the waveform to

be generated enter in purely symbolic form as numerical information

(btw, the French word for “digital” is numérique ). And lo! the device’s

DAC—in cahoots with the clock that (along with the power supply)

is essential to the device’s operation—emits an analog waveform of

the appropriate frequency and phase.

Dan Sheingold [dan.sheingold@analog.com]

THE ANALOG WORLD—FICTIONAL AND REAL

Analog gets a bad rap, even in popular culture.

In movies, TV shows, and magazines, people

are told that analog is dirty and old fashioned,

and that digital is clean and modern. In an

ad from one of the electronics superstores,

for example, a guy gets dumped for being

“too analog”. In The Teeth of the Tiger by

Tom Clancy 1 , readers are told that

“ The world was not digital, after all—it was an

analog reality, always untidy, always with loose ends that could never

be tied up neatly like shoelaces, and so it was possible to trip and fall

with every incautious step.” (page 172);

“ The world, one had to remember, was analog, not digital, in the way

it operated. And analog actually meant sloppy .” (page 286);

and

“ I think that we can depend on that.” “Yeah, unless he got an unexpected

phone call, or he saw something in the morning paper that caught his

interest, or his favorite shirt wasn’t properly pressed. Reality is analog,

Sam, not digital, remember?” (page 316).

Clancy is right—the world is analog. But that doesn’t make it dirty,

unpredictable, or imprecise. While digital signals are limited by inite

resolution, analog signals can have ininite resolution, limited only

by noise or quantum effects. Analog signal processing can respond

nearly instantaneously, without the computational delays inherent

to digital signal processing. Analog circuitry can often operate at far

lower power levels than digital circuitry providing the same function.

Yet it is dificult to maintain the speedy, pristine nature of an analog

signal through further signal processing for communications or

storage, especially over long distances, in hostile environments, or

over extended periods of time. Thus, the world needs precision data

converters, high-speed operational ampliiers, power management

components—and the expertise to use them.

The images in a digital camera are stored as 1s and 0s, but they are

acquired by a CCD analog imager. Processing the CCD signal requires

analog functions such as sampling, variable-gain ampliication, and

A/D conversion. Displaying the image on the liquid-crystal display

requires analog functions, such as D/A conversion, iltering, and

gamma correction. Many digital cameras include audio functions,

and therefore require audio codecs and ampliiers to drive the speakers

and microphones.

Wireless communication is also made possible by analog technology.

Cellular carriers brag about their all-digital networks, but humans

don’t speak in 1s and 0s, and don’t hear that way either. Voices must

be digitized by A/D converters and reconstructed by D/A converters.

And, while the data being transmitted is digital, the transmission

medium is analog. 1s and 0s can’t be transmitted as-is—they must irst

be modulated onto high-frequency carriers. On the receive side, weak

signals must be captured by low-noise ampliiers—and demodulated.

Power for all of these functions must be supplied by a small battery

that lasts for weeks between charges, can be recharged quickly, and

can be used while it is being charged. This requires complex analog

power-management techniques.

Analog Devices, with its technologies, products, application notes, data

sheets, application seminars, design tools, web site, ield application

engineers—and publications such as Analog Dialogue —seeks to help

foster both the technology and expertise that designers—trained in

either analog or digital—can use to cope with the realities of a mixed-

signal world.

www.analog.com/analogdialogue dialogue.editor@analog.com

Analog Dialogue is the free technical magazine of Analog Devices, Inc., published

continuously for 38 years—starting in 1967. It discusses products, applications,

technology, and techniques for analog, digital, and mixed-signal processing. It is

currently published in two editions— online , monthly at the above URL, and quarterly

in print , as periodic retrospective collections of articles that have appeared online. In

addition to technical articles, the online edition has timely announcements, linking to

data sheets of newly released and pre-release products, and “Potpourri”—a universe

of links to important and rapidly proliferating sources of relevant information and

activity on the Analog Devices website and elsewhere. The Analog Dialogue site is,

in effect, a “high-pass-iltered” point of entry to the www.analog.com site—the

virtual world of Analog Devices . In addition to all its current information, the

Analog Dialogue site has archives with all recent editions, starting from Volume 29,

Number 2 (1995), plus three special anniversary issues, containing useful articles

extracted from earlier editions, going all the way back to Volume 1, Number 1.

If you wish to subscribe to—or receive copies of—the print edition, please go to

www.analog.com/analogdialogue and click on <subscribe> . Your comments

are always welcome; please send messages to dialogue.editor@analog.com

or to these individuals: Dan Sheingold , Editor [dan.sheingold@analog.com]

or Scott Wayne , Managing Editor and Publisher [scott.wayne@analog.com] .

Scott Wayne [scott.wayne@analog.com]

1 Tom Clancy, The Teeth of the Tiger . New York: G. P. Putnam’s Sons, hardcover (2003).

2 Analog Dialogue Volume 38 Number 3

ISSN 0161-3626 ©Analog Devices, Inc. 2004

JPEG 2000 Image Compression

By Christine Bako [christine.bako@analog.com]

JPEG 2000 is frame accurate , in that every single frame of the input

is contained in the compressed format. MPEG systems, on the

other hand, reduce the amount of data through temporal compression

(which does not encode each frame as a complete image), so

MPEG compression is not frame-accurate . For this reason, legal

issues restrict the use of MPEG compression in some security

applications. To get around this problem, security system and

equipment providers have had to develop their own compression

schemes—or use the highly ineficient motion JPEG (M-JPEG)

compression standard—in order to provide a compressed stream

that contains every single ield of the original. They can now use

JPEG 2000 for new designs.

INTRODUCTION

The JPEG (Joint Photographic Experts Group) 2000 standard,

inalized in 2001, deines a new image-coding scheme using

state-of-the-art compression techniques based on wavelet

technology. Its architecture is useful for many diverse applications,

including Internet image distribution, security systems, digital

photography, and medical imaging.

A lot of confusion exists as to what JPEG 2000 is and how it compares

with other compression standards such as MPEG (Moving-Picture

Experts Group) -2, MPEG-4, and the earlier JPEG. With brief

comparisons to other compression standards, this article is primarily

intended to highlight some of the often misunderstood and rarely

mentioned potential-become-actual beneits of JPEG 2000.

Internet Image Distribution

Progressive coding , another feature of the JPEG 2000 standard,

means that the bit stream can be coded in such a way as to contain

less-detailed information at the beginning of the stream and more

detailed information as the stream progresses. This makes it ideal

for Internet/network applications—especially with large images

and low bandwidths—as the image can be seen instantly on the

decoding side, even with low-speed networks or image databases.

The lower subbands are shown irst, and more detail is added as

time progresses. The picture thus becomes sharper and more

detailed over time, and the entire image does not have to be

downloaded before it can be seen.

With the low-quality image instantly available, the user at the

receiving end can decide whether to view the picture in its fully

decoded version, or to pass it by and scan the next picture instead.

Clients can view images at different resolutions or quality levels

[ compression rates ] making them suitable for any transmission

bandwidth, connection speed, or display device. In addition,

JPEG 2000 coding provides the option to zoom in or out on a

particular area of the image—or to display a particular region of

the image at a different resolution or compression rate.

Applications

CCTV Security

When transmitting or storing picture information, compression

must be employed to maintain picture resolution while making

best use of limited channel bandwidth. Compression is deined as

lossless if full recovery of the original is available from the channel

without any loss of information; otherwise, it is lossy . Standards

are required to ensure interoperability. JPEG 2000 is the only

standard compression scheme that provides for both lossless and

lossy compression. As such, it lends itself to applications that

require high-quality images despite limitations on storage or

transmission bandwidths.

An important feature of systems based on JPEG 2000 is the ability

to extract a variety of resolutions, components, areas of interest,

and compression ratios from a single JPEG 2000 code stream. This

is not possible with any other compression standard because the

image size, bit rate, and quality must be speciied on the encode

side and can not be determined or changed on the decode side.

For example, a closed-circuit TV (CCTV) security system can

make use of this feature by sending a single JPEG 2000 code

stream over a low bandwidth network. High-resolution images

can be stored on a hard-disk drive (HDD), while several lower-

resolution images are displayed on monitors. The operator on

the receive side can decide what information to extract from

the single code stream sent.

High Deinition

At extreme compression levels, JPEG 2000 video starts to blur,

but is still quite viewable. MPEG or JPEG artifacts are much more

disturbing to the eye, with the picture visibly broken down into

small blocks at high compression ratios. The high image quality

of medium-to-high bit rate signals containing a lot of motion, the

lack of block artifacts, and high eficiency make JPEG 2000 ideal

for high-deinition (HD) applications, such as digital cinema, HD

recording systems, and HD camera equipment.

MILITARY

•HDSATELLITEIMAGES

•HIGH-QUALITYTRANSMISSION

•HIGH-QUALITYSTORAGE

•REMOTESENSING

INDUSTRIAL

•HIGH-QUALITYSTORAGE

•REMOTESENSING

MEDICAL

•HIGH-QUALITYSTORAGE

•HIGH-QUALITYPROCESSING

CONSUMER

•MOBILEPHONES

•PALMPILOTS

DIGITAL

STILL

IMAGES

OFFICE

AUTOMATION

HD/SDVIDEO

PRODUCTION

COPIER

NETWORK

SCANNERS

SERVERS

PROFESSIONAL

•PROFESSIONALCAMCORDER

•HDTVVIDEOEDITING

•DIGITALCINEMA

CONSUMER

•HDCAMCORDER

•DIGITALCINEMA

JPEG2000

CCTV

SECURITY

INTERNET

MOTIONDETECTION

NETWORKDISTRIBUTION

STORAGE

IMAGEDATABASES

STREAMINGVIDEO

VIDEOSERVERS

Figure 1. JPEG 2000 applications.

Analog Dialogue Volume 38 Number 3 3

Many applications require exact bit-rate control, which only

JPEG 2000 can provide. Exact bit-rate control is possible

because an entire frame or ield is transformed at once; it is then

broken down into bit streams or code blocks that can be processed

independently with the techniques described below. In systems

using DCT, quantization is the only technique used, and this

makes exact bit-rate control dificult. In order to control bit rate

in DCT systems, the information must be repeatedly re-processed

and re-quantized. The rate-control algorithm used in JPEG

2000 truncates each bit stream to meet a speciic target bit rate,

adjusting the truncation and re-quantization of each code block’s

data as required. In addition to programming the target bit rate,

the standard allows the user to specify a particular quality metric.

In this case, the target bit rate will vary to meet the speciied

quality factor, as long as the performance does not fall below a

speciic peak signal-to-noise ratio . The PSNR is an indication of

picture quality comparable to perceived picture quality .

JPEG 2000 Code Stream

A given input image or part of the image [ tile ] is sent to a set of

wavelet ilters, which transform the pixel information into

wavelet coefficients, which are then grouped into several

subbands [the use of wavelets in encoding was irst explained in

Analog Dialogue 30-2 (1996)]. Each subband contains wavelet

coeficients that describe a speciic horizontal and vertical spatial

frequency range of the entire original image. This means that

lower-frequency, less-detailed information is contained in the

irst transform level, while more-detailed, higher-frequency

information is contained in higher transform levels. For simplicity,

only two levels of transform are shown here. The irst transform

level results in subbands LH1, HH1, HL1, and LL1. Only subband

LL1 is passed on for further iltering, generating the next transform

level and creating subbands LH2, HH2, HL2, and LL2.

Equally sized code blocks, which are essentially bit streams of data,

are generated within each subband. This break-down is necessary

for coeficient modeling and coding, and is done on a code-block-

by-code-block basis. In essence, the actual compression is achieved

by truncating and/or re-quantizing the bit streams contained in each

code block. These bit streams are then optimally truncated using

a technique knows as post-compression-rate-control (PCRC).

Code blocks can be accessed independently. Their bit streams are

coded with three coding passes per bit plane. This process, called

context modeling, is used to assign information about the importance

of each individual coeficient bit. The code blocks can then be

grouped according to their signiicance. On the decoding side it is

then possible to extract information according to its signiicance,

allowing the most signiicant information to be seen irst.

PRECINCT0OFHL1

ORIGINALTILET0:

LL2

HL2

HL1

WAVELET

TRANSFORMINTO

SUBBANDSHL1,

HH1,LH1,LL2,

HL2,HH2,LH2

LH2

HH2

cb0

cb1

LH1

HH1

cb2

cb3

cb4

cb5

PRECINCT0OFLH1

PRECINCT0OFHH1

WAVELETCOEFFICIENTDATAISARRANGEDINTO

THEJPEG2000CODESTREAM

TILE0

RESOLUTION0

LAYER0

PRECINCT0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2

PACKET0

PACKET1

PACKET2

PACKET3

PACKET4

PACKET

HEADERFOR

PACKET0

DATAFOR

CODEBLOCK

0,SUBBAND

HL1

DATAFOR

CODEBLOCK

1,SUBBAND

HL1

DATAFOR

CODEBLOCK

2,SUBBAND

LH1

DATAFOR

CODEBLOCK

3,SUBBAND

LH1

DATAFOR

CODEBLOCK

4,SUBBAND

HH1

DATAFOR

CODEBLOCK

5,SUBBAND

HH1

Figure 2. ENCODE—image over wavelet transform into subbands and resolutions.

4 Analog Dialogue Volume 38 Number 3

TILE0

RESOLUTION0

LAYER0

PRECINCT0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2 Pr0 Pr1 Pr2

DECODER1:

HDDRECORDER

REQUESTSFULLRESOLUTION[R0]

LOSSLESS[L0]

ALLCOMPONENTSPRECINCT0,

PACKET0

DECODER2:

HIGHQUALITYPRINTER

REQUESTSFULLRESOLUTION[R0]

LOSSLESS[L1]

ALLCOMPONENTS

DECODER3:

CCTVDISPLAY

REQUESTSSMALLRESOLUTION[R1]

LOSSY[L0]

YCOMPONENTONLY

Figure 3. DECODE—one JPEG 2000 stream is received by several decoders.

JPEG 2000 can contain a user-deined number of layers, which

are deined by PCRC and context modeling. Each layer stands

for a particular compression rate, where the compression rate is

achieved from the quantization-, rate-distortion-, and context

modeling processes. Layer 0, for example, contains bit streams—

from the lossy WT transform—that are heavily truncated, contain

no coding passes, and thus provide the highest compression rate

and the lowest quality. Layer 16 can then contain bit streams that

are less truncated and use a higher number of coding passes, thus

providing low compression and high quality.

header information. Also, a table of contents can be stored on the

encode side, and allows a decoder to call up a certain resolution

on demand, without irst having to decode or download the entire

JPEG 2000 code stream.

DCT versus WT

JPEG 2000 uses the wavelet transform (WT) to reduce the amount of

information contained in a picture, while MPEG and JPEG systems

use the discrete cosine transform (DCT). It is true that the WT requires

more processing power than the DCT, but MPEG systems require

more than just the DCT. The DCT, or any type of Fourier transform,

expresses the signal in terms of frequency and amplitude—but only at

a single instant in time. The WT transforms a signal into frequency

and amplitude over time, and is therefore more eficient. The igures

on the following page demonstrate this.

To obtain the same amount of information as with one WT pass,

the DCT must be used for every frequency; and each of these

frequencies must be transformed at each time instant for each

8  8 pixel block. In addition, MPEG systems use inter-frame

compression [motion estimation] in order to reduce the amount of

data further for motion estimation. This requires storage of at least

two entire ields in external memory. The computation-intensive

motion estimation process requires a very powerful processor.

Temporal compression can be used in JPEG 2000 systems, but it

is not inherent in the JPEG 2000 standard.

Tiles or images are further partitioned into precincts . Precincts

contain a number of code blocks, and are used to facilitate access

to a speciic area within an image in order to process this area

in a different way, or to decode only a speciic area of an image.

The JPEG 2000 bit stream is generated by arranging code blocks

or precincts into an array of packets with the lower subbands

coming irst.

The JPEG 2000 stream starts with a main header containing

information such as: uncompressed image size, tile size, number

of components, bit depth of components, coding style,

transform levels, progression order, number of layers, code

block size, wavelet filter type, quantization level, etc. The

entire image data, grouped in code blocks of LL, HL, LH, and

HH subbands, follows the header. Data is not contained in the

Analog Dialogue Volume 38 Number 3 5

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