Browsing through High Quality Do cument Images with DjVu
Patrick Ha ner L eon Bottou Paul G Howard
Patrice Simard Yoshua Bengio and Yann Le Cun
AT T Labs Research
Schultz Drive
Red Bank NJ
fha ner leonb pgh patrice yoshua yanng research att com
Abstract Even if pictures and drawings are scanned and in
tegrated into the web page much of the visual asp ect
We present a new image compression technique
of the original do cument is likely to be lost Visual
cal led DjVu that is speci cal ly geared towards the
details including font irregularities pap er color and
compression of high resolution high quality images of
pap er texture are particularly imp ortant for histori
scanned documents in color With DjVu any scr een
cal do cuments and may also b e crucial in do cuments
connected to the Internet can access and display im
with tables mathematical or chemical formulae and
ages of scannedpages while faithful ly reproducing the
handwritten text
font color drawing pictures and paper texture A
typical magazine page in color at dpi can becom
A simple alternativewould b e to scan the original
pressed down to between to KB approximately
page and simply compress the image as a JPEG or
to times better than JPEG for a similar level of
GIF le Unfortunately those les tend to be quite
subjective quality B W documents are typical ly
large if one wants to preserv e the readability of the
to KBytes at dpi or to times better than
text Compressed with JPEG a color image of a
e cient version of CCITT G Areal time memory
typical magazine page scanned at dpi dots per
the decoder was implemented and is available as a
inch would be around KBytes to KBytes
plug in for popular web browsers
and would be barely readable The same page at
Keywords digital libraries image compression im
dpi would b e of acceptable quality but would o c
age segmentation arithmetic coding wavelet coding
cupy around KBytes Even worse not only would
JBIG
the decompressed image ll up the entire memory of
an average PC but only a small p ortion of it would
Intro duction
b e visible on the screen at once A just readable black
As electronic storage retrieval and distribution of
and white page in GIF would be around to
do cuments b ecomes faster and cheap er libraries are
KBytes
b ecoming increasingly digital Recent studies have
To summarize the current situation it is clear that
shown that it is already less costly to store do cuments
the complete digitization of the world s ma jor library
digitally than to provide for buildings and shelves to
collections is only a matter of time In this context it
house them Unfortunately the di culty of con
seems paradoxical that there exist no universal stan
verting existing do cuments to electronic form is a ma
dard for e cient storage retrieval and transmission
jor obstacle to the development of digital libraries
of high quality do cument images in color
Existing do cuments are usually re typ ed and con
verted to HTML or Adob e s PDF format a tedious Tomake remote access to digital libraries a pleasant
and exp ensive task sometimes facilitated by the use exp erience pages must app ear on the screen after only
of Optical Character Recognition OCR While the a few seconds delay Assuming a kilobits p er second
accuracy of OCR systems has b een steadily improv kbps connection this means that the most relevant
ing over the last decade they are still far from b eing parts of the do cument the text must b e compressed
able to translate faithfully a scanned do cumentinto a down to ab out to KBytes With a progressive
computer readable format without extensive manual compression technique the text would b e transmitted
correction and displayed rst Then the pictures drawings and
backgrounds would b e transmitted and displayed im background The p erformance of b oth of these meth
proving the quality of the image as more bits arrive o ds heavily relies on a new adaptive binary arithmetic
The overall size of the le should b e on the order of co ding technique called the Z co der also brie y de
to KBytes to keep the overall transmission time scrib ed Section intro duces the plug in that allows
and storage requirements within reasonable b ounds to browse DjVu do cuments through standard appli
cations such as Netscap e Navigator or Microsoft Ex
Another p eculiarity of do cument images their large
plorer with a DjVu plug in Comparative results on a
size makes current image compression techniques in
wide variety of do cumenttyp es are given in Section
appropriate A magazine size page at dots per
inch is pixel high and pixel wide Uncom
Image Based Digital Libraries
pressed it o ccupies MBytes of memory more than
The image based approach to digital libraries is
what the average PC can handle A practical do cu
to store and to transmit do cuments as images To
ment image viewer would need to keep the image in a
achieve that we need to devise a metho d for com
compressed form in the memory of the machine and
pressing do cument images that makes it p ossible to
only decompress on demand the part of the image that
transfer a high quality page over low sp eed links mo
is displayed on the screen
dem or ISDN in a few seconds OCR would only b e
The DjVu do cument image compression technique
used for indexing with less stringent constraints on
describ ed in this pap er is an answer to all the ab ove
accuracy
problems With DjVu scanned pages at dpi in full
Several authors have prop osed image based ap
color can b e compressed down to to KBytes les
proaches to digital libraries The most notable ex
from MBytes originals with excellent quality Black
ample is the RightPages system The RightPages
and white pages typically o ccupy to KBytes
system was designed for do cument image transmission
once compressed This puts the size of high quality
over a lo cal area network It was used for some years
scanned pages in the same order of magnitude as an
bytheAT T Bell Labs technical community and dis
average HTML page KBytes according to the lat
tributed commercially for customized applications in
est statistics DjVu pages are displayed within the
several countries The absence of a universal and op en
browser window through a plug in The DjVu plug in
platform for networking and bro wsing suchastoday s
allows easy panning and zo oming of very large images
Internet limited the dissemination of the RightPages
This is made p ossible by an on the y decompression
system Similar prop osals have b een made more re
metho d whichallows images that would normally re
cently
quire MBytes of RAM once decompressed to re
All of the ab ove image based approaches and most
quire only MBytes of RAM
commercially available do cument image management
The basic idea b ehind DjVu is to separate the text
systems are restricted to black and white bi level
from the backgrounds and pictures and to use di er
images This is adequate for technical and business
ent techniques to compress each of those comp onents
do cuments but insu cient for other typ es of do cu
Traditional metho ds are either designed to compress
ments such as magazines catalogs or historical do c
natural images with few edges JPEG or to compress
uments Many formats exist for co ding bi level do c
black and white do cument images almost entirely com
ument images notably the CCITT G and G fax
p osed of sharp edges CCITT G G and JBIG
standards the recent JBIG standard and the up
The DjVutechnique improves on b oth and combines
coming JBIG standard Using AT T s prop osals to
the b est of b oth approaches
the JBIG standard images of a t ypical black and
white page at dpi dots p er inch can b e transmit
Section reviews the currentavailable compression
ted over a mo dem link in a few seconds Work on
and displaying technologies and states the require
bi level image compression standards is motivated by
ments for do cument image compression Section de
the fact that until recently do cument images were
scrib es the DjVu metho d of separately co ding the text
primarily destined to b e printed on pap er Most low
and drawings on one hand and the pictures and back
cost printer technologies excel at printing bi level im
grounds on the other hand Section turns this idea
ages but they must rely on dithering and half toning
into an actual image compression format It starts
to print grey level or color images thus reducing their
with a description of the metho d used by DjVutoen
e ective resolution
co de the text and the drawings This metho d is a
variation of AT T s prop osal to the new JBIG fax The low cost and availability of high resolution
standard It also includes a description of the IW color displays is causing more and more users to rely
wavelet based compression metho d for pictures and on their screen rather than on their printer to dis
play do cument images Even mo dern low end PCs
can display x pixel images with bits per
pixel bitsperRGB comp onent while high end PCs
and workstations can display x at bits p er
pixel
Most do cuments displayed in bi level mo de are
readable at dpi but are not pleasanttoread At
dpi the quality is quite acceptable in bi level mo de
Displaying an entire x letter size page at such
high resolution requires a screen resolution of pix
els vertically and pixels horizontally whichisbe
yond traditional display technology Fortunately us
ing color or graylevels when displaying do cument im
ages at lower resolutions drastically improves readabil
ity and sub jective quality Most do cuments are read
able when displayed at dpi on a color or grey scale
display Only do cuments with particularly small fonts
require dpi for e ortless readability At dpi a
typical page o ccupies pixels vertically and
pixels horizontally This is within the range of to day s
high end displays Low end PC displays and high end
p ortable computer displays have enough pixels but in
the landscap e mo de rather that the desired p ortrait
mo de
Do cument Image Compression with
DjVu
Figure Example of color document hobby
As we stated earlier the digital library exp erience
cannot b e complete without a way of transmitting and
displaying do cument images in color Traditional color
image compression standards such as JPEG are inap
Let us consider a do cument image scanned at
propriate for do cument images JPEG s use of lo cal
dpi with bits per pixel such the catalog page
cosine transforms relies on the assumption that the
shown in Figure The main idea of our do cument
high spatial frequency comp onents in images can es
image compression technique is to generate and en
sentially be removed or heavily quantized without
co de separately three images from which the original
to o much degradation of quality While this assump
image can be reconstructed the background image
tion holds for most pictures of natural scenes it do es
the foreground image and the mask image The rst
not for do cument images A di erent technique is
two are low resolution color images and the latter is
required to co de accurately and e ciently the sharp
a high resolution bi level image dpi A pixel in
edges of character images so as to maximize their clar
the deco ded image is constructed as follows if the
ity
corresp onding pixel in the mask image is the out
put pixel takes the value of the corresp onding pixel It is clear that di erent elements in the color im
in the appropriately upsampled background image If age of a typical page have di erent p erceptual char
the mask pixel is the pixel color is chosen as the acteristics First the text is usually highly contrasted
color of the connected comp onent or taken from the from the background with sharp edges The text must
foreground image The background image see for be rendered at high resolution dpi in bi level or
instance the lower right image of Figure can be dpi in color if reading the page is to be a pleas
enco ded with a metho d suitable for continuous tone ant exp erience The second element in a do cument
images DjVu uses a progressive wavelet based com image is the pictures Rendering pictures at dpi
pression algorithm called IW for this purp ose The to dpi is typically su cient for acceptable quality
mask image the upp er left image of Figure can b e The third element is the background color and pap er
enco ded with a bi level image compression algorithm texture The background colors may not require more
than dpi resolution DjVu uses a metho d called JB for this purp ose
A complete description of used by the IW wavelet based enco der a multi scale
DjVu s foreground background separations algorithm successive projections algorithm which avoids
is beyond the scop e of this pap er so only the main sp ending bits to co de the parts of the background im
ideas are given here The image is partitioned into age that are covered by foreground ob jects The e
square blo cks of pixels A clustering algorithm nds vily draws on their use an ciency of IW and JB hea
the two dominant colors within each blo ck Then a e cient binary adaptive arithmetic co der called the
relaxation algorithm ensures that neighb oring blo cks ZP coder On average the ZP co der is faster and
assign similar colors to the foreground and the back yields b etter average compression than other approx
ground After this phase each pixel is assigned to the imate arithmetic co ders All these algorithms have
foreground if its color closer to the foreground cluster real time implementations and have b een integrated
prototyp e than to the background cluster prototyp e into a standalone DjVu enco der Each comp onentof
A subsequent phase cleans up and lters foreground the enco der is brie y describ ed b elow
comp onents using a variety of criteria
Co ding the Bilevel Mask Using JB
The bi level image compression algorithm used by
The DjVu Compression Format
DjVu to enco de the mask is dubb ed JB It is a vari
Here are the elements that comp ose a DjVu enco ded
ation on AT T s prop osal to the up coming JBIG
image le
fax standard Although the JBIG bi level image
compression algorithm works quite well it has b ecome
The text and drawings also called the Mask are
clear over the past few years that there is a need to
represented by a single bitmap whose bits indicate
provide b etter compression capabilities for b oth loss
whether the corresp onding pixel in the do cument
less and lossy compression of arbitrary scanned images
image has been classi ed as a foreground or a
containing b oth text and half tone images with scan
background pixel This bitmap typically contains
ning resolutions from to dots p er inch This
all the text and the high contrast comp onents of
need was the basis for JBIG which is b eing devel
the drawings It is co ded at dpi using an algo
opp ed as a standard for bi level do cumentcoding The
rithm called JB whichisavariation of AT T s
key to the compression metho d is a metho d for mak
prop osal to the up coming JBIG fax standard cf
ing use of the information in previously encountered
Section
characters without risking the intro duction of charac
The color of the text namely the Foreground con ter substitution errors that is inherent in the use of
tain a large number of neighb oring pixels with
Optical Character Recognition OCR metho ds
almost identical colors It can be considered as
The basic ideas b ehind JB are as follows
uniform for a given mark i e a connected com
The basic image is rst segmented into individual
p onent of foreground pixels
marks connected comp onents of black pixels
The Background is co ded at dpi using the
The marks are clustered hierarchically based on
wavelet based compression algorithm called IW
similarity using an appropriate distance measure
describ ed in Section
Some marks are compressed and co ded directly
The foreground background representation was
using a statistical mo del and arithmetic co ding
prop osed in the ITU MRC T recommendation
Mixed Raster Content The idea was used in
Other marks are compressed and co ded indirectly
Xerox s XIFF image format which currently uses
based on previously co ded marks also using a sta
CCITT G to co de the mask layer and JPEG to co de
tistical mo del and arithmetic co ding The previ
the background and foreground layers A similar for
ously co ded mark used to help in co ding a given
mat is used in Xerox s PagisPro desktop application
mark mayhave b een co ded directly or indirectly
for do cument scanning and indexing
DjVuachieves sup erior compression ratios by using
The image is co ded by sp ecifying for each mark
new compression algorithms for the mask layer as well
the identifying index of the mark and its p osition
as for the background and foreground layers Here are
relative to that of the previous mark
some of the novel techniques used by DjVu the soft
pattern matching algorithm used in the JB bi There are manyways to achieve the clustering and
level image compression algorithm for the mask layer the conditional enco ding of marks the algorithm that
the sparse set representation of wavelet co e cients we currently use is called soft pattern matching
This algorithm do es not yet attempt to optimize the ral to use wavelet based algorithms for enco ding the
clustering step image backgrounds However the requirements of the
DjVu pro ject set extreme constraints on the sp eed and
The key novelty with JB co ding is the solution to
memory requirements of the wavelet enco ding scheme
the problem of substitution errors in which an imp er
The background image is typically a dpi color im
fectly scanned symbol due to noise irregularities in
age containing one to two million pixels It mayonly
scanning etc is improp erly matched and treated as a
represent a nearly uniform background color It may
totally di erentsymbol Typical examples of this typ e
also contain colorful pictures and illustrations which
o ccur frequently in OCR representations of scanned
tally while the DjVu data should b e displayed incremen
do cuments where symb ols like o are often represented
is coming
as c when a complete lo op is not obtained in the
scanned do cument or a t is changed to an l when Our wavelet compression algorithm uses an inter
the upp er cross in the t is not detected prop erly By mediate representation based on a very fast ve stage
co ding the bitmap of eachmark rather than simply lifting decomp osition using Deslauriers Dubuc inter
sending the matched class index the JB metho d is p olating wavelets with four analyzing moments and
robust to small errors in the matching of the marks to four vanishing moments Then the wavelet co e
class tokens Furthermore in the case when a good cients are progressively enco ded using arithmetic co d
match is not found for the current mark that mark ing cf Section and a technique named Hierar
b ecomes a chical Set Di erence comparable to zero trees or token for a new class This new token is
set partitioning algorithms then co ded using JBIG with a xed template of previ
ous pixels around the current mark By doing a small
Finally we have develop ed a technique for co ding
amount of prepro cessing such as elimination of very
the background image without wasting bits on back
small marks that represent noise intro duced during
ground pixels that will b e masked by foreground text
the scanning pro cess and smo othing of marks b efore
This simple and direct numerical metho d sets a large
compression the JB metho d can b e made highly ro
number of wavelet co e cients to zero while trans
bust to small distortions of the scanning pro cess used
forming the remaining wavelet co e cients in order to
to create the bi level input image
preserve the visible pixels of the background only The
null co e cien The JB metho d has proven itself to b e ab out ts do not use memory and are co ded very
more e cient that the JBIG standard for lossless e ciently by the arithmetic co der
compression of bi level images By running the al
During decompression the wavelet co e cients are
gorithm in a controlled lossy mo de by prepro cessing
represented in a compact sparse array whichusesal
and decreasing the threshold for an acceptable match
most no memory for zero co e cients Using this tech
to an existing mark the JB metho d provides com
nique we can represent the complete background us
pression ratios ab out to times that of the JBIG
ing only a quarter of the memory required by the im
metho d for a wide range of do cuments with various
age pixels and generate the fully decompressed image
combinations of text and continuous tone images In
on demand This greatly reduces the memory require
lossy mo de JB is to times b etter than CCITT G
ments of the viewer
which is lossless It is also to times b etter than
Arithmetic Co ding
GIF
Arithmetic co ding isawell known algorithm
Wavelet Compression of Background
for enco ding a string of symb ols with compression ra
Images
tios that can reach the information theory limit Its
of Multi resolution wavelet decomp osition is one
mechanism is to partition the interval of the real
the most e cient algorithms for co ding color images
line into subintervals whose lengths are prop ortional to
and is the most likely candidate for future
the probabilities of the sequences of events they repre
multi level image compression standards The image
sent After the subinterval corresp onding to the actual
is rst represented as a linear combination of lo cally
sequence of data is known the co der outputs enough
supp orted wavelets The image lo cal smo othness en
bits to distinguish that subinterval from all others If
sures that the distribution of the wavelet co e cients is
probabilities are known for the p ossible events at a
sharply concentrated around zero High compression
given p ointin the sequence an arithmetic co der will
e ciency is achieved using a quantization and co ding
use almost exactly log p bits to co de an event whose
scheme that takes advantage of of this p eaked distri
ords the co der achieves en probabilityisp In other w
bution
tropic compression We can think of the enco der and
Because of the smo othness assumption it is natu deco der as blackboxes that use the probability infor
mation to pro duce and consume a bitstream the ELS Co der ab out the same as the QM Co der
and b etter than the Q Co der The di erences are
Arithmetic co ders unfortunately are computation
all small in the to p ercent range We also per
ally intensive For each string element a subroutine
formed two arti cial tests In a test of steady state
must provide the co der deco der with a table con
behavior co ding a long sequence of random bits with
taining estimated probabilities for the o ccurrence of
xed probabilities the ZP Co der p erformed ab out as
each p ossible symb ol at this p oint in the string The
well as the QM Co der better than the Q Co der
co der deco der itself must p erform a table search and
and much b etter than the ELS Co der
at least one multiplication
In a test of early adaptation co ding a long sequence
of random bits with xed probabilities but reinitializ
Binary Arithmetic Co ding
output bits the ZP ing the enco der index every
Binary adaptive arithmetic coders have b een devel
Co der did b etter than the QM Co der whichwas b et
op ed to overcome this drawback as computations can
ter than the Q Co der whichinturnwas b etter than
be approximated using a small number of shifts and
the ELS Co der
additions instead of a multiplication
The ZP Co der s deco ding sp eed is faster than that
Moreover Binary Adaptive Arithmetic Co ders in
of the QM Co der which is in turn faster than the
clude an adaptive algorithm for estimating the symbol
other two co ders
probabilities This algorithm up dates the integer vari
Browsing DjVu Do cuments
able along with the enco ding and deco ding op erations
Satisfaction of the digital library user dep ends crit
Complex probability mo dels are easily represented by
ically on the p erformance of the browsing to ols Much
maintaining multiple indices representing the condi
more time is sp ent viewing do cuments than formulat
tional probabilities of the symbols for each value of
ing queries As a consequence browsers must provide
the contextual information considered by the mo del
very fast resp onse smo oth zo oming and scrolling abil
The QM Co der used in the JBIG standard and
ities realistic colors and sharp pictures
in the lossless mo de of JPEG standard is an example
These requirements put stringent requirements on
of approximate binary arithmetic co der Other such
the browsing software The full resolution color image
co ders are the Q Co der and the ELS Co der
of a page requires ab out megabytes of memory We
cannot store and pro cess many of these in the browser
The Z Co der and the ZP Co der
without exceeding the memory limits of average desk
top computers However wewant to displaysuch im
Wehave implemented new approximate binary arith
ages seamlessly and allow users to drag them in real
metic co ders namely the Z Co der and the ZP Co der
time on their screen
The Z Co der was develop ed as a generalization of
We develop ed a solution called Multi threaded
the Golomb run length co der and it has inherited
two stage deco ding consisting of the following
its qualities of sp eed and simplicity Its inter
nal representation leads to faster and more accurate
A rst thread known as the decoding thread
implementations than either the Q Co der or the QM
reads bytes on the internet connection and par
Co der The probability adaptation in the Z Co der also
tially deco des the DjVu stream This rst stage
departs from the Q Co der and QM Co der algorithms
of the deco ding pro cess asynchronously up dates
in a way that simpli es the design of the co der tables
an intermediate representation of the page image
The ZP Co der is a variation on the Z Co der with
This representation is still highly compressed our
nearly exactly the same sp eed and p erformance char
implementation requires less than megabytes of
acteristics A rougher approximation in the optimal
main memory p er page
entropic Z value costs less than half a p ercent p enalty
in co de size
A second thread known as the interactive thread
Wehave compared the ZP Co der with three other
handles user interaction and repaints the screen
adaptive binary co ders the QM Co der the Q
as needed This thread uses the intermediate rep
Co der a variant of the Q Co der that uses bit
resentation to reconstruct the pixels corresp ond
registers instead of bit and the Augmented ELS
ing to the parts of the do cument that must be
Co der based on the ELS Co der
redrawn on the screen
In the main test various co ders including the ZP
Despite the complexity related to thread management Co der have b een incorp orated into the JB compres
and synchronization this organization provides many sion system The ZP Co der did slightly worse than
sec k the mask text K is loaded sec K The background is still blurred
K are necessary for this background
sec K Loading is nished image
Figure Downloading through a K modem progressive decompression of text rst fol lowed by the background
at increasing quality detail of Figure
advantages Since b oth threads work asynchronously
the browser is able to display images incrementally
while data is coming in Memory requirements are
limited b ecause the interactive thread computes im
age pixels only for regions smaller than the screen size
Scrolling op erations are smo oth b ecause they involve
just the second stage deco ding of the few pixels un
covered by the scrolling op erations
We implemented these ideas in a plug in for
Netscap e Navigator or Internet Explorer Each page
of a DjVu do cument is displayed byinvoking its URL
Behind the scenes the plug in implements information
JPEG at dpi only DjVu
caching and sharing This design allows the digital li
brary designer to set up anavigation interface using
Figure Comparison of JPEG at dpi left with
well known Web technologies like HTML or Java Fig
quality factor and DjVu right The images are
ure shows how a do cument is displayed while it is
cropped from hobby The le sizes are K for
downloaded through a K mo dem
JPEG and K for DjVu
Results and Comparisons with
Conclusion
Other Metho ds
As digital libraries are increasingly b ecoming a fact
Wehave selected seven images representing typical
of life they will require a universal standard for ef
color do cuments These images have b een scanned at
cient storage retrieval and transmission of high
dpi and bits pixel from a variety of sources Our
quality do cument images The work describ ed in this
compression scheme combines twomain chunks one
pap er is a substantial step towards meeting this need
wavelet compressed chunk for the background color
by prop osing a highly e cient compression format
one JBIG chunk for the bitmap whose combined size
DjVu together with a browser that enables fast
is rep orted in Figure
internet access With the same level of legibility
Figure gives a full comparison between JPEG
dots p er inch DjVuachieves compression ratios to
and DjVu with details from each image to assess the
times higher than JPEG
readability Those details do not show the signi cant
The DjVu plug in is freely available for download
amount of graphics and texture that all these images
at http djvu research att com This site con
contain However wegive the p ercentage of bits sp ent
tains an exp erimental Digital Library with do cu
on co ding graphics and texture in eac h image which
ments from various origins The DjVu enco der is also
ranges from to When compared to the original
available for researchandevaluation purp oses
dpi raw image DjVu achieves compression rates
It is p ossible to further optimize the compres
ranging from to
sion rate A version of DjVu that enco des sev
Compressing JPEG do cuments at dpi with the
eral pages together will be able to share JBIG
lowest p ossible quality setting yields images that
shap e dictionaries between pages Problems such
are of comparable quality as with DjVu As shown
as foreground background mask separation or con
in the JPEG dpi column le sizes are to
nected comp onent ltering are b eing rephrased in
times larger than DjVu le sizes
terms of compression rate optimization
For the sake of comparison we subsampled the do c
The addition of text layout analysis and optical
ument images to dpi with lo cal averaging and
cognition OCR will makeit p ossible to character re
applied JPEG compression adjusting the quality pa
index and edit text extracted from DjVu enco ded do c
rameter to pro duce les sizes similar to those of DjVu
uments
In the JPEG dpi column the fact that text is
hardly readable is not due to the dpi subsampling
References
but to ringing artifacts inherentinlow JPEG qual
ity settings
JBIG Progressive bi level image compression
Figure shows a more global comparison b etween ITU recommendation T ISO IEC Interna
DjVu and JPEG tional Standard
Image JPEG dpi JPEG dpi DjVu
Description Raw image detail quality size DjVu compressed
Magazine Add
image
K K K K ads freehand
Brattain
Noteb o ok
image
K K K K brattain
Scienti c
Article
image
graham K K K K
Newspap er
Article
image
lrr wpost lrr wpost K K K K
Cross Section
of Jupiter
image
planets jupiter K K K K
XVI I Ith
Century book
image
cuisine p K K K K
US First
Amendment
image
usa amend K K K K
Figure Compression results for seven selected images with compression format Raw applies no compression
JPEG quality ranges from to the value yielding the compression rate which is the closest to DjVu is
chosen The image value corresponds to the percentage of bits required to code for the background Each
column shows the same selected detail of the image Tomakeselection as objective as possible when possible the
are the le size in kilobytes rst occurrence of the word the was chosen The two numbers under each image
and the compression ratio with respect to the raw le size
M Lesk Practical Digital Libraries Books Bytes P G Howard and J S Vitter Arithmetic co ding
and Bucks Morgan Kaufmann for data compression Proceedings of the IEEE
G Story L O Gorman D Fox L Shap er and
JPEG Digital compression and co ding of contin
H Jagadish The RightPages image based elec
requirements and guide uous tone still images
tronic library for alerting and browsing IEEE
lines ITU recommendation T ISO IEC Inter
Computer
national Standard
T Phelps and R Wilensky Towards active ex
W B Pennebaker J L Mitchell G G Lang
tensible networked do cuments Multivalentarchi
don and R B Arps An overview of the basic
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I H Witten A Mo at and T C Bell Managing
Wm D Withers A rapid entropy co ding algo
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S W Golomb Run length enco dings IEEE
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Trans Inform Theory IT July
E H Adelson E Simoncelli and R Hingorani
L Bottou P Howard and Y Bengio The Z
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co der adaptive binary co der In Proceedings of
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IEEE Data Compression Conference Snowbird
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MA Octob er
L Bottou and S Pigeon Lossy compression of
J M Shapiro Emb edded image co ding using ze
partially masked still images In Proceedings of
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IEEE Data Compression Conference Snowbird
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UT
b er
Wim Sweldens The lifting scheme A custom
design construction of biorthogonal wavelets
Harmonic Journal of Applied Computing and
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Amir Said and William A Pearlman A new fast
and e cient image co dec based on set partitioning
in hierarchical trees IEEE Transactions on Cir
cuits and Systems for VideoTechnology
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R N Ascher and G Nagy A means for achiev
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P G Howard Text image compression using soft
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I H Witten R M Neal and J G Cleary Arith
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