diff --git a/doc/tb108wang1.page b/doc/tb108wang1.page new file mode 100644 index 0000000..6fa9888 --- /dev/null +++ b/doc/tb108wang1.page @@ -0,0 +1 @@ +
TUGboat, Volume 34 (2013), No. 3 313
Online publishing via pdf2htmlEX
Lu Wang and Wanmin Liu
Abstract
The Web has long become an essential part of our
lives. While web technologies have been actively
developed for years, there is still a large gap between
web and traditional paper publishing. For example,
the PDF format, the de facto standard for publishing,
is not supported in the HTML standard; and the
most powerful typesetting system, T
E
X, cannot be
integrated perfectly.
Despite of the long history of people trying to
convert T
E
X or PDF into HTML, some are focused on
only a small fraction of features, e.g. text, formulas
or images; some are too old to support new features
in the HTML standard such as font embedding or
linear transformations (e.g. rotation); some display
everything in images at the cost of larger sizes.
In this article, while we survey and compare
existing methods of publishing T
E
X or PDF docu-
ments online, a new approach is attempted to attack
this issue. We introduce an open source program,
called pdf2htmlEX, which is a general PDF to HTML
converter and publishing tool with high fidelity. It
presents PDF elements with corresponding native
HTML elements, in order to achieve high accuracy
and small size. The flexible design also makes it
useful for a variety of use cases in online publishing.
Obviously T
E
X users can immediately benefit with
zero learning cost, just like
dvipdf
while people were
still using DVI. More information is available at the
home page:
https://github.com/coolwanglu/pdf2htmlex
1 Introduction
rguably, for many people the World Wide
Web is the Internet. Indeed, web technolo-
gies have been so actively developed in the
past few years, nowadays web pages far
surpass plain text and images. HTML5 brings au-
dio, video, 3D graphics and many other rich features;
CSS3 defines brand new visual effects, and JavaScript
allows different kinds of user interactions. Modern
web browsers are literally operating systems, and
the boundary between web apps and local software
has been blurred. Today, we can access the WWW
with all kinds of devices such as watches, phones,
tablets, computers and even glasses. It has become
an essential part of our lives.
The web technologies provide brand new user
experiences compared to traditional media. Taking
Wikipedia as an example, it has rich contents: inside
an article, besides plain text, there are often images,
animations, audio and video that are relevant to the
topic; it is well organized: users may jump to rele-
vant articles by clicking links; it is interactive: users
may create or edit an article; it is personalized: the
appearance of the web site respects users’ preferences
such as language, theme or format; it is social: users
may leave comments and have discussions regarding
an article.
Compared with traditional publishing media, it
is more convenient and easier for users to obtain,
view and share the contents. While most features in
HTML are targeting visual effects, multimedia and
rich Internet applications, there is still a large gap
between the Web and traditional publishing. Many
existing publishing technologies cannot be perfectly
integrated online — especially two of them focused
on in this article, PDF and T
E
X, which are the most
popular format and typesetting system respectively.
PDF
The Portable Document Format, developed
by Adobe, is one of the most popular formats for dig-
ital documents. PDF is known for its wide support
of different types of fonts, encodings, raster images,
vector graphics, and many other features from pre-
press processing to user interaction. It is widely
supported in different operating systems and devices.
Nowadays, almost all documents can be exported to
PDF. Notably, with a virtual PDF printer, any docu-
ment that can be printed on paper can be converted
to PDF. It has become the de facto standard for
academic articles, technical reports, manuals, news-
papers and ebooks. As an example, the final format
for TUGboat is PDF.
PDF is a print-ready format; it is designed to
completely describe a fixed-layout flat document. A
PDF file clearly defines the appearance of the docu-
ment, independent of particular devices or viewers.
PDF is not supported in the HTML standard,
but it can be viewed directly in several web browsers.
Users of other web browsers usually have to read PDF
documents with web browser plugins, or download
the files and then read them with a local PDF reader.
In all these cases, PDF files are viewed in a closed
environment where users cannot utilize most web
features.
1
T
E
X
Designed and written by Professor Donald
Knuth, T
E
X is one of the most powerful typesetting
systems in the world.
2
It is well-known for its capa-
bility of producing high quality formulas and figures
1
PDF
does include features such as external links and
interactive functions within a document, but these are quite
limited compared to HTML.
2
When using ‘T
E
X’ in this article, most of the time we
will be referring to the whole T
E
X family.
Online publishing via pdf2htmlEX
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322 TUGboat, Volume 34 (2013), No. 3
Figure 8: The text layer
Figure 9: The image layer
Lu Wang and Wanmin Liu
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TUGboat, Volume 34 (2013), No. 3 323
Figure 10: Fonts embedded in the HTML file
Image overlay
For each PDF page, pdf2htmlEX
puts all non-text elements into a background image;
this image is then put behind all the text in that
page. However, it is possible that some text is in fact
covered by an image in the PDF, in which case in the
corresponding HTML file produced by pdf2htmlEX,
the text will be visible due to the superimposition.
We are still looking for efficient solutions for
this issue; fortunately, this issue is not common,
especially for T
E
X users. A workaround is to use the
fallback mode of pdf2htmlEX at the cost of larger
file size.
Image optimization
When generating the back-
ground image, pdf2htmlEX calculates the bounding
box of all non-text elements in that page, and ren-
ders everything inside. However, if there are only a
few images which are far away from each other, most
parts in the image are actually blank, which will be
a waste of bandwidth. It is possible to recognize and
split those small images and pack them into one small
image, such that they will be loaded using the CSS
sprite technique. In this way significant bandwidth
and computation can be saved.
4.8 Discussion
In this section we introduced pdf2htmlEX from sev-
eral perspectives. Due to space limitations here,
we cannot present everything — there are nearly 50
different options in total, and there are also tricky
implementations regarding font conversion, text han-
dling and image processing. Interested readers are
encouraged to visit the project web site for detailed
and up-to-date documentation.
5 Conclusion
In this article we tried to categorize and compare
existing methods of publishing T
E
X or PDF online.
We hope that readers may use this article as a guide
to choose the proper tool for their specific use cases,
or be inspired to create their own implementations.
We also introduced our program pdf2htmlEX, a
PDF to HTML converter and publishing tool which
is accurate and flexible for many different use cases.
We encourage interested users to get involved.
Acknowledgement
We thank Professor Haruhiko Okumura for his help
and great advice. We also thank Professor Makasata
Kaneko, Mr Rapha¨el Pinson and Mr Jason Lewis for
the nice sample files used in this article.
Online publishing via pdf2htmlEX
diff --git a/doc/tb108wang12.page b/doc/tb108wang12.page new file mode 100644 index 0000000..4626078 --- /dev/null +++ b/doc/tb108wang12.page @@ -0,0 +1 @@ +
324 TUGboat, Volume 34 (2013), No. 3
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Lu Wang
Department of Computer Science
and Engineering
The Hong Kong University of
Science and Technology
Hong Kong
coolwanglu (at) gmail dot com
http://coolwanglu.github.io/
Wanmin Liu
Department of Mathematics
The Hong Kong University of
Science and Technology
Hong Kong
wanminliu (at) gmail dot com
Lu Wang and Wanmin Liu
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314 TUGboat, Volume 34 (2013), No. 3
in many different areas. While it is most popular
in academia, it is also used for typesetting books,
magazines and sheet music.
T
E
X is a source format for authors. It contains
structured contents including text, formulas, figures
and possibly cross references between them. Users
can define their own concepts by writing macros.
Typically the layout of the document must be de-
termined by compiling the file with a T
E
X compiler;
different compilers may produce different results from
the same T
E
X source file.
People started trying to connect T
E
X to the Web
nearly since the Web began. There were some early
overviews, such as [
31
,
32
], [
34
, chapter 7], but we are
not aware of any recent surveys on the topic. Early
works were mainly focusing on correctly displaying
formulas produced by T
E
X. Different methods in-
clude using images, Unicode characters, MathML
or HTML5. However the power of T
E
X is far more
than formulas, it is also famous for its capability
of handling mathematical spacing, hyphenation and
justification, which is often ignored in these cases.
In the following sections, we are going to describe and
compare some popular existing approaches. We will
also introduce a new program, pdf2htmlEX [
25
], and
discuss its advantages and limitations with examples.
2 Preliminaries
he target audience of this article includes
those who need to publish both online ver-
sions and print versions of their documents
at the same time, especially those who want
to publish existing documents online.
We assume that the existing document is in PDF
format. It could be generated from T
E
X or any other
tool. We do not assume that the publisher is the
author, i.e. the source files may not be available to
the publisher.
We believe that the following requirements are
essential for most users. They are also the criteria we
will use to discuss and compare existing approaches.
Convenience
The publishing process should be
automated, with minimal manual adjustments in-
volved, such that publishers need focus on only one
version, while the other can be generated accordingly.
Consistency
Both the online version and the print
version should have a consistent appearance, some-
times including the same layout and format.
Evidently the contents should never vary be-
tween the two versions, but one may argue that
screen and paper are two completely different kinds
of media, and so fonts, spacing and even layouts
should be optimized individually. For example, users
1
Le premier lire de Moyſe,
Di Geneſe.
❦
.
Ce premierlire comprendl’origine caſes detotes choſes,principalement lacreation del’homme, q’ila eſtéd
commencement, ſachete releement : comment d’ntos onteſté procreés, porlers enormespechés Die
les a conſmés,par le delge,reſeré hi,dont laſemence a remplitote laterre. Pisil deſcritles ies, fais, reli-
gion, ligneesdes ſaintsPatriarches, qiont eſcdeant laLoy :Les benediions,promees, alliances dSei-
gner faies aecicex : Commentde lela terre deChanaan ſont deſcendsen Epte. Acnsont appeléce lire, le
lire desIſtes. Totefois ceci aobten entrenos predeceers nos,q’il eſtappelé Geneſe,qi eſtn motGrec,
gnifiant generation origine : d’atant q’eniceli eſtdeſcrite l’origine procreationde toteschoſes : nom-
mément des Peresanciens, qiont eſtétant deantq’apres ledelge, e eſgardà    deſcen-
d d’icex ſelonla chair.
.
I
Creation dciel de laterre, II, 10. detot ce qi yeſt
comprins. 3.14. De la lmiere a, 26 de l’homme, 18
qel tot eſtabietti. 2.2. 18 Diebenit totesſes œ-
res, 31 q’ila accompliesen x iors.
1
Ie
a
crea
b
a com
mence -
ment
c
le
ciel & la
terre.
2 Or la
terre eſ-
toit ſans
forme, &
vide, & les tenebres eſtoyent ſr les
abyſmes : & l’Eſprit de Die
d
eſtoit
eſpand par desles eax.
3 Adonc Die dît,
2
’il y ait lmie-
re.
e
Et la lmiereft.
4 Et Die vidq
̃
la lmiere eſtoitbon-
ne : & ſepara lalmiere des tenebres.
5 Et Dieappela la lmiereior,& les
tenebres ni. Lors ftfaile
f
ſoir &
le matin dpremier ior.
6 PisDie dît,
3
’il yait ne
g
eſ-
tende entre les eax, & qelle ſepare
les
h
eax daec leseax.
7 Die donc fit leſtende, & diiſa
I
Ce premier cha-
pitre eſt fort diffi-
cile : & por cette
caſe, il eſtoit de-
fend entreles He
briex dele lire&
interpreter deant
laage de trente
ans.
a
Fit de rien, &
ſans acne ma-
tiere.
1
Iob 38.4, Pſea.
33.6, 89.12.,
135.5, Eccleſtiaſti.
13.1, A. 14-15,
17.14
b
Tot premiere-
ment, & aãtq’il
y et acne crea-
tre, Iean 1.10.
2
Hebr. 11.3.
c
Le ciel & la
terre, les eax, les
abyſmes, ſe pren-
nent ici por vne
meſme choſe: aſç.
por ne matiere
cõfſe & ſans for-
me, q
̃
Die forma
& agença apres
par ſa Parole.
d
O, ſe mo-
voit. Ceſt, ſoſte-
noit et conſeroit
en ſon eſtre cette
matiere confſe.
Car il eſt impo-
ble, q
̃
acne cho-
ſe apres aoir eſté
faies,pie ſb-
ſter n ſel mo-
ment, Diene la
ſoſtient & cõſer-
ve par ſa vert,
Pſea. 130.
e
Cette lmiere
neſtoit point en-
core a ſoleil, car
il naoit pas eſté
creé, maiseſtoit en
la main de Die,
ayãt ſonordre ſc-
cef aecles tene-
bres, por faire le
ior & la ni &
ce iſqes a qa-
trieme ior, qe
Die fit le ſoleil
por eſtre miniſtre
& diſpenſater de
cette lmiere,aec
la lne &eſtoilles.
3
Pſea. 33.6,
136.5.
Ierem. 10.11
51.15.
f
Ici eſt lacaſe
les eax, qi eſtoyent ſos leſtende,
daec celles, qi eſtoyent ſr leſten-
de. Et ft ain fai.
8 Et Dieappela leſtende,Ciel. Lors
ft fai le ſoir & le matin d ſecond
ior.
9 Pis Die dît,
4 i
e leseax, qi
ſont ſos le ciel, ſoyent aemblees en
n lie, & qe le ſecapparoie. Et ft
ain fai.
10 EtDieappeꝉale ſec,Terre,& laem
blee des eax, mers. Et Die vid qe
celà eſtoit bon.
11 Et Die dît, e la terre prodiſe
verdre, herbe prodiſantſemence,&
arbre friier, faiſant fri ſelon ſon
eſpece, leqel aitſaſemẽce en ſoy-meſ-
me ſr laterre. Et ftain fai.
12 Laterre dõc proditverdre, her-
be prodiſant ſemẽceſelon ſon eſpece,
& arbre ſans fri, leqel aoit ſa
ſemence en ſoymeſme ſelon ſon eſpe-
ce. Et Die vid qecelà eſtoit bon.
13 Lors ft fai le ſoir & le matin d
troieme ior.
14 Apres Diedît,
5 k
’il yait lmi
naires en leſtende d ciel, por ſepa-
rer lani dior : & ſoyẽten
l
gnes,
a en
porqoy les He-
briex cõmencent
le ior natrel le
ſoir apres le ſoleil
cochant.
g
Ce mot d’Eſtẽ
de, comprẽd tot
ce qi ſe voit par
des nos,tãt en
la region celeſte,
qelementaire.
4
Pſea. 33.7.
h
Il eſt ici parlé
de dex manieres
deax : asçaoir,
celles q ſont ſos
leſtende, comme
la mer, lesflees,
& atres qi ſont
ſr la terre & cel-
les, qi ſont ſr
leſtende, comme
ſont lesnees plei-
nes dea ça hat
en lair par des
nos. Die a mis
entre ces dex for
ces deax ne grã
de eſtende, qon
appelle le ciel : de
là nos appelons
les oiſeax dciel.
i
Ceci appartiẽta
ſecõd ior, aqel
Die ſepara, & fit
apparoir la terre d
milie des eax.
k
Il inſtite n
noel ordre en
natre, qand il
fat & ordonne le
ſoleil diſtribter
de cette lmiere
q’il aoit creée
aant li,& aant
la lne & les eſ-
toilles.
5
Pſea. 136.7
l
Ceſt por -
gnifier dierſes di-
ſpotions qe les
corps ĩferiers ſe-
lon lordre de na-
tre ont des corps
celeſtes, cõme ca
ſes ſecõdes ordon
nees de Die à ce-
là. En qoy to-
teſfois fat firc-
rioté & ſperſti-
tion q
̃
les hõmes
ont cõtroee ſr
celà.
Figure 1
: Bible de Gen`eve, 1564 [
8
], typeset by
Rapha¨el Pinson with
X
E
T
E
X. The drop cap, fonts,
spacing and layout were carefully tuned in order to
duplicate the 16th century French Bible.
might want text in the document to be reflowed
according to the screen size of their mobile devices.
However, in many cases, fonts, spacing and lay-
outs are carefully designed to assist reading, and
sometimes they have already become essential parts
of the document, see Figures 1 and 2 as examples.
In such cases, a complete redesign may be involved
in order to optimize for specific media.
In our opinion both situations are important,
and we will try to cover both of them in this article.
Flexibility
An important purpose of the online
version is to provide better services and user experi-
ence. This version of the document should be flexible
enough for front-end designers to design interactive
web pages.
For example, text and other elements in the
documents should be accessible such that extra styles
or effects can be specified; the whole document should
be able to be embedded into existing frameworks with
well-defined behaviours and themes applied.
Optimization
There are concerns for web services
which may not be covered by traditional media: the
Lu Wang and Wanmin Liu
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TUGboat, Volume 34 (2013), No. 3 315
Organic Trader Pty Ltd. Ph. 02 83990122, Fax 02 8399 1766. Order by the carton and save 5%. 21
. . .continued fromprevious page.
Product Description Carton($) Unit($) U/C RRP($) Item No GST Barcode Organic
NEW BC Red Wine Vinegar Chips 142g 3.33 3.51 12 5.50 9197006 10% 708163114878
NEW BC Hummus Sesame Chips 142g 3.75 3.95 12 5.95 9197051 10% 708163300219
Chic Nuts - Roasted Chickpeas & Broad Beans
Fantastic packaging, available in 200g bags or mini packs, these scrumptious savoury snacks
are best-sellers! Toasted, roasted chick peas and broad (fava) beans. The oil used is Monola,
which has been developed through normal breeding of non GMO canola oil. 100% Australian
owned and grown.
Product Description Carton($) Unit($) U/C RRP($) Item No GST Barcode Organic
CN Chic Nuts- Lightly Salted 200g 3.95 N/A 5 6.45 9304201 10% 9318471000520
CN Chic Nuts- Sicil’n Herb & Garlic200g 3.95 N/A 5 6.45 9304202 10% 9318471000537
CN Fava Nuts- Lightly Salted 200g 3.95 N/A 5 6.45 9304203 10% 9318471000568
CN Chic Nuts- Lightly Salted 6x25g 4.00 N/A 5 6.95 9304301 10% 9318471000544
CN Fava Nuts- Lightly Salted 6x25g 4.00 N/A 5 6.95 9304302 10% 9318471000551
CN Split Chics- Lightly Salted 6x25g 4.00 N/A 5 6.95 9304303 10% 9318471000582
CN Fava Nuts- Moroccan Roast 6x25g 4.00 N/A 5 6.95 9304304 10% 9318471000575
Cobs - Favourites Range
Welcome to the new range of pop-choco-liscious treats. If you’re devoted to your popcorn, then you’ll
love our latest - a delectable coating of caramel, smooth milk or decadent dark chocolate over Cobs
pure popcorn. Chocolate varieties are only available in the Sydney Metro Area - extra freight charges
apply.
Product Description Carton($) Unit($) U/C RRP($) Item No GST Barcode Organic
COBS Caramel Popcorn 125g 2.43 N/A 10 3.95 9381400 10% 9334714000225
COBS Milk ChocolateCaramel Popcorn 175g 5.00 N/A 10 8.25 9381401 10% 9334714000232
COBS Dark Chocolate Caramel Popcorn 175g 5.00 N/A 10 8.25 9381402 10% 9334714000249
Cobs Organic & Natural Popcorn
This popcorn is completely gratifying and unquestionably delicious. It is very
crunchy and fresh and comes in three great flavours. The original recipe pop-
corn is slightly sweet andslightly salty, and for thosewho prefer amore savoury
flavour, Sea Salt is perfect. For optimal freshness it has a 3–4 month shelf life,
but it is so popular you won’t have any trouble keeping it moving.
Product Description Carton($) Unit($) U/C RRP($) Item No GST Barcode Organic
COBS Original Organic Popcorn 125g 2.72 N/A 10 4.95 9381001 10% 9334714000010 ACO
COBS Original Organic Popcorn 40g 1.22 1.28 24 2.20 9381002 10% 9334714000102 ACO
COBS Sea SaltOrganic Popcorn 80g 1.86 N/A 10 3.30 9381101 10% 9334714000041 ACO
COBS Sea SaltOrganic Popcorn 25g 1.11 1.17 24 1.95 9381102 10% 9334714000058 ACO
COBS Cheddar CheesePopcorn 100g 2.00 N/A 10 3.30 9381251 10% 9334714000140
COBS Coco Crunch Popcorn 120g 2.00 N/A 10 3.30 9381253 10% 9334714000218
NEW COBS Natural Sweet&Salty Popcorn 120g 2.00 N/A 10 3.30 9381254 10% 9334714000157
NEW COBS Natural SeaSalt Popcorn 80g 1.57 N/A 10 2.60 9381257 10% 9334714000096
COBS Popcorn Multipack (10x13g) 130g 3.39 N/A 8 5.95 9381300 10% 9334714000164
Cocolo Organic Fairtrade Chocolate
Velvety, smooth and delicious, Cocolo contains no refined sugar,
only evaporated cane juice. Cocolo is made in Switzerland from
the finest Organic and Fairtrade ingredients. Thecocoa and evap-
orated cane juicecome from Fairtrade co-operatives. These com-
munities are able to reinvest in their farms, schools and commu-
nities by selling their beans through the Fairtrade market. We find
this very exciting, and we hope you do too! We choose to keep
Cocolo absolutely GMO free. We only use ingredients that are
produced in the traditional way, with special attention to purity of the product and sustainability of production. All dark flavours are dairy
free and thewhole range isgluten and soy free. CocoloDisplay Kit includes12 units each of Dark Orange, Milk, 70% Dark and Dark Mint.
Ask us if you prefer a different configuration.
Grocery
Figure 2
: One page from a product catalogue
generated with L
A
T
E
X. Text paragraphs, images and
tables are well-organized for each category. The whole
catalogue contains more than 70 pages, including
information on 800–1000 products. Courtesy of
Jason Lewis [35].
size of the files should be as small as possible in order
to save storage space; the cache mechanism of web
browsers should be utilized when possible, in order
to save bandwidth; the readers should not need to
wait long before viewing the first few pages, even if
there are thousands of pages in the document.
Therefore special optimizations are necessary
when producing an online version from a traditional
document.
3 Existing approaches
uite a number of approaches have been
developed to publish T
E
X or PDF contents
online. Possible workflows are shown in
Figure 3. It is possible to compile
3
a T
E
X
file into HTML; or to convert
4
a PDF document into
HTML.
3
To determine the layout based on the information from
the source.
4
To transform between two presentation formats, in both
of which layout and appearance are clearly defined.
Converting a large T
E
X file with complicated
layouts into PDF is usually not a fast process. Be-
cause of this, it is a common practice to convert the
source format into web pages on the server side, the
results can be stored on the servers, and sent to users
upon request.
On the other hand, nowadays JavaScript is al-
ready powerful enough for many tasks, and it can be
embedded
5
into HTML, in which case HTML is used
as a container — the embedded files are to be parsed
and rendered on the client side with JavaScript.
In order to utilize existing technologies, it is also
common to introduce intermediate formats, which
are to be converted or embedded into HTML. In
particular, PDF may be viewed as an intermediate
format while compiling T
E
X to HTML,
In this section we try to describe the most pop-
ular approaches and discuss them from different as-
pects. Although some of them might not be originally
designed for publishing, they are still listed here be-
cause they can be used to facilitate the process.
3.1 Raster image-based approaches
Approaches of this type render source files into raster
images (e.g. PNG, JPEG), usually one image per page,
which are then embedded into HTML. Popular tools
of this type include:
• pdftocairo from Poppler [27]
• ImageMagick [20]
• mathT
E
X [9]
• “fallback” mode of pdf2htmlEX
Pros
Raster images were introduced in a very early
stage of HTML, and so are highly compatible with old
web browsers. All visual elements can be displayed
correctly.
6
Cons
The main disadvantage of this type of ap-
proach is that the image sizes are usually huge. It
is costly to convert text into images and it is usu-
ally not easy to balance quality and size. Large files
consume large bandwidth of both server and client,
which also cause delays. Another issue is that all
semantic information is lost, users can no longer copy
text out from the document, nor follow the links.
Raster image-based approaches are “universal”, in
that they are widely used to publish many differ-
ent formats, not limited to T
E
X or PDF. Famous
examples include the Look Inside feature of Springer-
Link [11] and Google Docs Viewer [3].
5
To keep the source format as it is inside the target format.
6
For T
E
X and
PDF
, there are also advanced features like
audio, video, animation or annotation, etc., which are beyond
the scope of this article.
Online publishing via pdf2htmlEX
diff --git a/doc/tb108wang4.page b/doc/tb108wang4.page new file mode 100644 index 0000000..4d5ea40 --- /dev/null +++ b/doc/tb108wang4.page @@ -0,0 +1 @@ +
316 TUGboat, Volume 34 (2013), No. 3
T
E
X
compile
compile
%%
compile/embed
&&
Intermediate
Formats
convert/embed
//
convert
}}
HTML
Other
Sources
//
PDF
convert
==
convert/embed
88
Figure 3: Different approaches to publishing online.
The disadvantages can be compensated for to
some extent: A hidden text layer can be overlaid
above the images in order to simulate user text selec-
tion, however generating this text layer itself actually
involves other conversion technologies; for a respon-
sive user experience, the input document may be
converted into images with different resolutions, and
images with high resolutions can then be split into
small blocks. When the document is rendered on
the client side, only the block being viewed by the
user is needed to transfer. However much more disk
storage and network bandwidth is required in this
way, which might not be affordable for all publishers,
especially individuals.
3.2 SVG-based approaches
Scalable Vector Graphics, developed by W3C, is an
XML-based format for presenting 2D graphics. It
supports a similar set of features as PDF, including
color, gradients, patterns, paintings and raster im-
ages. It also supports font definition within SVG as
well as external fonts defined in CSS.
Due to the large feature set, most visual ele-
ments can be rendered with SVG counterparts. Pop-
ular tools in this category include:
• Inkscape [21]
• pdftocairo from Poppler [27]
• pdf2svg [26]
• dvisvgm [17]
• “fallback” mode of pdf2htmlEX
Pros Due to the similar nature between SVG and
PDF, it is relatively easy to find an SVG counterpart
for each PDF element. SVG is one of the few meth-
ods that support advanced layout features such as
characters along a curved path and image clipping.
SVG is based on XML, hence it can be easily
parsed or edited manually. SVG can be well inte-
grated with HTML/CSS, and it can be easily accessed
and manipulated by JavaScript.
Cons
Old web browsers do not support SVG, and
the degree of support for SVG varies for modern web
browsers.
While SVG-based approaches are powerful when inte-
grated with HTML, CSS and JavaScript, most tools
in this category do not support such integrations,
probably because they were designed as an SVG con-
verter instead of an online publishing tool.
3.3 Semantic HTML-based approaches
Approaches of this type try to find the matching
HTML element for each T
E
X element, for example
\section
and
\textbf
in T
E
X might become
<h1>
and
<b>
in HTML respectively. Popular tools in this
category include
• HEVEA [19]
• L
A
T
E
X2HTML [1, 37]
• L
A
T
E
XML [24]
• plasT
E
X [5, 29]
• T
E
X4ht [6, 33]
• T
E
X2page [14]
• TtH [12]
all of which are designed to process general T
E
X
files. There are also programs designed for particular
documents, for example
• The Feynman Lectures on Physics [28]
• The Stacks Project [38]
• The TUG Interviews Project [30]
Pros
Semantic HTML files are normally expected
by most users. Semantic information is retained in
an XML-like format, such that they can be read or
edited by a human or further processed by other
programs.
Basic elements such as colors, font family and
sizes, paragraphs, links, images can all be supported.
Lu Wang and Wanmin Liu
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TUGboat, Volume 34 (2013), No. 3 317
CSS can be used to specify the layout and appear-
ance. Math formulas may be semantically retained
via Unicode characters, MathML or embedded T
E
X
snippets (see Section 3.5).
Approaches of this type can be used when the
publisher does not rely on the layout produced by a
T
E
X compiler. They are often used for simple text-
based files without complicated layouts. The final
layout is determined by the web browser based on
the semantic structure and CSS rules.
Cons
Approaches of this type usually don’t work
well for PDF files. In general, PDF files do not contain
semantic information, and so recognition is inevitable
to detect semantic meanings, which is considered to
be hard. This is also true for other intermediate files.
On the other hand, T
E
X users do not necessarily
expect the same appearance as compiled by T
E
X.
Most advanced layouts in T
E
X cannot be used, for
example, double columns. Specific layouts might be
simulated, but it is hard in general due to the essen-
tial differences between the page model of T
E
X and
HTML. While font embedding is possible nowadays,
most tools of this kind do not support it.
Furthermore, this type of approach can be con-
sidered a re-implementation of T
E
X, as these tools
parse and process T
E
X syntax in their own engines,
and therefore some macros and packages may not
work with them, especially those related to drawing,
page layout or PDF-specific features. Sometimes the
authors have to prepare different versions of T
E
X
files for both HTML and PDF, and HTML knowledge
might also be required.
It is possible to achieve HTML documents in rather
good quality, while reserving not only semantic infor-
mation, but also well organized links, elegant styles
and MathJaX-based math formulas. Good examples
are [
28
] and [
38
]. However, most of them employ
project-specific tools and lots of engineering work,
and there are also limitations or paradigms for au-
thors. Therefore their methods might not work for
general documents.
3.4 Presentation HTML-based approaches
Approaches of this type focus on the layout and
appearance of the result, utilizing CSS rules to set
accurate position and size for each element, mostly
text. Non-text elements are usually converted into
images, raster or vector, which are embedded in the
HTML. They are still significantly different from
raster image based approaches or SVG based ap-
proaches mentioned above, as they do not convert
the whole document into images.
Prior to pdf2htmlEX, the pdftohtml utility from
Poppler [
27
] is probably the best known tool that is
freely available to the community. While pdftohtml
focuses more on extracting semantic information,
pdf2htmlEX focuses on precise layout and appear-
ance. There seems not to be any tools that directly
produce presentation HTML files from T
E
X, because
of course T
E
X users may produce PDF files before
further converting it into HTML.
Pros
Comparing this output with images, text is
now represented with native HTML elements, such
that they can be selected by users or easily extracted
by programs; the file size is heavily reduced in this
way. Also it is easier to apply CSS and JavaScript
to tweak the appearance.
Comparing with semantic HTML files, the ap-
pearance of presentation HTML output is often closer
or even identical to the original document. T
E
X users
are free to use any advanced layout, macro or pack-
age, fine-tuning will also be reflected in the output,
as the T
E
X page model is simulated in HTML.
Cons
While text is still available, the semantic
meanings (e.g. title, section, table etc.) are likely to
be lost. The content may be too complicated to be
further processed. Precise layout and appearance
rely on advanced CSS features, like font embedding,
absolute positioning and linear transformation, which
might not be supported by old web browsers.
3.5 JavaScript-based approaches for T
E
X
While T
E
X is not directly supported in HTML, mod-
ern JavaScript technologies allow us to embed these
files in HTML, such that they will be parsed and
rendered directly in the web browsers. Similar tech-
nologies for PDF are covered in Section 3.6.
MathJaX [
7
] is a JavaScript display engine which
parses and renders T
E
X snippets on web pages with
HTML/CSS, SVG or MathML. MathJaX is designed
for online communications where users want to di-
rectly input formulas in the T
E
X syntax. Similar
projects include jsTeX [2], and jsMath [4].
L
A
T
E
X2HTML5 [
22
] is able to produce interac-
tive diagrams from PSTricks macros; it also utilizes
MathJaX for rendering math formulas.
Pros
This kind of approach is best for dynamic
content, especially that intended to be created or
modified by users. Any modification to the source
can be reflected in the result promptly without any
network transmission. It can also handle documents
with simple layout, while formatting can be specified
with CSS.
Cons
Approaches of this kind are usually focus-
ing on specific elements; while they may support a
Online publishing via pdf2htmlEX
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318 TUGboat, Volume 34 (2013), No. 3
small set of T
E
X syntax, they are not designed as
a JavaScript implementation of T
E
X. Therefore ad-
vanced commands or macros may not be supported,
and usually they are not capable of typesetting gen-
eral documents with complicated layout.
3.6 JavaScript-based approaches for PDF
PDF.js [
13
] is a JavaScript library for rendering PDF;
it is now a part of Mozilla Firefox. It is like the
raster image-based approaches except that all the
parsing and rendering are done on the client side.
Recent web browsers are necessary to support the
technologies used by the library.
PDF.js is one of a kind; there are no similar
alternatives to the best of our knowledge.
Pros
PDF.js renders PDF files into an HTML5 can-
vas, which is similar to a raster image; most PDF
elements can be rendered correctly. Furthermore, it
does not suffer from a huge network cost as only the
original PDF file need be transferred.
The library can be embedded into web pages,
and can be extended by publishers if needed.
Cons
PDF.js relies heavily on the computation
power on the client side, which might cause per-
formance issues in some environments.
It is designed as a PDF reader, and it does not
optimize for online publishing; for example users still
have to wait for the entire file to be downloaded
before they can read any page.
PDF elements are rendered into an HTML5 can-
vas, which may not be flexible enough for publishers.
3.7 Plugin-based approaches
Many web browsers support plugins to add new fea-
tures, especially plugins can be used to display T
E
X,
PDF, or other formats converted from them. Publish-
ers may also develop plugins for their own formats,
which are otherwise not supported by web browsers.
Adobe Reader includes plugins to display PDF
files within different web browsers. There are also
similar third-party plugins based on Adobe Flash.
There are also plugins to display math formulas inside
web browsers, e.g. MathPlayer [23].
Pros
Plugins are not limited to web technologies,
thus they are usually better in term of rendering
quality or supported features. For example, Adobe
Reader should be the plugin with the most complete
support for PDF features.
Cons
The crucial downside is that plugins usu-
ally create closed environments, which prevent an
interactive user experience on the web sites. Most
plugins are not easily customizable, except for a few
commercial ones. Due to the active development of
HTML5 technologies, plugins nowadays are no longer
so popular as before, for security, compatibility and
performance reasons.
3.8 Third-party services
Third-party services also exist such that embedded
T
E
X or PDF can be redirected to their servers for
processing and rendering, for example:
• QuickL
A
T
E
X [10]
• mathT
E
X [9]
• Google Docs [3]
• Crocodoc [15]
This kind of service accepts input uploaded
by publishers, converts it internally with their own
implementations and redirects the result to users.
The technologies behind them, open or proprietary,
should still fall into the categories mentioned above.
Pros
This kind of service is usually easy to deploy,
and convenient for publishing a few simple docu-
ments. The conversion process relies only on the
computation power of the third party. Some ser-
vices also provide an API for better integration with
publishers’ sites.
Cons
A crucial issue here that may concern a lot
of publishers is that the files must be accessible by
the third party. This may not be acceptable for
private, confidential or copyrighted materials. In
addition, the publisher’s service has to depend on the
availability of the third party. Further development
may also be limited by the API provided or other
issues such as different domains.
3.9 Discussion
In this section we categorized a number of popular
approaches, among which the most popular three
types of output are:
Image
is best for publishers who can afford large
volume of storage and bandwidth. There is no need
to fine-tune or even redesign the document, as layout
and format are already accurately preserved in the
output. Yet this highly compatible result can be
viewed by most users.
Semantic HTML
is best for simple T
E
X source
files. All semantic information is preserved in the
output, which can be further processed by other
tools. In particular, math formulas may be rendered
interactively with latest web technologies.
Presentation HTML
is best when complicated
layout, advanced T
E
X macros and packages are used.
It is also suitable when the source files are not avail-
able at all. PDF files produced from other tools can
Lu Wang and Wanmin Liu
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TUGboat, Volume 34 (2013), No. 3 319
also be supported. Flexibility of semantic HTML and
accuracy of image are cleverly balanced.
In general there is no best approach for all situations.
Users should carefully choose the best matching one
according their specific concerns.
While we tried our best to be complete and
accurate, it is quite possible that we have missed
or misunderstood some approaches due to the lim-
itations of our knowledge. Please contact us for
corrections or suggestions, and thank you.
4 A tour of pdf2htmlEX
n this section we introduce pdf2htmlEX,
created and mostly written by Lu Wang,
which is an open source PDF to HTML
converter. It generates presentation HTML
documents, utilizing modern Web technologies such
as HTML5, CSS3, JavaScript, etc., such that most
PDF features can be retained. Especially fonts, math
formulas and images can all be displayed correctly.
Figure 4: Logo of pdf2htmlEX
pdf2htmlEX is not only a converter, but also
a publishing tool. It is designed for many different
situations, for example:
Scenario 1
My sister wants to put her resum´e
on her online homepage. She wants the resum´e to
be stored into one single file such that it can be
easily downloaded by others. She also needs to add
JavaScript code to track how many people have read
her resum´e.
Scenario 2
A book publisher wants to put some
sample books online to attract readers. The publisher
does not want readers to wait for too long before they
can read any page, thus pages are better converted
and stored separately. Images and fonts should also
be stored in individual files such that users may
benefit from web caches.
Scenario 3
A cloud storage service provider wants
to provide a PDF preview feature to their service,
such that users may read their files online. The
service provider needs to design their own viewer to
match the theme and behaviour of their web site.
They also want to attach advertisements based on
the contents of the files. Advanced users may be
allowed to leave marks and discuss with others about
particular parts of the documents. In this case the
service provider needs the finest control — they need
to access every single element of the document for
their customizations.
We can see that different forms of HTML files are
desired in different scenarios, and flexibility is always
necessary. pdf2htmlEX is indeed designed for all
these scenarios and many others; some features have
been requested or implemented by users.
In this section we will introduce a few useful
features and explore some internal mechanisms of
pdf2htmlEX. More information, including source
code and license terms, is at the project home page:
https://github.com/coolwanglu/pdf2htmlEX
4.1 Quick start
Throughout this section, a sample PDF file is used to
demonstrate different features of pdf2htmlEX. The
file,
integral.pdf
, contains 4 pages from the book
Differential and Integral II [
16
,
36
], which consists
of Japanese characters, mathematical symbols and
formulas, figures, images and delicate layouts. We
believe that it reflects common elements used in real
use cases.
To start with, we simply execute
$ pdf2htmlEX --fit-width 1024 integral.pdf
which produces a single HTML file
integral.html
.
The result is shown in Figure 5,
7
and we challenge
the readers to find any evidence or clues that the
screenshot shows an HTML file instead of PDF. (Ex-
cept for the title bar of course.)
The
--fit-width 1024
option specifies that
each page should be squeezed or stretched to the
width of 1024 pixels. The zoom ratio can be adjusted
with similar options: --fit-height and --zoom.
It is possible to convert only a few pages of a
PDF file, for example
$ pdf2htmlEX -f 2 -l 3 integral.pdf
converts only the second page and the third page.
4.2 Separating resource files
By default everything is combined into one single
HTML file, which is good for creating archives or
performing tests. However, it is not a good practice
when publishing HTML documents online; often we
want resource files (fonts, CSS, JavaScript, images
etc.) to be stored separately in order to reduce size
and improve efficiency.
With the
--embed
option, we can decide which
types of resource files are embedded and which are
not. For example,
$ pdf2htmlEX --embed fi integral.pdf
7
Mozilla Firefox 24 on Ubuntu 13.04 is used for all the
demonstrations.
Online publishing via pdf2htmlEX
diff --git a/doc/tb108wang8.page b/doc/tb108wang8.page new file mode 100644 index 0000000..8076128 --- /dev/null +++ b/doc/tb108wang8.page @@ -0,0 +1 @@ +
320 TUGboat, Volume 34 (2013), No. 3
Figure 5: An HTML document produced by pdf2htmlEX.
Figure 6
: Above: by default all resources are
embedded in the HTML file. Below: with the
--embed
fi
option, fonts and images are stored into separate
files and linked to the HTML file.
stores all fonts and images in separate files, as shown
in Figure 6. There are also specific options including
--embed-css, --embed-font, --embed-image, etc.
4.3 Splitting pages
With a large PDF file containing hundreds of pages,
often we have to download the whole file even if we
want to take a look at only a few pages inside. On
the other hand, web pages are usually stored into
separate files, such that we just need to download
the pages we request.
Figure 7
: Above: by default all pages are embedded
in the HTML file. Below: with
--split-pages 1
, pages
are stored in separate HTML snippets, which can be
dynamically loaded to the main HTML file.
With the
--split-pages
option, it is possible
to store PDF pages into separate HTML snippets. In
this way, when the main HTML file is loaded on the
client side, only necessary pages will be dynamically
loaded via Ajax, as shown in Figure 7.
4.4 Image format for backgrounds
For each page, pdf2htmlEX generates a background
image to present all non-text elements. By default
Lu Wang and Wanmin Liu
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TUGboat, Volume 34 (2013), No. 3 321
all images are generated in the PNG format, and dif-
ferent formats can be specified via the
--bg-format
option. For example,
$ pdf2htmlEX --bg-format jpg integral.pdf
would generate all images in the JPEG format.
Currently pdf2htmlEX supports PNG and JPEG.
There is also preliminary support for SVG. Users
can also convert the images into other formats.
4.5 Customizing the output
integral.html
contains a default set of HTML, CSS
and JavaScript, which is designed for average use
cases. All of them can be found in the so-called
data-dir
(run
pdf2htmlEX -v
to see the location),
and they can be tweaked by the users.
HTML template
The
manifest
file determines
how pages should be combined into an HTML docu-
ment. It is a template for the output and users may
add their own HTML snippets into it. A typical use
case is enabling a traffic statistics service on the page.
CSS
Quite a number of features of pdf2htmlEX rely
on CSS; the default CSS styles determine the correct
appearance and behavior of the elements. Advanced
users can override existing properties by modifying
the CSS files.
JavaScript
A simple UI is implemented in the
default
pdf2htmlEX.js
file. This also serves as a
demonstration of accessing and manipulating HTML
elements produced by pdf2htmlEX. It can be a good
reference for advanced users who want to implement
their own UIs.
4.6 Secrets of pdf2htmlEX
Here we briefly introduce some internal mechanisms
of pdf2htmlEX for the curious readers.
integral.html
consists of two layers: the text
layer and the image layer, as shown in Figures 8 and 9.
pdf2htmlEX parses
internal.pdf
and extracts ele-
ments from it. The elements are then processed and
put into one of the layers.
Text
Unlike in HTML, in PDF text is set in fixed
positions. Text extracted from the PDF is translated
into native HTML text elements, and put into the
same position in the HTML as they were in PDF. In
this way text can be selected and copied by users,
while preserving the layout. Many fixed-position text
elements in HTML make the file very large in size
and very slow to render; to compensate, pdf2htmlEX
tries to recognize and merge text lines according to
their geometric metrics.
Font
Font embedding is one of the most important
features of PDF, without which it is nearly impos-
sible to preserve the appearance of PDF in HTML.
No similar feature has been supported in the HTML
standard until recently. Figure 10 shows a few fonts
used in
integral.pdf
. pdf2htmlEX is able to ex-
tract all the fonts from PDF and convert them into
web fonts via FontForge [
18
]; converted fonts are
then embedded or referred to in the HTML file. All
font formats supported in PDF are supported by
pdf2htmlEX, and different web font formats can be
specified for output.
Encoding
Unlike HTML, PDF uses two sets of en-
codings for text rendering, one for choosing correct
glyphs to display, and the other for meaningful text
that can be selected and copied by users. pdf2htmlEX
is able to combine both sets into one and re-encode
the font accordingly, such that text in HTML is cor-
rect both visually and meaningfully. This is another
essential feature of pdf2htmlEX, like font processing.
Images
PDF supports graphical instructions such
as drawing and image embedding. Such elements
are all rendered into images, and then put into the
image layer.
4.7 Future work
Several features are planned in the future versions
of pdf2htmlEX.
Reflowable text
Comparing with HTML files di-
rectly converted from T
E
X, text in HTML files gener-
ated by pdf2htmlEX is generally not reflowable, i.e.
the width of paragraphs cannot be self-adapting to
the size of the viewer. After all, that information is
generally not available in a PDF file, and it is not
easy for pdf2htmlEX to recover it.
On the other hand, reflowable text may be
extracted for specific document types and layouts.
Extracting such information would make it much
easier to further process HTML files generated by
pdf2htmlEX, such as to edit manually, to embed
accessibility information or to convert into other
formats like EPUB.
Preserving semantic information
While much
semantic information is lost in PDF as mentioned
above, theoretically it is possible for authors to em-
bed additional information into PDF, such that it
may be further recognized and used by pdf2htmlEX.
This kind of PDF file is called a tagged PDF, which
can also be generated with other tools.
Especially for T
E
X users, it is possible to mark
text paragraphs such that text will be reflowable in
HTML to some extent; also, mathematical formulas
may be marked such that they will be rendered with
MathJaX in HTML.
Online publishing via pdf2htmlEX