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Description  |
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This invention relates to electronic publishing, a technology employing
electronic means for creating, storing, revising, transmitting and
on-demand printing of documentation.
Many companies, particularly those engaged in highly technical product
development and sales, have many product lines and products in their
business portfolios. An exceedingly large number of different documents
needed to support each product may have to be kept on hand. A continuous
flow of requests for such documents tend to be constantly received from
prospects, customers, field salesmen, international sales, customer
training, distributors, and service. Literature shortages that delay the
fulfilling of such document requests may result in poor field morale,
unhappy customers, and, ultimately, lost business. A hiatus in supply, for
example of instruction manuals, may result in late shipments and delayed
or even diminished revenues.
If document shortages, and the problems they cause, are to be avoided,
printed material should be treated in the same manner as manufacturing
inventory. As new documents are printed, they should go through receiving,
be inspected, sent to the literature distribution room, logged into the
literature inventory, and placed in an assigned shelf space. To know when
it is time to reorder, either a continuous inventory should be maintained
by logging each piece of literature as it is sent out or, alternatively,
reorder points must be established and periodic inventories need be taken.
The costs of inventorying product support documentation, including the not
insignificant cost of the space taken up by the material, can be quite
high. In addition, one must also consider the cost of keeping artworks,
photographs, flats, printer's negatives and the like on file to allow
documents to be revised and reprinted.
A company's literature frequently needs revision because product
specifications tend to change, engineering revisions are often made on
existing products and must be communicated to field service personnel, new
applications for products arise and need to be documented for the field
sales force, and mistakes found in instruction manuals have to be
corrected. Since it is almost impossible to predict when a particular
document will require revision, it is difficult to estimate how many
should be printed at any time. Although the cost per copy of printing goes
down as the press run goes up, ordering a large press run risks having the
savings wiped out when a revision necessitates scrapping literature. Too
small a press run means an excessively high piece price, plus the price of
reordering and reinventorying. Even with the best of planning,
unanticipated revisions obsolete a significant fraction of the literature
inventory.
A company may either set up an in-house printing facility or send its
printing to outside shops. Inhouse facilities require additional trained
personnel, space and management time. Outside printing requires additional
scheduling, obtaining competitive bids, issuing of purchase orders,
inspecting incoming material for quantity and quality, and routing the
material to the literature inventory room.
The preparation of technical support documentation by conventional methods
without electronic publishing, may require considerable effort and
coordination among a large number of individuals such as engineers,
writers, photographers, designers, typesetters and printers. Writers must
work, often hand in hand with technical personnel such as engineers and
scientists, to produce technically accurate copy. Illustrators may be
needed to make drawings and diagrams, or photographers may be retained to
produce photographs to be included in the copy. The document must be laid
out. Copy needs to be typeset and proofread against the original text.
Drawings may be photostatted to size and pasted-up to produce artwork for
the printer. Using a special camera, the printer usually produces
negatives that are used to make proofs which must be examined for mistakes
in paste-up and for imperfections in the art work or film. The
reproduction of photographs also involves cropping, sizing and converting
the photograph into half-tone negatives for conversion to printing plates.
Only when all of these steps, and possibly many others, are completed, may
printing actually begin.
To circumvent the many problems encountered when documents are provided by
conventional means, digital computer-controlled electronic devices, known
as electronic publishing systems, are being increasingly used in the
preparation, revision, storage and printing of documentation. Such
publishing systems should be capable of handling documents containing all
of the various categories of printed materials such as any combination of
typographic characters, line art and continuous tone pictures. As used
herein, the term "typographic characters" is intended to include, but not
be limited to, letters of alphabets (e.g Roman, Russian, Greek, Arabic,
Armenian and Kanji), ideographs (e.g. Chinese and Japanese), numbers,
punctuation marks and accents, and mathematical and scientific symbols, in
any and all fonts, point sizes and spacing. As used herein, the term "line
art" is intended to include a variety of lines-on-plane images such as
graphs, charts, engineering drawings, schematics, outline sketches and the
lixe. The term, "pictures" refers to continuous tone images, such as
photographs, frames of video, half-tone reproductions and the like.
Electronic publishing systems typically comprise mass storage means or
memory for electronic storage of information, a workstation for the user
to provide input data and instructions for the creation and revision of
documents, an appropriately programmed digital host computer, and
electronic printing means for printing documents in accordance with
electrical signals provided by the computer. The term "electronic
printing", as used herein, includes means for producing, under computer
control, plain paper hardcopy or reproduction masters, e.g. printing
plates, photosensitive paper, film or like materials. An important type of
printing device, particularly useful in the present invention, is a
horizontal line-raster printer, (hereinafter simply referred to as a
line-raster printer) e.g. typically one in which a light beam is adapted
to be (1) focussed to a small spot on a photosensitive surface, (2)
intensity-modulated by an electrical signal, (3) rapidly deflected so as
to sweep the spot along a first line between margins, and (4) returned to
the beginning margin with a small displacement normal to the sweep line so
as to be positioned for sweeping along a second line parallel to the first
line. One type of such a line-raster printer, known as the laser printer,
employs a laser beam as the light beam, and forms a printable image on a
xerographic surface from which plain paper hardcopy may be produced by
conventional xerographic techniques. Another category of line-raster
printers, known as electronic typesetters, use a laser beam or light from
a fiber-optic cathode ray tube to produce a printable image on
photosensitive film. The film may be used to make printing plates for
document reproduction on conventional letterpress or offset presses.
A typical workstation includes a high-resolution electrooptical imaging
device, (e.g. 1000 to 2000 lines), typically a cathode ray tube (CRT)
terminal for displaying images of the pages being created and revised; a
keyboard for text entry and correction; and a screen-pointing and control
device such as a "mouse" or "trackball". The workstation eliminates the
time-consuming paste-up of blocks of typeset text and graphics onto flats,
thereby simplifying preparation and revision of documents. Through the
agency of the workstation and the assistance of the host computer,
documents can be created using a set of rules for page layout, including
such parameters as margin width, column width, type style or font, type
size, line spacing and justification.
To create a document, the text intended to appear on a page is entered into
the system either at the workstation or at a remote word-processing
terminal linked to the system computer by a conventional communications
line. A typeset version of the text is produced based on the key strokes
and operator-selected choices of font, margins, column width and line
spacing, thus permitting the operator to see a page image, i.e. a preview
of how each page will look when printed, and permits proof-reading and
editing of the typeset text directly on the screen. At a scale of
one-to-one, the page image will be the same size as the page to be
printed, the individual characters appearing in the same size, typestyle
and at the same coordinates as they will appear on the printed page. Some
systems also permit display of line drawings and other graphic elements,
as well as typographic characters.
Images of typographic characters, line art and other graphics are formed on
the workstation screen from a series of display pixels (basic picture
elements) provided by control of the excitation of the tube phosphor at
each point on the display. The visual intensity of the phosphor points are
controlled in a binary (i.e. on-off) manner by an electronically stored
array of single-digit binary numbers or bits, the array being known as a
bit-map. Each number of the array corresponds to a pixel on the screen,
the rows of the arrays corresponding to the raster lines. In most systems,
each raster line displayed on the CRT has a width or height about equal to
the pitch of the line, i.e. the spacing between raster lines, center to
center. Each raster line is divided into segments each of which
constitutes a pixel, each segment being dimensioned so that horizontal and
vertical lines on the screen, when one pixel wide, will have the same
width. Thus, the resolution, expressed in pixels/inch, is typically the
same as the pitch.
Similarly, a bit map may be used to carry out electronic printing on a
line-raster printing device. In such instance, a series of small pixels
are electronically printed onto a substrate under the control of a bit
map, the printed matter being rendered with an intensity contrasting with
the substrate or background. While it is possible to drive a line-raster
printing device with the same bit map used to generate the page image on
the CRT, this is not generally done because the printing is of inferior
quality because of the relatively low resolution of the bit map.
While there are obvious economic advantages in using the screen bit map to
produce electronically printed pages, limitations in reasonable-cost,
commercially-available technology limit CRT displays to about 2000 lines
of resolution. On the other hand, even a relatively low-resolution, laser,
line-raster printer with a resolution specification of 240 lines per inch
(or 2,640 lines to output an 11-inch page) has a higher resolution than
most high-resolution workstation screens. A 400 line per inch printer
requires 4,400 lines to output a page, and a 1000 line per inch
laser-to-film device requires 11,000 lines.
Thus, generally a second, higher resolution bit map is produced within the
line-raster printing device from a series of commands and text strings
sent from the workstation to processing means in the line-raster printing
device. Such processing means typically comprising a microprocessor,
memory and means for generating a bit map, uses digital descriptions of
the various typographic characters stored in its memory, to build a bit
map of greater detail than the one used to control the display. The use of
separate microprocessors and bit maps in the host computer and the raster
printing device increases the complexity and cost of the electronic
publishing system.
It is desirable that electronic publishing systems be able to display and
print continuous-tone pictures such as photographs and frames of video.
Consequently, continuous-tone pictures are typically digitized into an
array of numbers larger than one binary bit, wherein each number or
gray-scale pixel represents the level of gray at a point within the image
that has been sampled and expressed as a number. For example, an array of
two digit (or bit) binary numbers allows four levels of gray to be
displayed, whereas, eight-bit binary numbers or bytes, allow 256 levels to
be displayed. In practice, six-bit binary numbers (allowing 64 levels of
gray to be displayed) represent a good compromise between limiting the
size of the binary numbers used and maintaining the quality of the image
displayed. The use of less than six-bit numbers usually cause the display
of photographs and other gray-scale images to contain certain artifacts
due to the different levels of gray within the picture appearing as
visible bands.
Several limitations of the bit-map displays makes the use of gray-scale
displays preferable in electronic publishing systems. Bit map displays are
unable to display continuous-tone pictures and images except as
low-resolution dithered pictures, that is, crude images having the
brightness or darkness of relatively large local areas of the picture
represented by differing numbers of on and off display pixels at different
areas of the screen. Another limitation of the bit-mapped display is the
so-called staircase effect in which the diagonal edges of typographic
characters and line art displayed on the screen have a jagged or saw-tooth
appearance. The staircase effect can be largely overcome on gray-scale
displays by displaying the pixels that would form notches in diagonal
edges on a bit map display at intensities intermediate to the on and off
states. The technique, well known as anti-aliasing, is quite desirable
because, at any given screen resolution, the legibility of displayed
alphanumeric characters appears to be enhanced, making them look more like
the corresponding printed version.
As is well known to those acquainted with the printing arts, the
reproduction of continuous tone pictures (such as photographs) on plain
paper involves the use of a half-tone pattern, a family of small shapes,
typically dots or lines typically printed at regular intervals of, usually
50 to 150 per inch.
Half-tone patterns can be produced on the electronic printing device by
dividing the page into small, equalsized, rectangular, preferrably square
areas or cells. Each cell has a cluster of printed dots arranged within
it. A small cluster of printed dots corresponds to a light gray gray-scale
pixel and a large cluster corresponds a dark gray gray-scale pixel. The
family of these cells constitutes a set termed hereinafter "super-pixels."
Super-pixels are printed by the line-raster printing device by dividing the
bit map into small sub-arrays, the size of which determines the number of
different gray-scale values that can be expressed. For example, to print
images with 64 density levels of gray, a cell or super-pixel eight raster
lines in height and eight printing dots across can be utilized. Thus, one
can provide 64 cells each having a unique density level provided by a
respective matrix of dots or points. A light gray super-pixel can be
produced by printing only a few dots inside the cell, whereas a dark gray
super-pixel can be produced by printing all but a few of the maximum
possible 64 dots within the cell.
A coding scheme using weighted sets of two-dimensional functions, known as
area character coding, was developed by Altemus and Schaphorst to achieve
compression in facsimile transmission, but was apparently not considered
favorable for gray-scale imagery according to W. K. Pratt, Digital Image
Processing, John Wiley & Sons, N.Y., 1978, pp. 705-706.
To simplify the mapping process, each of the different super-pixels can be
assigned a unique super-pixel index number, usually in binary form. For
example, a super-pixel index number of 111111 can be assigned to a light
gray or white super-pixel and 000001 to a very dark gray super-pixel.
These index numbers can also be used to set the intensity of the CRT
screen display, 111111 turning a selected portion of the screen phosphor
on to full brightness and 000001 setting the screen phosphor intensity at
that or another portion to almost the minimum level. Super-pixel index
numbers thus representing the intensity of a gray-scale pixel in a picture
on the CRT screen can also be used to map the appropriate super-pixel
within the printing device. Further, the gray-scale super-pixel index
number (in the above example) is only six bits as opposed to the sixty
four bits used in the bit map to print the equivalent of the super-pixel.
This, in effect, represents a data compression of better than ten-to-one.
Some electronic typesetters (providing resolutions in excesss of 1000 lines
per inch) feature so-called half-tone screen generation, i.e. within
specified area of a page image, a half-tone picture can be printed from an
array of gray-scale values using a super-pixel scheme. However, when
applied to laser printers, the super-pixel scheme is of only limited
usefulness. In most publishing applications, continuous-tone images are
reproduced at resolutions of 50 to 150 gray-scale pixels per inch. To
reproduce pictures with a resolution of 100 gray-scale pixels per inch,
super-pixels eight raster lines in height are required to reproduce
pictures with 64 levels of gray. In order to print half-tone pictures at a
resolution of 100 super-pixels per inch, a laser printer with a resolution
of 800 lines per inch is required. This is much higher than that of the
inexpensive, currently-available laser printers typically having
resolutions in the range of 240 to 400 raster lines per inch. The
alternatives, so far, have been the printing of gray-scale pictures with
64, or more, levels of gray, but at resolutions far less than 100
gray-scale pixels per inch; the printing of pictures at 100 pixels per
inch, or higher, but with far fewer levels of gray than 64; or, most
frequently, the printing of pictures at resolutions of less than 100
gray-scale pixels per inch with less than 64 levels of gray.
When individual copies of documents are to be printed on-demand on a laser
printer, each page may be different. If the electronic publishing system
is be able to print the document at the rated printing speed of the
printing device, hardware for generating the printer bit map must be able
to generate new maps at not less than the printing rate of the printing
device. As the resolution of the printer is increased, the size of the map
grows as the square of the increase, limiting the on-demand printing
capability of the electronic publishing system. For example, to print an
81/2.times.11 inch page, a laser printer with a resolution of 240 lines
per inch requires a bit map containing 5,385,600 bits. Raising the printer
resolution to 800 lines per inch (needed to print 100 64-level
super-pixels per inch) requires a map containing 59,840,000 bits.
Reasonably-priced hardware is not currently available to generate such a
large map substantially in real time.
While the use of a gray-scale monitor allows digitized continuous-tone
pictures to be seen at full resolution and allows characters and line art
to be seen without the staircase effect, its use makes the electronic
publishing system more complex because separate data bases must be
produced to describe the areas of the page image that are text and that
are digitized pictures, and separate maps must be used for display and
printing. The need for these separate data bases makes the arrangement and
rearrangement of the page images more difficult and slower with any given
host computer.
A principal object of the present invention is therefore to provide a novel
electronic printing system that permits a high level of performance to be
achieved at significantly lower cost than has been possible with prior art
configurations. Yet another object of the present invention is to provide
such a system that permits the display of page images containing
typographic characters, line art and gray scale pictures, the typographic
characters and line art being anti-aliased for improved legibility.
Other objects of the present invention are to provide such a system in
which page images may be printed directly and with relatively high
resolution from an electronic map used to display substantially the same
image as an electrooptical display device; to provide such a system
capable of printing gray scale images with at least 64 gray levels and a
resolution of at least 100 super-pixels/inch on line-raster printing
devices with resolutions under 800 line/inch; to provide a system that
includes an electro-optical display and a graphic printer, which system is
capable of integrating typographic characters and/or graphics information
and half-tone screen information, all in a single data base from which one
may either (or both) print the data out on the printer or display the data
on the display; to provide such an electronic printing system that
requires substantially less working memory to display and print pages than
had been required by prior art electronic printing systems; and to provide
such a novel electronic printing system that is relatively independent of
the printing characteristics of its printer.
To effect these and other objects of the invention, there is provided a
novel system for displaying page images including typographic characters,
graphics and/or gray scale, which system comprises storage means
containing a set of substantially disjoint index numbers divided into two
different subsets. The term "disjoint", as used herein, means having no
members in common in a set, i.e. every number is unique. The term
"substantially disjoint", as used herein, is intended to indicate,
however, that not necessarily all, but most, of the members of a set are
unique.
The first subset of index numbers stored contains gray-scale information
and thus represents a set of gray-scale super-pixels corresponding in
number to the set of levels in the gray scale of the system.
In the present invention, the dots or points in selected cells are
arbitrarily ordered to represent one or more shapes embodying information
with respect to an edge of a character or graphic form as well as
incorporating a "gray-scale" aspect. Thus, the second subset of index
numbers includes such information regarding the shape (including
orientation) of an edge and preferably represents a set of another type of
super-pixels (i.e. shape-segments) corresponding to preselected fragments
of typographic characters and line art.
Means are provided for storing an image of the data to be displayed or
printed, as an array of the index numbers ordered in accordance with those
data. Means are also provided for setting the intensity of a corresponding
pixel on an electrooptical display screen in accordance with each of the
index numbers stored in the array, and for controlling the printing of a
pattern of dots with a cell to produce corresponding gray-scale
super-pixels or shape-segment super-pixels accordingly as the index number
is in the first or second subset. The spatial arrangement of dots in each
printed super-pixel embodying gray-scale or edge-shape information is to a
large extent arbitrary and is clearly dependent upon the capabilities of
the printing device itself. Thus, it is to be understood, in essence,
while the gray-scale and edge-shape information is abstract, the printed
embodiment is only an approximation of the abstract information, and that
embodiment may be varied according to the printing equipment employed or
improvements made to such equipment.
The system also includes main digital memory means for storing the data
(digitized text, line art, pictures etc.) as a plurality of binary-encoded
words each of the binary-encoded words containing one of the index
numbers.
The system of the present invention also includes digital-to-analog
conversion means connected to the output of the storage means, for
converting a sequence of the index numbers into a sequence of
corresponding analog signals. Means are included for coupling the output
of the digital-to-analog conversion means to a CRT so as to activate
selected pixels of the latter in accordance with the sequence of analog
signals.
In a preferred embodiment of the present invention, the system also
includes a video camera for forming photographic images and converting
same into at least some of the digital data to be displayed by the system.
The invention described hereinafter provides, inter alia, not only a system
for electronic editing of a page on a CRT and for printing that page
substantially as shown, but, in another sense, provides an improved data
compression and decompression system that permits one to both display and
print subtantially the same page of typographic characters, graphics
and/or pictures with a considerably reduced amount of electronic storage
and processing equipment.
Other objects of the invention will in part be obvious and will in part
appear hereinafter. The invention accordingly comprises the apparatus
possessing the construction, combination of elements, and arrangement of
parts which are exemplified in the following detailed disclosure and the
scope of the application of which will be indicated in the claims.
For a fuller understanding of the nature and objects of the present
invention, reference should be had to the following detailed description
taken in connection with the accompanying drawings wherein:
FIG. 1 is a block diagram illustrating the principal parts of a system
embodying the present invention;
FIG. 2 illustrates several idealized and enlarged typical gray-scale
matrices shown as FIGS. 2a-c inclusive;
FIG. 3 illustrates several idealized, enlarged typical micro-shapes or
shape-segment matrices shown as FIGS. 3a-e inclusive;
FIG. 4 is an enlargement of an alphanumeric character formed as a composite
array of selected shape-segment matrices; and
FIG. 5 is a graphical representation of a | | |
