WO1989006396A1

WO1989006396A1 - Bit-mapped graphic printer with direct screen raster uptake

Info

Publication number: WO1989006396A1
Application number: PCT/US1989/000081
Authority: WO
Inventors: Mark Crowley; Mark Gillies; Vincent Benjamin Ravo
Original assignee: Flanders Research Incorporated
Priority date: 1988-01-11
Filing date: 1989-01-10
Publication date: 1989-07-13
Also published as: AU2940989A

Abstract

Method and apparatus for displaying and printing a high resolution graphics image stored in a common bit map memory (200). Data from the common bit map memory (200) is sent to both a printer (230) and a display (220) so that the printer (230) and display (220) print and display, respectively, images which both correspond to the common bit map memory (200).

Description

BIT-MAPPED GRAPHIC PRINTER WITH DIRECT SCREEN RASTER UPTAKE Technical Field The present invention pertains to methods and apparatus for printing and displaying images. Background Art

The introduction of so-called "personal'*' or "desktop" computers spurred the development of many different cathode ray tube (CRT) monitor displays and controllers. The monitor displays used with early personal computers could display text but not pictures. The reason for this is that the early displays could not address a single dot position on the screen, referred to hereinafter as a pixel. Although subsequently designed display adapters can address single pixels, the screen resolution of the CRT display resolution is unacceptably small for many graphics applications.

Laser printers which can print an 8.5" x 11" page at 300 dpi (dots per inch) are also available. These have been employed to provide a so-called "desktop publishing system". The term "desktop publishing system" refers to a personal computer based system which can print pages incorporating text in various type styles or "fonts" in conjunction with pictures, thus approximating the appearance of printed matter produced by conventional publishing methods. In desktop publishing, one needs to control the lightness or darkness of the individual, dots printed by the laser printer in order to support various typefaces and to integrate graphics with text.

The desktop publishing market is growing. It is easier, and faster, to design and edit a page and get a copy from a desktop publishing system than it is to: (a) create text with a typewriter or word processor; (b) send it to a typesetter; (c) have a graphics artist paste up pages; and (d) then make proof copies for review. It is cheaper to print the page on the laser printer to determine what the page will look like, make the desired changes and then repeat this process, than it is to repeat the conventional proofing process described above. As a result, the turnaround time from conception to final copy is reduced by using a desktop publishing system. Moreover, the 300 dpi resolution provided by the desktop publishing system affords a level of print quality which is acceptable as the final printed copy in many applications. In these cases, the desktop publishing system can perform the entire task, and conventional printing process can be entirely omitted.

Creating intricate graphics and desktop publishing have a common need, i.e., the ability to accurately edit an image of a final copy before it is printed. However, the presently available systems do not fully satisfy this need. Present systems are normally equipped with a display apparatus which has a screen resolution of less than 150 pixels per inch (usually 72 pixels per inch) , whereas the resolution of a laser printer is typically 300 dots per inch. The disparity in resolution between the display apparatus and the laser printer makes it impossible for a user to view the final copy on his display apparatus precisely as it will appear when printed. Moreover, the systems typically available heretofore are complex and slow. FIG. 1 depicts the flow of information in a typical prior art desktop publishing system including a display apparatus 110 and a printer" 100. Printer 100 is arranged to print images at 300 dpi whereas display apparatus 110 displays images at a lower resolution, typically at 72 dpi. When the user inputs data via, for example, a keyboard entry system (not shown) , an element of a display list 120 is generated by application program 125 and stored within host computer 130 in accordance with well known methods. Display list 120 includes data denoting elements such as graphic figures and characters to be included in the i age, data describing where each such element is to be placed within the image, and other data further defining the image to be displayed. Thus, where characters are to be displayed, the display list would include data denoting the type style or "font" to be used for the characters. For example, if one entered 14 pt Helvetica text via the keyboard entry system, the display list 120 would include data indicating the text characters and also data indicating that the 14 pt Helvetica font should be used for their characters. In order to display this text on display apparatus 110, screen display driver 140 must first generate a "bit map" of the desired image of the 14 pt Helvetica characters. A "bit map" is a representation of a two-dimensional image as a set of digital values such that each individual value represents a visually perceptible characteristic such as brightness or darkness of a single point in the image. Inasmuch as each value in the bit map corresponds to a single point or pixel in a displayed image, the term "pixel value" can be used to refer to an individual value in a bit map. The bit map generated by display driver 140 typically includes a relatively small number of pixel values equal to the number of pixels available on the relatively low-resolution display 110. This bit map is stored in display bit map memory 155 for use by display apparatus 110. Display apparatus 110 creates and displays an image corresponding to this bit map in accordance with well known methods.

Once the user is ready to print the displayed image, the application program 125 interrogates display list 120 and causes page description statement builder 135 to build a description of the image. In accordance with present usage, a higher level printer language, called a page description language, such as Postscript, DDI, and Interpress, is used to encode the image defined by display list 120 into an intermediate form for transmission to printer 100. Thus, the indirect representation of the image embodied in the display list is encoded into the syntax of the higher level printer language for transmission between host computer 130 and printer 100 using printer driver 145. At printer 100, the encoded display list is stored as a set of "page description statements" in this higher level language. A page description statement interpreter 175 interrogates the stored page description statements and generates a printer bit map in printer bit map memory 180. A raster image processor (not shown) provides the computing hardware to power this interpreter. The printer bit map includes a pixel value for each dot in the image to be printed by printer 100, and hence includes more pixel values than the display bit map. Printer engine 185 prints in image corresponding to printer bit map 180 using well known techniques.

Prior art systems as described above incur several significant penalties. A designer of a host system stored in PC 130 needs to understand the high level page description language used to convert display list 120 into an intermediate form for transmission to printer 100. Further, the page description language and/or interpreter 175 typically is subject to substantial license fees; and significant processing delays are incurred as a result of the separate transformations of display list 120: (1) for displaying an image by display apparatus 110; (2) for building page description statements in host computer 130; and (3) for interpreting the page description statements into a separate printer bit map in printer 100. in summary, in the prior art system shown in

FIG. 1, the original information incorporated in display list 120 undergoes three different transformations prior to printing — once to form the display bit map for display on display apparatus 110; once for transmission to printer 100; and once to form the printer bit map. All of this results in a complex system which operates slowly. In particular, transformations to and from the high-level page description language are time-consuming. For example, the amount of time used for processing an image can slow down an eight-page-per-minute printer to a rate of one page every few minutes or less. Moreover, the complex hardware and software used in the system entail increased cost and increased probability of system failure. Despite all of this cost, complexity and delay, such systems still do not provide for display of an image which accurately corresponds to the printed image. Therefore, these systems do not fully meet the needs encountered in desktop publishing and graphics applications. Disclosure of the Invention

One aspect of the invention provides apparatus for printing and displaying an image. This apparatus preferably includes display means such as a cathode ray tube or the like for receiving a bit map and displaying an image directly corresponding thereto. The apparatus also includes printer means, desirably a laser printer or other dot-by-dot printer, for receiving a bit map and printing an image directly corresponding thereto. Means for converting a representation of the image to be displayed into a bit map, referred to herein as a "common" bit map, are also provided in this apparatus. Appropriate means are provided for transmitting replicas of the common bit map to the printer means and to the display means.

Because the bit map received by both the display means and the printer means are replicas of the common bit map, the printed and displayed images are accurate duplicates of one another. Preferably, the display means is arranged to display an image including a number of pixels equal to the number of dots in the printed image. Thus, each pixel in the displayed image corresponds to a single dot in the printed image. The brightness or darkness of each pixel in the displayed image, and of the corresponding dot in the printed image, are determined by the same pixel value in the common bit map. Thus, the displayed image may be a substantially perfect duplicate of the printed image.

The apparatus preferably includes common memory means for storing the common bit map. Each of the replica-transmitting means may include means for retrieving the common bit map from the common memory means. Thus, each replica-transmitting means may simply retrieve the pixel values constituting the common bit map and transmit these values to the printer means or to the display means. Thus, the replica of the common bit maps are provided as streams of pixel values to the printer means and to the display means. Preferably, each such stream of pixel values is provided at a rate substantially matching the rate at which the receiving device converts the values to the actual printed or displayed image. Where the operating rates of the printer and display are different from one another, the replica-transmitting means may be arranged to retrieve the pixel values at different rates. In preferred apparatus according to this aspect of the present invention, matching bit maps are provided to the printer means and to the display means simply by replicating the common bit map. The information such as a display list representing the image need only be transformed into a bit map one time. Apparatus according to this aspect of the present invention thus avoids the need for the complex, costly and slow components and software employed heretofore to encode the display list into high-level page description statements, to transmit these to the printer and then to construct a separate printer bit map from these statements at the printer.

Further aspects of the present invention provide methods of displaying and printing an image which incorporate method steps generally corresponding to the operations discussed above in connection with the apparatus. Yet another aspect of the present invention provides improvements in raster-based displays such as cathode ray tube displays. Brief Description of the Drawings The principles of the present invention may be clearly understood by considering the following detailed description in conjunction with the accompanying drawing, in which:

FIG. 1 shows, in pictorial form, a prior art display and print system;

FIG. 2 shows, in pictorial form, a display and print system in accordance with one embodiment of the present invention; and

FIG. 3 shows, in pictorial form, a less detailed, overview block diagram of the embodiment shown in FIG. 2.

To facilitate understanding, identical reference numerals have been used to denote identical elements common to the figures. Best Mode of Carrying Out Invention

FIG. 2 shows a preferred embodiment of the inventive display and print system. As shown in FIG. 2, ultra-high resolution or "UHR" controller 200 comprises the parts which are included within dotted line 210 and interfaces with high resolution CRT display 220 and a non-impact, dot-by-dot printer such as laser printer 230. UHR controller 200 is an ultra high resolution display and printer controller and, in this embodiment, can control a 2560 (horizontal) x 3300 (vertical) pixel display. More specifically, in this embodiment, UHR controller 200 can control a common bit map memory 360 and display it on CRT display 220 as an 8.5" x 11" display having a resolution of 300 elements (dots or pixels) per inch. Resolution figures stated in this disclosure in units of "dpi" should be understood as referring to the number of dots or pixels per inch. Note that this resolution matches the resolution of a typical laser printer and enables the inventive display and print system to provide a high resolution image on the screen of CRT display 220 which matches the resolution of an image printed by laser printer 230 from a single, common bit map memory 360. As a result, the inventive display and print system can provide a screen image which we term a WYSIWYG image, i.e., "what you see is what you get." This is so termed because the resolution of the image displayed on the screen of CRT display 220 duplicates the resolution of the image printed by laser printer 230. One should further note that the embodiment of UHR controller 200 disclosed in

FIG. 2 is also capable of controlling a display of 2480

(horizontal) x 3500 (vertical) pixels to provide a

WYSIWYG image of an image printed on Din A4 paper (210 mm x 297 mm) at 300 dpi.

In accordance with the embodiment of the present invention shown in FIG. 2, UHR controller 200 drives 300 dpi laser printer 230 by interfacing directly with laser engine 240, i.e., by transmitting and receiving signals thereto over leads 620. A laser engine is a term well known to those of ordinary skill in the art and refers to the combination of two parts of a laser printer which are known to those of ordinary skill in the art as the "mechanics" and the "laser controller." The "mechanics" includes that part of the laser printer which is concerned with the physical act of printing and loading paper, such as the motors and the rollers. The "laser controller" receives signals sent from UHR controller^' 200 over leads 620 and transmits signals from the "mechanics," which signals represent various printer conditions, such as, "paper is loaded", back to UHR controller 200 over leads 620. Further, it is well known in the art that print image data is transmitted to a laser printer in the form of a signal which mimics, in many respects, a TV video signal. By that, we mean that the signal includes horizontal and vertical synchronization signals, a blanking signal and a serial data stream. Still further it is well known that one may purchase a laser printer which only has a laser engine from many manufacturers. As a result, as will be described in greater detail below, in the embodiment shown in FIG. 2, signals transmitted from UHR controller 200 are directly input into the laser controller portion of laser engine 240. The laser controller portion of laser engine 240, in turn, interfaces with the "mechanics" portion of laser engine 240 to receive "mechanical" signals, such as "paper ready", "motor ready", "roller ready" and so forth, in a manner which is well known to those of ordinary skill in the art. The laser controller portion of laser engine 240 then relays these "mechanical" signals back to UHR controller 200 over leads 620. When laser printer 230 is ready to print, UHR controller 200 transmits horizontal and vertical synchronization signals, blanking signals and serial data to the laser controller portion of laser engine 240 over leads 620. Note, as will be described in detail below, laser printer 230 is supported directly by the same bit map which is used to provide the image formed on the screen of CRT display 220.

In accordance with one embodiment of the present invention, CRT display 220 utilizes the same bit map as laser printer 230 and has the same resolution as laser printer 230. Specifically, CRT display 220 comprises an ultra high resolution 15" or 19" 660 MHz CRT monitor display along with associated logic to provide the desired 8.5" x 11" or 210 mm x 297 mm area at a resolution of 300 dpi. CRT display 220 comprises the following parts which cooperate in a well known manner: CRT monitor 270; yoke 250; horizontal and vertical deflection logic 280; and video amplifier 260.

CRT monitor 270, which comprises a portion of CRT display 220, is a high resolution display which is capable of supporting a deflection rate of approximately 205 kHz and more than 9 x 10⁶ pixels. Such a CRT display is available commercially. Yoke 250, which for s a portion of CRT display 220, is a conventional stator-wound yoke designed for a deflection rate of approximately 205 kHz. Such a yoke is available commercially. Horizontal and vertical deflection logic 280, which forms a portion of CRT display 220 and interfaces with yoke 250, is fabricated in accordance with standard deflection designs well known in the art which utilize FET transistors. Deflection logic 280 drives yoke 250 at horizontal and vertical deflection ' rates of approximately 205 kHz and 60 Hz, respectively.

Finally, video amplifier 260, which forms a portion of CRT monitor 270 and interfaces with the electron gun of CRT display 270, is fabricated in accordance with ultra high frequency RF designs which utilize microwave stripline bipolar transistors. Video amplifier 260 is designed to operate at rates of 647 MHz and higher.

UHR controller 200 comprises the following parts which cooperate in a manner which will be explained in detail below: (1) host computer bus interface 300; (2) refresh and triple port memory controller 310; (3) UHR graphics processor 350; (4) common bit map memory 360; (5) UHR graphics processor memory 370; (6) raster/video controller 380; (7) printer interface 390; and (8) printer interface buffer 400.

A host computer system, not shown, receives data from a user to define a graphic image or text characters for display. In^' accordance with well known methods and apparatus, the host system generates and stores an element of a display list therein. Then, a display driver in the host computer system encodes the image defined by the display list elements into a specific syntax for transmission to UHR controller 200. Such syntax examples are defined by the host computer "environment" such as X-windows, Microsoft windows, DGIS, and so forth. Such host computer systems are commercially available and use computers such as the VAX computer sold by Digital Equipment Corporation, a computer sold by Sun Microsystems, a computer sold by Apollo Computer, the IBM PC-AT computer sold by IBM Corp., and the Macintosh computer sold by Apple Corp. An interface between the host computer system and UHR controller 200 is provided by host computer bus interface 300. Host computer bus interface 300 is a standard hardware interface which enables data to be transmitted between the^'host computer and UHR controller 200. Specifically, data from the host computer which represents the display list of the image input by the user is transmitted to common bit map memory 360 and to UHR graphics processor memory 370 by means of refresh and triple port memory controller 310. The specific destination is determined by the addressing features of the display interface protocol, which are well known to those of ordinary skill in the art. Specifically, the data transmitted from the host computer conforms to a display interface protocol which includes a set of commands and data in a well known format which allows applications programs executing in the host to communicate with peripherals in order to effect changes on displays.

Refresh and triple port memory controller 310 provides memory refresh of dynamic memories and also provides arbitration and contention monitoring for three-port access to common bit map memory 360 and UHR graphics processor memory 370. Port 320 of refresh and triple port memory controller 310 interfaces to host computer bus interface 300 over leads 640; port 330 interfaces to UHR graphics processor 350 over leads 650; and port 340 interfaces to raster/video controller 380 over leads 660. Refresh and triple port memory controller 310 is fabricated in a well known manner by utilizing a refresh controller and memory arbitrator logic circuits, along with programmed array logic circuits (PAL) and standard multiplexing logic. UHR graphics processor 350, for example, the TMS34010 graphics co-processor microprocessor sold by Texas Instruments, Inc. of Houston, Texas, periodically scans UHR graphics processor memory 370 for commands sent thereto from the host computer in the protocol of the well known display interface. UHR graphics processor memory 370 is dynamic RAM which is organized as 1,048,576 x 16 bits to serve as a first working memory for UHR graphics processor 350. UHR graphics processor 350 accesses UHR graphics processor memory 370 by means of refresh and triple port memory controller 310 over leads 650 and 670. Whenever UHR graphics processor 350 detects a specific predetermined command it generates a pixel representation of the image transmitted from the host computer in a manner which is well known to those of ordinary skill in the art. The pixel representation is stored as a bit map in common bit map memory 360. Common bit map memory 360 is a dynamic RAM, dual port memory which is refreshed by refresh and triple port memory controller 310. Common bit map memory 360 is organized as eight (8) segments of 64K x 32 bit RAM and has one 32 bit parallel input- output port and one serial input-output port. UHR graphics processor 350 accesses common bit memory 360 by means of refresh and triple port memory controller 310 over leads 650 and 680. The UHR graphics processor 350 performs only one transformation of the display list data into a bit map, which is stored in common bit map memory 360. Raster/video controller 380 reads the bit map stored in common bit map memory 360 over leads 630 which provide a 32 bit highway. In order to read the data stored in common bit map memory 360, raster/video controller 380 provides refresh and triple port memory controller 360 with an address over leads 660. Refresh and triple port memory controller 310 transmits this address, along with a transmit command, to common bit map memory 360 to cause it to transmit data including the individual pixel values constituting the common bit map over its serial port to raster/video controller 380 over the 32 bit highway formed by leads 630. The data which is transferred represents one raster scan line's worth of data for the raster scan of CRT monitor 270, specifically, a 32 bit wide x 500 bit deep slice of data from common bit map memory 360. Raster/video controller 380 then converts this data into a single, serial multiplexed data stream and shifts that data stream to video amplifier 260 over lead 600. Raster/video controller 380 also generates horizontal and vertical synchronization signals and a blanking signal for transmission to horizontal and vertical deflection logic 280. The electron beam within CRT monitor 270 sweeps across the screen of the monitor in accordance with these synchronization signals, while the amplitude of the beam is controlled by video amplifier 260 in accordance with the pixel value data. The pixel value data is supplied in synchronism with the moving beam, so that the brightness of each spot or pixel on the screen is controlled by a corresponding pixel value.

To provide the large number of pixels in the display, the pixel value must be furnished to video amplifier 260 at a high rate, typically about 647MHz. Raster/video controller 380 utilizes a standard commercial chip to provide video raster control functions such as horizontal and vertical line, synch width, front porch and back porch counters, as well as a memory counter. Such a chip provides a "dot clock" or series of intervals and the video synchronizing functions in synchronism with the dot clock. In conventional monitors, one bit or pixel value is transmitted to the video amplifier and hence to the brightness control circuitry of the cathode ray tube during each interval of the dot clock. Thus, the data rate of the display is limited to the maximum dot clock rate of the chip. However, commercially available chips for these functions have a maximum dot clock rate far below the dot rate" required in the present high- resolution display. According to this aspect of the present invention, this problem is solved by supplying a plurality of bits of brightness information, and hence a plurality of pixel values, during each interval of the dot clock. Preferably, eight bits of data are transmitted at each dot clock signal of the chip by reinserting the pixel value data from the common bit map into the video data stream. This enables the use of a standard, commercially available CRT controller chip at speeds not normally considered compatible with such a part, and avoids the alternative of building this logic with a large number, approximately sixty, of smaller, high speed chips. As discussed above, UHR graphics processor 350 periodically scans UHR graphics processor memory 370 for commands sent thereto from the host computer. When a predetermined command is detected which calls for printing an image which is stored in bit map memory 360, UHR graphics processor 350 controls this process as follows. UHR graphics processor 350 interfaces laser printer engine 240 by way of printer interface 390 to determine if laser printer 230 is available for printing, i.e., to determine if paper is loaded and so forth. If laser printer 230 is available for use, UHR processor 350 reads a portion of the common bit map from memory 360 by means of refresh and triple port memory controller 310 over leads 650 and 680. UHR processor 350 transmits this data over leads 720 for storage in one or the other of two segments of printer interface buffer 400. Printer interface buffer 400 is a dynamic RAM, dual port memory which is refreshed by refresh and triple port memory controller 310. Printer interface buffer 400 is organized as two 64K x 16 bit segments and UHR graphics processor 350 interfaces with printer interface 390 over lead 700.

In operation, printer interface 390 reads data from one segment of printer interface buffer 400 while UHR graphics processor 350 is filling the other, which operation alternates until the printing is done. In addition, UHR processor 350 transmits horizontal and vertical synchronization signals and blanking signals to printer interface 400. This is merely a design choice and not a requirement of the present invention, which design choice occurred because the particular commercially available chip designated above which was used to build UHR graphics controller 350 had this capability already built in. Printer interface 390 receives pixel value data from printer interface buffer 400 over leads 710, converts it to a serial bit stream, and transmits it, along with the horizontal and vertical synchronization signals and the blanking signals, to laser engine 240 over leads 620. Thus, laser engine 240 prints an image wherein the darkness or brightness of each dot corresponds to a pixel value in the common bit map stored in memory 360. Printer interface 230 is fabricated in accordance with methods well known in the art. In particular, the specific design is determined by the specific printer with which it interfaces.

If any error occurs during printing, such as a paper jam, printer interface 390 receives a signal from laser engine 240 and sends a status signal back to UHR graphics processor 350. In turn, UHR graphics processor 350 generates an appropriate bit map in a portion of video bit map memory 360 for subsequent display on CRT monitor 270 of CRT display 220. Once a page is printed, printer interface 390 transmits a signal to UHR graphics processor 350 to indicate that the print process has been completed and that CRT display 220 may now be put back "on line" for other purposes.

In a further embodiment of the present invention, UHR graphics processor 350 freezes the display, i.e., the image displayed on CRT monitor 270 of CRT display 220 is not changed, until the printing operation is completed by laser printer 230; i.e., UHR graphics controller 350 does not initiate the transformation of a new bit map until the printing is complete.

In still a further embodiment, printer interface 390 interfaces directly with laser printer engine 240 in the manner described above and also with an additional raster image processor (RIP) in laser printer 230. In this embodiment, printer interface 390 will send a special coded signal to the RIP of the printer. In response to this signal, the RIP is placed into a state wherein it "believes" that laser engine 240 is unavailable for use thereby. In this embodiment, the inventive system can be used with a laser printer which is connected to the host computer or to a network in the conventional way through an RIP in the printer. As a result, this enables system fabricated in accordance with the present invention and a conventional system to share the use of a common laser print engine. Further, this enables one to use laser printers without having to physically remove an existing RIP. FIG. 3 shows a less detailed block diagram of the embodiment of the inventive apparatus depicted in FIG. 2. In FIG. 3, host computer 800 interfaces with display apparatus 220 and printer 230 for example, a laser printer. The creator of a graphic image uses the system shown in FIG. 3 to build images for display on display apparatus 220 and to print the images using printer 230. In FIG. 3, printer engine 240 prints images at 300 dpi and display apparatus 220 displays images at 300 dpi. Of course, it should be clear to those of ordinary skill in the art that other embodiments of the invention may use other display and/or printing resolutions. When a user inputs data via, for example, a keyboard entry system (not shown) , the application program 225 builds an element of display list 810 within host computer 800. Display list 810 provides a means for describing where the element of the graphic image is to be placed on the printed image as well as defining the image to be displayed. In order to display the image on display apparatus 220, driver 820 encodes elements of display list 810 for transmission to the UHR controller 200 utilizing the syntax of the host computer "environment." In this embodiment, UHR controller 200 is configured as a series of boards which reside in host computer 800. As described above, UHR controller 200 forms a common bit map. UHR controller 200 then interfaces with display apparatus 220 to provide a display image and interfaces with laser printer 240 to provide a printed image which are each generated from the common bit map. As a result, laser printer engine 230 provides a printed image which is exactly the same as the image stored in the common bit map memory. Thus, in accordance with the inventive apparatus, we have provided a WYSIWYG system where an image in the common bit map memory is the same as the printed image.

In accordance with the above-described embodiment of the present invention, it will be recognized by those of ordinary skill in the art that, aside from the differing data rates, the serial data transferred to display apparatus 220 for display and to laser printer 230 for printing are the same. Further, other embodiments of the present invention may be formed by storing the bit map formed in common bit map memory 360 on storage devices. Still, further, the bit map may be recovered from these storage devices and printed even though the image is no longer simultaneously displayed on CRT display 220. In addition, the image provided by the bit map stored in common bit map memory 360 may be displayed and/or printed on any number of different displays or printers, such as on any of a number of well-known non-impact, dot-by-dot printers.

In particular, as has been described above, one particular advantage of the present invention results from the fact that the common bit map is created by a single transformation of a display list. This is contrasted with the many different transformations which are required in prior art systems to provide a display and a printed image.

In the embodiment described above, the data streams or replicas of the common bit map transmitted to the display means and to the printer are each "exact" replicas of the common bit map. That is, the pixel values in the replicas correspond 1:1 to the pixel values in the common bit map. Likewise, the printed and displayed images correspond exactly to the replicas; each such image includes a pixel or dot corresponding to each pixel value in the replica. This arrangement assures that the printed and displayed images are substantially identical to one another.

According to the broad compass of the invention, however, the replicas transmitted to the printer and display need not be exact. Thus, inexact replicas of the common bit map can be made by omitting some pixel values of the common bit map, or by creating each pixel value in the replica by averaging a plurality of pixel values from the common bit map, so as to form a replica with fewer pixels. Likewise, the printer and/or display can be arranged to disregard some pixel values in the replica transmitted to it, or to control the brightness of each pixel or dot depending on an average of a plurality of pixel values in the replica so that the image corresponds to the replica inexactly. These alternatives are generally less preferred. However, a replica with fewer pixels can be provided to the CRT display where the display is a relatively low-resolution device. Regardless of whether the replicated image is exact or inexact, conventional methods of data compression can be used in the transmission of same.

Although particular embodiments of the present invention have been shown and described herein, many varied embodiments incorporating the teachings of the present invention may be easily constructed by those skilled in the art. For example, the replicas and common bit map may be stored in means other than random access memory, such as disk, tape, etc. Industrial Applicability

The present invention can be used for in-house printing and publishing, as well as for commercial printing and publishing.

Claims

What is claimed is:

1. Apparatus for displaying and printing an image characterized by the combination of:

(a) display means (220) for receiving a bit map and displaying an image corresponding thereto;

(b) printer means (230) for receiving a bit map and printing an image corresponding thereto;

(c) means (350) for converting a representation of the image to be displayed and printed into a common bit map;

(d) means (630, 380) for transmitting a replica of said common bit map to said display means; and

(e) means (310, 350, 330, 650, 680, 400, 390) for transmitting a replica of said common bit map to said printer means, whereby said display means and said printer means will display and print, respectively, images which both correspond to said common bit map.

2. Apparatus as claimed in claim 1, characterized in that said transmitting means are operative to transmit exact replicas of said common bit map to said printer means and said display means and , characterized in that said printer means and said display means are operative to print and to display, respectively, images corresponding exactly to said replicas, whereby both the printed and displayed images correspond exactly to one another.

3. Apparatus as claimed in claim 2, characterized in that said display means and said printer means are operative to print and display images of the same resolution.

4. Apparatus as claimed in claim 1, further characterized by common memory means (360) for storing said common bit map, said means for transmitting including means (310, 630) for retrieving said common bit map from said common memory means.

5. Apparatus as claimed in claim 4, characterized in that both of said means for transmitting are operative to retrieve said common bit map from said common memory means simultaneously but at different rates.

6. Apparatus as claimed in claim 1, characterized in that said means for transmitting .are operative to transmit said replicas to said printer means and said display means at different rates.

7. Apparatus as claimed in claim 1, characterized in that the display means comprises a cathode ray tube display.

8. Apparatus as claimed in claim 1, characterized in that the printer means comprises a dot- by-dot printing means.

9. Apparatus as claimed in claim 8, characterized in that the dot-by-dot printing means is a laser printer.

10. Apparatus as claimed in claim 1, characterized in that said printer means is operative to print an image at a resolution of at least 300 dots per inch.

11. Apparatus as claimed in claim 10, characterized in that said display means is operative to display an image at a resolution of at least 300 pixels per inch.

12. Apparatus as claimed in claim 1, characterized in that said means for converting includes means for transforming a display list into said common bit map.

13. Apparatus as claimed in claim 12, characterized in that said means for transforming a display list includes means for transforming a display list including data denoting characters and data denoting fonts associated with said characters into sets of pixel values for incorporation into said bit map.

14. Apparatus as claimed in any one of the preceding claims, further characterized by means for altering the common bit-map.

15. Apparatus as claimed in Claim 14 further characterized in that said means for altering the common bit-map includes means for altering the representation of the image to be displayed and supplying said altered representation to said means for converting, whereby said means for converting will provide an altered common bit-map.

16. A method of displaying and printing an image which comprises the steps of:

(a) converting a representation of the image into a common bit map; (b) transmitting a replica of said common bit map to display apparatus;

(c) displaying on said display apparatus an image directly corresponding to the replica transmitted thereto; and (d) transmitting to a printer a replica of said common bit map; and

(e) printing on said printer an image directly corresponding to the replica transmitted thereto, whereby said printed and displayed images will both correspond directly to said common bit map.

17. A method as claimed in claim 16, characterized in that said steps of transmitting replicas to the printer and display apparatus include the steps of transmitting exact replicas of said common bit map to said printer and display apparatus, and , characterized in that said displaying and printing include the steps of displaying and printing images corresponding exactly to said transmitted replicas and hence corresponding exactly to said common bit map.

18. A method as claimed in claim 17, characterized in that said displaying and printing steps are performed so that said displayed and printed images are of substantially the same resolution.

19. A method as claimed in claim 16 further characterized by the step of storing said common bit map in a common bit map memory, each of said transmitting steps including the step of retrieving said stored common bit map.

20. A method as claimed in claim 19, characterized in that said transmitting steps are performed so as to transmit pixel values constituting said common bit map from said common bit map memory to said printer and said display apparatus at different rates.

21. A method as claimed in claim 16, characterized in that said converting step includes the step of transforming a display list including data denoting characters and data denoting fonts associated with said characters into pixel values and incorporating said pixel values in said common bit map.

22. A method as claimed in any one of Claims 16 through 21, further characterized by the step of altering the common bit-map and then repeating the steps of transmitting the common bit-map to the display apparatus and displayng so as to edit the common bit-map and the displayed image prior to said steps of transmitting the common bit-map to a printer and printing.

23. A method is claimed in Claim 22, further characterized in that the steps of altering the representation of the image to be displayed and repeating the converting step using the altered representation.

24. A method of operating a video display including a control chip characterized by the steps of:

(a) providing a series of dot clock intervals at said chip such that said clock intervals occur at a first rate less than the maximum clock rate of said chip;

(b) operating said chip to generate video control functions synchronized with said series of dot clock intervals and controlling the said video display according to said control functions; and

(c) passing a plurality of data bits to said display during each said clock interval in the series and controlling the brightness of the display according to the data bits so transmitted, whereby data bits are applied to control the brightness of the display at a second rate higher than said first rate.