GB2239582A - "Paintbox" system converts linework image to high resolution - Google Patents

Abstract

The system comprises a stylus and touch tablet combination 10 by which a user can draw low resolution data representing a continuous tone linework image into a store 13 and a monitor 7 for displaying the linework image while it is being created. Once created, the linework data is filtered 22 (see Fig 2) to produce high resolution binary (2-level) data which is stored in a bit store 23. The binary data is used to control a printer 28 such that high resolution picture data from a store 4 and user selected colour data defining the colour of the linework are selectively printed by the printer to produce colour separations for use in printing an image in which the picture and the linework are combined. This system overcomes the problem of blurred linework produced by previous "Paintbox"-type systems at high resolution. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO ELECTRONIC GRAPHIC SYSTEMS FIELD OF THE INVENTION The invention relates to electronic graphic systems.

BACKGROUND OF THE INVENTION Electronic graphic or image systems in which the painting or drawing of a colour. picture can be achieved by electronic means are known. One such system is included in our electronic graphic equipment sold under the trademark "PAINTBOX" and described in our British Patent No. 2,098,625 and corresponding US Patent No. 4,514,818, the teachings of which are incorporated herein by reference. This equipment includes user operable means, in the form of a stylus and touch tablet and a menu of facilities displayed on a display monitor, by which the user can select from a range of colours and a range of notional drawing implements for use in painting or drawing a picture.

The user paints or draws by choosing a desired colour and implement, and then manipulating the stylus on the touch tablet and thereby causing the touch tablet to generate a series of position signals defining the path or position of the stylus. A processing circuit derives pixels for a patch of points in the picture and these derived pixels are written to a picture store. To enable the user to observe the picture being created, the store is read repeatedly and the pixels are applied to a TV-type colour monitor, thus enabling the build-up of the picture to be observed. The number of pixels to be processed by the processor is dependent on the resolution of the system, that is to say the number of pixels per unit of picture area.While real time processing can usually be achieved in systems operating to television standards, including even high definition standards such as 1125 lines per frame at 60 fields per second, difficulties are encountered where print quality resolution of say 4000 x 5000 picture points or greater is required. Furthermore, there is a difficulty in displaying such high resolution pictures because TV-type monitors of this resolution are not readily available, and because the large number of pixels makes it difficult to display the image in real time as it is being drawn by the user.

We have previously proposed the use of commercially available TV-type monitors to display in real time a low resolution representation of a high resolution image as that image is being created. One system which adopts this approach uses a down converting circuit to create a low resolution representation of the initial image. This system is disclosed in our British Patent Application No.

8919852.7. In this system data relating to a low resolution control image is drawn by the user, by way of an arrangement similar to that in our abovementioned British Patent No. 2,098,625 and corresponding US Patent No. 4,514,818. The control image is used to control the combining of other image data, for example a user selected colour, with data defining the low resolution representation of the initial image so as to produce a low resolution combined image which is continuously displayed on the display monitor. This system is further arranged so that once desired modifications have been achieved by the user to the image displayed on the display monitor, the low resolution control image is converted into a high resolution control image.The high resolution control image is then used to control the combining of the other image data with the initial high resolution image to produce a modified high resolution image.

Thus, the above discussed systems each provide electronic means by which a user can create image data for display on a monitor and/or for subsequent printing.

Generally, the method of storing data in raster form is suitable for storing photographic type images, i.e. continuous tone pictures, wherein an image is composed of amorphous areas of shade or tone, rather than for storing images comprising straight sharply defined lines. This is because the storing of data in raster form limits reproduction of straight lines to dots in predetermined positions. As a result, a line made up from these dots will appear to be jagged ("jaggies"), because the dots follow the regular grid defined by the raster format rather than the true path of the line. The above discussed systems avoid the problem of jaggies in continuous tone pictures by producing smooth transitions from one area of shade to another as is per se well known.

The above described systems are accordingly particularly well suited for creating, modifying and storing continuous tone pictures and the like.

However, they are not particularly suitable for working with linework images, i.e. images composed of arbitrarily positioned lines, such as in calligraphy, alpha-numeric text or logos, even at high resolution, because the method of producing smooth transitions between adjacent areas of shade or colour inevitably leads to a slight blurring at the boundary between the areas. In the case of linework this will remove the sharpness from the edges of the lines and whilst this blurring may be acceptable in some situations, it will be unacceptable in many situations where printed images which include linework will require sharp boundaries to be defined between the picture and the linework.

OBJECTS AND STATEMENTS OF THE INVENTION The invention aims to provide a system in which a linework image, in which sharp line boundaries are defined, can be produced from image data stored in a raster type continuous tone format.

According to one aspect of the invention there is provided an electronic graphic system, in which low resolution pixel data relating to a continuous tone image representing at least one arbitrary positioned line or area is processed to produce corresponding high resolution binary pixel data which can be used in the production of a high resolution printed image comprising the said at least one line or area.

By defining linework at a high resolution, i.e. a high spatial resolution, and in terms of binary, i.e.

"print" or "no print" data, a linework image with sharp line boundaries can be produced.

The low resolution pixel data can be stored in a framestore and once linework has been created to the user's satisfaction patches of the low resolution pixel data are integrated to produce correspondingly high resolution pixel values which are each compared with a predetermined threshold to produce said binary data.

In an embodiment of the invention, as will be described in greater detail hereinafter, high resolution data representing a continuous tone picture is stored in a store means and together with the binary pixel data can be used in the production of a high resolution image in which the picture and the said at least one line or area are combined.

In order to facilitate use of the system the data representing the picture can be down converted to a low resolution representation thereof for display on a display monitor.

In the embodiment, with the picture displayed on the monitor the user can draw the linework at the required position or positions in the picture and to this end, user selectable colour data representing the colour of the said line or area is combined with the low resolution picture data under the control of the low resolution pixel data for display of the resulting combined image on the monitor.

Once the binary pixel data has been produced it can be stored in a bit store and from there delivered, together with the high resolution picture data and the colour data, to a printer for driving means to produce colour separations representing the image such that the binary pixel data controls switching of the said means between the picture data and the colour data.

In one preferred arrangement a separate linework separation is printed. Using this arrangement, registration of the separations during a subsequent printing process can be facilitated by arranging the system so that the high resolution pixel values are each compared with a lower and a higher predetermined threshold to produce two sets of said binary data.

When the separations representing the picture are being printed, one set of binary data is used to produce a relatively narrow gap to be filled by the linework, and when the separation representing the linework is being printed the other set of binary data is used to produce linework which is slightly wider than the gap. Subsequent use of the thus produced separations in the printing of the combined picture and linework results in a slight spreading of the linework ink beyond the gap in the picture inks thereby ensuring full coverage of the gap by the linework.

In another preferred arrangement separations representing the combined linework and picture are produced.

According to another aspect of the invention there is provided an electronic graphic system comprising user operable means for creating a linework image in the form of low resolution continuous tone linework data, storing means for storing said linework data, display means for displaying the linework image while it is being created, filter means for filtering the linework data to produce high resolution binary linework data, binary storing means for storing said binary linework data, and controlling means associated with a printer and responsive to said binary linework data for controlling production of an image including the linework image.

Preferably the system further comprises storing means for storing high resolution picture data defining a continuous tone picture, and wherein the controlling means is adapted to control delivery of the picture data and the binary pixel data to printing means within the printer thereby to enable an image including the continuous tone picture to be produced.

The above and further features of the invention together with advantages thereof will become clearer from consideration of the following detailed description of an exemplary embodiment of the invention given with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic block diagram of an exemplary electronic graphic system according to the present invention; Figure 2 is a more detailed diagram for explaining the functioning of a filter included in the graphic system of Figure 1; and Figure 3 is a graphical representation of the function performed by the filter of Figure 2.

DETAILED DESCRIPTION OF THE EMBODIMENT OF THE INVENTION An electronic graphic system 1 embodying the invention is shown in Figure 1 of the accompanying drawings. The system 1 comprises a bulk storage device or store 2, which for example may be a Fujitsu multi disc pack or any other suitable high capacity storage device, for storing data defining at least one and usually a large number of pictures to be printed.

The picture data held in the store 2 will normally have a resolution suitable for high quality colour printing and thus will typically have a resolution of up to say 5000 x 10000 pixels per picture and is held in the store 2 in a format determined by the manufacturer of the store. A buffer 3 is provided for converting the picture data output from the store 2 into byte serial bit parallel format for use by the rest of the system 1. It will be appreciated that the system 1 will also include further buffers, address signal generators and the like for controlling the transfer of data about the system. However, these parts of the system 1 have been omitted from Figure 1 for the sake of clarity of explanation.

Data, in the correct format, output from the buffer 3 is input to a picture framestore 4. Data in the picture framestore 4 is read to a combiner 5, the operation of which will be described in greater detail hereinafter, and from there is output to an optional matrix 6 which converts the data into the correct colour representation for display on a monitor 7.

Colours are normally defined in graphic systems as either a combination of Red, Green and Blue (RGB) components or a combination of Cyan, Magenta, Yellow (CMY) - and in some cases Black also (CMYK)components. The CMY(K) format is normally used in graphic systems where the picture is to be printed using CMY(K) inks, whereas the RGB format is normally used in systems where the picture is to be displayed on a colour TV monitor. The system 1 can be readily adapted to work with image data in either format, and indeed in any other suitable format, by the inclusion of the optional matrix 6 for converting data output from the picture framestore 4 into RGB format if required for display of the image in the correct colours on the monitor 7.A similar circuit may also be provided for converting the initial picture data from the store 2 into CMY(K) for printing if so required. Our own colour conversion circuit, as described in our European Patent Application published as EP-A-0,245,943 the teachings of which are incorporated herein by reference, is particularly well suited to this task.

Data output from the matrix 6 is down converted to a resolution suitable for display on the monitor 7 by a down converting circuit 8. That is to say, the down converting circuitry 8 derives a picture of say 1920 x 1035 pixels from the picture output from the framestore 4 to reduce the resolution of the picture to that compatible with the monitor 7. The low resolution picture data output from the down converter 8 is delivered to a viewing framestore 9 and is read in raster sequence for display on the monitor 7. The monitor 7, of course, includes analog to digital converters (not shown) for converting the digital format RGB data into voltage signals for driving the display of the monitor.The down converting circuit 8 comprises a two dimensional spatial filter which maintains the integrity of the image and accordingly the picture in the viewing framestore will be a good representation of the initial picture from the framestore 4.

The system 1 shown in Figure 1 also includes a stylus/touch tablet device 10 by which an artist may create a linework image which is displayed on the monitor 7. As the stylus is drawn across the touch tablet signals representative of the XY position of the stylus on the touch tablet and representative of the pressure of the stylus on the touch tablet are output. XY signals are normally output at a much higher resolution than required and are delivered to a patch address generator 11 and to a summer 12. The patch address generator 11 converts the XY signals to a patch of addresses and the summer 12 converts the Xv signals to an absolute address and sums them with the patch addresses from the patch address generator 11 to produce a patch of absolute addresses. This patch of absolute addresses is used to address a patch of picture locations in a linework image framestore 13.

A signal representing the instantaneous pressure of the stylus on the touch tablet is also delivered to a stylus pressure register 14.

As in the systems described in our abovementioned patents, notional drawing implements are used to draw a continuous linework image into the framestore 13 and a set of such implements are stored in a brush shape memory 15 as a numerical representation of a continuous three-dimensional shape which covers a patch of image pixels. Individual implements are selected by the user for example by way of a menu (not shown) of available implements displayed on the monitor 7. The brush shape memory 15 and the stylus pressure register 14 are addressed simultaneously by the patch address generator 11. Data output from the stylus pressure register 14 and the brush shape memory 15 as the stylus is moved across the touch tablet are multiplied together by a multiplier 16 to produce a coefficient k which is used by a brush processor 17 in writing image date to the store 13.

The brush processor circuit 17 performs a continuously cycling read-modify-write operation on a pixel-by-pixel basis on the image data in the framestore 13. As the user draws on the touch tablet with the stylus, data in the framestore 13 is addressed by the summer 12 and output to the brush processor 17 where it is subtracted by way of a subtracter 18 from a preset image intensity value held in an intensity register 19. The resulting output is multiplied by way of a multiplier 20 with the coefficient k and this product is added to the data output from the framestore by way of adder 20a. The resulting data output from the adder 20a is written back to the framestore 13 to replace the original data at the addressed location.Thus the brush processor 17 reads data from the framestore 13, modifies the data in accordance with a coefficient k which determines the contribution from the old data and from the newly drawn data, and then writes the modified data back to the store. This process is per se well known and avoids the problem of jagged lines at boundaries between areas in the image at display resolution by producing gradually changing, i.e. nonstepped, boundary profiles.

The framestore 13 is also continuously read to extract the linework image data for use in controlling the merging of artist defined colour data, stored in a colour data register 21, with the viewing image data for display on the monitor 7. Linework is normally shown in a printed image in black or white or a primary or a secondary colour and in view of this the colour register 21 may be limited to storing only these colours.

The linework, in combination with the low resolution representation of the picture ie. the viewing image, is displayed on the monitor 7 as the linework is drawn by the user into the store 13. The addressing of the linework image from framestore 13 and of the viewing image from the viewing framestore 9 are synchronised so that pixels at corresponding locations are read from the two stores at the same time. Picture data from the viewing store 5 is input to the combiner 5 together with data from the register 21 representing a colour selected by the user by way of selection means not shown. The combiner 5 interpolates the viewing picture data and the artist selected colour data such that they are selectively combined.

The linework image data in the store 13 is used on a pixel-by-pixel basis as an interpolation coefficient a which determines the contribution to the image displayed on the monitor 7 from the image in the picture framestore 4 and from the artist selected colour. Thus, the linework image data in the store 13 is used as a weighting factor such that for low coefficient a values the contribution from the selected colour will be small and the contribution from the picture will be large, whereas for higher coefficient a values the contributions will be reversed.

In this way the contents of the picture framestore 4 and the linework framestore 13 are kept separate from each other at all times and the data in the viewing framestore 9 is continuously updated by the combiner 5 under the control of data in the store 13. The user is therefore free to experiment with the form of the linework he creates without affecting the picture held in the picture framestore 4. The linework image need only be monochrome and thus one byte is sufficient to define any pixel of the linework image in the framestore 13.

Once a linework image has been created to the users satisfaction the linework data is output from the framestore 13 and converted from bytes defining individual pixels to bits defining individual subpixels which can be used to drive a printer. One way in which this can be done is by way of a filter such as the filter 22 in Figures 1 and 2 of the accompanying drawings.

The operation of the filter 22 will now be described with reference to Figure 2 of the accompanying drawings. Because of the way in which it has been created, as described hereinabove, the linework data is stored in the framestore 13 in the form of data defining the grey scale intensity of individual pixels, i.e. the linework is defined in the store 13 in terms of a continuous tone image.

This low resolution data is read by the filter 22 and integrated by a recursive process to provide an integrated high resolution representation of the image at sub-pixel resolution. The value of each subpixel of the integrated representation is then compared to a threshold value and if the sub-pixel value exceeds the threshold value a binary '1' is output from the filter 22 otherwise a binary '0' is output. The resolution of the sub-pixel data output from the filter 22 corresponds to that of the initial image held in the picture framestore 4 and the subpixel data can therefore be delivered directly to a printer for printing.

More specifically, an area of pixel data, for example the sixteen pixels A to P shown in Figure 2, is read from the store 13 by the filter 22 and is integrated by an integrator 22a within the filter to define a sub-pixel notionally located at the centre of an area of integration defined by the integrator 22a, as explained in greater detail hereinafter. The subpixel resulting from the integration is output to a thresholding circuit 22b. The thresholding circuit 22b compares the value of the sub-pixel with a predetermined threshold value and outputs a "print" command in the form of, for example, a binary '1' which is stored at a corresponding location in a bit store 23 if the value of the sub-pixel exceeds the threshold value. Otherwise a "no print command, e.g. a binary '0', is stored at the corresponding location in the bit store 23.The threshold value is set to a level, which may, for example, be a level corresponding to say half of the maximum intensity, to give a sharply defined edge running with high probability along the centre of the original softly defined edge.

Integration of the image data in the store 13 is repeated by moving the area of integration over the pixels extracted from the store 13 by an amount corresponding to the required sub-pixel resolution.

For example, the required sub-pixel resolution may be four times greater in each (x and y) direction than that of the image data in store 13. In this case the area of integration would be moved by a distance corresponding to one quarter pixel, which would be the same as one sub-pixel in distance and the integration repeated for each pixel or part of a pixel covered by the area of integration.

In the simplest case the area of integration would be a notional square having an area equivalent to sixteen pixels. In this case the integrator would simply sum the values of the pixels A to P and divide the sum by sixteen to produce a sub-pixel value.

However a square area of integration can result in undesirable directional sensitivity and in order to avoid this a notional circular aperture 24 is preferably used to define the area of integration.

This circularity is achieved by weighting the contribution made by each pixel according to the area of a pixel covered by the notional circular aperture 24. Thus, in Figure 2, the pixels A, D, M and P will have a weighting of say 30% of their true value, pixels B, C, E, H, I, L, N and 0 will have a weighting of say 75%, and pixels F, G, J and K will have a weighting of 100%.

Once this integration has been performed for pixels A to P the circular aperture is notionally moved by a distance corresponding to the size of a sub-pixel to the position represented by the broken line aperture 24a. The integration is then repeated for the pixels A to T covered by the aperture 24a. Of course, the weighting of each pixel A to T is selected according to the area covered by the aperture 24a.

Integrations are performed for each movement of the aperture in both horizontal and vertical directions, by a distance corresponding to a sub-pixel, until all pixels in the store 13 have been integrated as described.

It should be noted that the above description of the filter 22 using an integration circuit and comparator is by way of example only. It will be appreciated that many methods are available to those skilled in the art for converting between low resolution pixel bytes in the store 13 and the high resolution pixel bits in the bit store 23. It will also be appreciated that the relationship between the resolution of the control data in store 13 and the print data in bit store 23 will depend both on the size of the store 13 and the required resolution of the print as determined by the resolution of the initial image in the picture framestore 4. The invention is therefore not limited to the above described filtering method.

The effect of the functions performed by the filter 22 is to produce linework data in the form of on or off, i.e. "print" or "no print", signals for each sub-pixel which are stored in the bit store 23.

As may be seen from Figure 3 of the accompanying drawings, the filter 22 causes pixel data representing a smoothly changing boundary of a line or area 25 spanning several pixels in the continuous tone linework image data held in the framestore 13 to be converted into bit data defining an abruptly changing, i.e. step, boundary or line 26. The comparator 22b only outputs a binary "print" signal when a given subpixel value exceeds a threshold value 27 and in this way the comparator causes the boundary or line to be sharply defined as a series of hard lines having edges with high probability along the centre or any other defined threshold level of the original soft line edges.While Figure 3 notionally represents the intensity distribution of a portion of a line drawn by the user, it will be appreciated that the difference between a line and an area is only a matter of degree and that the above explanation applies equally to an area.

Returning now to Figure 1 of the accompanying drawings, once the linework data has been converted into sub-pixel format and stored in the bit store 23 it can be used in the production of individual colour separations which together represent both the initial picture held in the picture framestore 4 and the user created linework. The system includes a printer 28 which may for example be a laser printer comprising a control network 29 which provides connections to modulators 30 which control the recording density during the printing of a picture or other image on a print receiving medium. The printer may for example be a Scitex Rays tar printer or any other printer capable of printing images of say 1200 lines per inch for newspaper work or of say 2400 line per inch for high quality work.

The printer 28 is normally arranged to print individual colour separations 31 for each of the Cyan, Magenta, Yellow and Black components of the picture (these separations are represented by the boxes labelled C,M,Y and K in Figure 1). The linework data in bit store 23 can be used to drive directly the modulators 30 thereby to produce another, i.e.

linework, separation (represented by the box L in Figure 1). This linework separation is used subsequently together with the other C,M,Y,K separations in the printing of a picture in which the initial picture and the user created linework are combined. When this approach is adopted the linework will eventually be printed directly over the C,M,Y and K printings.

This approach can be refined to facilitate registration of the separations during printing by producing two separate sets of linework bit data which are stored in respective areas (not shown) of the bit store 23. The first of these sets of bit data is produced, as described above, with the threshold value set to say half the maximum intensity. The second of these sets is produced by setting the threshold to a higher value, say 70%. Thus, the two sets of data will represent the same linework image, but will have corresponding edges at slightly different locations. The first set of linework data is used as described above to drive the modulators 30 to produce a linework separation for subsequent use in the printing of a combined picture.The second set of data however, is used via control lines 32 to control the control network 29 of the printer such that pixels representing the initial picture are only output from the control network 29 to the modulators 30 when there is no corresponding "print" data in the second set of linework data. In this way, C,M,Y,K colour separations are produced with blank areas substantially corresponding to the areas in which linework is to be printed. The use of different thresholds in the production of the two sets of linework bit data will result in a slight overlap between printing using the C,M,Y,K separations and printing using the linework separation and this use of so-called "chokes and spreads" will give a greater tolerance in the registration of the separations during subsequent printing.

The control network 29 comprises a switching arrangement whereby signals can be input to the printer along either first data lines 33 or second data lines 34. The switching between these two sets of lines is controlled by the control lines 32. In order to eliminate the need to produce an extra linework separation the linework data and the picture data can be combined, under the control of the control network 29, as they are input to the printer. In this method the reading of data from the store 2 and the bit store 23 is synchronised, with data from the bit store 23 being delivered to the control lines 32, the data from the colour register being delivered along the first printer data lines 33, and data from the buffer 3 being delivered along the second data lines 34.

When a "no print" sub-pixel is output from the bit store 23 to the control lines 32, the control network is configured such that the picture pixel data from the buffer 3 is applied via the data lines 34 to the modulators 30 to drive the lasers. When a pixel output from the bit store 23 represents a "print" command the control network 29, in response to this command, is reconfigured such that a linework pixel, the colour of which is defined by data in the colour register 21, is applied via the data lines 33 to the modulators 30. Thus the data representing the artist selected colour is instead delivered to the modulators 30 and in this way a linework pixel of the desired colour is printed on appropriate colour separations instead of a picture pixel.The process is repeated for each and every pixel of the picture in the store 2 and of the linework in the bit store 23, with the modulators 30 being switched between the linework colour data and the picture pixels by the control network under the control of the linework data in the store 23, thereby to produce C,M,Y and K separations representing a combined image composed of a continuous tone picture and of linework.

This method can be refined in order to produce linework in more than one colour; which may be desirable for example where linework of a chosen colour would otherwise tend to merge into an area of the picture. One way in which multicoloured linework could be produced would be to use a separate bit store for linework of each colour. However, this would be wasteful of resources because linework colour is unlikely to change from one pixel to the next at high resolution. Instead, a colour is likely to remain constant through a substantial area of the picture.

Therefore, the preferred approach is to replace the colour register 21 with a store for storing data representing the colour of linework in different areas of the image. The resolution of this store need not be high and for example may be of a similar resolution to the store 13 or possibly even coarser.

In this arrangement, the colour of an area of linework can be selected by the user while the linework is being created and the colour store can be addressed in synchronisation with other stores for display and printing of the combined image colour separations.

Whilst the foregoing embodiment has been described in relation to user created linework drawn into store 13, it is also possible to modify the system to include a library of predefined character shapes which may be selected by the user and 'drawn' at the desired location into the bit store 23 by way of the stylus and touch tablet combination 10.

Furthermore, the system of Figure 1 may be further enhanced by extra circuitry to handle run length encoding of the linework, thereby reducing in most circumstances the size of store required for storing the linework image data. Such enhancement is within the scope of understanding of those skilled in the art and requires no further explanation herein.

Linework will normally only be shown in a portion or plurality of portions of the image as a whole, and in order to reduce the time taken by the filter to process the linework data the system may be further modified such that only the portion or portions of the image that contain linework are processed. Whilst this will increase the speed at which linework data is processed, it is unimportant from the user's aspect because a fast processing time is only required to provide interaction with the user with the linework image being displayed on the monitor as it as "drawn" into the store.

Moreover, the system may be further arranged such that once the separation data has been produced it is not used immediately to drive modulators in the printing of colour separations, but is instead stored in a bulk storage device, for example the store 2, for later use.

Whilst the invention has been described in relation to a relatively narrow line drawn by a user, it will be appreciated that the invention extends to other types of drawings made by a user. For example, the above described embodiment is capable of handling blocks or areas of colour drawn by the user and in this case, the effect of filtering the drawn image will be to produce binary pixel data which can be used in the production of a high resolution image comprising corresponding areas each having a single tone thoughout. The terms "linework" and "line" should be construed accordingly to include both lines and areas drawn by the user. Thus, the invention provides a means for producing a combined image comprising a continuous store picture and lines or areas having edges or boundaries which are sharply defined.

Having thus described the present invention by reference to a preferred embodiment it is to be well understood that the embodiment in question is exemplary only and that modifications and variations such as will occur to those possessed of appropriate knowledge and skills may be made without departure from the spirit and scope of the invention as set forth in the appended claims and equivalents thereof.

Claims (13)

CLAIMS :

1. An electronic graphic system, in which low resolution pixel data relating to a continuous tone image representing at least one arbitrary positioned line or area is processed to produce corresponding high resolution binary pixel data which can be used in the production of a high resolution printed image comprising the said at least one line or area.

2. An electronic graphic system as claimed in claim 1, in which patches of the low resolution pixel data are integrated to produce corresponding high resolution pixel values which are each compared with a predetermined threshold to produce said binary data.

3. An electronic graphic system as claimed in claim 1 or 2, in which high resolution data representing a continuous tone picture is stored in a store means and together with the binary pixel data can be used in the production of a high resolution image in which the picture and the said at least one line or area are combined.

4. An electronic graphic system as claimed in claim 3, in which the data representing the picture is down converted to a low resolution representation thereof for display on a display monitor.

5. An electronic graphic system as claimed in claim 3, in which user selectable colour data representing the colour of the said line or area is combined with the low resolution picture data under the control of the low resolution pixel data for display of the resulting combined image on the monitor.

6. An electronic graphic system as claimed in claim 5, in which the high resolution picture data, the binary pixel data and the colour data are delivered to a printer for driving means to produce colour separations representing the image such that the binary pixel data controls switching of the said means between the picture data and the colour data.

7. An electronic graphic system as claimed in claim 6, in which a separate linework separation is produced.

8. An electronic graphic system as claimed in claim 7, in which the high resolution pixel values are each compared with a lower and a higher predetermined threshold to produce two sets of said binary data which are used respectively in the printing of the separation representing the linework and the separations representing the picture.

9. An#electronic graphic system as claimed in claim 6, in which separations representing the combined linework and picture are produced.

10. An electronic graphic system as claimed in any preceding claim, in which the low resolution pixel data is defined by a user by way of user operable input means and stored in a framestore.

11. An electronic graphic system comprising user operable means for creating a linework image in the form of low resolution continuous tone linework data, storing means for storing said linework data, display means for displaying the linework image while it is being created, filter means for filtering the linework data to produce high resolution binary linework data, binary storing means for storing said binary linework data, and controlling means associated with a printer and responsive to said binary linework data for controlling production of an image including the linework image.

12. An electronic graphic system as claimed in claim 11, further comprising storing means for storing high resolution picture data defining a continuous tone picture, and wherein the controlling means is adapted to control delivery of the picture data and the binary pixel data to printing means within the printer thereby to enable an image including the continuous tone picture to be produced.

13. An electronic graphic system substantially as described herein with reference to the accompanying drawings.