GB2309807A

GB2309807A - Printing apparatus

Info

Publication number: GB2309807A
Application number: GB9602115A
Authority: GB
Inventors: Sharee Mcnab
Original assignee: Esselte NV
Current assignee: Esselte NV
Priority date: 1996-02-02
Filing date: 1996-02-02
Publication date: 1997-08-06
Anticipated expiration: 2016-02-02
Also published as: DE29701676U1; GB9602115D0; GB2309807B

Abstract

A printing apparatus has a keyboard for inputting data defining an image comprising at least one character and/or symbol to be printed on tape. First storage means are provided for holding font data with each character and/or symbol defined as a bit map of n bits. Second storage means hold a sizing algorithm, the printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is double the first size. Characters and/or symbols of the second size are generated from the font data according to the sizing algorithm so that each bit of the bit map of n bits is used to generate four pixels in the double sized printed character and/or symbol. The status of each of the four pixels is separately determined based on the status of the bits immediately surrounding the bit. The sizing algorithm is arranged to double the size of the symbols and/or characters defined by the n bit maps and to smooth the outline of curved and/or angled portions of at least some of the characters and/or symbols.

Description

PRINTING APPARATUS The present invention relates to a printing apparatus and is particularly but not exclusively concerned with tape printing apparatus.

Known tape printing apparatus of the type with which the present invention is generally concerned are disclosed in EP-A-322918 and EP-A-322919 (Brother Kogyo Kabushiki Kaisha) and EP-A-0267890 (Varitronics). These tape printing apparatus generally have a cassette receiving bay for receiving a cassette or tape holding case. In EP-A-0267890, the tape holding case houses an ink ribbon and a substrate tape, the latter comprising an upper image receiving layer secured to a backing layer by an adhesive. In EP-A-322918 and in EP-A-322919, the tape holding case houses an ink ribbon, a transparent image receiving tape and double-sided adhesive tape which is secured at one of its adhesive coated sides to the image tape after printing and which has a backing layer peelable from its other adhesive coated side. With both of these apparatus, the image transfer medium (ink ribbon) and the image receiving tape (substrate) are in the same cassette.

The present applicants have developed a different type of tape printing apparatus which is described for example in EP-A-578372, the contents of which are herein incorporated by reference. In this printing apparatus, the substrate tape is similar to that described in EP-A-0267890 but is housed in its own tape holding case while the ink ribbon is similarly housed in its own tape holding case.

In all of these cases, the image receiving tape passes in overlap with the ink ribbon to a print zone consisting of a fixed print head and a platen against which the print head can be pressed to cause an image to transfer from the ink ribbon to the image receiving tape. There are many ways of doing this, including dry lettering or dry film impression, but the most usual way at present is by thermal printing where the print head is heated and the heat causes ink from the ink ribbon to be transferred to the image receiving tape. Alternatively, the print head may be direct contact with the thermally sensitive image receiving tape whereby when the print head is heated, an image is defined on the image receiving tape.

Printing apparatus of this type generally also include a display and an input means such as a keyboard for selecting characters to be printed. The selected characters are displayed on the display and in this way a user can compose a label to be printed. When a label has been composed, a print instruction is given and the tape printing apparatus proceeds to print a label.

Such tape printing apparatus also generally includes a cutter for separating the image receiving tape on which an image has been printed from the supply of image receiving tape to thereby define a label.

One known tape printing apparatus is arranged to be used with a range of different widths of tape, for example 6,9 and 12mm.

A 48 dot character font is used to generate the characters so that each character is defined by a 48 x 48 bit map. This known apparatus has a 180 dot per inch print head and therefore generates a maximum character height of 6.75mm which is suitable for use with the 9 or 12mm tapes but has to be halved to produce 24 dot characters having a maximum character height of 3.38mm high which can be used with the 6mm tape as well as for multiline printing on the wider tapes 24 dot characters are defined by 24 x 24 bit maps. In order to obtain the smaller 24 dot characters, the 48 dot character font is halved using a suitable algorithm. This has been found to produce characters which are reasonably smooth and pleasing to the eye.

It has been proposed that the above-described tape printing apparatus be used with wider tapes, such as l9mm wide tapes.

With l9mm tapes it is desirable to be able to print characters with a larger size than 6.75mm, particularly when only a single line of text is to be printed. To generate larger characters for the 19mm tape, the following proposals have been considered.

Firstly, the option of storing a larger dot font, for example a 96 dot font was considered. Each character would then be defined by a 96 x 96 bit map. However, the 48 dot font described above could, for example take up 16 kilobytes of the microprocessor ROM. To store a 96 dot font might, for example take up an additional 64 kilobytes of a microprocessor ROM. It was estimated that this option could increase the manufactured cost of the tape printing apparatus by between 10 and 20t as a result of the extra ROM capacity that would be required. The second option which has been considered was to simply scale up the 48 dot font by use of a simple doubling algorithm. Thus, each pixel in the 48 dot font would be represented by four pixels arranged in a square in the 96 dot font. Therefore, if a bit in the 48 dot character is set (set bits result in printed pixels), it will be represented by four set pixels arranged in a square in the 96 dot font. However, with characters having angled or curved edges, the resulting printed image appears jagged and is of a low quality.

Accordingly, it is an object of certain embodiments of the present invention to overcome or reduce the problems outlined above.

According to a first aspect of the present invention, there is provided a printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium; first storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, said sizing algorithm being arranged to double the size of the symbols and/or characters defined by said n bit maps and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.

By using a single set of font data to define the first and second sized fonts, the total memory required is relatively small. Additionally, as the largest sized font is generated by considering each of the pixels immediately surrounding the bit to be enlarged, the appearance of the printed characters can be improved as compared to the case when a simple doubling operation is applied to the font data. Thus, curved and/or angled portions of some of the characters are smoothed, thus improving the appearance thereof. Additionally, by separately determining the status of each of the four pixels, it has been found that the appearance of the characters can be further improved but in a relatively simple way. As will be appreciated, there are eight bits immediately surrounding each bit of the n bit map which is to be enlarged. The four pixels in the enlarged dot font corresponding to each bit in the n dot font are arranged in two rows each of two pixels so as to achieve a double sized character with double the width and double the height.

Preferably, the processing means is arranged to determine the presence of corners in at least some of the characters and/or symbols by determining the status of the corresponding said bit and the immediately surrounding bits and to generate four pixels which maintain said corners in the printed characters and/or symbols. This further improves the appearance of the printed characters of the second size.

It is preferred that the second storage means holds a plurality of smoothing masks for selective application to pixels generated by the sizing algorithm prior to generating the print information. Thus, for certain characters, it is possible to further improve the appearance of the printed characters. The mask allows further smoothing to be achieved with particularly curved characters and/or symbols or with characters and/or symbols with angled lines. Generally, the. mask is only applied to some, but not all, symbols and/or characters. Each of the smoothing masks preferable comprises a plurality of selected bits, each of said selected bits causes the bit in the corresponding position in the double sized character and/or symbol to be reversed. The masks may only consist of a maximum of 20 bits which need to be altered. Typically, a mask is applied to the following characters: k, s, v, w, x, C, G, N, O, P, Q, S, V, W, X Preferably, said processing means is arranged to determine if the corresponding said bit is set and either of the two bits of the n bit map bordering two adjacent sides of the corresponding said bit, which together define a corner region, are also set, and if so to set the pixel of said four pixels in the bit map of the double sized character and/or symbol which defines a corresponding corner region.

It is preferred that said processing means is arranged to determine if the corresponding said bit is set and the bits immediately surrounding said corresponding bit of the n bit map which define a right angle about one of the corner regions of the corresponding said bit are all not set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corner region corresponding to said one corner region of the corresponding bit.

In some embodiments, the processing means is arranged to determine if the corresponding said bit of the n bit map is setand the two bits adjacent diagonally opposed corners of the corresponding said bit are set and if so to set two pixels of the four pixels in the bit map of the double sized character and/or symbol which define corners corresponding to the corners of the corresponding said bit which are not adjacent said two adjacent bits in the n bit map.

Preferably, the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and both of the two bits bordering two adjacent sides of the corresponding said bit which together define a corner region of the corresponding said bit are set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corresponding corner.

It is preferred that, the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and the bits surrounding the corresponding said bit which define a right angle about one of the corner regions of the corresponding said bit are set, and if so then the pixel of said four pixels of the bit map of the double sized character and/or symbol which define a corner region corresponding to said one corner region of the corresponding said bit is not set.

In a preferred embodiment of the present invention, the processing means is arranged to determine whether or not any of the five conditions outlined above exist and to set the state of the corresponding pixel of the four pixels accordingly. Where both of the last two conditions are satisfied, then the last condition takes precedence and the pixel in question would not be set. Preferably, if none of the conditions described above are met, then the corresponding pixel in the enlarged characterand/or symbol is not set. By looking for the five conditions outlined above, it is possible to ensure that smoothing of the characters can be achieved simply and without requiring a large additional memory capacity. These five conditions are checked to determine separately the status of each of the pixels in the double size font.

The printing apparatus defined above is preferably a tape printing apparatus. This tape printing apparatus has means for receiving a supply of image receiving tape on which the printing means, in the form of a print head, is operable to print an image to thereby define a label.

Preferably, characters and/or symbols can be printed in a third size, which is half the size of said first size, a sizing algorithm for generating said half size characters being stored in said second storage means and said processing means is arranged to generate print information for characters and/or symbols in said third size.

According to a second aspect of the present invention, there is provided a tape printing apparatus for printing an image on an image receiving tape to thereby define a label, said apparatus comprising: means for receiving a supply of image receiving tape; means for receiving input data defining an image to be printed on the image receiving tape, said input data including at least one character and/or symbol; first storage means holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size, which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate : herefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according : o said sizing algorithm, wherein each bit of said bit map of n Dits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels seing determined in accordance with the status of the bits immediately surrounding said bit, said sizing algorithm being arranged to double the size of the symbols and/or characters Sefined by said n bit maps and to smooth the outline of curved md/or angled portions of at least some of said characters and/or symbols ; and a print head for printing the image on the image receiving : ape in accordance with the print information. rape printing apparatus are generally small, portable devices which are usually provided with limited memory capacity in order : o reduce the cost of the apparatus and also its size. By generating first and second sized fonts from a single set of font lata, the memory capacity required is relatively low, thus ninimising the cost of the tape printing apparatus.

Preferably, a motor is provided for driving the image receiving : ape through a print zone defined adjacent said print head, said image being printed on a portion of the image receiving tape in said print zone. The image receiving tape is generally driven Dy the motor past the print head.

Che print head is preferably arranged to print an image on the image receiving tape column by column. Accordingly, the print information is supplied to the print head in a column by column basis. The data is preferably input using a keyboard, although other types of input means can be used.

Cutting means are preferably provided for separating the image receiving tape on which an image has been printed from the supply of image receiving tape to thereby define a label.

In one embodiment of the present invention, the size of characters and/or symbols printed on the image receiving tape is determined by the processing means in accordance with the width of the image receiving tape. The processing means can receive information concerning the width of the tape generally in two ways. Firstly, the tape printing apparatus can be arranged automatically to detect the width of the image receiving tape.

Alternatively or additionally, the tape printing apparatus can be arranged in order to receive tape width information input by the user. It is of course possible that the user can also or alternatively manually select the size of characters and/or symbols to be printed.

According to a third aspect of the present invention, there is provided a method of generating from a pre-stored bit map of n bits defining a character and/or symbol in a first size, a bit map defining the character and/or symbol in a second size, double the first size said method comprising using each bit of said n bit map to generate four pixels in bit map for the double size character, the status of each of the four pixels being separately determined in accordance with the status of the pixels immediately surrounding the corresponding bit.

According to a fourth aspect of the present invention, there is provided a method of printing an image onto an image receiving tape comprising the steps of: selecting symbols and/or characters to define the image to be printed; storing font data defining symbols and/or characters from hich the selected symbols and/or characters are selected, each character and/or symbol being defined as a bit map of n bits; selecting the size for each selected symbol and/or character, wherein selected characters and/or symbols can be printed in a first size as a bit map of n pixels or in a second size, double the first size; generating print information comprising a plurality of pixels in accordance with the selected characters and/or symbols nd the selected size, the print information for characters in : he first size being generated from the stored font data so that ach bit of the n bit map corresponds to a single pixel in the printed image and applying a sizing algorithm to generate print Lnformation for characters of said second size, wherein each bit ) f the stored n bit map corresponds to four pixels in the printed Lmage, the status of each of the four pixels being separately ietermined in accordance with the status of the bits immediately surrounding the corresponding said bit, said sizing algorithm lso smoothing the outline of curved and/or angled portions of t least some of the characters and/or symbols; and printing an image onto an image receiving medium in iccordance with the generated print information.

3oth of the above-described methods have the advantage that the nemory capacity required in order to use the methods in order to ach ve smoothed double sized characters is advantageously -educed.

? referably, the presence of corners in at least some of n bit map : haracters and/or symbols is determined by determining the status ) f the bit to be enlarged in the n bit map and the immediately surrounding bits, the double sized characters and/or symbols are generated which also include corresponding corners.

Preferably, smoothing masks are applied to selected pixels of bit naps for selected double sized characters and/or symbols produced -rom the associated n bit map. The use of a smoothing mask for selected characters improves the appearance of certain of the enlarged characters.

Preferably, the method comprises the step of determining if the bit to be enlarged is set and whether either of the two bits of the n bit map bordering two adjacent sides of said bit to be enlarged, which together define a corner region, are set and, if so to set the pixel of said four pixels of the bit map of the double size character and/or symbol which defines a corresponding corner region.

It is preferred that the method comprises the step of determining if the bit to be enlarged is set and the bits surrounding the bit to be enlarged, which define a right angle about one of the corner regions of said bit to be enlarged, are not set and, if so, to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged.

Preferably, the method comprises the step of determining if the bit to be enlarged is set and the two bits adjacent diagonally opposed corners of the bit to be enlarged are set, and if so to set two pixels of the four pixels in the bit map of the double size character and/or symbol which define corners corresponding to the corners of the bit to be enlarged which are not adjacent said two adjacent bits in the n bit map.

It is preferred that the method comprises the step of determining if the bit of the n bit map which is to be enlarged is not set and if both of two bits bordering two adjacent sides of said bit to be enlarged, which together define a corner region of the bit to be enlarged, are set and, if so to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corresponding corner.

Preferably, the method comprises the step of determining if the bit to be enlarged of the n bit map is not set and the bits surrounding the bit to be enlarged which define a right angle about one of the corner regions of the bit to be enlarged are all set, and if so then the pixel of the four pixels of the 2n bit map of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged is not set.

Preferably, if both of the last two conditions are satisfied, the given pixel of the bit map of the double size character and/or symbol is not set. Where none of the conditions are met, the pixel in the enlarged font is not set.

According to a further aspect of the present invention, there is provided a printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium; first storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm said algorithm comprising a plurality of Boolean equations, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is different to the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate a plurality of pixels in the double second printed character and/or symbol, the status of each of the pixels in the second size of characters being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, a Boolean equation being provided for determining the status of each pixel of the character and/or symbol of the second size, said sizing algorithm being arranged to change the size of the symbols and/or characters defined by said n bit maps to said second size and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.

For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a plan view showing the front of a tape printing apparatus; Figure 2 is a plan view of the underside of the tape printing apparatus of Figure 1; Figure 3 is a simplified block diagram of control circuitry for controlling the tape printing apparatus of Figure 1; Figure 4 shows the scaling of a bit from a 48 dot font to four bits in a 96 dot font; Figure 5 shows a diagrammatic representation of a bit of the 48 dot font which is to be scaled up, with eight surrounding bits; Figure 6a shows the letter S in a 96 dot font, where the 48 dot font has simply been doubled; Figure 6b shows the letter S in a 96 dot font to which a scaling algorithm embodying the invention has been applied; Figure 6c shows the letter S in a 96 dot font which has been scaled using the scaling algorithm embodying the invention and which further has been masked; and Figure 7 illustrates different forms of a lower case b to illustrate production of half size characters.

Figure 1 shows a simplified plan view of a tape printing apparatus 2. The tape printing apparatus 2 comprises a keyboard 4. The keyboard 4 has a plurality of data entry keys and in particular comprises a plurality of numbered, lettered and punctuation keys 6 for inputting data to be printed as a label and function keys 8 for editing the input data. These function keys 8 are arranged for example Go change the size or font of the input data. The keyboard 4 also comprises a print key 10 which is operated when it is desired that a label be printed as well as tape feeding keys 12.

The tape printing apparatus 2 also has a liquid crystal display (LCD) 18 which displays the data as it is entered. The display 18 allows the user to view all or part of the label to be printed which facilitates the editing of the label prior to its printing.

Additionally, the display 18 can also display messages to the user, for example error messages or an indication that the print key 10 should be pressed. The display 18 is driven by a display driver 28 which can be seen in Figure 3.

On the underside of the tape printing apparatus 2 which can be seen from Figure 2, there is a cassette receiving bay 40. The cassette receiving bay 40 includes a thermal print head 42 and a platen 44 which cooperate to define a print zone 46. The print head 42 is pivotable about a pivot point 48 so that it can be brought into contact with the platen 44 for printing and moved away from the platen 44 to enable a cassette to be removed and replaced. A cassette inserted into the cassette bay 40 is denoted generally by reference numeral 50. The cassette 50 holds a supply spool 52 of image receiving tape 54. The image receiving tape 54 comprises an upper layer for receiving a printed image on one of its surfaces and has on its other surface an adhesive layer to which is secured a releasable backing layer.

The image receiving tape 54 is guided by a guide mechanism (not shown) through the cassette 50, out of the cassette 50 through an outlet 0, past the print zone 46 to a cutting location C. The same cassette 50 also has an ink ribbon supply spool 56, an ink ribbon take up spool 58 and a supply of ink ribbon 60. The image receiving tape 54 and the ink ribbon 60 are arranged to pass in overlap between the print head 42 and the platen 44. In particular, the image receiving layer of the image receiving tape 54 is in contact with the ink ribbon 60.

The platen 44 is driven by a motor 30 (see Figure 3), for example a dc motor or a stepper motor so that it rotates to drive the image receiving tape 54 in a direction which is parallel to the lengthwise extent of the image receiving tape through the print zone 46. In this way, an image is printed on the image receiving tape 54. The image receiving tape 54 is fed from the print zone 46 to the cutting location C which is provided at a location on a portion of the wall of the cassette 50 which is close to the print zone 46. The portion of the wall of the cassette 50 where the cutting location C is defined is denoted by reference 62.

A slot 64 is defined at the wall portion 62 and the image receiving tape 54 is fed past the print zone 46 to the cutting location C where it is supported by facing wall portions on either side of the slot 64.

A cutting mechanism 66 is provided and includes a cutter support member 68 which carries a blade 70. The blade 70 cuts the image receiving tape 54 and enters the slot 64. The cutting mechanism 66 is arranged to cut off a portion of the image receiving tape on which an image has been printed by the print head 42 to thereby define a label. The printed label is thus separated from the remaining supply of image receiving tape.

In those embodiments where the motor is a dc motor, the image receiving tape is driven continuously through the print zone during printing. Alternatively, in those embodiments where the motor is a stepper motor, the platen 44 rotates stepwise to drive the image receiving tape 54 in steps through the print zone 46 during the printing operation.

The print head 42 is a thermal print head comprising a column of a plurality of printing elements. The print head is preferably only one printing element wide and the column extends perpendicular to the lengthwise direction of the image receiving tape 54. The height of the column of printing elements is preferably equal to or slightly less than the width of the image receiving tape 54 to be used with the label printing apparatus 2. Where more than one width of image receiving tape 54 is used, the print head column will generally have a height corresponding to the largest width of tape 54. An image is printed on the image receiving tape 54 column by column by the print head 42.

It should be appreciated that an image can be printed on the image receiving tape 54 via the ink ribbon 60. Alternatively, if the image receiving tape 54 is of a suitable thermally sensitive material, an image can be applied directly by the print head 42 to the image receiving tape 54. In such circumstances, an ink ribbon would not be required.

As an alternative to the one cassette system shown in Figure 2, the cassette receiving bay may be arranged to receive a separate image receiving tape cassette and a separate ink ribbon cassette which are arranged so that the ink ribbon and image receiving tape are passed in overlap through the print zone. This particular cassette arrangement is described for example in our earlier European Patent Application No. 578372, the contents of which are herein incorporated by reference. Any other suitable arrangement for providing a supply of image receiving tape can of course be used in embodiments of the present invention.

Figure 3 shows the basic control circuitry for controlling the tape printing apparatus 2 of Figures 1 and 2. There is a microprocessor chip 20 having a read only memory (ROM) 22, a microprocessor 24 and random access memory capacity indicated diagramatically by RAM 26. The microprocessor 24 is controlled by programming stored in the ROM 22 and when so controlled acts as a controller. The microprocessor chip 20 is connected to receive label data input via the keyboard 4. The microprocessor chip 20 outputs data to drive the display 18 via the display driver 28 to display a label to be printed (or a part thereof) nd/or a message or instructions for the user. It should be appreciated that in certain embodiments of the present invention, : he display driver 28 may form part of the microprocessor chip 20. Additionally, the microprocessor chip 20 also outputs data : o drive the print head 42 which prints an image onto the image receiving tape 54 to form an image. Finally, the microprocessor : hip 20 also controls the motor 30 for driving the image receiving tape 54 through the tape printing apparatus 2. The nicroprocessor chip 20 may also control the cutting mechanism 66 : o allow lengths of image receiving tape 54 to be cut off after in image has been printed thereon to thereby define a label.

Data relating to each character or symbol etc., printable on the Lmage receiving tape is stored in the RAM 26. The data stored Ln the ROM 22 is in the form of a 48 dot font data which represents each character by a 48 x 48 bit map. It should be appreciated that some characters may be stored in other bit map , izes. For example, narrower characters could have a bit map of L8 x 40 bits. These bit maps may also include spaces around the characters. As a 180 dot per inch print head 42 is used, the 48 c 48 bit map provides a maximum character height on the tape of ;. 7Smm. This is appropriate for printing on 9 or 12mm wide tape.

In order to print a character in the 48 dot font, the following teps are carried out. Font data defining the character to be printed is retrieved by the microprocessor 24 from the font data stored in the ROM 22. The processor 24 then creates print Lnformation in accordance with the font data and information -elating to the size. As there is a one to one correlation between the stored bits of the 48 dot font in the ROM 22 and the pixels in the print information, no change is made to the bit nap. The generated print information, in the form of pixel data, Ls passed to the print head 42 on a column by column basis. Each : olumn of pixel data defines the status of each of the printing elements of the print head. In other words, the pixel data lefines whether each printing element is on or off.

Jhen it is desired to produce half size characters, the 48 dot character font is halved to produce 24 dot characters. Thus, the 48 x 48 bit map is halved to produce a 24 x 24 pixel image on the image receiving tape. The maximum height of these half size characters is 3.38mm high which is suitable for printing on 6mm tape or multi-line printing on 9 and 12mm tapes. The 48 x 48 pixel bit map is algorithmically halved so that four pixels in the 48 x 48 bit map are represented by a single pixel in the half size font. In order to print half sized characters, the following steps are carried out. rhe font data defining the character to be printed is retrieved from the ROM 22 along with information defining the character size from RAM 26. The processor 24 then defines print information for the half size character. That print information is generated in accordance with the bit map retrieved from the ROM 22 and the size retrieved from the RAM 26. More particularly, the print information is generated using an algorithm stored in the ROM 22. This algorithm as discussed boxe is a simple halving algorithm and reduces four bits in the 18 dot font to a single bit. in particular, since each half size character is half the width and half the height of the full sized equivalent, each group of E dots in the full sized character needs to be converted into a single dot in the half sized character. This is illustrated in ligure 7 which represents the effect of transforming a full size Lower case letter b designated by numeral 111 into half size ~ower case letter b's designated by numerals 112 and 113 using different rules for converting each set of 4 dots in the full size character to a single dot in the half size character. A Dlock 114 of four dots in the full size character 112 are ; converted to the single dot 115 in the half size character 112 and into the single dot 116 in the half size character 113. Similarly the block 117 of 4 dots in the full size character 111 ire converted into the single dot 118 in the half size character 112 and into the single dot 119 in the half size character 113. Che half size characters 112 and 113 illustrate the result of applying two different reduction methods to the full size character 111. The reduction rules are defined by appropriate 4 bit pixel masks. That is, a two by two matrix is used to logically manipulate each four bits to derive one bit therefrom, the logical manipulation depending on the bit settings of the matrix. If any of the 4 dots in the block 114 of the full size character 111 is black, then the single dot 115 in the half size character 112 is set to black as illustrated by mask 120. If the top left hand dot of the block of 4 dots 114 of the full size character 111 is black then the single dot 116 in the half size character 113 is set to black as illustrated by mask 121.

The resultant half size characters are significantly different.

The set of 3 horizontal dots 122 in the half size character 112 is missing in half size character 113 and the bottom left inner corner dot 123 of half size character 112 is missing in half size character 113. Since there are 16 combinations of one or more dots from a block of 4, there are 16 different half size characters which can be produced depending on what rule is used to provide the dot in the half size character from the block of 4 in the full size character. If a single fixed combination of dots is used to form all half size characters many half sized characters look subjectively unsatisfactory. However, all of these half size characters can be made to look subjectively satisfactory by choosing an appropriate rule for reducing the four dots. The identifier ID2 is a number representing one of the possible 16 combinations of the pixel masks definining how the block of 4 dots is to be used in creating the half size character. Four bits are needed to store this number. The total additional memory required to store the half size font for 160 characters is therefore 160 half bytes or 80 bytes. As for the compression algorithm, the best combination of 4 bits to produce a satisfactory half size character is determined experimentally in advance.

The pixel mask is used in the preferred embodiment as follows. Each bit of the mask is logically AND-ed with the corresponding bit of a set of four bits of the character. If the result is four zeros then a black dot is not printed. If the results includes a 1 at any location then a black dot is printed. The location of the 1 can of course be determined by the configuration of the selected pixel mask for each character.

In order to produce double sized characters, the 48 dot font is algorithmically scaled up to form a 96 x 96 pixel bit map (96 dot character font). This will give a maximum character height of 13.50mm which is suitable for use with 19mm or wider tape. The double sized characters are generated in a similar way. In particular, in order to print a selected character, font data defining that character is retrieved by the processor 24 from the ROM 22. Data defining the size of the selected character is retrieved from the RAM 26. The processor 24 then generates print information for the double sized character. The font data is manipulated by the processor 24 in accordance with a double sized algorithm stored in the ROM 22 in order to produce the print information.

The algorithm which is used to produce the 96 dot font will now be described. Each bit 80 in the 48 dot font is scaled up to form four pixels 82 in the printed image arranged in a 2 pixel x 2 pixel square as shown in Figure 4. An algorithm is provided for calculating for each bit in the 48 dot font from the value of each of the corresponding four pixels in the 96 dot font. The algorithm for each of these corresponding pixels is as follows: TOP LEFT = [E. [ (D+B) + ("A.'B.'C.'D.'G) + (G. C)] + [~E. (D. B)]] .' ['E. (A. B. C. D. G)] TOP RIGHT = [E. [ (B+F) + (~A. ~B. ~C. ~F. ~I) + (A. I)] + [~E. (B. F)]] . ~ [~E. (A. B. C. F. I)] BOTTOM LEFT = [E. [ (D + H) + (~A. ~D. ~G. ~H. ~I) + (A. I)] + ['E. (D. H)]] . ~ [~E. (A. D. G. H. I)] BOTTOM RIGHT = [E. [ (H+F) + ('C."F.'I.'H."G) + (G. C)] + [~E. (H. F)]] . ~ [~E. (C. F. I. H. G)] Reference is made to Figure 5 which shows nine bits marked A to I of a 48 dot font character. Bit E is the bit which is to be scaled up. The letters included in the above expressions represent the values of those bits shown in Figure 5 surrounding the bit (bit E) which is to be scaled up. In other words, Figure5 shows nine bits of a 48 dot font bit map. The bits are either set (on) and have a value of 1 or are not set (off) and have a value of 0. If a bit is on, the corresponding printing element of the print head will be heated during printing to provide a pixel on the image receiving tape. If the bit is off, the corresponding printing element will not be heated during printing.

The algorithms are expressed in the form of Boolean logic. The use of Boolean logic is particularly advantageous in that when used with a microprocessor efficient processing can take place.

. represents an AND operation + represents an OR operation represents a NOT operation As can be appreciated from the above expression, the state of the eight bits immediately surrounding the bit to be upsized are taken into consideration.

Each of the above logic expressions has five separate terms.

Each of those separate terms will now be described using the expression for the top left bit as an example. The first term E. (D+B) carries out basic smoothing. It sets the top left pixel in the double size font into an on state if either of the two bit are set immediately bordering bit E in the direction of the corner being upsized. For example: X 0 X 1 X 1 1 X sets X X X X X 48 dot font 96 dot font where 1 represents a set (on) bit, 0 represents a bit which is not set or off, X represents a don't care for the state for that bit, in other words, the bit can be on or off.

In other words, if the bit (bit E) to be upsized is set (on) and either of bits D and B are also activated, then the top left bit is set (on) in the double sized font.

The second term E. (-A.-B.-C.-D.-G) maintains sharp right angled corners of letters. If the original bit (bit E) is set and it has a white space right angle surrounding it in the direction of the bit to be upsized, then the top left bit will also be set.

For example: 000 in 0 1 X sets X X 0 X X 48 dot font 96 dot font The third term E. (G. C) sets the top left bit in the 96 dot font if all three bits are set in the main 45 line perpendicular to the upsized corner bit. For example: Xi in X 1 X sets X X 1 X X 48 dot font 96 dot font Thus, if bits C, E and G are on, then the top left bit in the upsized font will also be on.

The fourth term-E. (D. B) smooths 45 angles. If the original bit, i. e. bit E, is not set (off) and the two bits in the closest 45 angle perpendicular to the direction, and closest to the upsizing corner, are set then the upsized top left corner bit is also set. In other words, if bit E is not set and bits D and B are set, then the top left bit in the 96 dot font is set. For example: Xi in 1 0 X sets X X X X X 48 dot font 96 dot font The fifth term-[-E. (A. B. C. D. G.)] overrides all the previous terms in the case where it is found that bit E is off in the corner of a right angle. This prevents the upsized bit from being set and prevents smearing of right angles. For example: 1 1 1 0 X 1 0 X sets X X 1 X X 48 dot font 96 dot font Thus, if bit E is not set but bits A, B, C, D and G are set, then the top left bit is not set.

The expressions for the top right, bottom left and bottom right bits in the double size font each contain analogous terms to those discussed in relation to the expression for the top left bit. If none of the five terms in each expression is met, then the pixel is not set. To calculate the value of the four pixels for bits which are on the edge of the 48 bit map, the missing surrounding pixels are assumed to have a zero value.

Figure 6a shows the letter S in a 96 dot font. The 48 dot font has simply been doubled to provide the character of Figure 6a. In other words, if a bit is set in the 48 dot font, all of the four corresponding bits in the 96 dot font will be set. Likewise, if a bit is not set in the 48 font dot, all of the four corresponding bits will not be set in the 96 dot font. As can be seen from Figure 6a, the resulting character has a stepped and ragged appearance.

Figure 6b shows the letter S in the 96 dot font form which has been produced from the 48 dot font using the above described algorithm. The appearance of the letter S has been improved greatly as compared to the letter S in Figure 6a. However, the appearance of the letter S of Figure 6b may be regarded as still being ragged. This problem generally occurs with letters having curves.

Accordingly, to further improve the appearance of certain of the characters, character specific masks are stored which can be overlaid onto the 96 dot font, after the smoothing algorithm described above has been performed but prior to printing. The masks consist of up to twenty selected bits per character. Each mask bit causes the upsized character bit at the same position to be reversed. In other words, if the selected bit is set in the 96 dot font, the mask will cause the bit to be off and vice versa. In this way, appearance of a number of characters can be improved. It should be appreciated that the masks are stored in the ROM 22 and are applied by the processor to modify the print information generated after the application of the double sizing algorithm. The generated print information is then sent to the print head 42 on a column by column basis, with each column including a plurality of pixels. Figure 6c shows the letter S inthe 96 dot font to which a mask has been additionally been applied. As can be seen from a comparison with Figure 6b, the appearance of the letter may further be improved.

The following characters are generally masked: k, s, v, w, x, C, G, N, 0, P, Q, S, V, W, X.

By using the simple algorithm outlined above with a small number of masks each of which has a relatively few dots, the memory space required to provide a 96 dot font with an acceptable appearance is significantly reduced as compared to an arrangement in which data for each character is stored in the 96 dot font form in addition to the 48 dot font form.

The size of the characters to be printed on the tape can be determined by the user and/or automatically. In the case of user selection, the user inputs the desired character size using the keyboard. It would be possible in certain embodiments of the invention to compare the selected character size with the width of the tape present in the tape printing apparatus and prevent printing where the character size exceeds the tape width.

Alternatively, an error message could be provided. As mentioned above, it would also be possible to automatically determine the size of the characters to be printed on the tape. This determination would be made in accordance with the width of tape detected and the number of lines to be printed on the tape.

There are a number of different methods which can be used to detect the tape size. For example, sensors can be used to detect the width of tape and in this regard, references made to our copending application, EP application no. 93304136 which is hereby incorporated by reference and which includes such an arrangement. Alternatively, a switch operable by the user can be provided so as to indicate to the tape printing apparatus the width of the tape. This switch can be located at the base of the cassette receiving bay or form part of the keyboard. In the case where the tape size switch is located in the base of the cassette receiving bay, it can be arranged so as to interact with cassettes. In particular, for each position of the tape switch, there is a corresponding aperture in the cassette of the given size which accommodates a part of the switch which extends above the floor of the cassette receiving bay. Insertion of the tape into the cassette receiving bay is only possible when the tape width indicated by the switch and the width of the tape included in the cassette are the same. In this way, it can be ensured that the width of tape indicated by the tape size switch and the width of tape included in the cassette are the same. There are of course a number of other different ways which can be used in order to provide an indication to the tape printing apparatus as to the tape width. For example, a number of switches may be provided on the base of the cassette receiving bay. One or more of these switches can be activated according to the width of image receiving bay included in the cassette.

It should be appreciated that for some embodiments of the invention, masking may not be necessary. Whilst the embodiment has been described in relation to a 48 dot font doubled to provide a 96 dot font, the present invention is equally applicable to other font sizes. In certain embodiments of the invention, the Boolean equations can be modified to provide characters of different size multiples. For example characters of one and a half or three times the size of the stored font can be generated. Of course, the present invention is also applicable to other resolutions of print head other than the 180 dot per inch print head described.

In the embodiment described in relation to the present invention, the font data, masks and algorithms have been described as being stored in a common ROM 22. However, as will be appreciated, separate memories can be provided for the font data, the masks and the sizing algorithms.

It should also be appreciated the data compression techniques can be used to store the 48 dot font in the ROM 22, thus reducing the memory capacity required. Decompression algorithms required to decompress the data may be stored in the ROM 22.

Claims

CLAIMS: 1. A printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium ; first storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing-algorithm, wherein each bit of said bit map of n bits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, said sizing algorithm being arranged to double the size of the symbols and/or characters defined by said n bit maps and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.
2. A tape printing apparatus as claimed in claim 1 or 2, wherein said processing means is arranged to determine the presence of corners in at least some of said characters and/or symbols by determining the status of the corresponding said bit and the immediately surrounding bits and to generate four pixels which maintain said corners in the printed characters and/or symbols.
3. A printing apparatus as claimed in claim 1 or 2, wherein the second storage means holds a plurality of smoothing masks for selective application to pixels generated by said sizing algorithm prior to generating said print information.
4. A printing apparatus as claimed in claim 3, wherein a mask is applied to one or more of the following characters: k, s, v, w, x, C, G, N, O, P, Q, S, V, W, X
5. A printing apparatus as claimed in claim 3 or 4, wherein each of said smoothing masks comprises a plurality of selected bits, each of said selected bits causes the bit in the corresponding position in the double sized character and/or symbol to be reversed.
6. A printing apparatus as claimed in any one of the preceding claims, wherein said processing means is arranged to determine if the corresponding said bit is set and either of the two bits of the n bit map bordering two adjacent sides of the corresponding said bit, which together define a corner region, are also set, and if so to set the pixel of said four pixels in the bit map of the double sized character and/or symbol which defines a corresponding corner region.
7. A printing apparatus as claimed in any one of the preceding claims, wherein said processing means is arranged to determine if the corresponding said bit is set and the bits immediately surrounding the corresponding said bit of the n bit map which define a right angle about one of the corner regions of the corresponding said bit are all not set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corner region corresponding to said one corner region of the corresponding bit.
8. A printing apparatus as claimed in any one of the preceding claims, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is set and the two bits adjacent diagonally opposed corners of the corresponding said bit are set and if so to set two pixels of the four pixels in the bit map of the double sized character and/or symbol which define corners corresponding to the corners of the corresponding said bit which are not adjacent said two adjacent bits in the n bit map.
9. A printing apparatus as claimed in any preceding claim, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and both of the two bits bordering two adjacent sides of the corresponding said bit which together define a corner region of the corresponding said bit are set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corresponding corner.
10. A printing apparatus as claimed in any preceding claim, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and the bits surrounding the corresponding said bit which define a right angle about one of the corner regions of the corresponding said bit are set, and if so then the pixel of said four pixels of the bit map of the double sized character and/or symbol which define a corner region corresponding to said one corner region of the corresponding said bit is not set.
11. A printing apparatus as defined in claim 9 and 10, wherein if the conditions set out in claims 9 and 10 are both satisfied then the relevant pixel in the bit map for the character in the second size is not set.
12. A tape printing apparatus as claimed in any preceding claim, wherein characters and/or symbols can be printed in a third size, which is half the size of said first size, a sizing algorithm for generating said half size characters being stored in said second storage means and said processing means is arranged to generateprint information for characters and/or symbols in said third size.
13. A printing apparatus as defined in any preceding claim, wherein said printing apparatus is a tape printing apparatus, said tape printing apparatus comprising means for receiving a supply of image receiving tape on which said printing means, which is a print head, is operable to print an image to thereby define a label.
14. A tape printing apparatus for printing an image on an image receiving tape to thereby define a label, said apparatus comprising: means for receiving a supply of image receiving tape; means for receiving input data defining an image to be printed on the image receiving tape, said input data including at least one character and/or symbol; first storage means holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size, which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels being determined in accordance with the status of the bits immediately surrounding said bit, said sizing algorithm being arranged to double the size of the symbols and/or characters defined by said n bit maps and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and a print head for printing the image on the image receiving tape in accordance with the print information.
15. A tape printing apparatus as claimed in claim 14, wherein the second storage means holds a plurality of smoothing masks for selective application to pixels generated by said sizing algorithm prior to generating said print information.
16. A tape printing apparatus as claimed in claim 13,14 or 15 comprising: a motor for driving said image receiving tape through a print zone defined adjacent said print head, said image being printed on a portion of the image receiving tape in said print zone.
17. A tape printing apparatus as claimed in any of claims 13 to 16, wherein said print head is arranged to print an image on said image receiving tape column by column.
18. A tape printing apparatus as claimed in any one of claims 11 to 15, wherein said means for inputting data comprising a keyboard.
19. A tape printing apparatus as claimed in any of one claims 13 to 18, wherein cutting means are provided for separating the image receiving tape on which an image has been printed from the supply of image receiving tape to thereby define a label.
20. A tape printing apparatus as claimed in any one of claims 13 to 19, wherein the size of the characters and/or symbols printed on the image receiving tape is determined by the processing means in accordance with the width of the image receiving tape.
21. A method of generating from a pre-stored bit map of n bits defining a character and/or symbol in a first size, a bit map defining the character and/or symbol in a second size, double the first size said method comprising using each bit of said n bit map to generate four pixels in bit map for the double size character, the status of each of the four pixels being separately determined in accordance with the status of the pixels immediately surrounding the corresponding bit.
22. A method of printing an image onto an image receiving tape comprising the steps of: selecting symbols and/or characters to define the image to be printed; storing font data defining symbols and/or characters from which the selected symbols and/or characters are selected, each character and/or symbol being defined as a bit map of n bits; selecting the size for each selected symbol and/or character, wherein selected characters and/or symbols can be printed in a first size as a bit map of n pixels or in a second size, double the first size; generating print information comprising a plurality of pixels in accordance with the selected characters and/or symbols and the selected size, the print information for characters in the first size being generated from the stored font data so that each bit of the n bit map corresponds to a single pixel in the printed image and applying a sizing algorithm to generate print information for characters of said second size, wherein each bit of the stored n bit map corresponds to four pixels in the printed image, the status of each of the four pixels being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, said sizing algorithm also smoothing the outline of curved and/or angled portions of at least some of the characters and/or symbols; and printing an image onto an image receiving medium in accordance with the generated print information.
23. A method as claimed in claim 21 or 22, wherein the presence of corners in at least some of said n bit map characters and/or symbols is determined by determining the status of the bit to be enlarged in the n bit map and the immediately surrounding bits, and double sized characters and/or symbols are generated which also include corresponding corners.
24. A method as claimed in claim 21,22 or 23, wherein smoothing masks are applied to selected pixels of bit maps for selected double sized characters and/or symbols produced from the associated n bit map.
25. A method as claimed in any one of claims 21 to 24 comprising the step of determining if the bit to be enlarged is set and whether either of the two bits of the n bit map bordering two adjacent sides of said bit to be enlarged, which together define a corner region, are set and, if so to set the pixel of said four pixels of the bit map of the double size character and/or symbol which defines a corresponding. corner region :
26. A method as claimed in any one of claims 20 to 25 comprising the step of determining if the bit to be enlarged is set and the bits surrounding the bit to be enlarged, which define a right angle about one of the corner regions of said bit to be enlarged, are not set and, if so, to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged.
27. A method as claimed in any one of claims 21 to 26 comprising the step of determining if the bit to be enlarged is set and the two bits adjacent diagonally opposed corners of the bit to be enlarged are set, and if so to set two pixels of the four pixels in the bit map of the double size character and/or symbol which define corners corresponding to the corners of the bit to be enlarged which are not adjacent said two adjacent bits in the n bit map.
28. A method as claimed in any one of claims 20 to 27 comprising the step of determining if the bit of the n bit map which is to be enlarged is not set and if both of two bits bordering two adjacent sides of said bit to be enlarged, which together define a corner region of the bit to be enlarged, are set and, if so to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corresponding corner.
29. A method as claimed in any one of claims 21 to 28, comprising the step of determining if the bit to be enlarged of the n bit map is not set and the bits surrounding the bit to be enlarged which define a right angle about one of the corner regions of the bit to be enlarged are all set, and if so then the of the four pixels of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged is not set.
30. A method as claimed in claim 21 or any claim appended thereto comprising the step of printing an image onto an image receiving tape, and separating the portion of the image receiving tape on which the image has been printed to define a label.
31. A printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium; first storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm said algorithm comprising a plurality of Boolean equations, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is different to the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate a plurality of pixels in the double second printed character and/or symbol, the status of each of the pixels in the second size of characters being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, a Boolean equation being provided for determining the status of each pixel of the character and/or symbol of the second size, said sizing algorithm being arranged to change the size of the symbols and/or characters defined by said n bit maps to said second size and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.

31. A printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium; first storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm said algorithm comprising a plurality of Boolean equations, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is different to the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate a plurality of pixels in the double second printed character and/or symbol, the status of each of the pixels in the second size of characters being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, a Boolean equation being provided for determining the status of each pixel of the character and/or symbol of the second size, said sizing algorithm being arranged to change the size of the symbols and/or characters defined by said n bit maps to said second size and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.

Amendments to the claims have been filed as follows 1. A printing apparatus for printing an image onto an image receiving medium comprising: means for receiving input data defining an image comprising at least one character and/or symbol to be printed on the image receiving medium; storage means for holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said storage means, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means and each bit of said bit map of n bits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, the processing means when determining the status of each respective one of the four pixels being arranged to consider the status of the corresponding bit and additionally the status only of the five bits which make up a right angle adjacent the position of the respective pixel and said processing means being arranged to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and printing means for printing the image on the image receiving medium in accordance with the print information.

2. A tape printing apparatus as claimed in claim 1 or 2, wherein said processing means is arranged to determine the presence of corners in at least some of said characters and/or symbols by determining the status of the corresponding said bit and the immediately surrounding bits and to generate four pixels which maintain said corners in the printed characters and/or symbols.

3. A printing apparatus as claimed in claim 1 or 2, wherein the second storage means holds a plurality of smoothing masks for selective application to pixels generated by said sizing algorithm prior to generating said print information.

4. A printing apparatus as claimed in claim 3, wherein a mask is applied to one or more of the following characters: k, s, v, w, x, C, G, N, O, P, Q, S, V, W, X 5. A printing apparatus as claimed in claim 3 or 4, wherein each of said smoothing masks comprises a plurality of selected bits, each of said selected bits causes the bit in the corresponding position in the double sized character and/or symbol to be reversed.

6. A printing apparatus as claimed in any one of the preceding claims, wherein said processing means is arranged to determine if the corresponding said bit is set and either of the two bits of the n bit map bordering two adjacent sides of the corresponding said bit, which together define a corner region, are also set, and if so to set the pixel of said four pixels in the bit map of the double sized character and/or symbol which defines a corresponding corner region.

7. A printing apparatus as claimed in any one of the preceding claims, wherein said processing means is arranged to determine if the corresponding said bit is set and the bits immediately surrounding the corresponding said bit of the n bit map which define a right angle about one of the corner regions of the corresponding said bit are all not set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corner region corresponding to said one corner region of the corresponding bit.

8. A printing apparatus as claimed in any one of the preceding claims, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is set and the two bits adjacent diagonally opposed corners of the corresponding said bit are set and if so to set two pixels of the four pixels in the bit map of the double sized character and/or symbol which define corners corresponding to the corners of the corresponding said bit which are not adjacent said two adjacent bits in the n bit map.

9. A printing apparatus as claimed in any preceding claim, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and both of the two bits bordering two adjacent sides of the corresponding said bit which together define a corner region of the corresponding said bit are set, and if so to set the pixel of said four pixels of the bit map of the double sized character and/or symbol which defines a corresponding corner.

10. A printing apparatus as claimed in any preceding claim, wherein the processing means is arranged to determine if the corresponding said bit of the n bit map is not set and the bits surrounding the corresponding said bit which define a right angle about one of the corner regions of the corresponding said bit are set, and if so then the pixel of said four pixels of the bit map of the double sized character and/or symbol which define a corner region corresponding to said one corner region of the corresponding said bit is not set.

11. A printing apparatus as defined in claim 9 and 10, wherein if the conditions set out in claims 9 and 10 are both satisfied then the relevant pixel in the bit map for the character in the second size is not set.

12. A tape printing apparatus as claimed in any preceding claim, wherein characters and/or symbols can be printed in a third size, which is half the size of said first size, a sizing algorithm for generating said half size characters being stored in said second storage means and said processing means is arranged to generateprint information for characters and/or symbols in said third size.

13. A printing apparatus as defined in any preceding claim, wherein said printing apparatus is a tape printing apparatus, said tape printing apparatus comprising means for receiving a supply of image receiving tape on which said printing means, which is a print head, is operable to print an image to thereby define a label.

14. A tape printing apparatus for printing an image on an image receiving tape to thereby define a label, said apparatus comprising: means for receiving a supply of image receiving tape; means for receiving input data defining an image to be printed on the image receiving tape, said input data including at least one character and/or symbol; first storage means holding font data defining characters and/or symbols printable on said image receiving medium, each character and/or symbol being defined as a bit map of n bits in said first storage means; second storage means holding a sizing algorithm, said printing apparatus being operable to print characters and/or symbols selectively in a first size as a bit map of n pixels and in a second size, which is double the first size; processing means connected to receive said input data, said font data and size selection data and operable to generate therefrom print information comprising a plurality of pixels, wherein characters and/or symbols of said second size are generated from said font data by said processing means according to said sizing algorithm, wherein each bit of said bit map of n bits is used to generate four pixels in the double size printed character and/or symbol, the status of each of the four pixels being determined in accordance with the status of the bits immediately surrounding said bit, said sizing algorithm being arranged to double the size of the symbols and/or characters defined by said n bit maps and to smooth the outline of curved and/or angled portions of at least some of said characters and/or symbols; and a print head for printing the image on the image receiving tape in accordance with the print information.

15. A tape printing apparatus as claimed in claim 14, wherein the second storage means holds a plurality of smoothing masks for selective application to pixels generated by said sizing algorithm prior to generating said print information.

16. A tape printing apparatus as claimed in claim 13,14 or 15 comprising : a motor for driving said image receiving tape through a print zone defined adjacent said print head, said image being printed on a portion of the image receiving tape in said print zone.

17. A tape printing apparatus as claimed in any of claims 13 to 16, wherein said print head is arranged to print an image on said image receiving tape column by column.

18. A tape printing apparatus as claimed in any one of claims 11 to 15, wherein said means for inputting data comprising a keyboard.

19. A tape printing apparatus as claimed in any of one claims 13 to 18, wherein cutting means are provided for separating the image receiving tape on which an image has been printed from the supply of image receiving tape to thereby define a label.

20. A tape printing apparatus as claimed in any one of claims 13 to 19, wherein the size of the characters and/or symbols printed on the image receiving tape is determined by the processing means in accordance with the width of the image receiving tape.

21. A method of generating from a pre-stored bit map of n bits defining a character and/or symbol in a first size, a bit map defining the character and/or symbol in a second size, double the first size said method comprising using each bit of said n bit map to generate four pixels in bit map for the double size character, the status of each of the four pixels being separately determined in accordance with the status of the pixels immediately surrounding the corresponding bit.

22. A method of printing an image onto an image receiving tape comprising the steps of: selecting symbols and/or characters to define the image to be printed; storing font data defining symbols and/or characters from which the selected symbols and/or characters are selected, each character and/or symbol being defined as a bit map of n bits; selecting the size for each selected symbol and/or character, wherein selected characters and/or symbols can be printed in a first size as a bit map of n pixels or in a second size, double the first size; generating print information comprising a plurality of pixels in accordance with the selected characters and/or symbols and the selected size, the print information for characters in the first size being generated from the stored font data so that each bit of the n bit map corresponds to a single pixel in the printed image and applying a sizing algorithm to generate print information for characters of said second size, wherein each bit of the stored n bit map corresponds to four pixels in the printed image, the status of each of the four pixels being separately determined in accordance with the status of the bits immediately surrounding the corresponding said bit, said sizing algorithm also smoothing the outline of curved and/or angled portions of at least some of the characters and/or symbols; and printing an image onto an image receiving medium in accordance with the generated print information.

23. A method as claimed in claim 21 or 22, wherein the presence of corners in at least some of said n bit map characters and/or symbols is determined by determining the status of the bit to be enlarged in the n bit map and the immediately surrounding bits, and double sized characters and/or symbols are generated which also include corresponding corners.

24. A method as claimed in claim 21,22 or 23, wherein smoothing masks are applied to selected pixels of bit maps for selected double sized characters and/or symbols produced from the associated n bit map.

25. A method as claimed in any one of claims 21 to 24 comprising the step of determining if the bit to be enlarged is set and whether either of the two bits of the n bit map bordering two adjacent sides of said bit to be enlarged, which together define a corner region, are set and, if so to set the pixel of said four pixels of the bit map of the double size character and/or symbol which defines a corresponding. corner region.

26. A method as claimed in any one of claims 20 to 25 comprising the step of determining if the bit to be enlarged is set and the bits surrounding the bit to be enlarged, which define a right angle about one of the corner regions of said bit to be enlarged, are not set and, if so, to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged.

27. A method as claimed in any one of claims 21 to 26 comprising the step of determining if the bit to be enlarged is set and the two bits adjacent diagonally opposed corners of the bit to be enlarged are set, and if so to set two pixels of the four pixels in the bit map of the double size character and/or symbol which define corners corresponding to the corners of the bit to be enlarged which are not adjacent said two adjacent bits in the n bit map.

28. A method as claimed in any one of claims 20 to 27 comprising the step of determining if the bit of the n bit map which is to be enlarged is not set and if both of two bits bordering two adjacent sides of said bit to be enlarged, which together define a corner region of the bit to be enlarged, are set and, if so to set the pixel of the four pixels of the bit map of the double size character and/or symbol which defines a corresponding corner.

29. A method as claimed in any one of claims 21 to 28, comprising the step of determining if the bit to be enlarged of the n bit map is not set and the bits surrounding the bit to be enlarged which define a right angle about one of the corner regions of the bit to be enlarged are all set, and if so then the of the four pixels of the bit map of the double size character and/or symbol which defines a corner region corresponding to said one corner region of the bit to be enlarged is not set.

30. A method as claimed in claim 21 or any claim appended thereto comprising the step of printing an image onto an image receiving tape, and separating the portion of the image receiving tape on which the image has been printed to define a label.