IL96118A - Process for making printed matter and matter obtained by said process - Google Patents

Description

PROCESS FOR MAKING PRINTED MATTER AND MATTER OBTAINED BY SAID PROCESS PROCESS FOR MAKING PRINTED MATTER AND MATTER OBTAINED BY SAID PROCESS This invention relates to a process for making printed matter, and to the matter made by said process. More particularly it relates to printed matter that should not be readable at any time by mere inspection, but only at predetermined times and/or by predetermimed persons. An example of such matter is printed texts containing information that should not be understood without a certain effort, such as certain educational material, or printed texts containing information that it is desired to protect from casual prying.

Printed educational material often contains questions, the answers to which must be provided to the reader and checked against a set of answers. Thus, in exercise books relating to natural sciences or other subjects, problems are set forth in a part of the book, and the solutions to the problems are set forth in a different part of the book, e.g. an appendix, to which the reader must continuously refer. In more complex cases, a text may be provided in which some words or figures are missing and the missing words or figures are supplied in a different part of the book. The necessity of constantly referring to a different part of the exercise book creates inconvenience and fatigue, is the source of not uncommon mistakes, such as when the reference numerals or other indications' which correlate the questions to the corresponding answer are not accurate, and greatly limits the possibility of inserting within the printed text indications that must be supplied by the reader and may present increasing degrees of difficulty, in order gradually to advance the learner's knowledge.

It would be highly desirable to provide printed matter which includes elements which cannot be read unless the reader wishes it, e.g. answers to questions or data which must be supplied by the reader. In addition to said purpose, such printed matter would serve other important purposes in educational material. One of them is the teaching of languages, which would be greatly facilitated if printed matter were provided in which a text in a language known to the learner were printed in the usual way and a translation of it were printed in such a way as to be readable only if the learner wishes it. A particular application would be to teaching the punctuation of hebrew and arabic, in which symbols representing vowels are not ordinarily printed. As far as the applicant is aware, no printed matter of the said kind is available, and no process for making it is provided by the state of the art.

Another purpose which the invention achieves is to protect information, which it is desired to keep private, from casual prying. For instance, information as to the balance of bank accounts is often exposed to the eyes of strangers and is readable at a glance; or certain confidential data may be contained in office documents which pass through the hands of employees who may not be completely trusted not to divulge them. Encryption methods are of course known in the art, but they are more or less complex and cannot be carried out in the course of ordinary printing processes, though they may guarantee a degree of secrecy which is not required and not particularly desired in the situations with which this invention is concerned.

The invention solves the problem of providing printed matter of the kind described and a process for making it in an easy and economical way, as a part of conventional printing operations.

The process according to the invention comprises the following steps: 1- defining, at least ideally, at least one blank grid; 2- creating a reference grid consisting of a scrambled distribution, as hereinafter defined, of at least two digitizable values in the cells of the blank grid; 3- creating at least coded one font by: a. individually superimposing, at least ideally, each character to be comprised in the font to at least a portion of the reference grid, and b. changing the digital values of the reference grid in the cells thereof comprised in the area covered by the superimposed character, whereby to create a scrambled character grid which represents the character; 4- storing the character grids in the memory of a print-controlling device; 5- storing in the memory of a text composing device commands causing the print-controlling device alternatively to select and store characters or character grids, as desired; 6- defining by means of said text composing device the desired text, wherein any characters not comprised in a coded font -hereinafter "clear characters" - are represented in a conventional way and any characters comprised in a coded font - hereinafter "coded characters" - are represented by the corresponding character grids, this operation being sometimes called hereinafter "composing the text"; 7- impaginating the composed text, and preferably providing correspondence marks at least in each page; 8- printing the composed and impaginated text by graphically defining: a) any clear characters in the conventional way , b) any coded characters by signs representing the digitizable values of the respective character grids, and preferably c) said correspondence marks; and 9- providing on a transparent sheet at least a copy of the reference grid and further, preferably, providing thereon reference marks matching the correspondence marks; whereby when said transparent sheet is superimposed to a printed text so that a reference grid is superimposed to the grid of the coded characters which are to be read, preferably by suitably aligning the correspondence and reference marks, said coded characters become detectable and identifiable.

The blank grid consists of a number of cells defined by intersecting grid lines, the nature and spacing whereof may vary according to the specific application that is made in each individual case. Preferably a Cartesian grid is used, wherein each grid line may have one of two orientations, the two orientations being perpendicular to one another, and the spacing of successive parallel grid lines, or "grid pitch", being constant. More preferably, the grid pitch is not smaller than one tenth of millimetre. Large grid pitches will render the coded characters less sharp and less well defined to the reader's eye, but will facilitate the exact superimposition of the reference grid to the character grids and thus the reading thereof. The optimal pitch grid is chosen in each case so as to strike an optimal balance between the advantages and disadvantages of the larger, or conversely the smaller, pitches.

The blank grid may be graphically defined on a screen or may only be ideally defined by its pitch or pitches or by the number of its cells in the unit area or by a subroutine or other program stored in the memory of a word processor or printer or other print-controlling device. It should be considered as "defined" whenever it is possible to assign to any given cell thereof a digitizable value.

By "digitizable values" is meant characteristics which can be represented by digital values. They may actually be digital values or, e.g., graphic symbols, or black and white or additionally degrees of gray, to which digital values may correspond, or again, different colors which may conventionally be represented by digital values. Preferably only two digital values are used, since this is more desirable for the purposes of the invention, and they may be represented in digital form by the values 0 and 1 or black and white. If two digital values are used, the reference grid will consist of a distribution of O's and l's, or blacks and whites, in a random manner in the cells of the blank grid.

By "scrambled grid" is meant a grid which is sufficiently randomized to make the coded characters illegible without using the reference grid, and yet preferably contains less accumulations or "clots" of black (or 1-) cells than would a truly random - or more exactly a practically random - grid. A convenient way of building a scrambled grid is the following. Routines are known for building what is called a "random grid", though in practice it is not exactly, but only approximately, random. The routine will define successively for each cell whether the cell is white or black. If the cell is white, this value will be retained in any case and marked on the grid. If it is black, the routine will verify whether the preceding cell was white or black. If it was white, the ensuing black value will be retained. If it was black, the ensuing black value will be rejected and the routine will move forward and determine a new value. In this way the probability of having two adjacent black cells in the grid will be halved. This procedure may be repeated, if it desired to reduce this probability further. However if it is repeated too many times, the "scrambling" of the grid, viz. the degree of its randomization, will decrease so much and the white cells will become so predominant that the coded characters will become deciferable, and this should be avoided. On the other hand, it is to be understood that the use of a truly, or better practically, random grid, as created by conventional, unmodified programs or routines intended for this purpose, is comprised in this invention, and therefore the expression "scrambled grid" is to be construed as including such random grids, though not preferentially.

By "charactei-s" is meant letters, numerals, punctuation marks, mathematical or any other symbols, and in general any graphic signs. Characters in general will be considered to be "clear" when they represent themselves, viz. have an aspect that is recognizable by the typical reader as conveying the information that the character is ordinarily intended to convey; while they will be considered as "coded" when they do not have such an aspect, viz. represent something that is not ordinarily associated with their aspect and the information that they are intended to convey is not immediately recognizable by mere direct inspection.

By "superimposing at least ideally, the character to at least a portion of the reference grid" is meant establishing a correspondence between the points of the character and the cells of the reference grid. This can be done in many ways. One may draw or represent on a screen, e.g., a computer screen, the reference grid, and actually draw the character over the reference grid. Alternatively, one might draw a blank grid which is a replica of that originally used and draw the character on the replica blank grid, and then establish a correspondence between the cells occupied by the character in said blank grid and the corresponding cells of the reference grid. In order to do this, one need not actually draw the character over the replica blank grid, but can draw or show on a screen said blank grid and then fill the cells thereof with appropriate symbols so as to create the outline of the character. The word "draw" should be construed as including any operation which defines the "drawn" character or outline or area, comprising the creation and/or use of a defining subroutine or other program.

Changing the digital values in the cells in the area covered by the superimposed character can be effected in any desired way. Of course, once again, the said area may be defined only ideally and not actually in a graphic manner, or in other words, it may be "drawn" in the broad sense defined hereinbefore. Since the digital values of the reference grid are preferably only two, the change which is carried out in the cells comprised in the superimposed character will preferably be an inversion of the digital value, viz. a change from 0 to 1 or from black to white, or vice versa. The two operations 3a and 3b can be combined by showing on a screen or generally "drawing" the reference grid and inverting the digital values in the cells which are designated as being comprised in the area occupied by the character. The cells, in which the inversion is carried out, may be graphically indicated in any suitable way, e.g. by a mark, so as to be apparent to the operator's eye, who thus defines, concurrently with the inversion, the area comprised in the outline of the character, where the inversion is to be effected.

By "a print-controlling device" is meant any device that determines what will be printed and thus, generally, a text composing device, such as a word processor - to which non-limitative reference will be made hereinafter in describing the embodiments of the invention - or the like and a printer or the like, but possibly an interface or other device that may be provided for this specific purpose. According to different ways of operating different equipment available, the commands which determine how the printing is carried out will generally be stored in a word processor memory or in a printer memory. The word processor may compose, in the sense hereinbefore defined, an entire page or an entire text and transmit it to the printer, which will store it, or it may compose single words or even single characters and transmit them immediately to the printer, which will store them in its memory. The word processor and the printer may be of any kind known in the art, and, for instance, they may be respectively a microcomputer and a laser or other kind of printer, or they may be Linotypes or other apparatus used for book-printing or the like. The character grids, therefore, may be stored either in the memory of the word processor, in which the text will be printed as defined, or in the memory of the printer, in the same way in which in various types of word processors and printers the various fonts may be stored in the memory of the first or of the second, or even in the memory of an interface or other device.

All the character grids deriving from a given reference grid will constitute a "coded font". A printer - whatever its type, e.g. a laser printer - may store a number of coded fonts. In this case, the text composing device will communicate to the printer the font with which it should print and the several characters, identified as plain characters, e.g. by their ASCII symbols. The input to the printer will thus be the same as if plain characters were printed, except for the single, initial command, to print a given coded font. Alternatively, the printer may receive from the text composing device severally the individual coded character in the same way in which it would receive a purely graphic input, viz. the text composing device will input to the printer the coded characters in graphic language, and the printer will be able to understand such graphic language by means well known in the art, e. g. as POSTSCRIPT language.

The word processor will compose the desired text by means of characters. Most of the text, more precisely the parts thereof which are to be printed plainly in the usual way, and not by means of a font created according to the invention, may be represented in any known and conventional manner, and in many cases by ASCII symbols, while the characters comprised in the coded fonts will be represented by the corresponding character grids. In order thus to define the text, the word processor must register a command which indicates how each character is to be represented. In practice it will be sufficient to indicate what parts of the text are to be printed in a coded font. This can be done either by attributing to each coded character a symbol of its own, as is often done with conventional fonts, or by indicating by means of an appropriate symbol the point at which the coded text begins and the point at which the coded text ends. Such commands will be stored in the memory of the device which composes the text, generally the word processor, but they will be executed either by the word processor or by the printer or by any device controlling the printing operation, depending on which device stores the coded fonts.

In order to carry out the invention, the composed text must be impaginated and correspondence marks must be provided at least on each page or possibly on each predetermined portion of a page. Depending on the nature of the text and of the coded fonts, and on the degree of precision desired, as well as on the size of the text characters, correspondence marks of different kinds may be used. For instance, a printed word may serve as a correspondence mark, or a graphic sign of any kind may be used, as, for instance, a cross or a circle or the like. It is convenient, in a preferred embodiment of the invention, to use pairs of relatively simple graphic signs.

In an embodiment of the invention, the commands determining the beginning and the end of the coded text will also cause the printing of a ccorrespondence mark. In this manner, each coded text portion - grahic character or characters, word or number of words - will be provided with its own correspondence marks, in its immediate vicinity, wthereby facilitating the alignment. In this case, the transparent sheet will carry a number of reference grids of different lengths, each provided with reference marks, and in each case the reference grid will be used which has the same length as the coded text portion to be read.

- - Once a text has been composed and impaginated, the coded characters must be printed by attributing the appropriate color values to the various cells of the character grids. In the most common way of carrying out the invention, where the digitizable values are only two and can be represented by 0 and 1, the cells to which the 1 value is associated will be printed in black or black pixels will be printed therein, and the cells in which the 0 value is marked will receive no mark and remain void, viz. white. Alternatively, suitable color combinations could be used; and again, more than two digital values, requiring more than two colors or shades of color, may be required.

The transparent sheet on which a copy of the reference grid is printed should be dimensionally stable. Dimensionally stable transparent plastics are known and the art knows how to print thereon words and graphic signs. The transparent sheet will carry the same marks as those used as correspondence marks on the printed page, which have been designated as reference marks. A complex reference sign can be used for each page or, more conveniently, a pair of simple graphic signs, or a plurality of pairs of graphic signs for each page. The reason for using a plurality of pairs of graphic signs as reference marks is that there may be some dimensional irregularities in the printed page or in the transparent sheet and therefore if only two references signs are used for an entire page, the dimensional irregularities might make the superimposition of the printed text to the reference grid imperfect and the coded font characters would not be easily identified. In order to minimize the consequences of dimensional irregularities, one may either print on a single page a plurality of pairs of reference signs, or provide, instead of a transparent sheet having the size of a printed page, a transparent strip having a height that is equal to the height of one or a few printed lines, and print on the printed page a plurality of pairs of reference marks for each strip of the page having the size of the transparent strip.

The invention will be better understood from an embodiment thereof, with reference to the appended drawings, wherein: - Fig. 1 shows a sentence from a printed page, including a question and answer, printed entirely in plain characters; - Fig. 2 represents a reference grid, at a greatly enlarged scale; - Fig. 3 shows how the character H is defined on the blank grid, shown at a greatly enlarged scale; - Fig. 4 shows a character grid representing the said letter H, at a greatly enlarged scale; - Fig. 5 represents a strip of a transparent material with the space in which the reference grid is to be printed and the reference marks piunted thereon; - - - Fig. 6 represents the portion of the page of Fig. 1 wherein the answer to the question of Fig. 1 is represented by a character grid and wherein the correspondence marks are also printed; - Fig. 7 shows how the superimposition of the transparent strip of Fig. 5 to portion of printed page of Fig. 4 permits to read the answer to the question; and Fig. 8 illustrates in flow chart form a way of carrying into practice an embodiment of the device.

In contructing the blank and the reference grids, the degree of resolution possessed by the printer to be used is to be taken into account. A laser printer, connected e.g. with a microcomputer used as word processor, may print as many as 90,000 cells per square inch; and if the printer is a Linotype, the resolution is much higher. A random grid may be created by a subroutine or other program easily devised by persons skilled in the art, since the creation of random successions of two or more digital values is very commonly practiced. The program or routine, modified if desired in the way explained hereinbefore, to reduce the probability of an accumulation of black cells, will therefore create the reference grid by introducing in all the cells of the blank grid a digital value chosen in a more or less randomized way, generally either white (0) or black (1). However, the resolutions mentioned - - above are usually excessive: as has already been stated, the linear dimensions of the cells should preferably not be less than one tenth of a millimetre and therefore the number of grid cells should preferably not be higher than about 625 per square inch. Therefore each cell will include a number of dots, which will receive the same digital value, e.g. be all white or black: in the case of a laser printer, each cell of the blank grid may include about 144 dots or more. Correspondingly, the printer, when printing on a transparent sheet the reference grid, will insert black dots in all the areas of the cells where the digital value is 1 , and will not print anything in the areas of the cells where the digital value is 0. It will be possible to use shades of gray instead of black, by inserting black dots only in a greater or smaller part of said cell areas. Therefore the word "black" should be construed, wherever appropriate, as possibly including gray.

All this of course will not occur if the printer is of the Dotmatrix type, which has a much less fine resolution.

The shape of the dots printed may depend on the type of printer. Some printers, in particular Linotypes, will print a black square which covers the entire space available for the dot, and this is very convenient for carrying out this invention. In other cases, e.g. in the case of some laser printers, the printer will print in each dot, which is in the area of the 1. value, a black mark that does not cover the entire dot and may have different shapes, for instance a - - diamond shape. At any rate a reference grid will be formed, which is schematically illustrated by way of example in Fig. 2. However, since the cells of the grid are extremely small, for clarity's sake the grid has been greatly enlarged in Fig. 2 and only a portion of it is shown.

The subsequent operation, that of creating the font, can be carried out in various ways. It will be understood that for each reference grid at least a font may be created and more than one font can be stored in the memory of a word processor or a printer or in general a print-controlling device.

A portion of the blank grid sufficient to accommodate the desired character is shown on the screen of the word processor. It is shown at the largest possible scale, compatibly with the size of the screen, in order to facilitate the following operations. If the grid cells will generally be too small, even when enlarged, for the operator to carry out the operations that will be described, the grid will be preferably be shown on the screen with cells each of which comprises a number of the true cells of the grid, say, four or more. The cells which define the area of the desired character will now be marked on the screen in any appropriate way. In Fig. 3 it is assumed that said cells have been completely blackened, so that the letter H appears in its normal shape, but they could be marked in any other visible way, say by entering an 'χ' mark in each cell or in squares or rectangles representing each a cell or a number - - of cells, until the desired character appears in recognizable manner on the screen. The word processor will memorize the result of said operation and associate it -with the character, in this case the letter H. The word processor will now compare each area comprised in the definition of the character with the corresponding area of the reference grid and invert the digital values associated with each cells of said grid area, viz., in the case of binary digital values, will change 0 to 1 and 1 to 0. The skilled person will encounter no difficulty in providing the required software. The resulting grid is the character grid, illustrated, still at a greatly enlarged scale, in Fig. 4, which will of course be scrambled or even random, as the reference grid was scrambled or even random. For each character and each reference grid at least a character grid is provided, so that if different reference grids have been prepared and stored in the memory of the word processor, an equal number of fonts may be prepared.

It is however highly desirable that the the printing operator should not be required to go through the time consuming procedure described. It is therefore preferable to provide to him a coding program, in the form of a disc or in other suitable form, which contains all the necessary data which can be trasferred to the word processor memory, e.g. to a hard disk, or to another memory of a print controlling device or a printer. Each reference grid can be considered as ■ a "key" which transforms clear characters into coded characters. The word processor or other - - device used will have a number of clear fonts in its memory, identified e.g. by ASCII or other symbols, and other clear fonts may be created or introduce by the operator. The coding program has stored therein a number of keys (reference grids) and the instructions for creating a characters grid whenever a clear character is fed to the word processor or other device and a key is selected. In other words, each key (reference grids) generates a font corresponding to any clear font fed to the device. The operator need only select a key and, when he comes to the part of the text that is to be coded, give the appropriate command in any suitable way and give once again the same command or a different command when he wisnhes to return to clear printing. The commands will be of the type "START CODING" and "END CODING", these commands being represented on the screen by suitable signs. Alternatively, the passage to the coded font could be effected by depressing a key, in the way in which in ordinary keyboards capitals are obtained by depressing a "CAPS LOCK" key; or by depressing a key which also generates a correspondence mark at the beginning and at the end of the coded text. Further, a number of clear fonts may be included in the program fed to the word processor or other device, in place of or in addition to the fonts that are present in the said processor or device.

It will also be clear that different coded fonts may be created, not only by employing different reference grids, but also by employing different conventional fonts, e.g., the coded font may be created by - - ideally or actually superimposing each of the conventional fonts, which the word processor can use, to the same reference grid. If the font used in the ideal superimposition is, e.g., in bold characters, the coded font will correspondingly be bold. This permits to obtain a variety of effects by carrying out the invention.

The characters shown on the screen will preferably be in the conventional, directly readable font, although they might also be in the coded font.

Fig. 5 represents a transparent strip, with the reference grid shown only schematically - viz. as uniformly shaded - for simplicity of illustration, and with reference marks in the shape of crosses. The strip will be at least as high as a coded character and may be as high as an entire printed page, but generally its size will be intermediate between those two extremes and it will be high enough to cover a number of lines of the printed text. Its height will be determined in such a way as to satisfy several requirements. It must not be so large as to cover an area in which significant dimensional inaccuracies may arise in the printed page. However it must not be so small that its use will be inconvenient and that too many pairs of correspondence marks will be required in the printed page. Each strip will carry reference marks that are sufficient correctly to position it on the printed page. If such marks are in pairs, as in the example illustrated, the strip will have at least one pair of them, but it may - - have a plurality of pairs, depending on its height and on the dimensional incaccuracies that are likely to occur in a portion of the printed page having the same height.

In a preferred embodiment of the invention the transparent strip will include several repetitions of the same reference grid set side by side. The reference grid, in general, will have a width that is of the same order of magnitude as its height, say from one to three times its height, while a printed line, and therefore the transparent strip, may be much wider. Thus the strip may comprise a number, say, e.g., ten to twenty, but quite possibly less or more, of identical reference grids or of different repetitions of the same reference grid. The distance between homologous point of adjacent grids may be called the "horizontal pitch" of the reference grids in the multi-grid strip. The shaded rectangle of Fig. 5 may optionally be taken as schematically representing such a multi-grid strip. If such a strip is used, the printer will be so programmed as to print adjacent character grids in such a way that their homologous points will have the same mutual distance, viz. the "horizontal pitch" of the character grids in the print will be the same as that of the reference grids in the multi-grid strip. It is clear that when this latter is superimposed to a printed line, all the coded characters in the line will register with a reference grid and will become concurrently readable. Further, the transparent strip may be high enough to cover more than one printed line, say to cover "n" printed lines. In this case its height - - will be at least equal to "n" times that of a printed line plus "n-l" times the vertical pitch between printed lines. The several reference grids will then be distributed in the strip not only side by side, but also the ones below the other, viz., if the strip covers "n" printed lines, the reference grids will be distributed in "n" rows, having the same vertical pitch as the printed lines, each row compi'ising a plurality of reference grids side by side. This arrangement will be effective on the sole condition that the coded character be printed in such a positioned relationship on the page, that when the transparent strip is superimposed thereto and the correspondence and reference marks are aligned, each character grid will be exactly register with a reference grid. The software required to achieve this can easily be provided by skilled persons.

Fig. 6 represents the same portion of page shown in Fig. 1 , wherein the answer to the question is represented by character grids and correspondence mai'ks are printed at the sides of said grids. If several answers were present on several lines, pairs of correspondence marks would be provided at suitable intervals, e.g. intervals equal to the height of the transparent strip of Fig. 5. Thus said strip may be slid up or down along the page and its reference marks successively aligned with the various pairs of corresponding marks and any desired portion of the page can be covered in this way. Of course, if the transparent element were a sheet as high as the whole page, only one pair of correspondence marks would be strictly required, but for greater precision several - 23 - 96118/2 pairs could preferably be provided both in the printed page and on the transparent sheet.

Fig. 7 shows how the transparent strip of Fig. 5 is superimposed on pertinent portion of printed page of Fig. 6 to read the coded answer .

Fig. 8 illustrates a particularly simple way of carrying the invention into practice e.g. by means of a program and an associated printer. The program will comprise a randomizer, (A), which is able to construct random, or, with the suitable program modifications, scrambled reference grids. Each reference grid is identified by a numeric key. Since a large number of random grids may be constructed, the keys are here assumed to be from 1 to 60,000. To construct a coded font, a key is firstly chosen, (B). The program also has a number of files, identified by name, comprising all the plain characters which it may be desired to use, defined on the blank grid, as shown in Fig. 3. A file will be chosen by name, (C). The program will then construct, in the manner explained hereinbefore, all the coded characters corresponding to the chosen reference grid and the chosen plain character file, and save the resulting coded font under any suitable identification, e.g. OLDFILE .KEYX, depending on the key and the file, (D). The coded font can now be downloaded to the printer and stored therein, (E). If it is wished to print a text that will be partly in plain and partly in coded characters, the name of the file chosen for constructing the coded font will be 96118/2 - 24 - entered, (F), and the printer will print with the plain fonts which are normally available to it, inserting the corresponding coded characters between the "code" marks, indicated in the figure by #, (G). If it is wished to modify a coded font thus constructed, (H), the editing command will be given and the file identified by its name, (I). Any coded characters that it is wished to modify will now be called up one by one, (J), the processor screen will show the corresponding grids, (K), the required modifications will be made on the grid, and the result will be saved, until all desired characters have been amended. The new file will be the basis for constructing a new, amended, coded font.

It will be clear to skilled persons that the invention should not be used whenever secrecy is a primary consideration and does not provide means for achieving secrecy. A text encoded according to the invention can be deciphered by expert persons. However it cannot be. read by a mere inspection and thus permits the user on the one hand to read it only when he so wishes, and on the other to keep its contents from persons who may accidentally see it. This latter case is common e.g. in the transmission of bank documents, which are not particularly secret, but nevertheless should be protected from casually prying eyes, and in the transmission of office documents which may briefly pass through the hands of persons from whom certain data should be shielded. Balance sheets or receipts carrying significant figures are often handed to clients in the presence of other clients, e.g. in a queue or from an automatic machine, and it is desirable that these other clients not be able to read such figures at a glance. By using the invention, every client can be provided with a piece of transparent material carrying his reference grid, which piece may be small enmpough, as it need not exceed the size of the maximum figure that is likely to be printed, and may be able to read said figure at leasure, while other people, which see the document, will not be able to do so. It is to be noted that texts encoded according to the invention can be photographed and transmitted by telefax, and still be readable without any difficulty. This is quite surprising, as it was to be expected that the minute dimensional variations caused by the copying and the transmission would render decoding impossible.

On the other hand, the invention can be carried out in the course of a a normal printing operation, since all that is needed, besides the normal manipulations, is to depress one command key. No such simple and efficient way of assuring limited, but significant privacy, has been taught in the prior art, as far as the applicant knows.

It is to be noted that if the printing of the reference grid on a transparent sheet is carried out in a conventional way, when the sheet is superimposed to a sheet of paper or a book page or in general a backing bearing a character grid, the thickness of the transparent sheet will separate the character from the reference - - grid. This tends to produce a parallax effect, so that if the observer looks at the superimposed prints from a side, he may experience some difficulty in identifying the coded character; and further, exact alignment of the superimposed prints may not be as easy and the coded character may not appear as neat and precise as is desirable. These difficulties may be overcome by printing the reference grid on the back surface of the transparent sheet, viz. the surface that will contact the sheet or page or other backing on which the character grid is printed. Actually the two faces of the transparent sheet as equivalent, but the reference grid will be printed as required for it to be seen through the transparent sheet viz., so to speak, reversed. This can be easily done by any skilled person.

Further, one could, in theory, print the refenrece grid on an opaque backing and the character grids on transparent sheets, and superimpose the latter to the former, without departing from the scope of the invention, but this would be generally impractical.

While an embodiment of the invention has been described by way of illustration, it will be obvious that the same can be carried out in many ways and with many modifications and adaptations by persons skilled in the art, without departing from its spirit or fr o m t h e s c o p e o f th e c l a i m s .

Claims (26)

C L A I M S 1 - Process for producing printed matter, which comprises the steps of:

1. - defining, at least ideally, at least one blank grid; 2- creating a reference grid consisting of a scrambled distribution of at least two digitizable values in the cells of the blank grid; 3- creating at least one font by: a. individually superimposing, at least ideally, each character to be comprised in the font to at least a portion of the reference grid, and b. changing the digital values of the reference grid in the cells thereof comprised in the area covered by the superimposed character, whereby to create a character grid which is scrambled and which represents the coded character; 4- storing the character grids in the memory of a print-controlling device; 5- stoi-ing in the memory of a text composing device commands causing the print-controlling device alternatively to select and store the clear characters or the coded character, as desired; 6- composing, by means of said text composing device, the desired text, wherein any clear characters are represented in a conventional way and any coded characters are represented by the corresponding character grids; 7- impaginating the composed text; 8- printing the composed and impaginated text by graphically defining: a) any clear characters in the conventional way and b) any coded characters by signs representing the digitizable values of the respective character grids; and 9- providing on a transparent sheet at least a copy of the reference grid ; whereby when said transparent sheet is superimposed to a printed text so that a reference grid is superimposed to the grid of the coded characters which are to be read, preferably by suitably aligning the correspondence and reference marks, said coded characters become detectable and identifiable.

2. - Process according to claim 1 , wherein correspondence marks are provided at least in each page of the impaginated text and graphically defined in printing the same, and wherein reference marks matching the correspondence marks are provided on the transparent sheet, whereby to aid in the detection and identification of the coded characters, when the printed text and the transparent sheet are superimposed, by aligning said reference marks with said correspondence marks.

3. - Process according to claim 1 , wherein the blank grid is a Cartesian grid.

4. - Process according to claim 1, wherein two digital values - 0 and 1 or black and white - are used.

5. - Process according to claim 1 , wherein the superimposition of the character to at least a portion of the reference grid is effected by representing the reference grid on a screen and drawing the character over the reference grid.

6. - Process according to claim 1 , wherein the superimposition of the character to at least a portion of the reference grid is effected by drawing a blank grid which is a replica of the aforementioned blank grid, drawing the character thereon, and establishing a correspondence between the cells occupied by the character in said replica grid and the corresponding cells of the reference grid.

7. - Process according to claim 1 , wherein the digital values of the reference grid are two, the change which is carried out in the cells comprised in the superimposed character is an inversion of the digital value associated therewith.

8. - Process according to claim 1 , wherein the superimposition of each character comprised in the font to at least a portion of the reference grid and the change of the digital values of the reference grid in the cells thereof comprised in the area covered by the superimposed character are carried out concurrently.

9. - Process according to claim 1 , wherein a plurality of coded fonts are ci-eated and stored in the memory of a text composing device, which fonts correspond to different reference grids.

10. - Process according to claim 1, wherein a plurality of coded fonts are created and stored in the memory of a text composing device, comprising fonts which correspond to the same reference grid and to different conventional fonts.

11. - Process according to claim 1, wherein the text composing device composes the desired text by defining the clear characters thereof by the coresponding ASCII symbols and the coded characters by the corresponding character grids.

12. - Process according to claim 1 , wherein a command is stored in the memory of the text composing device indicating the point at which the coded text begins and the point at which the coded text ends.

13. - Process according to claim 1, wherein the character grids are stored in the memory of the text composing device.

14. - Process according to claim 1, wherein the character grids are stored in the memory of the device which prints the text.

15. - Process according to claim 2, wherein graphic signs constituting zeroing devices are used as correspondence and reference marks.

16. - Process according to claim 15, wherein the correspondence marks are provided in pairs, a pair on each horizontal band of the page, and the transparent sheet is a strip having a height that is not less than the height of said bands.

17. - Process according to claim 15, wherein the transparent sheet is a strip and the correspondence marks are provided in pairs on the printed page, the vertical distance between pairs being related to the height of the strip.

18. - Process according to claim 15, wherein the transparent sheet is a strip comprising a plurality of reference grids set at given mutual positioned relationships and the character grids are printed in the same mutual positioned relationships, whereby when the strip is superimposed to the printed page at the appropriate position all coded characters printed on said page become concurrently identifiable and readable.

19. - Process according to claim 1 , wherein the digitizable values are two digital values and the coded characters are printed by printing a black mark in correspondence of one such value and printing no colour in correspondence to the other value.

20. - Process according to claim 1 , wherein the scrambled reference grid is so constructed that the probability of two black cells being adjacent is substantially less than in a random grid.

21. - Process according to claim 20, wherein the scrambled grid is constructed by rejecting for each cell at least the first black value which follows another black value.

22. - Process according to claim 1 , wherein the cells of the various grids include each a number of dots of the printer to be used.

23. - Process according to claim 1 , wherein the pitch of the various grids is not substantially less than one tenth of a millimetre.

24. - Process according to claim 1 , wherein the reference grid is so printed as to be seen through the transparent sheet, and this latter is superimposed to the printed text with its face bearing the reference grid in contact with the printed text.

25. -Process for producing printed matter, substantially as described and illustrated.

26. - Printed matter comprising clear characters and coded characters, obtained by the process of claim 25.