GB1560535A

GB1560535A - Image printing process

Info

Publication number: GB1560535A
Application number: GB3323776A
Authority: GB
Original assignee: FRANCE FA NORBERT BEYRARD; PROCEDES OPTOELECTRONIQUES SOC
Current assignee: FRANCE FA NORBERT BEYRARD; PROCEDES OPTOELECTRONIQUES SOC
Priority date: 1975-08-11
Filing date: 1976-08-10
Publication date: 1980-02-06
Also published as: JPS5245401A; DE2634841A1

Description

(54) IMAGE PRINTING PROCESS (71) We, NORBERT BEYRARD FRANCE, a French Body Corporate, of 68, rue Pierre Charron, Paris, France; and SOCIETE D'EX- PLOITATION DES PROCEDES OPTOELECTRON- IQUES S.E.P.O., a French Limited Company, of 51 bis Quai Alphonse le Gallo, Boulognesur-Seine, (Hauts-de-Seine), France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for the reproduction of a large number of printed copies of images, videograms, photographic documents or any information in analogue form or information coded at high density.

It is known to record high density information on magnetic or photosensitive media or on etched media. It is in this manner that whole television programmes may be recorded on discs, drums or films, as video recordings; the density with which the information is recorded may be so high that, in the case for example of a colour television programme, the luminance, chrominance and sound information as a whole, corresponding to a programme lasting tens of minutes, may be recorded on a disc or on a film having an acceptable diameter or length. Very high density recordings of coded information on photosensitive supports are also used as back-up memories for computers.

Up to now, the information media which have just been mentioned, notably "video" discs and films, were photographically reproduced by contact, which required the use, as media for the reproductions, of photosensitive media of high quality, which are therefore expensive (but of a limited definition in any case), and necessitated recourse to long and complex techniques in the photographic laboratory. This need for stringently controlled conditions has not up to now permitted "video" discs or films, photographically recorded, to be reproduced in large numbers at a low unit cost price.

It is an object of the present invention to overcome this difficulty at least partially.

According to one aspect of the present invention there is provided a process for recording encoded high density information on paper-like sheets comprising the steps of: forming a beam of coherent light, generating a signal representing the information to be applied, encoding said information signal by deriving therefrom during each of a succession of time intervals a pulse signal representing the value of said information signal during the interval, modulating a parameter of said beam by an optical modulator controlled by said encoded signal, deflecting said beam so as to scan an area of a support, said scanning of said support by said beam of coherent light with subsequent treatment if necessary being such as to produce in said area a pattern of perforations through such support in accordance with said encoded information and passing a printing medium through the perforations in said support to print high density information on to paper-like sheets.

The laser beam may be deflected in synchronism with an electro-optical analysis of the image to be reproduced, while modulating in intensity the laser beam with coded information obtained by the electro-optical analysis, so that the document is reproduced on the printing matrix in the form of perforations. A colouring material may then be injected through the perforations in the surface of the matrix to print the image or a pattern representing it.

The use of a very narrow laser beam, having, for example, a diameter of the order of a micron, enables perforations to be made in the surface of a printing matrix, having for example circular openings with very small diameters and spaced at very small distances apart. Such a process enables the very compact information of the document to be reproduced to be transferred to the printing matrix without this transfer being accompanied by a substantial reduction in the density of the information or even by loss of information. Moreover, the perforations may overlap in certain instances and produce continuous lines, which improves the definition.

The laser beam, may, of course, be used to perforate a plastics foil if it is sufficiently thin. However, such a process requires considerable instantaneous power from the laser.

In a modification there may be used a photosensitive resin foil which is receptive to the wavelength of the coherent light used to form the matrix. The points which are struck undergo a physico-chemical transformation and become soluble in a certain number of solvents, such as alkaline solutions, for example. It is therefore necessary, after the illumination by the laser source, to pass the matrix through a bath of an appropriate solvent in order that the perforations appear. So as to obtain a better image definition (of the order of ().4 to 0.6 microns) the photosensitive support is advantageously disposed on a support made up of microchannels of glass, and known in the art under the name of Capillary Array Glass.

In this way. even if the laser beam has a diameter of the order of a micron, it is possible to obtain the better definition which is necessary more especially in the case of back-up memories for computers or in that of video images. It is known that, unlike silver emulsions, photosensitive remains do not have any grain and as a consequence the definition results solely from the dimensions of the beam at the point where it strikes the resin.

The subsequent transfer of the information thus recorded onto the matrix, which may be in the form of a printing frame or cylinder. by a simple ink printing process is particularly advantageous in that on the one hand the process permits the use of reproduction media which are especially cheap, such as foils or webs of paper or synthetic materials, and on the other hand it does not require recourse to long and complex operations dependent on the techniques of the photographic laboratory. In addition, the transfer of the information onto the surface of the printing cylinder may be effected by devices which are entirely automatic, the electro-optical reading of a "video" disc and its reproduction by the laser beam lasting only a few seconds to a few minutes, according to the devices used. In actual fact the problem of time in the production of the matrix is not crucial since it is a matter of a single operation and it is not usually necessary (except perhaps for television} to perforate the support or matrix in real time.

Subsequently, the printing cylinder allows information which has been recorded on the surface, to be transferred for example continuously on a paper web, at an extremely high speed onto rotary printing machines.

It is also possible to use a printing cylinder having a removable curved surface or matrix, preferably formed by a thin skin of a flexible material, for example a synthetic material.

this skin being applied to a rigid core, the laser radiation beam being capable of perforating the said skin only. With this arrangement, the information to be reproduced is transferred only onto the removable spin which forms the curved surface of the printing cylinder, so that the core of the cylinder which is not affected substantially by the laser radiation beam can be used almost without a limit on its lifetime for the reproduction of any number of different documents, using each time a new skin.

All the methods and processes known in printing techniques can evidently be used to inject the ink into the holes in the surface of the printing cylinder. Since the ink used shows a certain viscosity, an excess pressure of the order of 5 to 10 bars is advantageously provided inside the cylinder to increase the speed with which the ink diffuses through the perforations and so provide an increased printing speed.

However, there may be used a printing cylinder comprising a tubular curved surface formed of a rigid material which the laser radiation beam is capable of perforating, and the ink is injected inside the surface of the printing cylinder.

This method of inking, which is particularly simple and advantageous, may equally be employed when there is used a printing cylinder with a removable surface, preferably formed by a thin skin of a flexible material; in this case in fact the printing cylinder would have a tubular core, the curved wall of which has very fine perforations which are extremely close together and the ink would be injected into the interior of the said tubular core. The perforations in the surface of the tubular core may equally have been produced by means of a very fine laser radition beam, in which case they are preferably regularly distributed; nevertheless it is possible also, according to the present invention, to make the tubular core of the printing cylinder of a porous material, produced for example as a frit or by a chemical process.

The ink in the holes or the perforations in the curved surface of the printing cylinder may be transferred onto the printing support by any suitable methods and means. However, the ink in the holes or perforations of the printing cylinder may be transferred directly onto the printing support, by rolling the printing cylinder without sliding over the printing support. It is also possible to use a gas which is enclosed inside the cylinder and which reacts with a specially treated support of paper or plastics material in such a manner that a jet of gas passing through one of the perforations produces a black or a coloured dot, or possible a white dot on a coloured or black surface. In this case, the gas entering the core of the cylinder is advantageously guided by a fixed axial part in the shape of a narrow sector and whose ends form a junction with the inside of the drum.

The reproduction process may be implemented using a continuous laser beam of a constant size adapted to the density of the information to be reproduced; a size of about 1 micron is suitable for example, for the reproduction of "video" discs. In the first embodiment the intensity of the laser beam is modulated by pulses all having substantially the same duration and amplitude and a repetition frequency varying as a function of the video information obtained during the course of the electro-optical analysis of the document to be reproduced.

With this embodiment of the process information is therefore reproduced on the matrix or the lateral surface of the printing cylinder in the form of holes, for example with circular openings, of the same diameter and with variable spacing as a function of the "video" information obtained by analysis of the document to be reproduced; oonse- quently, on the printing support, information is produced in the form of dots of the same size side by side but with variable spacing, which imparts a dot pattern to the document reproduced. In the case in which the original document does not have such a dot pattern, that of the reproduced document should always be sufficiently fine not to be a hindrance. This embodiment is particularly well suited to the reproduction of high quality photographs. When video information is given in the form of three colour signals R. G. B, corresponding to the primary colours red, green and blue, it is possible to etch or to perforate three matrices simultaneously corresponding to the colours red and blue on the one hand and on the other hand to obtain a "yellow" matrix by supplementing the green signal taking account of the fact that synthesis of colours is additive in television and subtractive in printing. It is thus possible to print images or photographs in three colours.

The modulated laser signal may indeed be separated into three parts each of which is modulated by a colour signal provided by the electro-optical analysis.

In an alternative embodiment, a pulsed laser beam of variable size is used and the size of the said laser radiation beam is modulated dependent on the "video" information obtained during the course of the optical analysis of the document to be reproduced; if this latter is a "video" disc, the size of the laser beam may be modulated, for example, between 0.6 and 4 microns. In this case again, the document reproduced has of necessity a structure which should be sufficiently fine not to be a hindrance. This embodiment is particularly intended for producing sketches which do not require an appreciable definition. It may be used for example for cutting operations in the manufacture of or for the printing on fabrics.

In another embodiment the intensity of the laser beam may be modulated by pulse sequences all having substantially the same duration and amplitude, these pulse sequences being coded from the "video" information obtained during the course of the electro-optical analysis of the document to be reproduced. This embodiment is particularly adapted to the case in which the information of the document to be reproduced is already itself coded (for example a back-up memory for a computer).

When a television signal is concerned, a binary coding is obviously not economical, taking into consideration the number of bits to be transmitted. In an alternative embodiment according to the present invention, the composite signal is used to modulate the laser beam by pulses whose size or spacing varies as a function of the signal. In a first case the printed image is shown in the form of a series of dashes and dots. In a second case, one line of the matrix is made up of a group of irregularly spaced dots. The lateral dimension of the dashes or the dots is of course always the same and corresponds to the diameter of the beam. The length of the dashes may be a function, in the first case, of alternations in the frequency modulated signal.

It is known that television images are made up of two interlaced frames comprising a definite number of lines to avoid flickering of the image. This constrain does not exist at the level of the process according to the invention and it is not necessary to follow the television raster. On the contrary, the information must be recorded in a certain order, and, taking into account the adopted method of scanning, it is distributed over lines which do not correspond necessarily to the television lines. It is in this manner that one line of the matrix can contain the information of several lines or even of a frame of a television image. In the remainder of the description, one lines of the matrix corresponds to the scanning amplitude of the recording laser.

On the other hand the television signal is composite insofar as it inclines a luminance component, possibly two chrominance components, one sound component and synchronisation signals.

Although the coding by frequency modulation is referred to in particular, it is obvious that any other method of coding can be used.

The present invention likewise covers all printed documents which have been obtained from coded originals, printed or photographed, by the reproduction process according to the present invention.

By way of example there has been described below and illustrated schematically in the accompanying drawings, several embodiments of the present invention. In the accompanying drawings: Figure 1 is a generalised diagram of the formation of the matrix by a laser; Figure 2 illustrates apparatus for transferring to a paper web information which has previously been recorded on the matrix: Figure 3 is a view of the apparatus of Figure 2 in section through a central vertical plane; Figures 4, 5, 6 and 7 are diagrams illustrating different ways of recording the information to be reproduced on the surface of the matrix; and Figure 8 is the diagram of a read-out device.

Figure 1 is a schematic diagram representing the first phase of the process, that is, the etching of the matrix. In this diagram the beam of coherent light emanating from a laser 1 is modulated in its intensity by a cell 5, this modulation being in two-level for. Then the beam is focussed on a deflection cell 7 which ensures horizontal scanning of the matrix support 10.

The beam coming from the cell 5 is directed onto the deflection cell 7 which ensures the horizontal scanning of the matrix support at a known rate and over a suitable length. To do this, the cell 5, which is, for example. a cell with an electro-acoustic action, is controlled by a generator 6 of relaxation oscillations, which generator may be controlled by the exposure stage 3 if an etching of the matrix in real time is desired.

At the output of the deflection cell 7, the laser beam is divided into a principal beam 9 and a secondary beam 8 which is deflected at a variable angle a. The beam 9 is blocked by a mask (not shown) and only the deflected beam 8 acts upon the matrix 10. It can be noted that the horizontal deviation of the beam 8 allows the possible magnification or reduction of the image, in combination with the vertical scanning device which has not been illustrated, but which may be of a wellknown mirror type, taking into account that the vertical scanning is generally much slower than the horizontal scanning. The vertical scanning may alternatively be obtained by electro-mechanical displacement of the matrix support.

The television camera 3 analyses the "video" disc to be reproduced following the parallel lines, and the laser beam 6 similarly scans the lateral surface of the printing matrix 10 following the parallel lines, for example along generatrices of a curved cylindrical surface, if the matrix is to be disposed on a cylinder. Each pulse of laser radiation produces a hole in the surface of the printing matrix 10, for example with a circular opening with a diameter of approximately 1 micron. The speed at which each line is scanned being uniform, the holes produced by successive pulses of laser radiation are closer together as the repetition frequency of the said pulses becomes greater, and vice versa. As the repetition frequency of the pulses is modulated by the "video" signal coming from the television camera 3, it is evident that the information recorded photographically from the image 2 is reproduced over a definite zone of the surface of the matrix 10, in the form of a configuration of juxtaposed holes, with substantially the same diameter, whose spacing varies locally as a function of the information to be reproduced. As a result of the very small diameter of the holes produced by the laser radiation beam in the lateral surface of the printing cylinder 10, these holes can be very close together, which allows high density information of the "video" disc 2 to be reproduced without a reduction in the density of the information and without any loss of information.

In a particular embodiment, a printing cylinder 10 having a special structure shown in section in Figure 3, forms the matrix. This printing cylinder 10 is essentially made up of a tubular core 11 of a material having very fine pores with average diameter much smaller than that of the holes produced by the later radiation beam 6 (about 1 micron).

A porous core such as 11 may be produced as a frit or by known chemical processes. A thin skin 12 of synthetic material is applied to the outside of this tubular core 11. This skin 12, which is obtained for example by applying to the external surface of the core 11 a foil of synthetic material of appropriate dimensions, and by joining the two ends of this foil, for example by glueing, in this case constitutes the removable curved surface of the printing cylinder 10. The maximum intensity of each pulse of laser radiation, produced by the emitter 1 is then adjusted so that each of the said pulses perforates the skin 12 accurately at the point of impact, without however penetrating the external surface of the porous core 11, which, as mentioned previously, may advantageously be made up of microchannels formed in a fritted glass to increase the definition.

The printing cylinder 10, onto the surface of which there has been transferred all the information photographically registered on the "video" disc 2, is then mounted, as shown in Figures 2 and 3 in a printing machine consisting of means, for example, rollers 13, for conveying a paper web 14 at a uniform speed. The printing cylinder 10 comprises in a manner known per se end plates equipped with journal pins 15a and 15b (Figure 2) capable of being located, in a detachable manner, in fixed bearings 16a and 16b. These fixed bearings 16a and 16b are equipped with known means which on the one hand allow the printing roller to be pressed against the paper web 14 with a predetermined force, the web 14 being supported by one of the rollers 13, and on the other hand allow the printing cylinder 10 to be driven in a rotary manner at a uniform speed such that the said cylinder rolls, without sliding, in contact with the paper web 14.

Means are also provided to inject the ink (17 in Figure 3) inside the tubular core 11 of the printing cylinder 10. These means may be arranged in a manner to assure a continuous replenishment of the ink contained inside the printing cylinder 10. A conduit 18, equipped with a regulating and closure valve 19 leads from a source of compressed air (not shown )to reach, via the intermediary of the bearing 1 6b and the journal pin 15b for example, of the printing cylinder 10, into the interior of the latter, into which the conduit 18 feeds. The end of the conduit 18 does not rotate with the printing cylinder 10, and may support a fixed scraper 20 (Figure 3) disposed in such a manner as to concentrate the ink 17 near to the lower generatrix of hte inner surface of the porous core 11.

When the compressed air is admitted through the conduit 18 into the interior of the porous core 11 of the printing cylinder 10, an excess pressure is created there which accelerates the diffusion of the ink 17 through the porous core 11, the perforated skin 12 onto the paper web 14. Since the dimensions of the pores of the core 11 are very much less than those of each of the perforations of the skin 12, all the said perforations are fed with ink practically in the same manner and the quantities of ink which are thus injected through them are transferred onto the upper face of the paper web 14 in the form of uniform spots, all of practically the same diameter, approximately 1 micron. The size of the spots may be reduced by using a further layer of porous material beneath the matrix. The local variations in the spacing of these spots represent the information previously read by the television camera 3 from the "video" disc to be reproduced. The paper web 14, freshly inked, then passes beneath a drying apparatus 21 (Figure 3).

Figure 4 represents schematically a square zone of the matrix 10 on which there is reproduced for example a part of a blackand-white photograph, of average even brightness. The zone under consideration is subdivided as a result of its scanning by the laser beam into 10 lines of 10 boxes each, each box having for example, the shape of a square with sides of 0.5 microns. For this zone of average brightness one box in two has a perforation p of a diameter of approximately 0.4 microns. All the boxes would be perforated if the zone was black and none of the boxes would be perforated if the zone was white.

Figure 5 represents schematically the same zone of the matrix used in a process which is slightly different from the embodiment described above. In this variation to which Figure 5 corresponds, a laser radiation beam of variable size is used and the modulator 5 (Figure 1) is designed so that it modulates the size of the said beam 6, for example between 1 and 4 microns, dependent on the "video" signal transmitted by the television camera 3. So that Figures 4 and 5 can be compared it is necessary to assume that, in the case of Figure 5, the spacing of the analysis lines of the disc to be reproduced is ten times greater than it is in the case of Figure 4; on this hypothesis it may then be seen that a zone of average brightness may be represented on the surface of the matrix by a single hole P, the diameter of which is selected such that its surface area is substantially equal to the sum of the surface areas of the 50 small holes p of Figure 4.

This embodiment is more especially intended for applications which do not require high precision. Amongst these applications there may be cited printing on fabrics. It is known that at the present time the printing of fabrics is carried out by means of rollers bearing patterns which it is necessary to preserve for several years. This represents a high immobilisation of capital, considering the number of patterns to be preserved. By means of the present invention it is possible to preserve the printing patterns on paper supports or on plastics supports occupying very low volume, without having to immobilise the printing rollers, which allows a considerable economy to be made.

Figure 6 represents a zone of the surface of the printing matrix used when implementing the reproduction process according to the present invention, this zone corresponding to a cell of a back-up photographic memory for a computer. It is evident that the transfer of binary information contained in this cell has been effected by using a laser beam of constant size, which has produced in the said lateral surface of the printing cylinder small holes p centered in the boxes where the presence of such a hole p indicates, for example, the binary information "1" or the binary information "'0". It is obvious that this transfer of information could be effected by modulating the intensity of the laser beam by sequences of pulses all having substantially the same duration and amplitude, these pulse trains being themselves derived from pulse signals obtained during the course of the reading of the back-up photographic memory, for example by means of a television camera. The method of transferring coded information illustrated in Figure 6, may likewise be used in the case in which the document to be reproduced carries analogue information and not numerical information. In this last case, however, the pulse sequences used for modulating the intensity of the laser beam may be derived from the analogue "video" signal provided by the television camera which optically analyses the document to be reproduced by means of electronic conversion circuits which may be of known type, such as for example, a pulse width modulation circuit.

Figure 7 represents schematically the same zone as Figure 4 or 6 intended more specifically for the recording of a "video" signal which may represent with the aid of pulses which are size coded, either the luminance signal, or a chrominance signal (in the case of colour television), or again alternately line by line the luminance and chrominance signals, or more generally combinations of the two.

The size of the dashes may correspond to the duration of the alternations of a frequency-modulated signal, a zero deviation being expressed by the absence of a dot. On the other hand some dashes may take up, for example, the whole line. Since the signals are coded, the reading of a printed document may be carried out with the aid of an appropriate reader detector decoder which may consist of a strip of photodiodes of the kind used in the optical recognition of characters.

The present invention is not limited to the embodiments described above. In particular, the ink injected through the perforations in the curved surface of the printing cylinder may be transferred indirectly to the printing support, for example by means of a rubber cylinder of the kind used in offset printing. The tubular core 11 of the printing cylinder 10 (Figure 3) may, instead of being porous, have a plurality of very fine perforations preferably regularly spaced produced in a chemical manner.

It is not necessary to use the particular means selected for putting into effect the reproduction process described above. Of the special means which have been described above, the majority may be replaced by equivalent functional means, as, for example, the constitution of the printing cylinder and the printing machine in which it is used.

With regard to the means for transferring the information from the document to be reproduced onto the curved surface of the printing cylinder, as they are illustrated more particularly in Figure 1, the television camera 3 may be replaced by any known apparatus allowing optical analysis of a printed document or of a photographic document, and providing during the course of this analysis, a "video" signal as well as scanning synchronisation signals. It has already been pointed out that the means for modulating some of the parameters of the laser beam can take numerous forms, each adapted to the parameter of the radiation beam which has to be modulated. The same applies to the deflection device 7 of the laser radiation beam in synchronism with the optical analysis of the document to be reproduced; numerous deflection devices which are functionally equivalent may be used for implementing the process. It is also possible to use a device producing a horizontal deviation only of the laser beam following the "scanning lines", the printing cylinder 10 then being mounted in a device driving it in a rotary manner either little by little at a suitable stepping frequency or at a suitable

It is thus possible to provide an image transmission device since the scanning and the modulation, which is binary or two-state, of the laser may be operated by remote control. The invention may also be applied to fabric printing.

The process according to the invention may also be applied to the field of electroacoustics and more specifically to the field of high-fidelity. In this example the sound signal is translated into a visible image for printing.

It is known that the quality of reproduction of a sound "image" depends on the one hand on the intrinsic qualities of the reproduction assembly for the sounds and on the other hand on the quantity of information which is applied to the input of this apparatus.

The problem which is solved by the use of the invention is that of the quantity of information applied to the input of the reproduction apparatus.

The transcription by recording of the sound signal in the form of a coded image allows almost a complete sound image to be obtained by analysing the sound vibrations by means of electro-acoustic sensors operating in the adjacent frequency bands.

The reading of the printed tape is advantageously carried out by means of a strip of photodiodes in front of which the band, suitably illuminated, passes at a relatively high speed. As there is no physical contact between the reproducing head and the support there is no wear on the support when it is played.

The printed sound image may have the form either of a group of dots, or of a group of dots and dashes as described above.

As shown in Figure 8 a paper web 31 carries this information which corresponds to the zero passages of the sound signal when frequency modulated on to a carrier.

By way of example the carrier frequency may be 1 MHz and the printing may correspond to 10 to 15 different channels with a width of 75 kHz. Under these conditions, there is easily obtained a dynamic range of 60 decibels, which gives a listening quality equal to that of a concert hall. These channels may be read separately or together.

The paper web 31 spooled on the rollers 32 and 33 passes at a constant speed beneath a strip of photodiodes 34 which consists, for example, of 1,024 cells. A decoder 35 followed by a demodulation apparatus of the "tuner" type (not shown) allows the channels to be associated or selected.

The speed at which the paper passes is of the order of one centimetre per second for example.

In Figure 8, in the coding of the sound information as frequency modulation, the dashes and dots represent in fact the duration of the alternations of a signal with variable amplitude. It is well known that it is possible from these data to reconstitute the complete amplitude-molulated signal by means of a discriminator.

This process apart from allowing a reproduction of incomparable quality, permits the cost of the recordings to be substantially reduced, because of the low cost of printing the paper webs. On the other hand the reading of the supports of the sound information in paper does not require apparatus which is any more expensive than that which is at present on the market.

It goes without saying that the present invention is in no way limited to the embodiments which have just been described, and that many modifications can be introduced to it without departing from the invention.

WHAT WE CLAIM IS:- 1. A process for recording encoded high density information on paper-like sheets comprising the steps of: forming a beam of coherent light.

generating a signal representing the information to be applied, encoding said information signal by deriving therefrom during each of a succession of time intervals a pulse signal representing the value of said information signal during the interval, modulating a parameter of said beam by an optical modulator controlled by said encoded signal, deflecting said beam so as to scan an area of a support, said scanning of said support by said beam of coherent light with subsequent treatment if necessary being such as to produce in said area a pattern of perforations through such support in accordance with said encoded information and passing a printing medium through the perforations in said support to print high density information on to paper-like sheets.

2. A process according to claim 1, wherein the beam of coherent light is of constant diameter, and said signal comprises a sequence of pulses of the same duration and amplitude, the intensity of the beam being modulated by said sequence of pulses.

3. A process according to claim 1, wherein the beam of coherent light causes, by local removal of the material of the support, the formation in the support of the perforations.

4. A process according to claim 1 or 2, wherein the support has a photo-sensitive surface and the beam of coherent light causes a modification of the physico-chemical properties of the sensitive surface of the support, said support then being treated by a solvent which dissolves the parts acted upon by the beam to form the perforations.

5. A process according to any one of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. It is thus possible to provide an image transmission device since the scanning and the modulation, which is binary or two-state, of the laser may be operated by remote control. The invention may also be applied to fabric printing. The process according to the invention may also be applied to the field of electroacoustics and more specifically to the field of high-fidelity. In this example the sound signal is translated into a visible image for printing. It is known that the quality of reproduction of a sound "image" depends on the one hand on the intrinsic qualities of the reproduction assembly for the sounds and on the other hand on the quantity of information which is applied to the input of this apparatus. The problem which is solved by the use of the invention is that of the quantity of information applied to the input of the reproduction apparatus. The transcription by recording of the sound signal in the form of a coded image allows almost a complete sound image to be obtained by analysing the sound vibrations by means of electro-acoustic sensors operating in the adjacent frequency bands. The reading of the printed tape is advantageously carried out by means of a strip of photodiodes in front of which the band, suitably illuminated, passes at a relatively high speed. As there is no physical contact between the reproducing head and the support there is no wear on the support when it is played. The printed sound image may have the form either of a group of dots, or of a group of dots and dashes as described above. As shown in Figure 8 a paper web 31 carries this information which corresponds to the zero passages of the sound signal when frequency modulated on to a carrier. By way of example the carrier frequency may be 1 MHz and the printing may correspond to 10 to 15 different channels with a width of 75 kHz. Under these conditions, there is easily obtained a dynamic range of 60 decibels, which gives a listening quality equal to that of a concert hall. These channels may be read separately or together. The paper web 31 spooled on the rollers 32 and 33 passes at a constant speed beneath a strip of photodiodes 34 which consists, for example, of 1,024 cells. A decoder 35 followed by a demodulation apparatus of the "tuner" type (not shown) allows the channels to be associated or selected. The speed at which the paper passes is of the order of one centimetre per second for example. In Figure 8, in the coding of the sound information as frequency modulation, the dashes and dots represent in fact the duration of the alternations of a signal with variable amplitude. It is well known that it is possible from these data to reconstitute the complete amplitude-molulated signal by means of a discriminator. This process apart from allowing a reproduction of incomparable quality, permits the cost of the recordings to be substantially reduced, because of the low cost of printing the paper webs. On the other hand the reading of the supports of the sound information in paper does not require apparatus which is any more expensive than that which is at present on the market. It goes without saying that the present invention is in no way limited to the embodiments which have just been described, and that many modifications can be introduced to it without departing from the invention. WHAT WE CLAIM IS:-

1. A process for recording encoded high density information on paper-like sheets comprising the steps of: forming a beam of coherent light.

5. A process according to any one of the

preceding claims, wherein ink is applied through the perforations in the support for producing a print of the information.

6. A process according to claim wherein jets of gas are passed through the perforations in the support for causing a colour change on a surface of the paper-like sheets at the point of impact of the gas.

7. A process according to claim 5, wherein the support is of a flexible material and is wrapped onto a printing cylinder forming thereon a removable curved surface, the printing cylinder having a core of rigid material, the beam of coherent light is of such power as to be capable only of perforating the flexible material, and the ink is applied to the inside of the curved surface formed by the flexible material.

8. A process according to claim 7, wherein the printing cylinder has a tubular core, the curved surface of which has fine perforations which are close together, and the ink is applied to the inside of said tubular core.

9. A process according to claim 1, wherein tfie information controlling the beam of coherent light is frequency-modulated onto a carrier signal, and the perforations produced in the support by the beam include dashes and dots representing the duration of the alternations of the frequency modulated signal.

10. A process for recording high density information on to paper-like sheets substantially as described herein with reference to Figures 1, 2 and 3 of the accompanying drawings, or modified as described with reference to any of Figures 4 to 8 of the accompanying drawings.

11. A paper-like sheet bearing information applied by a process according to any preceding claim.