FR2497043A1 - Laser imaging system - is controlled by binary image signals converted for modulation of beam intensity to control spot size - Google Patents

Abstract

THE DEVICE INCLUDES MEANS OF TRANSCODING 7 IMAGE DATA DEFINING THE TINT LEVEL OF EACH OF THE ELEMENTARY IMAGE POINTS INTO A SET OF R BINARY WORDS CORRESPONDING TO A MATRICIAL DECOMPOSITION OF THE ELEMENTARY POINT IN R AFFECTED TASKS FROM THIS POINT, A LASER 8 WHOSE ENERGY DENSITY HAS A GAUSSIAN DISTRIBUTION WHOSE BEAM IS MODULATED BY THE SUCCESSIVE WORDS DELIVERED AND DEVIATION MEANS 12-14, 30 OF THE LASER BEAM MODULE ON THE SUPPORT 6 FOR THE PRINTING OF THE TASK MATRIX FOR EACH OF THE ELEMENTARY POINTS ALONG AN IMAGE LINE. THE DEVICE ALLOWS IMAGE RESTORATION WITH A LARGE NUMBER OF TINT LEVELS.

Description

Device for printing an image
The present invention is in the field of image printing systems in several different levels of gray, from the background level of a reproduction medium giving for example the level of white (or conversely the level of black), in using two levels of color intensity of this support corresponding to the white level and the black level, respectively, and by varying dosing according to the desired gray level for each elementary point of image, the ratio between the white surface and the black surface within the total area assigned to each elemental point.

 More precisely, in such a system, it relates to a device for printing on a sensitive support of an image defined by binary data reflecting different levels of hue or gray levels of elementary image points, the image inscribed by this device may only be a latent image which, after development then fixation either on this sensitive support or on another support on which the latent image developed has been previously transferred, will constitute a visible image in half-tones, c ' that is to say a visible image in different levels of gray.

 The sensitive support on which the printing device inscribes the image may for example be a photosensitive paper such as a photographic paper or a drum covered with a layer of a photoconductive material such as selenium in the case of an application. from this device to an electrophotographic type printing system.

 We already know a device for printing on a photosensitive medium of an image defined by binary data reflecting different levels of hue of elementary points of the image. This device comprises a light source whose beam ensures the printing of the elementary image points on the support, means for deflecting the beam on the support in a direction X for scanning the areas assigned to the elementary image points of each image line and means of entratement of the support in a direction Y substantially perpendicular to X for scanning the surfaces assigned to the elementary image points of various image lines.For the rendering of different levels of gray, the device comprises a opaque screen said beam interposed on the beam for example at a short distance from the support and having a plurality of rows of diaphragms transparent to the beam and arranged in columns substantially parallel to the Y direction; the number of columns corresponds to the number of elementary points per image line while, on each of the columns, the diaphragms are different from each other to define said hue levels. In this screen, the diaphragms of the same row are arranged at the pitch defined for the elementary image points on each image line while the rows of diaphragms are arranged at m times the pitch defined for the image lines. m is equal to unity or a few units.The device further comprises means for converting said successive data into binary words each translating, in the column of diaphragms corresponding to the position of each elementary point concerned, the rank r each diaphragm to be used to define the level of hue of the elementary point, the rank r being counted from the first row of diaphragm encountered by the support, and means for processing the binary words from the conversion means. These processing means apply offsets corresponding to the duration of movement of m (rl) image lines of the support relative to the screen and control means of deflection of the beam to direct the beam on those diaphragms of each column whose ranks respective ones are indicated by the words from the processing means.

 By this device the rendering of the various levels of hue is obtained by forming spots of variable dimensions by means of the diaphragm screen. In this device however, the number of elementary points per image line and the number of hue levels are limited by the material realization of the diaphragm screen: the diaphragms of the same row give the step of the points, the most large diaphragms defining the surface units of image formation, while the diaphragms of the same column give the various levels of hues, except for the level given by the bottom of the support, that is to say the dimensions spots formed in the respective surface units defined by the larger diaphragms.

 The object of the present invention is to enable the printing of images having a higher definition and a larger number of hue levels.

 It relates to a device for printing an image on a sensitive medium, said image being defined by binary data applied to the device and translating different levels of hue of elementary points along each of successive image lines characterized by it comprises - transcoding means receiving said binary data and delivering, in response to data relating to each elementary point to be inscribed on the support, a set of R ordered words respectively defining the dimensions of individual spots to be formed on the support , for the registration of the considered point in R areas of a defined elementary surface assigned to this point and decomposed in a substantially matrix manner in these R zones, said transcoding means delivering in response to data reflecting different levels of hue sets of R words, respectively assigned to these different levels for rendering them salt a specific transcoding law; a laser whose spatial energy density of the beam has a Gaussian distribution for printing on the support of the individual spots from said ordered words of the successive sets of words delivered by said transcoding means, means for deflecting the laser beam on the support, able to direct this beam on each of the zones of each of the elementary surfaces assigned to the elementary points of each image line on the support driven perpendicular to a given direction parallel to which the lines images are registered, - modulation means of said laser beam, controlled from the ordered words of the successive sets of words supplied by said transcoding means, for modulating in power said laser beam as a function successively of the value of these words and temporal coordination means controlling said deflection means and determining the rate of modulation of the laser beam and the rate of driving the support perpendicular to said given direction, from a time base, so as to ensure the inscription, by the laser beam, on the support, of individual spots defined by the words of the sets of words delivered by said transcoding means in the respectively corresponding areas.

 Other features and advantages of the present invention will become apparent from the description given with reference to the accompanying drawing. In this drawing - Figure 1 illustrates a first embodiment of the device according to the invention, - Figure 2 illustrates the decomposition of the area affected to an image point, - Figure 3 represents different laws of restitution of the various levels. of the image dots, - Figures 4 to 6 illustrate various renderings of one of the hue levels of an image point.

FIG. 7 illustrates a second embodiment of the device according to the invention.

 In Figure 1, there is shown an embodiment of the printing device of an image according to the invention. The image to be inscribed is defined by data resulting for example from an analysis of successive image lines of an original image. These data reflect gray levels, among n possible different gray levels, for example 32 possible levels, including the level (white or black) given by the original background image, for the various elementary points entering each line of picture. These data are considered here from a data source 10 having first outputs in parallel equal in number to that of the bits forming the data relating to each elementary image point, in the example considered five first outputs in parallel. these first outputs in parallel with the source 10, the data relating to the same elementary point are delivered simultaneously, those relating to the successive points along each image line are delivered one after the other.

 These data are applied to first inputs of the device, respectively connected to the first outputs of the source 10 and thus here to the number of five, referenced 1 to 5, for printing on a photosensitive paper 6, in latent form, the elementary points entering into each image line, in order to obtain, after development and fixation of the latent image inscribed, using means not shown or described herein because not directly related to the invention, of the image corresponding visible, in halftones.

 The device comprises a read-only memory 7 advantageously an EPROM memory (erasable programmable read only memory) for transcoding the binary data applied to the first inputs of the device. This memory 7 which receives these data on first addressing inputs, respectively connected to the first inputs of the device, delivers, in response to the data relating to each elementary point to be written, a set of R ordered binary words respectively defining the task dimensions. individual (some of which will be of zero size) to form on the paper 6, for the inscription of the point considered, in R areas of a defined elementary surface assigned to this point and decomposed substantially matrix in these R areas, the value of each word defining a task dimension and the rank of that word in the set, the location in the elementary surface of the area where this task is to be formed. In response to the data reflecting different levels of hue or gray of elementary points, the memory 7 delivers sets of R words, respectively assigned, according to a specific transcoding law, to these different levels for their rendering, each set defining in a way the a pattern to be formed in the elementary surface, decomposed into R areas, assigned to a point for rendering the gray level of that point, to which this set is affected.

The memory 7 is therefore capable of delivering n sets of
R ordered words corresponding, respectively, according to said transcoding law, to n different levels of tint that can be translated by the data it receives on its first inputs.

These n sets are stored in this memory where they form a group which is selected, for the printing of said image on the paper 6, from among a plurality of groups of n sets of R ordered words, contained in the memory and respectively corresponding to a plurality of possible transcoding laws. This selection is effected by a so-called group selection command, expressed in the form of parallel bits applied respectively to second addressing inputs of the memory. This command, which is expressed for example in the form of three bits in parallel, for eight groups of n sets stored in the memory, is determined according to characteristics of the print medium used, that is to say paper 6, such as its sensitometric response, and for example as a function of characteristics of the image to register such as its extreme levels of hue, so as to ensure the selection in the memory of a group of n sets, that is to say the choice of a group of patterns for rendering different levels of hue, adapted to these characteristics in view of the good appearance of the visible image that will be obtained after development and fixation of the latent image recorded by the device. st considered also from the source 10, it consists of additional data, formed here by three bits, applied by this source on second inputs in parallel of the device, here 100, 200 and 300, which are respectively connected to said second inputs addressing the memory 7, these additional data remain invariant while the binary data defining the hue levels of the various elementary pixels of the image are applied successively to the first inputs 1 to 5 of the device.

 It will of course be understood that the n sets of R words of the same group may not all be different from each other, some neighboring gray levels may be rendered by the same pattern.

 It is considered by way of example with regard to the embodiment illustrated in FIG. 1 that at each elementary point is affected a surface area of 200 F m × 200 μm divided into 16 zones, each of 50 μm × 50 μm, arranged according to an arrangement. 4-by-4-dot matrix and to which 16 words in each set correspond, that the spots are defined with eight possible dimensions for which the words are coded at 3 bits. It is also considered that an image line contains 256 elementary points each defined, as specified above, by data of 5 bits, that is to say with 32 possible levels.

 The memory 7 has as many outputs in parallel as there are bits forming each word in each set of words, or three outputs in parallel in the example considered. The additional data applied to the second addressing inputs of the memory 7 ensure the addressing of the memory block in which the group of n sets selected for the printing of the image on the paper 6 is recorded, while the data of each elementary image point applied to the first addressing inputs of the memory 7 ensure the addressing in this memory block of the appropriate sub-block so that the words of the corresponding set are successively delivered on the outputs in parallel of the memory, the bits of the same word being delivered simultaneously on the outputs in parallel of the memory respectively.

 The device comprises for the registration of the image defined by the successive data applied to it on these first inputs, a laser 8 whose spatial energy density has a Gaussian distribution. To this laser is associated an acousto-optic modulo-deflector circuit 12 receiving the laser beam schematized by mixed lines while at this circuit 12 is associated another deflection circuit 30 of the laser beam which it receives through the circuit 12 .

 The acousto-optic modulo-deflector 12 is a circuit of known type, for example the circuit marketed by SORO under the reference MB59 or the reference IM50, ensuring the deflection and the modulation of the incident laser beam by diffraction of the beam in a crystal. under the control of a high frequency electric wave transmitted to the crystal through an input transducer. It is controlled by a high frequency source 13, itself controlled by a selection set 14. The source 13 comprises four oscillators 15 to 18 capable of delivering waves whose frequencies are different from one oscillator to another and between 60 and 80 MHz.The selection assembly 14, shown schematically by four switches or switches 20 to 23, successively controls the oscillators which successively deliver the four waves of different frequencies to the acousto-optic modulodéflector circuit 12. This set receives four successive signals of clock delivered from a time base, respectively applied to the four switches for their closure. The four sclclllators are connected by a cable 25 to the acousto-optic modulo-deflector circuit 12 to define, as a function of the successive frequencies, four possible positions of the laser beam, shown in dashed lines, corresponding to the four frequencies transmitted successively.

 9 these four successive positions of the laser beam will correspond after returning by the second deflection circuit 30 a scan in a direction opposite to that indicated by Y of the support or photosensitive paper 6, the height of a column of the matrix that each form elementary surfaces assigned to the elementary points, and to positions corresponding to the rows of the matrix.

 For a clearer representation of these four positions of the laser beam, they have been illustrated parallel to each other, in practice the laser beam from the circuit 12 is slightly deviated angularly with respect to the path of the direct beam as a function of the frequency of the beam. wave which is transmitted to this circuit 12.

These four positions are slightly divergent with each other at the exit of this circuit 12.

 The successive words delivered by the memory 7, in response to the input data applied to it, are used to control the power level of the respective high frequency waves transmitted to the acousto-optic modulo-deflector circuit 12. Thus, each of the oscillators 15 to 18 can receive in command, through the selection set 14, the word present on the outputs of the memory 7 and converted into an analog signal in a digital-analog converter 26. This analog signal applied to the four the selection set is transmitted by the only closed switch to the oscillator connected thereto to define the power level of the wave delivered and applied to the circuit 12.The wave from the source 13 and applied to this circuit 12, frequency selected by the selection set 14 and power level defined by the value of the word then received from the memory 7, therefore defines by its frequency one of the positions of the laser beam among the four possibilities according to Y, and modulates by its power that of the laser beam at the output of the circuit 12 thus defining by its power the dimensions of the latent spot formed on the support or photosensitive paper at the point of impact of the laser beam on this support.

 The deflection circuit 30 of the laser beam delivered successively according to the four positions illustrated by the acousto-optic modulodéflector circuit 12 is intended to ensure a scanning of the support or photosensitive paper 6 in each successive line of this medium assigned respectively to the image lines. successive defined by the successive image data, or in the direction X illustrated, substantially perpendicular to Y. This circuit 30 is here constituted by an oscillating mirror. This mirror oscillates about an axis 31 on which it is mounted and is arranged to intercept the laser beam delivered by the circuit 12, in one of four possible positions, and return it to the photosensitive medium 6 according to one of the four possible positions according to Y.This mirror 30 is entráné by a set 32 drive of the mirror and an associated control circuit 33. The control circuit 33 will for example a voltage generator sawtooth or voltage ramp generator ; it is itself controlled by clock pulses taken from the time base, to develop an increasing voltage signal as and when the words provided by the memory 7 to the high frequency source 13 through the converter 26, so as to control the deflection of the beam along the line of the support considered as and when the application of these words to the source 13 for printing the corresponding image line. The mirror training unit 32 is, for example, formed by the so-called "G 100 PD optical scanner" and "CCX-100 Servo Controller" circuits of the General Scanning Inca Company, ensuring a very precise positioning of the mirror by function of the received voltage, in a possible excursion of the mirror of the order of 400 centered around a rest position. In the example described, the extreme levels of the overall control signal 32 are chosen to allow a deviation of the laser beam over the total width of the support (including or not including one or longitudinal margins) during the oscillation of the mirror between its two extreme angular positions defined.

 For the inscription of successive lines of image, the support or photosensitive paper 6 will also itself entratné step by step, according to the Y direction, the step of definition of its lines.

 It should be noted that, in practice, each time a spot of zero dimension must be inscribed on the support 6, that is to say in fact each time an area of the elementary surface of this support assigned to a point elementary image must not undergo any modification, the analog-digital converter 26, which then receives a word of zero value, delivers a null signal, the oscillator of the source 13 which is then connected to this converter has zero power at the output, and the beam at the output of the acousto-optic modulo-deflector circuit 12 has zero power, that is to say in fact is off.

 The device further comprises time coordination circuits making it possible to develop the various signals that drive it from the time base or the clock represented at 40. The clock 40 delivers a signal designated by H from which these time coordination circuits (not referenced globally) will give the control rate of the selection set 14, the rate of the words successively delivered by the memory 7 as well as the rate of the data applied to the first inputs of the device or data of image points and will control the development of the voltage signal sawtooth control of the assembly 32 drive the mirror 30, that is to say definitively will determine the control of deflection of the laser beam 8 and the modulation rate of this beam, as well as the entrainment rate of the carrier or photosensitive paper 6 in the Y direction.

 This signal H is applied to a divider or counter by 16, 41 and is transformed into a signal HD formed of pulses each of duration equal to a period of the signal H and for example translating here that the state of the counter 41 is the value 1. This HD signal is applied to the source 10 to give the rhythm of image point data successively applied by this source to the device. The signal HD is also applied to the input of a counter 42, here 256 for 256 elementary points per image line, of which only 255 are actually to be printed, the 256th being for example here only a fictitious point The output of the counter indicating that the state thereof is at the value 255 is connected to a monostable 43 delivering, at the passage of the state of the counter 42 to the value 255, an output pulse of chosen duration. to define a return-line time interval, i.e., the time slot assigned to the positioning of the beam from the end of one line to the beginning of the next line, this output pulse of the monostable being elsewhere transmitted to the member (not shown) which drives the paper 6 for the control of movement of a paper step. The signal delivered by the monostable 43 is also used to prevent new image point data from being applied to the device during the time allocated to the line return of the laser beam. For this purpose, it is applied as a zero-set command. counter 41 so as to interrupt the HD signal during each return-line. it follows that the sampling of the image point data from the source 10 is at a frequency sixteen times lower than that of the signal H in the absence of a pulse at the output of the monostable and is interrupted by the presence of such an impulse.

 In order to give the rate of delivery of the words of each set of words corresponding to the data applied to the device, the signal H is applied to a binary counter by 16, 48, with four outputs in parallel, connected to the memory 7. The four outputs of this counter 48 are connected to third address inputs of the memory 7 and the bits present on these outputs, joined to those present on the first and second inputs of the device which are respectively connected to the first and second inputs of memory, define the complete addressing of the memory 7, that is to say, define 4096 addresses for the 8 groups each of 32 sets each of 16 words.

 Each of the 16 words of a set of words corresponding to image data relating to an elementary point will thus be delivered at the rate given by the signal H.

 As a result of each line return, the state of the counter 48 is initialized to the same value, here the value 0, by the line return pulse delivered by the monostable whose output is connected to a control input of reset this counter.

 The control of the selection set 14 is provided by a so-called selection clock circuit 49. This selection clock circuit receives as input the clock signal H 40 and successively detects four consecutive pulses of this signal. it delivers respectively, in the form of a pulse of duration substantially equal to a period of the signal H, on four different outputs, in the absence of the line return pulse delivered by the monostable. This circuit 49 has in fact an inhibition input to which the output of the monostable 43 is connected to block the detection of the ranks of 1 to 4 of the pulses of the signal H during the line return. The four outputs of the selection clock circuit respectively control the four switches 20 to 23 which define the order that is to say the rank of the controlled oscillator according to the command given by the selection clock circuit and which transmit to it the power command defined by the analog signal from the converter 26. It will be noted that the inhibition of the circuit 49 by each pulse delivered by the monostable 43, ensuring the open maintenance of the four switches 20 to 23 and therefore the maintenance off of the laser beam at the output of the modulo circuit - acoustoopticdeflector 12 during each line-return, avoids any inscription on the support during each return-line.

 The selection clock circuit 49 can be realized simply by means of a counter by four or two parallel outputs, receiving the signal H, from a decoder of the state of this counter connected to the two outputs in parallel with that of and having four outputs respectively corresponding to the four possible values of the state of this counter and on each of which the presence or the absence of a pulse, indicates that the state of the counter has or not the value corresponding to the output considered, and four inhibition gates respectively connected to the four outputs of the decoder and controlled by the output signal of the monostable to ensure the inhibition of the pulses delivered by the decoder during each return-line.

 Note also that the counters 41, 48 and the selection clock circuit 49 can of course be made using a common counting circuit.

 In addition, the output of the monostable 43 is connected to the circuit 33 voltage ramp generator which also receives the signal H.

Successive pulses of the signal H control the growth of the output signal of this circuit 33 while each output pulse of the monostable ensures its resetting, as symbolized by the notation RAZ, or its reset to a reference level, for the return of the mirror to the extreme angular position corresponding to the positioning of the laser beam at the beginning of the line. This generator 33 will consist for example of a counter 4096 with parallel outputs, receiving on a counting input the clock signal H and on a forced entry to zero the output pulses of the monostable 43, followed by a digital-to-analog converter.

 Note that to avoid any risk of marking spurious spots during transient time intervals, it will be provided to further inhibit the selection clock circuit 49 for a very short time following each active edge of the signal. H clock by means for example of a detector of these fronts (not shown) whose output signal, formed by very short pulses, would be applied, with the output signal of the monostable 43, inhibition control of this circuit 49.

 The operation of the device will be better understood with reference to the illustrations made in FIG. 1 on the support or photosensitive paper 6, of FIG. 2 illustrating the elementary surface assigned to an elementary image point, the curves represented in FIG. complementary tables given below, as well as, Figures 4, 5 and 6 illustrating the rendering of a hue level of an elementary point.

 By the illustrations made on the support 6, FIG. 1, a line of the support as scanned by the laser beam between the two extreme positions is shown schematically according to the width of the paper, that is to say according to X, data-by the oscillating mirror, this line being defined between the two lines 60 and 61 and having a width of 200 m according to example considered. The scanning of the support 6 by the laser beam, over the width of the line, obtained by the acousto-optic modulo-deflector defining the four positions of the beam according to Y, has also been schematized by the arrow lines 62.

We have further schematized, by doubly shaded surrace 63, the elementary surface assigned to each elementary point of image.

 In FIG. 2, the elementary surface 63, of 200 mx 200 m, assigned to each elementary point, decomposed in a frame of 4 × 4 individual zones denoted respectively A, B, C, D, is illustrated on a large scale. E .... P, each of 50 mxx 5D F m.

In these 16 zones, the spots defined by the 16 words delivered successively on the outputs of the memory in response to the data defining the hue level of the elementary point considered will be respectively performed. These spots will be of dimensions defined by the values of the words respectively. They will vary substantially from 50? Lm x 50 pm, being then maximum, to 0. For the convenience of the representation, the columns of the frame QU matrix are illustrated rigorously perpendicular to its rows, in practice they will be here slightly obliquely due to the progress of the uninterrupted mirror during the course of each oscillator selection sequence of the source 13.

 In FIG. 3, several curves are represented, here eight curves Z0 to Z7, each defining a law for rendering the 32 possible hue levels of the input data. These 32 levels noted n0 to n31 are carried, regularly distributed in abscissa, the level nO translating the whitest level, the level n31 the darkest level. Each of these curves gives the variations of the percentage of black surface to be formed in the total elementary surface - SN assigned to the elementary point, note SNT c1, that is to say gives the percentage that must be reproduced by the overall value of the 16 words assigned to each of these levels nO to n31. The rendering of the level of hue of an elementary point then takes place by making correspond to the 16 words concerned tasks whose distribution is defined by the following words and whose dimensions are defined by their values. respectively.

In Table I below, we have indicated the different percentages SN deduced from the curves, according to the law of restitution chosen,
ST for the same level of hue of the data relating to an elementary point, ie the level n10. In addition, according to these values, a distribution of non-zero size spots and their dimensions in the corresponding individual zones is indicated, by adopting the letters designating them in figure 2, which are affected for some of them, when the stain does not fill the area, fractions translating their dimensions in the respective areas.

<tb> Curve <SEP> SN / ST <SEP> Spots
<tb> Zo <SEP> 31.25 <SEP> B, I <SEP>, <SE> P, D <SEP>, <SEP> K
<tb> Z1 <SEP> 25 <SEP> B, <SEP> I, <SEP> P, <SEP> D
<tb> Z2 <SEP> 22.50 <SEP> B, <SEP> I, <SEP> P, <SEP> 3/5 <SEP> D
<tb> 3 <SEP> 16.25 <SEP> C, <SEP> I, <SEP> 3/5 <SEP> P
<tb> Z4 <SEP> 16.25 <SEP> A, <SEP> P, <SEP> 3/5 <SEP> J
<tb> Z5 <SEP> 9.36 <SEP> C, <SEP> 1/2 <SEP> I
<tb> Z6 <SEP> 9S36 <SEP> 1/3 <SEP> F, <SEP> 1/2 <SEP> 0, <SEP> 2/3 <SEP> L
<tb> 7 <SEP> 9,36 <SEP> 1/2 <SEP> C, <SEP> 1/2 <SEP> K, <SEP> 1/2 <SEP> I
<Tb>

BOARD
This table I makes it possible to show the great flexibility of restitution of the hue levels, obtained by adopting a law of restitution adapted according to the extreme levels of hue of the image to register and the contrasts between levels which can be rendered on the support, but also by assigning to each level, a sequence of words translating the distribution and the dimensions of the spots in the elementary surface of the point, this sequence of words and their relative values can also be modified without changing the overall value of the 16 words.

In addition, Table II below shows the sequence of the 16 words delivered successively during the 16 consecutive times of the clock 40, t1 to t16, allowing, during the scanning of the successive zones A to P associated in parentheses with these 16 times, the restoration of the shade level n10, in application of the laws of restitution given by the curves Z5 to Z7 and according to the distribution of the spots indicated in Table I above

<tb><SEP> Z5 <SEP> Z6 <SEP> Z7
<tb> t1 <SEP> (A) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t2 <SEP> (B) <SEP> 000 <SEP> 000 <SEP> 00C
<tb> t3 <SEP> (C) <SEP> 111 <SEP> 000 <SEP> 011
<tb> t4 <SEP> (D) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t5 <SEP> (E) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t6 <SEP> (F) <SEP> 000 <SEP> 010 <SEP> 000
<tb> t7 <SEP> (G) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t8 <SEP> (H) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t9 <SEP> (I) <SEP> 011 <SEP> 000 <SEP> 011
<tb> t10 <SEP> (J) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t11 <SEP> (K) <SEP> 000 <SEP> 000 <SEP> 011
<tb> t12 <SEP> (L) <SEP> 000 <SEP> 101 <SEP> 000
<tb> t13 <SEP> (M) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t14 <SEP> (N) <SEP> 000 <SEP> 000 <SEP> 000
<tb> t15 <SEP> (O) <SEP> 000 <SEP> 011 <SEP> 000
<tb> t16 <SEP> (P) <SEP> 000 <SEP> 000 <SEP> 000
<Tb>
TABLE II
The rendering of this level n10, respectively for the previous curves Z5 to Z7, is illustrated in FIGS. 4, 5 and 6 given with reference to FIG. 2.

 The hatched spots occupy the position defined by the sequence of words delivered while the laser beam occupies successively the four positions on each column of the matrix and one after the other sweeps the columns of the matrix, their dimensions are defined by the value of the respective words. It will of course be understood that these spots, formed at the point of impact of the laser beam on the support will not in practice have a shape as angular as that adopted in these Figures 4 to 6 for convenience of representation.

 In Figure 7 there is illustrated a second embodiment of the device according to the invention. In this FIG. 7, the same references have been retained for the elements identical to those appearing in FIG. 1; the complete description of Figure 7 will not be made below, only the changes from Figure 1 will be described.

 In the device according to FIG. 7, the read-only memory 7 and the set 14 of sequential selection of the oscillators of the high-frequency wave source 13 according to FIG. 1 are replaced by a read-only memory 7 'and an assembly 14' respectively. sequential selection of the oscillators of the source 13, the digital-analog converter 26 of the device according to Figure 1 no longer exists while a set of variable attenuators, referenced 50, appears.

The read-only memory 7 ', advantageously of the EPROM type, is like the memory 7 (FIG. 1) a transcoding memory of the binary data reflecting the hue levels of the elementary points of the image to be written on the photosensitive paper 6; it has like it first addressing inputs respectively connected to the first inputs 1 to 5 of the device and the second addressing inputs respectively connected to the second inputs 100, 200 and 300 of the device; it contains as it does a plurality of groups of n sets of R ordered binary words, n and R being again considered equal to 32 and 16 respectively, respectively corresponding to a plurality of possible transcoding laws of the binary data relating to the elementary points of the image, the R words of each set of each group respectively defining the dimensions of the individual spots to be formed in the
R areas of the elementary surface assigned to a point for rendering a given hue level to which this set is assigned according to the transcoding law concerned.However, the R words of each set, constituted for example here each of two bits for three possible sizes of spots, are not recorded at R different addresses of this memory 7 ', as was the case previously for the words in the memory 7, but at addresses in number equal to that of the columns of the matrix that forms the elementary surface assigned to an elementary point that is to say here in number equal to four, the words defining the spots to be formed in the areas of the same column being stored at the same address, and constituting what the hereinafter referred to as a subset.

 The additional data applied by the source 10 on the second inputs 100, 200 and 300 of the device and which are therefore received by the memory 7 'on its second addressing inputs ensure the addressing of the memory block where is registered the group of n sets chosen for printing the image on the paper 6 among the different possible groups in a number equal for example still to eight. The data of each elementary point of this image, which the memory 7 'receives on these first inputs of addressing, ensure the addressing in this memory block of the appropriate sub-block so that the subsets of words of the corresponding set are delivered successively at the output of the memory, all the bits of the words of the same sub-block. together being delivered simultaneously on so many parallel outputs different from the memory 7 ', and the subsets of words being delivered in the order of the subsets of increasing ranks that is to say of in the order of the subsets defining the spots to be formed in the columns of increasing ranks of the matrix that forms the elementary surface affected at this point. For this issue of the different subsets of the set of words, the memory 7 'has thirds. addressing inputs, two in number here for four subsets per set, ie for four columns per array, respectively connected to the two highest parallel bit outputs of counter 48, the other two of which Parallel outputs have not been shown in Figure 7.

 As indicated above, each of the R words of each set of words in the memory 7 'consists of two bits for three possible sizes of spots, these three dimensions being for example 0, 1/2 (spot filling substantially half of the corresponding area) and 1 (spot substantially filling the corresponding area); a first of these bits indicates whether the task defined by this word has a zero dimension or not, the dimension of this task, when it is not zero being specified by the other bit or second bit of the word.

 The parallel outputs of the memory 7 ', which are here eight in number corresponding to four words of two bits per subset, are divided into first outputs, four in number, on which are delivered the first bits of the words, and in second outputs, also four in number, on which are delivered the second bits of the words. The outputs of the memory 7 'delivering the two bits of the same word will be described hereinafter associates.

 The first parallel outputs of the memory 7 'are connected to the oscillator selection assembly 14' of the high frequency wave source 13. This set is composed of four switches or switches 20 'to 23' respectively connected to these first outputs of the memory 7 'and further connected for their respective commands to the four outputs of the selection clock circuit 49 respectively. It is connected to the source 13 through the set of variable attenuators 50. It is composed of four variable attenuators, 51 to 54, respectively arranged between the four switches 20 'to 23' and the four oscillators 15 to 18 of the source 13. The four variable attenuators 51 to 54 are identical to each other and each have two possible attenuation rates for two possible non-zero sizes of the spots to be formed, here a rate 1 and a rate 1/2. They are connected for their respective commands to the second parallel outputs of the memory 7 'respectively, each to that associated with that of the first outputs of the memory 7' connected to the switch to which the attenuator in question is itself connected. In each of the pairs formed by a switch and the variable attenuator connected thereto, this switch and this attenuator thus receive the two bits of the same word.

 During each sequence (of four periods of the 'signal H) defined by the selection clock circuit 49, the four switches of the selection set 14' simultaneously receive the first bits of the four words respectively of the subset of the set. words then provided by the memory 7 ', that is to say here each a zero or non-zero voltage depending on whether the task that defines 16 word concerned has a zero or non-zero dimension, while the four variable attenuators simultaneously receive the second bits of these words respectively ;; 11 together 14 'successively selects the four oscillators of the source 13 which thus each receive successively a voltage modulated by the word received from the memory 7' by the switch and the attenuator to which this oscillator is connected, this voltage defining the power level of the wave which it then delivers and which is applied to the acousto-optic modulo-deflector circuit 12 to define firstly the position of the laser beam among the four possible according to Y and secondly the power of the beam c ' that is, the (latent) spot size formed on the photosensitive paper 6 at the point of impact of the beam on the paper. Of course, the connections between the memory 7 ', the selection set 14', the set of variable attenuators 50 and the source 13 will be set so that each of the four words of each subset of words delivered by the memory 7 ', which respectively define the spots to be formed in the four zones of the the same column of the matrix that forms the elementary surface assigned to an elementary point, modulates the output voltage of the oscillator whose frequency defines that of the four possible positions of the laser beam at the output of the acoustooptic modulo-deflector circuit 12 which corresponds to the location of the area concerned in the column.

In Table III below, according to the SN, different percentages ST derived from the curves represented in FIG. 3 have been indicated, for each of the reproduction laws that these curves translate, and for the same level of hue data relating to a elementary point being the level n10, a distribution of the non-zero dimensional spots and their dimensions in the corresponding individual areas of the elementary surface, assigned to the point, by adopting the same notations as in Table I given above; because of the smaller number of possible SN dimensions for stains, some of the different ST percentages deduced from the curves shown in Figure 3 are only approximated by the indicated stain patterns; when this is the case, the precise percentage corresponding to the reason indicated was written in parentheses next to that deduced from FIG.

<Tb>

Curve <SEP> SN / ST <SEP> Spots
<tb><SEP> ZO <SEP> 31.25 <SEP> B, <SEP> I, <SE> P, <SE> D, <SEP> K
<tb><SEP> Z1 <SEP> 25 <SEP> B, <SEP> I, <SEP> P, <SEP> D
<tb><SEP> Z2 <SEP> 22.50 <SEP> (21.88) <SEP> B, <SEP> I, <SEP> P, <SEP> 1/2 <SEP> D
<tb><SEP> 3 <SEP> 16.25 <SEP> (15.6) <SEP> B, <SEP> I, <SEP> 1/2 <SEP> P
<tb><SEP> 4 <SEP> 16.25 <SEP> (15.6) <SEP> A, <SEP> F, <SEP> 1/2 <SEP> I
<tb><SEP> Z5 <SEP> 9.36 <SEP> C, <SEP> 1/2 <SEP> I
<tb><SEP> Z6 <SEP> 9.36 <SEP> A, <SEP> 1/2 <SEP> K
<tb><SEP> Z7 <SEP> 9.36 <SEP> D, <SEP> 1/2 <SEP> M
<Tb>
TABLE III
Of course, it would be possible according to this second embodiment of the invention to have a number of possible sizes of spot larger than that of three considered here. The first embodiment of the invention described is, however, more advantageous in practice when it is desired to have a large number of possible stain dimensions.

Claims (6)

1 / Apparatus for printing an image on a sensitive medium, said image being defined by binary data applied to the device and translating different levels of hue of elementary points along each of the successive image lines, characterized in that it comprises - transcoding means (7-7 ') receiving said binary data and delivering, in response to the data relating to each elementary point to be inscribed on the support, a set of R ordered words respectively defining the dimensions of individual tasks at forming on the support, for the inscription of the considered point, in R zones of a defined elementary surface assigned to this point and decomposed in a substantially matrix manner in these R zones, said transcoding means delivering in response to data reflecting different levels of hue sets of R words, assigned respectively to these different levels for their rendering according to a l determined transcoding, - a laser (8) whose spatial energy density of the beam has a Gaussian distribution for printing on the support of the individual spots from said ordered words successive sets of words delivered by said transcoding means - means (12 to 14, 30 to 33 - 12, 13, 14 ', 30 to 33) of deflection of the laser beam on the support, able to direct this beam on each of the areas of each. elementary surfaces assigned to the elementary points of each image line on the carrier driven perpendicularly to a given direction parallel to which the image lines are to be inscribed, - means (12 to 14 - 12, 13, 14 ', 50) modulating said laser beam, controlled from the ordered words of the successive sets of words provided by said transcoding means, for modulating in power said laser beam as a function of the value of said words, and time coordination means (41). 43, 48, 49), controlling said deflection means and determining the rate of modulation of the laser beam as well as the training rate of the support perpendicular to said given direction, from a time base (40), in order to inscribe, by the laser beam, on the support, individual spots defined by the words of the sets of words delivered by said transcoding means in the corresponding areas respectively. 2 / Apparatus according to claim 1, characterized in that said transcoding means are constituted by a memory containing the sets of R ordered words, assigned respectively, according to said transcoding law, the different levels of hue likely to be translated by said binary data applied to the device. 3 / Apparatus according to claim 2, characterized in that said memory is EPROM type. 4 / Apparatus according to one of claims 2 and 3, characterized in that the sets of R ordered words, assigned respectively, according to said transcoding law, the different levels of hue may be translated by said binary data applied to the device form in said memory a group which is selected from a plurality of groups of sets of R ordered words contained in this memory and respectively corresponding to a plurality of possible transcoding laws, by a so-called group selection command applied to said memory , this command being a function of at least one of the two elements which constitute the medium used and the image to be recorded taken as a whole. 5 / Apparatus according to one of claims 1, 2, 3 and 4, characterized in that said deflection means are constituted by first means (12, 13, 14 - 12, 13, 14 ') providing a deflection of beam substantially perpendicular to said given direction, on the height of a column of the matrix that forms the elementary surface assigned to an elementary point, and by second means ensuring a deviation substantially in said given direction, the beam deviations substantially perpendicular to and in said given direction ensuring scanning, according to said matrix decomposition, of each of the elementary surfaces assigned to the elementary points to be inscribed. 6 / Apparatus according to claim 5, characterized in that said first means and said modulation means comprise, in common, an acousto-optic modulo-deflector circuit (12) receiving the laser beam and a wave source (13) high frequency controlling this circuit, the acousto-optical modulo-deflector circuit ensuring the deviation of the laser beam, according to said height, on successive positions corresponding to the rows of the matrix, by diffraction of the laser beam in a crystal under the control of waves different frequencies assigned respectively to the successive positions corresponding to the rows of the matrix and successively applied by said source to said circuit, and further ensuring the modulation of said beam also under the control of said waves, modulated in power successively the value of the words provided by said transcoding means.