WO1982004352A1

WO1982004352A1 - High resolution optical-addressing apparatus

Info

Publication number: WO1982004352A1
Application number: PCT/US1982/000738
Authority: WO
Inventors: Kodak Co Eastman; Jose Manuel Mir
Original assignee: Kodak Co Eastman
Priority date: 1981-06-01
Filing date: 1982-05-28
Publication date: 1982-12-09
Also published as: EP0079958A1; CA1165026A; EP0079958B1; JPS58500882A; DE3278836D1; EP0079958A4; US4377753A; SG79888G

Abstract

Apparatus which is useful in electronic imaging systems for optically addressing each of a plurality of discrete picture elements (pixels) of an optical image. Such apparatus comprises a lens array (34) comprising a plurality of lens elements (L1-Ly), each being adapted to focus light incident thereon from a plurality of different predetermined directions (D1-Dx) onto a like plurality of different pixels (P1-Px) located at a discrete, multi-pixel zone (Z1-Zy). Electrooptic means (36-39) are provided for sequentially illuminating the lens array (34) from such different predetermined directions. When combined with an array of light modulators (e.g. a light valve array) to form images on a photosensitive medium, the apparatus of the invention reduces the number of modulators/cm to produce an image of predetermined resolution (i.e. pixels/cm).

Description

HIGH RESOLUTION OPTICAL-ADDRESSING APPARATUS

The present invention relates to the field of electronic imaging and more particularly to improvements in apparatus for optically addressing (i.e. exposing with light) each of a plurality of discrete picture elements (pixels) which collectively define either (a) an image to be formed by the addressing light (e.g. by intensity-modulating the addressing light on a pixel-by-pixel basis) or (b) an image to be scanned by the addressing light to produce, in cooperation with a photodetector, an electrical signal representative of the scanned image information.

To form (or scan) optical images of even moderate detail using electronic imaging techniques, a relatively large number of pixels per image line must be optically addressed. The number of pixels per line increases in accordance with the resolution requiremets of the imaging (or scanning) application, becoming, for example, as large as 100 pixels per centimeter for high resolution continuous tone imaging.

Prior art devices for optically addressing the pixels of an image line are generally of two types. One type is that which addresses such pixels in a serial manner, i.e., one at a time, one after the other. Such a device may comprise, for example, a laser scanner in which a single laser beam is swept across each pixel in an image line. The disadvantage of this type of device is that it is relatively slow in producing (or scanning) images because of its serial nature of addressing pixels. The other type of optical addressing device is that which addresses all picture elements in an image line in parallel (i.e. simultaneously). Such apparatus may comprise, for example,. a light valve array for producing a plurality of light beams, one for each pixel in an image line. (See, e.g., the light valve apparatus disclosed in U.S. Patent No. 4,229,095). While conceptually much faster than the serial-type of addressing devices, the parallel-type of device is considerably more complex and costly, particularly in the case of the above-mentioned high resolution imaging.

The object of this invention, therefore, is to provide a relatively simple apparatus for optically addressing the pixels of a high resolution image at high speed. The optical addressing apparatus of the invention basically comprises a linear array of lens, each lens being adapted to focus incident light from a plurality of different predetermined directions onto a different pixel of an associated multi-pixel address zone, and electrooptic means for directing light onto each lens of the array sequentially from such different predetermined directions. The apparatus of the invention is particularly useful with a light valve array to form images , such light valve array functioning to intensity-modulate with image information the light used to optically address each pixel of an image to be formed.

The subsequent detailed description of preferred embodiments of the invention is made with reference to the attached drawings wherein:

Figures 1 and 2 are schematic illustrations of prior art light valve imaging apparatus;

Figure 3 is a schematic and perspective view illustrating a preferred embodiment of the optical-addressing apparatus of the invention as incorporated in electronic imaging apparatus; Figure 4 is a diagrammatic top view of an apparatus similar to that shown in Fig. 3; Figure 5 is an enlarged diagram of a portion of the optical-addressing apparatus shown in Figs. 3 and 4; Figures 6a and 7 are respectively plan and sectional views of a portion of the light valve array shown in Figs. 3 and 4;

Figure 6b is a plan view of an alternative light valve array useful with the present invention; Figure 8 is a schematic perspective view of a portion of a scaϊining apparatus embodying the present invention; and

Figure 9 is a schematic illustration of a multiple station color imaging apparatus embodying the present invention. Referring first briefly to Figs. 1 and 2, there is illustrated schematically a typical prior art light valve imaging apparatus 10. In use, as light-sensitive recording medium M is moved past exposure station 11, light from source 12 is electrooptically modulated in an imagewise manner by light valve array 13. The array 13 comprises an electrooptic panel 14 (e.g. PLZT) sandwiched between crossed polarizers 15 and 16. The panel 14 comprises a plurality of separately-addressable light-modulating valve portions P^' ₁, P'₂...P'_x, one for each pixel to be addressed at exposure station 11. As shown in Fig. 2, the discrete light-modulating portions of the panel are defined by grounding and addressing electrodes 24 and 25 respectively. Address means, e.g. shift register 27, provides image signals to high voltage switches 26, thereby selectively applying high voltage +V to the addressing electrodes in accordance with image information input to the shift register. Thus each pixel of the exposure zone requires its own electrode and switch structure. Referring now to Figs. 3 and 4, there is shown a preferred embodiment of the present invention embodied in an electronic imaging apparatus. The electronic imaging apparatus 30 has a linear exposure region 31 and drive means 32 for transporting a recording medium M therepast. In general, the electronic imaging apparatus 30 comprises a low resolution linear light valve array 33 and apparatus for optically addressing high-resolution pixels of the linear exposure region with light beams of correspondingly high resolution. The optical addressing apparatus, in general, includes: (1) a linear lens array 34 (which can be positioned in front of the light valve array, as shown in Fig. 3, or behind such array as shown in Fig. 4) comprising a plurality of discrete spherical lens elements L₁, L ₂, L₃, L₄, L_y, each adapted to focus incident collimated light, from one of a plurality of discrete incidence directions D₁-D_x, onto respectively different pixels within an associated multi-pixel zone Z₁, Z₂, Z₃, Z₄ or Z_y, which form the linear exposure region 31; and (2) electrooptic means for directing light onto lens array 34 sequentially from a plurality of different incidence directions D₁...D_x. In the preferred embodiment shown in Figs. 3 and 4, the means for so directing light includes acoustooptic deflector 36, collimating lens 37, a linear array 38 of cylindrical lenticular elements C₁-C_x and cylindrical or spherical collimating lens 39.

The operation of the optical-addressing apparatus can be better understood by referring to Fig. 5 together with Figs. 3 and 4. Thus, deflector 36 is adapted to sequentially deflect an incoming circular light beam B, e.g. from a laser (not shown) along one of the directions B₁-B_x, each aimed at reεpective cylindrical elements C₁-C_xof array

38. In the illustrated embodiment, cylindrical lens 37 is provided to direct the beams B₁-B_x generally normal to the plane of array 38. As shown in Figs. 3 and 4, each of cylindrical elements C₁-C_xrefracts its respective beam B₁-B_xinto a diverging sheet beam S₁-S_x directed toward collimating lens 39 from a different direction. Collimating lens 39 refracts the expanded light from the cylindrical elements C₁-C_xand directs it toward the lens array 34. More specifically, lens

39, which can be, e.g., a spherical or cylindrical lens, is located one focal length f from array 38 and one focal length from array 34. Thus it will be seen that the array 34 is sequentially Illuminated with a plurality of collimated sheet beams, each emanating from a different direction in accordance with the initial deflection by deflector 36.

The advantageous result from this optical configuration and operational mode is that each lens element, L₁-L_y, focuses incident light on a different pixel, P₁-P_x, within a multi-pixel zone Z for each of the different directions of incident collimated light. Thus during the sequence wherein beam B is deflected between B₁-B_x, array 34 is sequentially illuminated by collimated light from directions D₁ (solid line path in Figs. 3-5) through D_χ (dotted line path in Figs. 3-5). This causes sequential optical addressing of each of the pixels in the multi-pixel zones Z₁-Z_y, all of such zones being addressed simultaneously.

More specifically, when collimated light from direction D₁ (see Fig. 5) is incident on a lens array element, e.g. L₁, light is focused by the lens element to a pixel P₁ within the multispot zone Z₁. A similar result is occurring con currently at each of the other zones Z₂-Z_yvia lens L₂-L_y, respectively. As deflector 36 shifts beam B to position B₂ (at element C₂), pixel P₂ of zone Z₁ is illuminated by lens L₁ (as are pixels P₂ of all other zones illuminated by lenses L₂-L_y). It will be appreciated, therefore, that in the complete line exposure sequence, i.e. a deflection of from B from B₁-B_x, a total of x.y pixels of the exposure region will be illuminated, where, in the illustrated embodiment, x is the number of discrete cylindrical elements in lens array 38, and y is the number of discrete lenses in array 34.

Now consider how the high-resolution optical-addressing device just described can be used in cooperation with low-resolution light valve array 33 to provide improved electronic Imaging. One preferred configuration for the array 33 is illustrated in Figs. 6a and 7. As shown, array 33 comprises an electro-optic panel 61 (e.g. PLZT material) sandwiched between crossed polarizers

62,63. (An alternative electrode configuration is shown in Fig. 6b.) Grounded electrodes 65 define a plurality of discrete light-modulating portions

V₁-V_y which are each of low resolution, relative to pixels P₁-P_χ, and which are each independently addressable via activating electrodes 66.

As shown best in Fig. 4, the low-resolution light valve array 33 is located with respect to lens array 34 so that each modulation portion V₁-V_yis optically aligned to control light of corresponding lens elements L₁-L_y. Thus modulating portions V₁-V_yrespectively regulate the light for multi- spot zones Z₁-Z_y. As shown, each modulating portion V₁-V_yhas a single high-voltage switch 68 that is addressed by shift register 69 to control its energization with voltage +V. One further point εhould be explained at this stage. It will be noted that In Fig. 3 light valve array 33 is behind lens array 34 and the opposite is true in Fig. 4. The Fig. 4 arrangement is preferred to maximize the operative area of the light valve, which enhances uniformity.

One preferred mode of electronic imaging with apparatus 30 shown in Fig. 3, under the control of synchronization and control logic 70, is as follows. Synchronization and control logic 70 includes timing circuitry which regulates the movement of recording medium M past the exposure station to define line exposure periods for successive lines of an image to be recorded on recording medium M. During each such line exposure period, logic 70 actuates a plurality of sequential frequency shifts of frequency generator 71 to respectively effect deflection of beam B through each of its B₁-B_x positions. This results in corresponding sequential exposures of pixels P₁-P_xof each of multispot exposure zones Z₁-Z_y, during separate subperiodε of the line exposure period. That is, pixels P₁ of all zones (P₁ set) are optically addressed concurrently, pixels P₂ of all zones (P₂ set) are optically addressed concurrently, etc.

During each such sub-exposure period, the individual light valves V₁-V_yof light valve array 33 are addressed with appropriate off-on information for the respective pixel sets (P set through P_x set), optically addressed during that sub-period. For example if pixel P₃ of zone Z₁ is to be exposed for a particular image line, the modulating portion V₁ will be energized during the B- sub-period of line exposure. It will be appreciated that the format of the image signal provided to array 33 is tailored in accordance with the number of lens element L_y and the number of line sub-periods B_x. This can be accomplished by appropriate time delay and storage circuitry in logic unit 70, or more directly by scanning apparatus such as shown in Fig. 8. Also, gray scale can be obtained by activating pulse length modulation or modulation of the voltage amplitude of the activating pulse as described in more detail in U.S. Patent 4,229,095. The optical-addressing device of the electronic scanning apparatus 80 shown in Fig. 8 is identical to that shown in Figs. 3 and 4. In fact, if the scanning apparatus 80 is used in cooperation with imaging apparatus 30, elements such as deflector 36 can be used commonly. Thus, during successive sub-periods of beam deflection B₁-B_x, collimated light is directed to lens array 84 at different directions from collimating lens 89. As a record member R, which is to be scanned, is moved past scan region 82, pixels P₁-P_xof zones Z₁ -Z_y of the scan region are illuminated in sets as described above. In the illustrated embodiment the record member R is a transparency; thus opticaladdressing light passes the record member in accord with information thereon. A lens array 83, e.g. of gradient index optical fibers, directs light from zones Z ₁-Z_yrespectively to separate photosensor elements, S₁-S_y, of a low-resolution scan detector array 84. Thus it will be appreciated that the signals from elements S₁-S_yof detector array 84 can be transmitted via logic 70 to light valve array 33 to control exposure of recording medium M. Alternatively such signals can be transmitted to a storage device for future processing or access.

One skilled in the art will appreciate that color imaging can be effected in accordance with the present invention by modifying the Fig. 1 apparatus to provide three colinear different color laser beams deflected by an acoustooptic means and by providing properly timed actuation of light valve array 33 during three successive color line exposure periods. In an alternative color imaging embodiment shown schematically in Fig. 9, three separate exposing stations (each containing elements 38', 39', 34' and 33') are located to discharge separate portions of a charged photoconductor web in accordance with the different color separation information for a particular image to be reproduced. Upon development of each such image with different color toner and registered transfer of the different images to a single transfer sheet, a multicolor image is produced. As shown in Fig. 9, such an embodiment comprises a single deflector 91 and separate exposure stations 92, 93, 94, each receiving light from deflector 91 via beam splitters 95, 96 and mirror 97 respectively.

Also, it should be understood that there are various alternative optical configurations for practice of the present invention. For example, in some applications it may be useful to construct array 38 as an array of higher lenslet periodicity than the number of illuminating directions, with the laser beam sequentially incident on different multi-lenslet groups (i.e. lenticule means). Further, beam scanning means other than acousto-optic deflectors, e.g. galvanometers or rotating polygon reflectors are useful for practice of the present invention. From the foregoing disclosure, it will be appreciated that the optical-addressing apparatus of the invention is capable of addressing image pixels at a rate which is considerably faster than conventional laser printers and scanners, since it addresses a multitude of pixels in an image line simultaneously, rather than one at a time. Further, since each lens in array 34 optically addresses a plurality of pixels in multi-pixel addresε zone, the apparatuε of the Invention is considerably simpler in construction as compared with those prior art devices which produce a multitude of optical-addresεing light beams, one for each pixel in an image line.

Claims

What is claimed is:

1. Apparatus for optically addressing a plurality of discrete pixels located at respective positions across a linear, optical-address region, said apparatus being characterized by:

(a) a linear lens array (34) including a plurality of discrete lens elements (L₁-L_y), each adapted to focus incident light, from a plurality of different directions, onto respec tively different pixels of an associated, multi pixel address zone (Z) within said optical address region; and

(b) electrooptic means (36, 37, 38, 39) for directing light onto said linear lens array sequentially from different ones of a plurality of different directions.

2. The apparatus defined in Claim 1 characterized in that said electrooptic means comprises: (i) means (36) for sequentially deflecting a light beam to different positions along a linear path, (ii) a linear lenticule array (38) including a plurality of discrete lens elementε (C₁-C_x) located at respective positions along said beam path, each of said elements being adapted to refract such light beam into a sheet beam (S₁-S_x) and (iii) collimating lens means (39), located between said lenticule array and said linear lens array, for collimating and directing sheet beams from said lenticule array onto said linear array.

3. The apparatus defined in Claim 2 characterized in that said deflecting means Includes an acoustooptic deflector (36) adapted to deflect light to "x" different positions along said path, in that said lenticule array compriεes "x" lenticule means, and in that said lens array comprises "y" spherical lenslets, whereby x^.y of said pixels will be optically addressed In "x" sets by deflection of said light beam to all of said "x" positions.

4. An electronic imaging apparatus having means for transporting a light-sensitive image medium paεt a linear exposure region, and electrooptic means for optically addressing with light of varying intensity each of a plurality of pixels which collectively define an image to be formed on such medium, characterized in that said optical addressing means comprises:

(a) a linear lens array (34) including a plurality of discrete lens elements (L₁-L_y), each adapted to focus incident light, from a plurality of different incidence directions, onto respectively different pixels of an associated, multi-pixel exposure zone within said linear exposure region;

(b) Tight control means (36, 37, 38, 39) for directing light onto said linear lens array sequentially from different ones of a plurality of different incidence directions; and

(c) a linear light valve array (33) having a plurality of diεcrete light-modulating portions (V₁-V_y) which are each independently addres sable electrically to control the passage of light and optically aligned with a respective one of said discrete lens elements.

5. The defined in Claim 4 characterized in that said light control means comprises: (i) acoustooptic means (36, 71) for sequentially deflecting a light beam to different positions along a linear path, (ii) a linear lenticule array (38) including a plurality of discrete lenticules (C₁-C_x) located at respective positions along said beam path, each of said lenticules being adapted to refract such light beam into a sheet beam (S₁-S_χ) and (iii) collimating lens means (39), located between εaid lenticule array and said linear lens array, for collimating and directing sheet beams from said lenticule array onto said linear lens array.

6. Apparatus for optically scanning the individual pixels of successive image lines of a record member at a scanning region past which such member Is transported, said apparatus comprising: (a) a linear lens array (34) including a plurality of discrete lens elementε (L₁-L_y) each adapted to focus incident light, from a plurality of different incidence directions, onto reεpectively different pixels of an associated, multi-pixel scan zone within said scanning region; (b) electrooptic means (36-39) for directing light onto said linear lens array sequentially from different ones of a plurality of different incidence directions; and

(c) a linear array (84) of discrete photo sensor elements each located to receive light from a reεpective lenε element of said lens array after reflection or transmission by the pixels of a record member image line at said scanning region.

7. The apparatus defined in Claim 6 characterized in that said electrooptic means comprises: (i) acoustooptic means (36, 71) for εequentially deflecting a light beam to different poεitionε along a linear path, (ii) a linear lenticule array (38) including a plurality of discrete lenticules (C₁-C_x) located at respective positions along said beam path, each of εaid lenticules being adapted to refract such light beam into a sheet beam (S₁-S_x) and (iii) collimating lens means (39) , located between said lenticule array and said linear lens array, for collimating and directing sheet beams from εaid lenticule array onto said linear lens array.