Digital printer using a modulated white light exposure source

Abstract: A method and apparatus for writing onto a photosensitive material (46) with a single light source (12). The apparatus includes a light source (12) for producing light composed of at least two color components, a collimating lens (18) for collimating the light emanating from the light source (12) so as to form a beam (20) of light, and a beam splitter (22) for splitting the beam (20) of light into a plurality of individual predetermined beams (24, 26, 28) of light, each having a different color. A modulator (30, 32, 34) is also provided for a respective one of the beams (24, 26, 28) for modulating the intensity thereof individually in accordance with image data for each of the colors. The individual light beams (24, 26, 28) are then recombined into a single beam (20') of light and directed onto a photosensitive material (46).

Description: Field of the Invention The present invention relates to a method and apparatus for modulating a beam of white light so as to allow simultaneous writing of a red, green, and blue image onto a photosensitive media. Background of the Invention In many instances it is desirable to expose photosensitive media (such as photographic emulsions), which are sensitive to red, green, and blue light simultaneously. Numerous techniques to form continuous tone digital images exist which include three-color laser printing, rotating light-emitting diodes (LEDs), and cathode ray tube (CRT) exposure systems. The optical mechanical portion for the three-color laser writer are relatively inexpensive, however, the cost of the blue and green laser sources are relatively expensive, making the prior art systems cost prohibitive. LED and CRT printers are relatively slow and are also relatively expensive to manufacture and operate. JP-A-04076553 discloses a recording device for use with a white laser beam. The white laser beam is split by a beam splitter and the resulting beams modulated by a single optical modulating means. WO 91/06175 also discloses a recording device for use with a laser light source. US 5237435 discloses a projector comprising an illumination system, a light modulation device and a projection optical system. The present invention provides a printer which is relatively inexpensive to make and use which is reliable for writing of white light onto a photosensitive material, which allows high speed writing of color images and the use of existing photosensitive material. Summary of the Invention In accordance with one aspect of the present invention, there is provided a photographic printer comprising: a light source for producing light composed of at least two colors; collimating means for collimating light from the light source so as to form a beam of light; beam splitting and recombining means comprising three diffraction gratings where the pitch of the first and third diffraction gratings are the same and the pitch of the second diffraction grating is twice that of the first diffraction grating; modulating means for modulating the intensity of each of the colored beams of light individually in accordance with imaging data for each of the colors; and beam directing means for directing the recombined beam of light onto a photosensitive material. recombining means for recombining the plurality of colored beams of light into a single beam of light; and beam directing means for directing the recombined beam of light onto a photosensitive material. The light source may comprise a white light source, the recombined beam comprising a single beam of white light. The modulating means may comprise a PLTZ modulator. Alternatively, the modulating means may comprise a LCD modulator. The beam directing means may include a rotating polygon mirror which scans the light beam across the page of a photosensitive material. In one embodiment, the beam directing means includes a achromatized cylindrical lens which focuses the combined beam of light onto a rotating polygon mirror which then deflects the recombined light beam onto a anamorphic, achromatic, F- lens for focusing of the recombined beam of light to a small spot onto the photosensitive material. In accordance with another aspect of the present invention, there is provided a method of simultaneously modulating a plurality of different primary colors in a beam of light, the method comprising the steps of:- providing a first beam of light; splitting the beam of light into a plurality of predetermined colored beams of light using a first diffraction grating; modulating each of the individual beams of colored light simultaneously in accordance with image data for each of the colors; and recombining the individual beams of colored light which have been modulated to again form a single beam of light using a second and third diffraction grating, the pitch of the second grating being twice that of the first grating and the pitch of the third grating being the same as the first. It is preferred that the first beam of light comprises a beam of white light, the single beam also comprising white light. The method may further comprise the step of exposing the recombined beam of light onto a photosensitive material. The beam of light may be split into three colored beams of light, preferably, three beams of colored light comprise blue, red and green. Brief Description of the Drawings For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:- Figure 1 illustrates a diagrammatic view of a light modulation system made in accordance with the present invention; Figure 2 is a side view of the device of Figure 1; and Figure 3 is a block diagram of the information flow of the device of Figures 1 and 2. Detailed Description of the Invention Referring to Figures 1 and 2, there is illustrated in diagrammatic form, a light modulating system 10 made in accordance with the present invention. In particular, light modulating system 10 includes a light source 12 which produces light having a plurality of color components. In the embodiment illustrated, the light source 12 comprises a white light source 14 having a reflector 16 which concentrates the light produced from white light source 14. A suitable light source that can be used is a xenon arc lamp which may be purchased from Oriel Company or Optical Radiation Corporation. The output of the white light source 14 is collimated with an achromatic collimating lens 18 so as to produce a beam 20 of white light. The collimated white light beam 20 is then incident onto a diffraction grating 22 which disperses light according to wavelength. A suitable grating that may be used is a holographic grating fabricated using a dichromated gelatin plate, such as the KSP 155-01 grating sold by the Eastman Kodak Company having a spacing of 1 to 2 µm. In particular, the diffraction grating 22 divides the light into red, blue, and green light beams 24, 26, 28, respectively. Three separate intensity modulators 30, 32, 34 are inserted in the path of beams 24, 26, 28, respectively, such that the modulator 30 controls the red light beam, modulator 32 controls the blue light beam, and modulator 34 controls the green light beam. The modulators 30, 32, 34 can be electro-optic, acoustic-optic, LCD (liquid crystal display), or PLZT modulators. In the particular embodiment illustrated, the modulators 30, 32, 34 each comprise a PLZT modulator. However, any other type modulators capable of modulating the light beam in accordance with image data may be utilized. The modulators 30, 32, 34 control the intensity of the respective light beam in accordance with the digital image data provided, for example, image data provided by a digital image source such as the Eastman Kodak Photo CD scanner. The CD scanner produces a digital output image signal which is representative of each of the primary colors (e.g., red, blue, and green). After each of the light beams 24, 26, 28 have been modulated in accordance with the appropriate image data for that color, the beams 24, 26, 28 are recombined using a second diffraction grating 36. The second diffraction grating 36 has a pitch which is twice that of the first grating which provides a compensating dispersion for recombining the beams of light. The light beams 24, 26, 28 are then incident on a third diffraction grating 38, which has a grating pitch equal to that of the first diffraction grating 22 to form recombined beam 20'. Grating 38 diffracts the modulated light so that it is parallel to the original optical axis and the three color beams are coincident. The recombined light beam 20' is focused to a line by an achromatized cylindrical lens 40. The beam 20' then is incident on a rotating polygon mirror 42 which causes the light to be deflected in proportion to the rotating angle of the polygon mirror. After deflection, light beam 20' is incident onto an anamorphic, achromatic F- lens 44 which focuses the recombined beam to a small spot which is scanned across a photosensitive material 46 as polygon mirror 42 rotates. Thus, the present invention allows the simultaneous writing of red, green, and blue images and eliminates the need for precise mechanical registration of the three color images written at different times as in printing presses and in other three-color electrophotographic systems. The system of Figures 1 and 2 is most useful in a photographic printer for printing a photosensitive material, such as film and/or paper. Figure 3 illustrates in diagrammatic form a photographic printer incorporating the system of Figures 1 and 2. In particular, there is illustrated a printer 50 having a modulating system illustrated in Figures 1 and 2, like numerals representing like parts. In particular, the modulated white light is focused onto a photosensitive material which is then processed so as to develop the image as is customarily done in the prior art. Referring to Figure 3, there is illustrated a block diagram illustrating how the system of Figures 1 and 2 operates. In particular, image data from, for example, a digital scanner, would be provided to the printer 50. The printer includes a digital signal processor 52, a microprocessor 53, and a stepper motor driver 54 which produces a signal used to control a motor (not shown) which drives the photosensitive material 46 through the device. A second stepper motor driver 56 is provided which produces signals controlling a second motor (not shown) which rotates the polygon mirror 42. The digital image data that is sent to the printer 50 is transferred from the digital signal processor to a three-channel lookup table 58 wherein the appropriate intensity values for the incoming information for the red, green, and blue colors are determined. The information regarding each of the colors is then sent to digital/analog converters 60, 62, 64, for each color, which is then forwarded to its respective modulator 30, 32, 34, and is then used to modulate each of the respective colored beams of light as previously described. The recombined beam 20' of light is focused on to the photosensitive material 46 for forming an image thereon. Various modifications and changes may be made without departing from the scope of the present invention. While in the preferred embodiment illustrated, white light source is provided which is divided up into three primary colors, other combinations may be provided wherein a light source other than white may be divided up into other individual component colors wherein by each of the colors are modulated with respect to the information for that particular color which are then recombined to the original color for exposing onto the photosensitive material. Additionally, while the preferred embodiment illustrated is used for a photosensitive material, for example, as in photographic emulsions used in film and paper, the present system could also be used in other systems such as electrophotographic-type printers. Thus, the present invention provides a system for modulating a light source to generate a multi-colored writing beam in parallel which provides a low cost, high speed printing of color images and allows the use of existing photosensitive media. It is to be understood that various other changes and modifications may be made without departing from the scope of the present invention, the present invention being defined by the claims that follow.

Claims: A photographic printer (50) comprising: a light source (20) for producing light composed of at least two colors; collimating means (18) for collimating light from the light source so as to form a beam (20) of light; beam splitting and recombining means (22, 38) comprising three diffraction gratings where the pitch of the first and third diffraction gratings are the same and the pitch of the second diffraction grating (36) is twice that of the first diffraction grating; modulating means (30, 32, 34) for modulating the intensity of each of the colored beams (24, 26, 28) of light individually in accordance with imaging data for each of the colors; and beam directing means (40, 42, 44) for directing the recombined beam (20') of light onto a photosensitive material (46). A printer according to claim 1, wherein the light source (20) comprises a white light source, the recombined beam (20') comprising a single beam of white light. A printer according to claim 1 or 2, wherein the modulating means (30, 32, 34) comprises a PLTZ modulator. A printer according to claim 1 or 2, wherein the modulating means (30, 32, 34) comprises a LCD modulator. A printer according to any one of the preceding claims, wherein the beam directing means (40, 42, 44) includes a rotating polygon mirror (42) which scans the light beam (20') across the page of a photosensitive material (46). A printer according to any one of claims 1 to 5 wherein the beam directing means (40, 42, 44) includes a achromatized cylindrical lens (40) which focuses the combined beam (20') of light onto a rotating polygon mirror (42) which then deflects the recombined light beam (20') onto a anamorphic, achromatic, F- lens (44) for focusing of the recombined beam (20') of light to a small spot onto the photosensitive material (46). A method of simultaneously modulating a plurality of different primary colors in a beam of light, the method comprising the steps of:- providing a first beam (20) of light; splitting the beam (20) of light into a plurality of predetermined colored beams (24, 26, 28) of light using a first diffraction grating; modulating each of the individual beams (24, 26, 28) of colored light simultaneously in accordance with image data for each of the colors; and recombining the individual beams (24, 26, 28) of colored light which have been modulated to again form a single beam (20') of light using a second and third diffraction grating, the pitch of the second grating being twice that of the first grating and the pitch of the third grating being the same as the first. A method according to claim 7, wherein the first beam (20) of light comprises a beam of white light, the single beam (20') also comprising white light. A method according to claim 7 or 8, further comprising the step of exposing the recombined beam (20') of light onto a photosensitive material (46). A method according to any one of claims 7 to 9, wherein the beam (20) of light is split into three colored beams of light.

Inventors: MEYERS MARK MARSHALL, WESS RAYMOND, MEYERS, MARK MARSHALL, WESS, RAYMOND, MEYERS, MARK MARSHALL, C/O EASTMAN KODAK CO., WESS, RAYMOND, C/O EASTMAN KODAK CO.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: B41J3, B41J2, H04N1, G03G15, G02B27, G02B26