Method and apparatus for writing onto a photosensitive material using a modulated light beam

Abstract: A method and apparatus for printing onto a photosensitive material is described herein. The apparatus (10) includes a light source (12) for producing light composed of at least two colors, a collimator (14) for collimating the light produced by the light source (12) so as form a beam (16) of light, a modulator (18) for modulating the beam (16) in accordance with one of the predetermined color components, a filter (22, 24, 25, 26, 27, 28, 29) for filtering out the color component which has been modulated, and a beam directing device (32) for directing the modulated colored filter beam (16') onto a photosensitive material (30).

Description: Field of the Invention The present invention is directed to a method and apparatus which uses digital image information for writing onto a photosensitive material. In particular, the present invention is directed to a method and apparatus, which utilizes a modulated light beam for digitally printing onto a photosensitive material. Background of the Invention There has been suggested in the prior art several methods for providing continuous tone digital printing. Examples of such digital printers are illustrated by laser, thermal, Light Emitting Diode (LED), and CRT printers. A significant problem associated with these types of digital printers include print speed, hardware expenses, print size, and media expense. For example, laser printing is very fast, however, laser printers are very expensive and require special photosensitive material. LED and CRT printers are relatively slow and are also relatively expensive to manufacture and operate. WO-A-91/06175 discloses a laser printer for color imaging. The printer comprises three lasers, each of which emits a light beam at a different wavelength. Each light beam passes along a separate channel where it is modulated and collimated before being combined into a single beam that is scanned onto a receiving medium that is sensitive to the infrared. 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 invention, there is provided a printer for exposing a photosensitive material comprising: a light source for producing light composed of at least two colors; a collimator for collimating the light produced by said light source so as form a beam of light; a modulator for modulating the beam in accordance with image data for one of said at least two colors; a filter for filtering out a beam of light having a color which has been modulated; and a beam directing device for directing the modulated colored filtered beam onto a photosensitive material. Advantageously, the light source is a white light source, the modulator modulating the beam of white light in accordance with image data for a predetermined color. An achromatized cylindrical lens may be provided for focusing of the modulated beam of white light prior to directing it onto the filter. The beam directing means may comprise a lens for focusing of the colored filtered beam onto the photosensitive material. The filter may comprise a reflective mirror having a reflective filter coated onto the surface thereof. The filter may comprise a rotating polygon mirror having a plurality of mirror facets, the facets having alternating reflective filters coated thereon, each corresponding to one of the modulated beams of light such that the only the colored beam of light will be reflected. Alternatively, the filter comprises a diffraction grating having a spacing such that the central wavelength is in the center wavelength bands of the beam of light being modulated. It is preferred that the modulator modulates the beam in accordance with three primary colors, that is, red, blue and green. The modulator may comprise a PLZT or an LCD device. In accordance with another aspect of the present invention, there is provided a method of writing an image onto a photosensitive material using a modulated light beam having a plurality of color components, the method comprising the steps of: sequentially modulating each of the color components of the light beam one at a time in accordance with image data with respect to at least one color component; and selectively filtering out each of said modulated at least one color component so as to form a colored beam, and sequentially exposing a photosensitive material with each of said at least one modulated filtered colored beams of light so as to form an image in accordance with the image data. Preferably, the light beam comprises white light, the white light beam being modulated in accordance with image data for a plurality of preselected colors, and then selectively filtering each of the modulated colored beams of light and sequentially exposing a photosensitive material with the modulated colored beams of light so as to form an image in accordance with predetermined image data. 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 schematic diagram of a printing apparatus made in accordance with the present invention; Figure 2 is a block diagram of a digital printer made in accordance with Figure 1; Figure 3 is a top plan view of diffraction grating for use in the printing apparatus of Figure 1; and Figure 4 is an enlarged cross-sectional view of the grating of Figure 3 as taken along line 4-4. Detailed Description of the Invention Referring to Figures 1 and 2, there is illustrated a printer 10 made in accordance with the present invention. The printer 10 includes a white light source 12. In the particular embodiment illustrated, the white light source 12 comprises a xenon arc lamp, however, any suitable white light or other appropriate light source may be utilized. A suitable xenon arc lamp may be purchased from the Oriel Company or Optical Radiation Corporation. A collimating lens 14 is provided which collimates light emanating from the white light source 12 to form a beam of white light 16. The beam of white light 16 is then passed through a modulator 18 for modulating the intensity of the beam of white light 16 in accordance with image data with respect to a predetermined color. For example, digital image data obtained from a digital source such as the Photo CD scanner, sold by the Eastman Kodak Company. The modulator 18 may take a variety of different forms. For example, modulator 18 may comprise a PLZT or LCD, or any other appropriate light modulator. In the particular embodiment illustrated, the modulator 18 comprises a PLZT. A suitable PLZT that may be used is the Motorola SCS 1108A solid state ceramic shutter. A cylindrical lens 20 converts the beam 16 into a spot image, which can be used for writing on photosensitive material. The beam 16 is then passed on to a rotating polygon mirror 22 having a plurality of sides/facets 24, 25, 26, 27, 28, 29. The sides 24, 25, 26, 27, 28, 29 of the polygon mirror 22 are designed to reflect the light through an F- lens 32 which focuses the beam 16' onto a photosensitive media 30. In the particular embodiment illustrated, the photosensitive media comprises photographic paper. However, the photosensitive material may comprise of any photosensitive media such as photographic film, electrostatic drum, etc. The sides of polygon mirror 22 are provided with absorption filters which are coated on sides/facets 24, 25, 26, 27, 28, 29 such that light corresponding to the color that has been modulated will be reflected onto the photosensitive media 30. In the particular embodiment illustrated, sides 24 and 27 reflect green light, sides 25 and 28 reflect blue light, and sides 26 and 29 reflect red light. Thus, as the polygon mirror 22 rotates, various beams of colored light will be reflected onto the photosensitive media 30. The modulator 18 modulates the particular colored beam of light that is being reflected by the side upon which the beam 16 is being directed. For example, as illustrated, the modulator 18 is modulating the green color in the beam of light 16, such that the beam of light 16' being reflected from the polygon mirror 22 will be exposed onto the photosensitive media 30. As the polygon mirror 22 rotates, a different reflective beam of light 16' will be scanned across the photosensitive material 30. F- lens 32 focuses the spot as the beam 16 is deflected across the photosensitive media 30. As the polygon mirror 22 rotates, image information (red, green, or blue data, which corresponds to the filter laminate on the polygon mirror) is used by modulator 18 to modulate the light beam 16. A single red, green, or blue line of information is exposed onto the photographic media 30 as the polygon 22 rotates. A full line of color image is made by exposing the red, green, and blue information sequentially onto the photosensitive material 30. Once a single line has been fully exposed, the photosensitive media 30 is moved by two pairs 35 of pinch rollers which are rotated by stepper motor 34 so that the next line can be written onto the photosensitive material. This process of writing each line of image is repeated until a full color image has been exposed onto the photosensitive media 30. Referring to Figure 2, there is illustrated in diagrammatic form, how the digital printing apparatus 10 for exposing of photosensitive material. Image data, which is representative of digital information with respect to a particular image, for example, as obtained from a digital scanner which has scanned a developed film negative, is sent to the printer 10 with the appropriate image data being sent to digital signal processor 42. A three-channel 12-bit lookup table (LUT) 44, is used for determining the values that are appropriate for generating the intensity levels of density on the photosensitive material. The output of the LUT 44 is converted to an analog signal by converter 46, which is amplified as required by the modulator 18. A start of scan pulse synchronizes the rotation of the polygon mirror 22 in face with the data stream being supplied. Stepper motor drives 48, 49 provide signals for controlling motor 34 and a second motor (not shown) for rotating the polygon mirror 22 so that photosensitive media will be properly exposed. The process is completed when all the data information has been transferred and written onto photosensitive material. An microprocessor 45 is provided for controlling the operation of the printer 10 as is well known in the art. It is to be understood that various changes and modifications may be made without departing from the scope of the present invention. For example, in the preferred embodiment illustrated, a rotating polygon mirror is used for selecting out the modulated color of light and for presenting it onto the photosensitive material. This could be accomplished by other methods, for example, a rotating diffraction grating having a plurality of different sections, each corresponding to a different color. For example, referring to Figures 3 and 4, there is illustrated a rotating diffraction grating 50 having sections 51, 52, 53, 54, 55, 56, 57, 58, 59. Grating 50 may be used in the apparatus of Figure 2 taking the place of rotating polygon mirror. Sections 51, 54, and 57 selects out a first predetermined colored light, for example, green, whereas diffraction grating sections 52, 55 and 58 select out the blue colored light, and sections 53, 56 and 59 select out the red colored light. Referring to Figure 4, there is illustrated a cross-sectional view of one of the section of grating 50. The grating comprises a surface relief or modulated refractive index with transmissive features spaced by the grating pitch d. By varying d to change the centrally diffracted wavelength, the desired color may be obtained, e.g., red, green or blue. As the diffraction grating is rotated about axis 60, each successive color will be selected out and diffracted through the lens onto the photosensitive material. The remaining part of the system will be identical to that previously described. In the preferred embodiment, a white light source is provided which is modulated in accordance with the three primary colors (e.g., red, blue, and green). However, the light source may provide any other combination of colored light and any desired color component may be modulated. Thus, there is provided a method and apparatus which is relatively low cost to manufacture and operate and can produce a relatively high volume of digital images. 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 following claims.

Claims: A printer (10) for exposing a photosensitive material (30) comprising: a light source (12) for producing light composed of at least two colors; a collimator (14) for collimating the light produced by said light source (12) so as form a beam (16) of light; a modulator (18) for modulating the beam (16) in accordance with image data for one of said at least two colors; a filter (22, 24, 25, 26, 27, 28, 29; 50, 51, 52, 53, 54, 55, 56, 57, 58, 59) for filtering out a beam (16') of light having a color which has been modulated; and a beam directing device (32) for directing the modulated colored filtered beam (16') onto a photosensitive material (30). A printer according to claim 1, wherein the light source (12) is a white light source, the modulator (18) modulating the beam of white light in accordance with image data for a predetermined color. A printer according to claim 2, wherein an achromatized cylindrical lens (20) is provided for focusing of the modulated beam (16) of white light prior to directing it onto the filter (22). A printer according to any one of claims 1 to 3, wherein the beam directing means (32) comprises a lens (32) for focusing of the colored filtered beam (16') onto the photosensitive material (30). A printer according to any one of the preceding claims, wherein the filter (22, 24, 25, 26, 27, 28, 29) comprises a reflective mirror (22) having a reflective filter coated onto the surface thereof. A printer according to any one of claims 1 to 4, wherein the filter (50, 51, 52, 53, 54, 55, 56, 57, 58, 59) comprises a diffraction grating (50) having a spacing such that the central wavelength is in the center wavelength bands of the beam of light being modulated. A printer according to any one of claims 1 to 4, wherein the filter (22, 24, 25, 26, 27, 28, 29) comprises a rotating polygon mirror (22) having a plurality of mirror facets (24, 25, 26, 27, 28, 29), the facets (Z4, 25, 26, 27, 28, 29) having alternating filters coated thereon, each corresponding to one of the modulated beams of light such that only the colored modulated beam of light will be reflected by the filter. A printer according to any one of the preceding claims, wherein the modulator (18) modulates the beam (16) in accordance with three primary colors. A method of writing an image onto a photosensitive material (30) using a modulated light beam (16') having a plurality of color components, the method comprising the steps of: sequentially modulating each of the colour components of the light beam (16) one at a time in accordance with image data with respect to at least one color component; and selectively filtering out each of said modulated at least one color component so as to form a colored beam (16'), and sequentially exposing a photosensitive material (30) with each of said at least one modulated filtered colored beams (16') of light so as to form an image in accordance with the image data. A method according to claim 9, wherein the light beam comprises white light, the white light beam being modulated in accordance with image data for a plurality of pre-selected colors, and then selectively filtering each of the modulated colored beams (16') of light and sequentially exposing a photosensitive material (30) with the modulated colored beams of light so as to form an image in accordance with predetermined image data.

Inventors: MEYERS MARK M, WESS RAYMOND E, MEYERS, MARK M., WESS, RAYMOND E., MEYERS, MARK M., C/O EASTMAN KODAK CO., WESS, RAYMOND E., C/O EASTMAN KODAK CO.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1995
Main classification: B41J2
IPC codes: G03G15, G02B5, B41J2, G02B26