WO2004068188A2

WO2004068188A2 - Reflective area modulation imaging system

Info

Publication number: WO2004068188A2
Application number: PCT/US2004/002174
Authority: WO
Inventors: Jae Eun Yu; Jinyong Wu
Original assignee: Umi Group Incorporated
Priority date: 2003-01-27
Filing date: 2004-01-27
Publication date: 2004-08-12
Also published as: WO2004068188A3; WO2004068147A2; TW200500642A

Abstract

An apparatus and method of printing two-dimensional swaths of area onto a photosensitive media (80) uses at least one reflective liquid crystal spatial light modulator (60). In the apparatus and method, illumination optics receive light from a light source (20) and image the light at a polarization beam sputter element (50). The polarization beam splitter element (50) images one polarization state of light at the spatial light modulator to create a substantially collimated illumination at the spatial light modulator.

Description

REFLECTIVE AREA MODULATION IMAGING SYSTEM

Of which the following is a

SPECIFICATION

FIELD OF THE INVENTION

[0001] This invention relates generally to an apparatus and method for spatially and temporally modulating a light beam and imaging modulated light onto a photosensitive media.

BACKGROUND OF THE INVENTION

[0002] Prior art digital printing systems either use laser or light emitting diode (LED) light sources, which are very complicated and expensive. These systems cannot be easily retrofitted into existing mini-lab or photosensitive media printing systems. Existing technology uses liquid crystal modulator which does not have sufficiently high fill factor and thus requires interpolation. Current systems do not have straightforward light uniformization systems resulting in inefficient and expensive systems.

[0003] Photographic images are traditionally printed onto photographic paper using conventional film based optical printers. Currently, the photographic industry is converting to digital imaging. One step in the digital imaging process is to utilize images obtained from digital cameras or scanned film exposed in traditional ER559320034US 079-01 photographic cameras to create digital image files that are then printed onto photographic paper. Towards this end, the current invention relates to the area of digital image printing of digital image files onto photographic paper.

[0004] A more contemporary approach uses a single spatial light modulator such as a Texas mstruments digital micromirror device (DMD) as shown in U.S. Pat. No. 5,061,049 or liquid crystal device (LCD) modulator to modulate an incoming optical beam. Spatial light modulators provide both significant advantages in cost, and have been proposed for a variety of different printing systems from line printing systems such as the printer depicted in U.S. Pat. No. 5,521,748, to area printing systems such as the system described in U.S. Pat. No. 5,652,661.

[0005] The first approach, using the Texas Instruments DMD, shown in U.S. Pat. No. 5,461,411 offers advantages common to spatial light modulator printing such as longer exposure times using light emitting diodes as a source as shown in U.S. Pat. No. 5,504,514. However, this technology may be expensive and not easily scaleable to a higher resolution. The currently available resolution is not sufficient for all printing needs. Furthermore, there is no steady path to increased resolution at a reasonable cost.

[0006] The second approach is to use a liquid crystal spatial light modulator. Liquid crystal modulators are a low cost solution for applications involving spatial light modulators. Several photographic printers using commonly available LCD technology have been proposed. Some examples of such systems are described in U.S. Pat. Nos. 5,652,661; 5,701,185; and 5,745,156. Most designs revolve around the use of a transmissive spatial light modulator such as depicted in U.S. Pat. Nos. 5,652,661 and 5,701,185. Until recently, most spatial light modulators have been designed for use in transmission. While such a method offers several advantages in ease of optical design for printing, there are several drawbacks to the use of conventional transmissive LCD technology. Transmissive spatial light modulators generally have reduced aperture ratios and the use of (thin film transistor) TFT on glass technology does not promote the pixel-to-pixel uniformity desired in many printing applications. Furthermore, in order to ER559320034US 079-01 provide large numbers of pixels, many high resolution transmissive LCDs possess footprints of several inches. Such a large footprint can be unwieldy when combined with a print lens. As a result, most LCD printers using transmissive technology are constrained to either low resolution or small print sizes. To print high resolution 8 in. by 10 in. images with at least 300 pixels per inch requires 2400 by 3000 pixels. Transmissive spatial light modulators with such resolutions are not readily available. Most of the activity in spatial light modulators has been directed at projection display. The projectors are optimized to provide maximum luminous flux to the screen with secondary emphasis placed on contrast, resolution and uniformity. Another drawback for transmissive LCD systems is that the image formed on the photosensitive material does not appear continuous because the aperture ratio is low. Although the use of spatial dithering may compensate for some of the low aperture ratio, spatial dithering involves the use of complicated and expensive mechanic equipment and the introduction of line artifacts. An object of the present invention is to overcome the above-mentioned drawbacks of digital image printing on photographic paper, namely cost and resolution, The recent advent of high resolution reflective LCDs with high contrast (greater than 100:1), such as described in U.S. Pat. Nos. 5,325,137 and 5,805,274 has opened possibilities for printing that were previously unavailable. Specifically, the inventive printer is based on a reflective LCD spatial light modulator illuminated sequentially, and where the LCD spatial light modulator may be sub-apertured and dithered in two directions, and possibly three to increase the resolution. This method has been applied to transmissive LCD systems due to the already less than perfect fill factor. Incorporating dithering into a reflective LCD printing system would allow high- resolution printing while maintaining a small footprint. Also, because of the naturally high fill factor present in many reflective LCD technologies, the dithering can be omitted with no detriment to the continuity of the printed image. The use of a single LCD serves to significantly reduce the cost of the printing system. Furthermore, the use of an area spatial light modulator sets the exposure times at sufficient length to avoid or significantly reduce reciprocity failure. ER559320034US 079-01

[0007] The progress in the reflective LCD device field made in response to needs of the projection display industry have provided opportunities in printing applications. One aspect of the inventive design is that a reflective LCD designed for projection display can be incorporated into the printing design with little or no modification to the reflective LCD itself. By designing the exposure system and data path such that an existing projection display device requires little or no modification allows inexpensive incorporation of a commodity item into a print engine.

[0008] Therefore, there exists a need to increase the resolution of a photographic image, and to retrofit mini-lab devices for improved technology with cost savings.

SUMMARY OF THE INVENTION

[0009] In one aspect of the present invention, a method of exposing an area of photosensitive media using at least one reflective area modulator comprises the steps of collecting light from a light source, such as LED, laser, quartz halogen light, fiber optic source, and the like, focusing the collected light through a light uniformization unit where light from the light uniformization unit will be uniform in distribution for uniform illumination, sequentially illuminating the at least one reflective area modulator with light of different colors matching the sensitivities of the different layers in the photosensitive media with a color wheel, using the light of different colors for periods of time corresponding to sensitivities of the corresponding layers of the photosensitive media, passing the light through an optical assembly comprising lens elements to control the light for proper size onto the reflective area modulator, passing the light through a polarization beam splitter element to polarize the light and to discriminate from undesired non-image-forming light reflected by the reflected area modulator, sending image data to the reflective area modulator sequentially to match the corresponding color wheel portion, with a control system, passing polarized light to the reflective area modulator and sequentially to the projection lens and light sequentially received by the photosensitive media. ER559320034US 079-01

[0010] In a further aspect of the present invention, a method of retrofitting conventional mini-lab photographic systems comprises the above methods and upgrading the mini-lab system to use the apparatus to convert the conventional mini-lab system into a system that uses the present inventive method without replacing the entire mini-lab system.

[0011] hi a still further aspect of the present invention, a method of exposing an area of a photosensitive media, using at least one reflective area modulator, comprises the steps of illuminating with a light source (halogen lamp, laser, LED, and the like) to produce red, green, and blue light in sequence; passing the light through a fiber optic component, light pipe, diffuser box, light valve or lenslet arrays to uniformize the light, condensing the light to illuminate digital film, storing digital images in computer memory, reading the digital images into a computer system, sharpening the image resolution, removing red-eye defects, inserting additional data, transferring processed images onto a reflective area modulator, passing light through a polarization beam splitter, through a projection lens, passing desired light onto digital film, while rejecting undesirable light.

[0012] Other aspects, advantages and features of the invention will become more apparent and better understood, as will equivalent structures, which are intended to be covered herein, with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 illustrates a layout of a reflective spatial light modulator printing system according to the present invention, using a halogen lamp and a light pipe.

[0014] Figure 2 illustrates a layout of a reflective spatial light modulator printing system according to the present invention, using a halogen lamp and a fiber optic unit. ER559320034US 079-01

[0015] Figure 3 is a top plan view of a reflective LCD modulator.

[0016] Figure 4 illustrates a layout of a reflective spatial light modulator printing system according to an alternative embodiment.

[0017] Figure 5 illustrates a typical mini-lab imaging apparatus, with a negative carrier according to the prior art.

[0018] Figure 6 illustrates a mini-lab imaging apparatus, comprising a retrofit kit according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide a high resolution reflective modulator of superior design and performance.

[0020] The present description will be directed in particular to elements forming part, or in cooperation more directly with an apparatus in accordance with the present invention. It is understood that the elements not shown specifically or described may take various forms well known to those skilled in the art.

[0021] Referring now to the drawings, wherein like reference numerals represent identical or corresponding parts throughout the several views, FIG. 1 illustrates a printer referred to in general by numeral 10. A light source in the form of a broadband visible source with a color filter wheel can be employed. More specifically, a light source such as a halogen lamp 20 can be employed in conjunction with a color filter wheel 40 to ER559320034US 079-01 provide the required color sequential illumination. Rotating color filter wheel 40 separates the illumination in time into red, green and blue spectral bands, and also provides a light blocking position to provide zero illumination blocking intervals. Printer 10 is comprised of a light source 20 which can be in the form of a halogen lamp; light uniformizer, such as a light pipe, 30; a polarization beamsplitter element 50 which can be in the form of a beamsplitting cube; a reflective spatial light modulator 60 in the form of a reflective liquid crystal device (LCD) modulator; a data path (not shown) for providing image information to modulator 60; and a print lens assembly 70. Printer 10 provides a two dimensional image or swaths of area to light sensitive media 80 located at an image plane 150.

[0022] The color wheel 40 is rotated to select desired colors, for example, red, green, and blue Color wheel 40 spins to three distinct positions for the three distinct colors. Light pipe 30 is designed to illuminate a nearly square or rectangular aperture matching the aspect ratio of the reflective LCD. In general, axially symmetric components are employed in the illumination. Following color wheel 40 is a relay lens 90 is positioned immediately before polarization beamsplitter element 50.

[0023] Because polarization beamsplitter element 50 may not provide adequate extinction between s polarization state of light and p polarization state of light, a linear polarizer 38 may be incorporated prior to beamsplitter element 50. Linear polarizer 38 is used to isolate the polarization state parallel to the axis of polarization beamsplitter element 50. This serves to reinforce the polarization state determined by polarization beamsplitter element 50, decrease leakage light and increase the resulting contrast ratio.

[0024] Spatial light modulator 60 of this system is designed for a two dimensional reflective polarization based spatial light modulator as is shown in FIG. 3. Modulator 110 includes a plurality of modulator sites 92 that are individually modulatable. Light passes through modulator 110, is reflected off the back of the modulator 110, and returns through modulator 110. If a modulator site 92 is "on" or bright, during the round-trip through modulator 110, the polarization state of the light is rotated. In an ER559320034US 079-01 ideal case the light is rotated 110 degrees. However, this degree of rotation is rarely easily achieved. If a given modulator site is "off or dark, the light is not rotated. The light that is not rotated is not passed straight through the beamsplitter element 50 but is redirected away from the media plane by beamsplitter element 50. It should be noted that light that is rotated by LCD modulator 110 might become elliptically polarized. Upon passing through a linear polarizer, the light will regain linearity. However, light that is not passed through a linear polarizer will retain ellipticity. For this reason, a second linear polarizer 48 may be located between the beamsplitter element 50 and the print lens assembly 70.

[0025] Following modulator 60 and beamsplitter element 50 in FIG. 1 is a print lens assembly 70. Lens assembly 70 provides the correct magnification of the image of modulator 60 to image plane 150 where media 80 is located. Print lens assembly 70 is designed to provide magnification relating to a given image size at image plane 150. In another embodiment it is possible for the printing system to create images corresponding to different print sizes. For instance, some prints may be 4 in. by 6 in. while others may be 8 in by 10 in. To switch between print sizes, the print lens assembly 70 must be exchanged. Ideally, the illumination and modulator assemblies remain unaltered and a different print lens assembly 70 is positioned.

[0026] Another embodiment of this invention is illustrated in Fig. 2. Printer 10 is comprised of a light source 20 which can be in the form of a halogen lamp, fiber optic component 100; a relay lens 120; a polarization beamsplitter element 50 which can be in the form of a beamsplitting cube; a reflective spatial light modulator 60 which can be in the form of a reflective liquid crystal device (LCD) modulator; a data path (not shown) for providing image information to the modulator 60; and a print lens assembly 70. Printer 10 provides a two dimensional image or swaths of area to light sensitive media 80 located at an image plane 150.

[0027] The color wheel 40 is rotated to select desired colors, for example, red, green, and blue. Color wheel 40 spins to three distinct positions for the three distinct colors. ER559320034US 079-01

Optical fiber component 100 is provided to carry the light from light source, which can be remote from the printer to the spatial light modulator. In general, axially symmetric components may be employed in the illumination. Following fiber optical component 100 is a relay lens 120 that may be positioned immediately before polarization beamsplitter element 50.

[0028] A fiber optic element 100 uniformizes light from the light source, 20. The light source 20 may be in the form of a broad band visible source (for example, a halogen lamp) in conjunction with a color wheel 40 to provide color sequential illumination. Rotating color filter wheel 40 may separate the illumination in time into red, green and blue spectral bands, and also may provide a light blocking position to provide zero illumination blocking intervals.

[0029] In yet another embodiment of the invention as shown in Fig. 4, an LED lamp 200 is used as light_ source of the printer 10. More specifically, the LED lamp is comprised of integrated red, green, and blue LEDs 210, 220, 230, to provide red green, and blue spectral bands. The LED components of the LED lamp may be comprised of the type manufactured by the Norlux Corporation with model number HEX-RGB-A. The LED lamp may be modulated in accordance with the spectral sensitivity of the photosensitive media 80 used and synchronized to the image data provided to modulator 60 by an electronic control circuit (not shown). Printer 10 is thus comprised of an LED lamp 200, light uniformizer, such as a light pipe 30; a relay lens 90; a polarization beamsplitter element 50 which can be in the form of a beamsplitting cube; a reflective liquid crystal device (LCD) modulator; a data path (not shown) for providing reflective spatial light modulator 60; and a print lens assembly 70. Printer 10 provides a two dimensional image or swaths of area to light sensitive media 80 located at an image plane 150.

[0030] Light pipe 30 is designed to illuminate a nearly square or rectangular aperture matching the aspect ratio of the modulator. In general, axially symmetric components ER559320034US 079-01 are employed in the illumination. Following the light uniformizer 30 is a relay lens 90 that is positioned immediately before polarization beamsplitter element 50.

[0031] Once imaged at image plane 150, the printer moves the media to a next position and another image is recorded. Some of the advantages of this invention are using commodity technology to produce low cost, high-resolution prints, without excessive dithering, at faster printing speeds with shorter exposure times.

[0032] A conventional mini-lab imaging apparatus 320 is illustrated in Figure 5. Such an apparatus may comprise a lens deck station 210, a negative carrier 290, a processor section 220, a culler section 230, a sorter 240, a replenisher tank 250, a paper deck section 250, a printer control section 270, and a light source section 280. A photographic negative (not shown) is inserted into the negative carrier 290, which may also comprise an RGB dichloric filter (not shown).

[0033] Figure 6 depicts a mini-lab imaging apparatus 330 retrofitted according to the present invention. The mini-lab imaging apparatus 330 may be a conventional mini-lab imaging apparatus 320, retrofitted to print digital images. The mini-lab imaging apparatus 330 may comprise a lens desk station 210, a retrofit kit 300, a processor section 220, a culler section 230, a sorter 240, a replenisher tank 250, a paper deck section 250, a printer control section 270, a light source section 280, and a computer 340 for controlling exposure of images. The mini-lab imaging apparatus 320 may be retrofitted to process and print digital images by inserting a retrofit kit 300 into the light path of the mini-lab imaging apparatus, for example, between the light source section 280 and the lens deck section 210. One may also connect a computer 340 and software. Other components of the mini-lab imaging apparatus 320 may be removed to facilitate retrofitting, and additional components may be used to enable and improve the processing and printing of digital images.

[0034] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and ER559320034US 079-01 modifications can be effected within the scope of the invention as described above, and as described by the appended claims, by a person of ordinary skill in the art without departing from the scope of the invention.

[0035] In the foregoing specification, the invention has been described with reference to one or more specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, it is to be understood that the system may or may not use a color wheel. Also, instead of the light pipe or fiber optic element, other light uniformization devices known in the art can be used.

Claims

WE CLAIM:

1. A method for exposing an area of photosensitive media, using at least one reflective area modulator, comprises the steps of: collecting light from a light source; focusing the collected light through a light uniformization umt where light from the light uniformization unit will be uniform in distribution for uniform illumination; sequentially illuminating the at least one reflective area modulator with light of different colors matching the sensitivities of the different layers in the photosensitive media with a color wheel; using the light of different colors for periods of time corresponding to sensitivities of the corresponding layers of the photosensitive media; passing the light through an optical assembly comprising lens elements to control the light for proper size onto the reflective area modulator; passing the light through a polarization beam splitter element to polarize the light and to discriminate from undesired non-image-forming light reflected by the reflected area modulator; ER559320034US 079-01 sending image data to the reflective area modulator sequentially to match the corresponding color wheel portion; passing polarized light to the reflective area modulator; sequentially passing light to the projection lens; and, receiving light by the photosensitive media.

2. A method of printing as in claim 1 wherein images are juxtaposed by repeatedly exposing the photosensitive media, repositioning the media, and exposing the media again.

3. A method for exposing an area of photosensitive media, using at least one reflective area modulator, comprises the steps of: collecting light from a light source; transmitting the collected light through an optical fiber element; sequentially illuminating the at least one reflective area modulator with light of different colors matching the sensitivities of the different layers in the photosensitive media with a color wheel; using the light of different colors for periods of time corresponding to sensitivities of the corresponding layers of the photosensitive media; passing the light tlirough an optical assembly comprising lens elements to control the light for proper size onto the reflective area modulator; passing the light tlirough a polarization beam splitter element to polarize the light and to discriminate from undesired non-image-forming light reflected by the reflected area modulator; sending image data to the reflective area modulator sequentially to match the corresponding color wheel portion; passing polarized light to the reflective area modulator; sequentially passing light to the projection lens; and, receiving light by the photosensitive media. ER559320034US 079-01

4. The method of claim 3, further comprising mechanically dithering the reflective area modulator.

5. A method for exposing an area of photosensitive media, using at least one reflective area modulator, comprises the steps of: collecting light from an LED light source; focusing the collected light through a light uniformization unit where light from the light uniformization unit will be uniform in distribution for uniform illumination; sequentially illuminating the at least one reflective area modulator with light of different colors matching the sensitivities of the different layers in the photosensitive media; using the light of different colors for periods of time corresponding to sensitivities of the corresponding layers of the photosensitive media; passing the light through an optical assembly comprising lens elements to control the light for proper size onto the reflective area modulator; passing the light through a polarization beam splitter element to polarize the light and to discriminate from undesired non-image-forming light reflected by the reflected area modulator; sending image data to the reflective area modulator sequentially to match the corresponding color; passing polarized light to the reflective area modulator; sequentially passing light to the projection lens; and, receiving light by the photosensitive media.

6. The method of claim 5, further comprising mechanically dithering the reflective area modulator.

7. A retrofit kit for a mini-lab apparatus, said retrofit kit comprising: a light source, ER559320034US 079-01 a light uniformization unit, a polarization beam splitter element, a reflective area modulation element, and a projection lens, said reflective area modulation element comprising modulator sites that rotate a polarization state of incident light and reflects the light through the reflective area modulation element and back to the polarization beam splitter element.

8. The retrofit kit in claim 7, further comprising a color wheel.

9. The retrofit kit in claim 7, wherein the light source is comprised of at least one LED.

10. The retrofit kit in claim 9, wherein the light source emits light at three or more wavelengths.

11. The retrofit kit in claim 10, wherein the LEDs are operable in a color sequential manner.

12. The retrofit kit in claim 7, wherein the light uniformization unit is a light pipe.

13. The retrofit kit in claim 7, further comprising a first polarization element located upstream of said polarization beam splitter element.

14. The retrofit kit in claim 13, comprising a second polarization element located downstream of said polarization beam splitter element.

15. A retrofit kit for a mini-lab apparatus, said retrofit kit comprising: a light source, a fiber optic component, ER559320034US 079-01 a polarization beam splitter element, a reflective area modulation element, and a projection lens, said reflective area modulation element comprising modulator sites that rotate a polarization state of incident light and reflects the light through the reflective area modulation element and back to the polarization beam splitter element.

16. The retrofit kit in claim 15, further comprising a color wheel.

17. The retrofit kit in claim 15, further comprising a first polarization element located upstream of said polarization beam splitter element.

18. The retrofit kit in claim 17, comprising a second polarization element located downstream of said polarization beam splitter element.

19. A retrofit kit for a mini-lab apparatus, said retrofit kit comprising: a light uniformization unit, a polarization beam splitter element, and, a reflective area modulation element, said reflective area modulation element comprising modulator sites that rotate a polarization state of incident light and reflects the light through the reflective area modulation element and back to the polarization beam splitter element.

20. The retrofit kit in claim 19, wherein the light uniformization unit is a light pipe.

21. The retrofit kit in claim 19, wherein the light uniformization unit is a fiber optic component.

22. The retrofit kit in claim 19, further comprising a first polarization element located upstream of said polarization beam splitter element. ER559320034US 079-01

23. The retrofit kit in claim 22, comprising a second polarization element located downstream of said polarization beam splitter element.

24. An imaging apparatus comprising: a computer for controlling exposure of digital images; a light source section; a lens deck section, and; a retrofit kit for a mini-lab apparatus; said retrofit kit comprising; a light uniformization unit; a polarization beam splitter element; and, a reflective area modulation element, said reflective area modulation element comprising modulator sites that rotate a polarization state of incident light and reflects the light through the reflective area modulation element and back to the polarization beam splitter element.

25. The imaging apparatus in claim 24, wherein the light uniformization unit comprises a light pipe.

26. The imaging apparatus in claim 24, wherein the light uniformization unit comprises a fiber optic component.