WO2010008359A1

WO2010008359A1 - Additional illumination onto digital micromirror device imaging system

Info

Publication number: WO2010008359A1
Application number: PCT/US2008/008604
Authority: WO
Inventors: Youngshik Yoon
Original assignee: Thomson Licensing
Priority date: 2008-07-15
Filing date: 2008-07-15
Publication date: 2010-01-21

Abstract

An imaging system and a method provides a watermark in an image displayed on a screen includes at least one digital micromirror device provided with a least one micromirror. The micromirror is rotatable about at least one axis between an off position and an on position. A light source projects a light onto the micromirror. The micromirror reflects the light to a screen when the micromirror is in the on position and the micromirror reflects the light to a light dump when the micromirror is in the off position. A security light source is arranged in the light dump. The security light source projects a security light onto the micromirror. The micromirror reflects the security light to the screen when the micromirror is in the off position.

Description

ADDITIONAL ILLUMINATION ONTO DIGITAL MICROMIRROR DEVICE IMAGING SYSTEM

FIELD OF THE INVENTION ioooi I The invention relates to an imaging system and a method of providing a watermark in an image displayed on a screen wherein at least one digital micromirror device is provided with a least one micromirror and a security light source is arranged in a light dump of the imaging system and emits a security light reflected by the micromirror onto a screen of the imaging s^vstem.

BACKGROUND

10002) Recent methods for protecting against the illicit copying of digital data use the principle of data watermarking which consists in inserting a marking item, commonly referred to as a "watermark", into a multimedia content (still image, video, sound, etc.). Watermarking can be perceptible or imperceptible. The watermark can be, for example, a signal indicating that the content can not be copied or any other item allowing the supplier of the multimedia content to detect illegal copies. The watermark must be robust to transformations of the watermarked content, whether the transformations are made intentionally by a pirate attempting to erase the watermark or whether the transformations result from distortions which occurred during the transmission of the signal containing the watermarked data.

[0003] The effectiveness of the watermark, however, is affected by the type of imaging system used to generate the signal, the frequency, and the frame rate. It is therefore desirable to provide a method for watermarking a visual image wherein the watermarking can be implemented to any type of imaging system regardless of frequency or frame rate.

SUMMARY |0004| An imaging system and a method of provides a watermark in an image displayed on a screen comprising at least one digital micromirror device provided with a least one micromirror. The micromirror is rotatable about at least one axis between an off position and an on position. A light source projects a light onto the micromirror. The micromirror reflects the light to a screen when the micromirror is in the on position and the rnicrornirror reflects the light Lo a light dump when the micromirror is in the off position. A security light source is arranged in the light dump. The security light source projects a security light onto the micromirror. The micromirror reflects the security light to the screen when the micromirror is in the off position.

BRIEF DESCRIPTION OF THE DRAWINGS |0005| Figure 1 is a schematic illustration of an imaging system according to a first embodiment of the invention.

[0006| Figure 2 is a schematic illustration of a total internal reflection prism assembly and a digital micromirror device of the imaging system of Figure 1.

|0007| Figure 3 is a schematic illustration of a path of light in the total internal reflection prism assembly and the digital micromirror device of the imaging system of Figure 1.

[0008| Figure 4 is a schematic illustration of an imaging system according to a second embodiment of the invention. DETAILED DESCRIPTION OF THE EMBODIMENT(S)

|0009| Figure 1 shows an imaging system 1 according to a first embodiment of the invention. The imaging system 1 can be, for example, a digital light processing imager. The imaging system 1 includes a white light source 2, which can be, for example, a high intensity lamp, an arc lamp, or a light emitting diode. The light source 2 emits light 3 that passes through condenser optics 4. The condenser optics 4 focuses the light 3, for example, on a color wheel 5. The color wheel 5 can have, for example, a red section, a green section, and a blue section, through which the light 3 passes as the wheel rotates to convert the light 3 into primary colors. The coior wheel 5 can rotate, for example, once per frame of a displayed image so that the light 3 passes through each of the red, green, and blue sections.

|OO1O| After passing through the color wheel 5, the light 3 passes through an integrator rod 6 to produce a uniform beam using multiple internal reflections in a transparent optical medium. From the integrator rod 6, the light 3 passes through a lens assembly 7. The lens assembly 7 can include, for example, a first lens 8, a second lens 9, and a third lens 10, which shape the beam to fit an optical aperture of a total internal reflection prism assembly 1 1. The light 3 passes into the total internal reflection prism assembly 11 and is incident on a first prism surface 12. The light 3 reflects off of the first prism surface 12 and onto a surface of a spatial light modulator or digital micromirror device 13. iooii I The digital micromirror device 13 includes a plurality of micromirrors 14, mounted, for example, on a semiconductor chip. Each of the micromirrors 14 is associated with a digital memory cell (not shown). The micromirrors 14 can be individually adjusted to rotate about at least one axis. Each of the micromirrors 14 can be adjusted so that the light 3 striking the micromirror 14 can be selectively directed as necessary to create a desired visual image formed according to an input from an image source 15, such as, a broadcast television station, a digital video disk (DVD), or a game playing device. While the source 15 provides indications of the desired visual image, a control 16 generates an input for storage in the digital memory cells (not shown) that will ultimately determine the position of each of the micromirrors 14 at any given time period. The position of the micromirrors 14 will thereby dictate the visual image that will be displayed on a screen 23. jθθi2j As shown in Figures 2-3, each of the micromirrors 14 is rotatabie between an on position ON and an off position OFF. The total internal reflection prism assembly 1 1 guides the light 3 onto the micromirror 14 of the digital micromirror device 13 at an incident angle x. In order to direct the light 3 onto the screen 23, the micromirror 14 is tilted to the on position ON wherein the micromirror 14 is tilted at about half of the incident angle x/2. In the on position ON, the light 3' is reflected from the micromirror 14 through a second prism surface 19 onto a projection lens 17 and onto the screen 23. In order to direct the light 3 away from the screen 23 so that the screen 23 is substantially black or without illumination, the micromirror 14 is titled from the on position ON to another position. The micromirror 14 can be positioned to an intermediate off position, wherein the micromirror 14 is tilted at about half of the incident angle x/2 but in an opposite direction from the on position ON. The micromirror 14 can also be positioned to an off position OFF, wherein the micromirror 14 can be tilted at about the incident angle x in an opposite direction from the on position ON. In the intermediate off position or in the off position OFF, the light 3" can be reflected from the micromirror 14 through a second prism surface 19 onto a heat sink or light dump 18 where the light 3" and the heat energy associated therewith can be properly dissipated.

|00i3| As shown in Figure 1, a security light source 20 is arranged in the light dump 18 or vicinity of the light dump. The security light source 20 emits security light 21. The security light source 20 can be, for example, a laser array that produces collimated light. The security light 21 can be, for example, visible or infrared light depending on the desired security application, the wavelength and the frame rate. A controller 22 controls the emission of the security light 21 from the security light source 20. The security light 21 can be emitted, for example, pixel by pixel or by frame rate in synchronization with the visual image that is to be displayed. The security light source 20 projects the security light 21 from the light dump 18 onto the second prism surface 19. The second prism surface 19 directs the security light 21 onto the micromirrors 14 of the digital micromirror device 13. As shown in Figure 2, when the micromirrors 14 are in the off position OFF, the security light 21 is reflected from the micromirror 14 through the second prism surface 19 onto the projection lens 17 and onto the screen 23. 10014] In an embodiment according to the invention, the security light 21 making the watermark is generally undetectable by a viewer directly watching the visual image on the screen 23. However, the security light 21 will be detected by a camera or other device recording the visual image from the screen 23. The security light 21 thereby generates watermarks in the visual image that are captured by the camera or other device. The watermarks can be just markings or actual message patterns that contain warning messages that explicitly indicate that the recording of the visual image is unauthorized. When the security light 21 is emitted at a high frequency, such as about 50 Hz or greater, or when the security light 21 is emitted at a frame rate in synchronization with the visual image that is to be displayed, the viewer has even less ability to detect the watermarks due to the natural tendency of the viewer's eyes to integrate the visual image being displayed. Thus, the watermarks can be only visible to the camera or other device recording the visual image from the screen 23. The imaging system 1 therefore provides a security system that is easily adaptable to different types of imaging systems. Additionally, the watermarks according to the imaging system 1 are capable of being flexibly and temporally controlled.

|00i5| Figure 4 shows an imaging system 100 according to a second embodiment of the invention. The imaging system 100 can be, for example, a digital light processing imager. The imaging system 100 includes a white light source 102, which can be, for example, a high intensity lamp, an arc lamp, or a light emitting diode. The light source 102 emits light 103 that passes through a lens assembly 107. The lens assembly 107 focuses the light 103 and shapes the beam to fit an optical aperture of a total internal reflection prism assembly 1 1 1. The light 103 passes into the total internal reflection prism assembly 1 1 1 and is incident on a first prism surface 1 12. The light 103 reflects off of the first prism surface 1 12 and into color splitting prisms 124a, 124b, 124c. The color splitting prisms 124a, 124b, 124c separate the light 103 into red light, green light, and blue light. The red light, the green light, and the blue light are each reflected onto a surface of a corresponding spatial light modulator or digital micromirror device 113a, 1 13b, 1 13c, respectively. For example, the digital micromirror device 1 13a only receives the red light, the digital micromirror device 1 13b only receives the green light, and the digital micromirror device 1 13c only receives the blue light. (00i6| Each of the digital micromirror devices 1 13a, 1 13b, 1 13c includes a plurality of micromirrors 1 14, mounted, for example, on a semiconductor chip. Each of the micromirrors 1 14 is associated with a digital memory cell (not shown). The micromirrors 1 14 can be individually adjusted to rotate about at least one axis. Each of the micromirrors 1 14 can be adjusted so that the light 103 striking the micromirror 1 14 can be selectively directed as necessary to create a desired visual image formed according to an input from a source (not shown), such as, a broadcast television station, a digital video disk (DVD), or a game playing device. While the source (not shown) provides indications of the desired visual image, a control (not shown) generates an input for storage in the digital memory ceils (not shown) that will ultimately determine the position of each of the micromirrors 1 14 at any given time period. The position of the micromirrors 1 14 will thereby dictate the visual image that will be displayed on a screen 123.

|OO17| Similar to the micromirrors 14 shown in the imaging system 1 according to the first embodiment of the invention, each of the micromirrors 1 14 is rotatable between an on position and an off position. Each of the color splitting prisms 124a, 124b, 124c guides the red light, the green light, and the blue light onto the micromirrors 1 14 of the digital micromirror devices 1 13a, 1 13b, 1 13c, respectively, at an incident angle. In order to direct the red light, the green light, and the blue light onto the screen 123, the micromirrors 1 14 are tilted to the on position wherein the micromirrors 1 14 can be tilted at about half of the incident angle. In the on position, the red light, the green light, and the blue light is reflected from the micromirrors 1 14 through the color splitting prisms 124a, 124b, 124c where the red light, the green light, and the blue light are recombined and the light 103' is reflected back through the total internal reflection prism assembly 1 1 1 onto a projection lens 1 17 and onto the screen 23.

|ooi8| In order to direct the light 103 away from the screen 123 so that the screen 123 is substantially black or without illumination, the micromirrors 1 14 are titled toward or to the off position wherein the micromirrors 1 14 can be tilted at about half of the incident angle but in an opposite direction from the on position. However, it should be pointed out that the intermediate position does not have to be halfway between the on position ON and the off position OFF. In this off or intermediate position, the red light, the green light, and the blue light is reflected from the micromirrors i i4 onto a heat sink or light dump 1 18 associated with each of the digital micromirror devices 1 13a, 1 13b, 1 13c where the light 103" and the heat energy associated therewith can be properly dissipated. The light dumps can be light filters or beam splitters and can be position before or after the security light source.

10019) A security light source 120 can be arranged in each of the light dumps 1 18. The security light sources 120 emit security light 121. Each of the security light sources 120 can be, for example, a laser array that produces collimated light. The security light 121 can be, for example, visible or infrared light depending on the desired security application, the wavelength and the frame rate. At least one controller (not shown) controls the emission of the security light 121 from each of the security light sources 120. The security light 121 can be emitted, for example, pixel by pixel or by frame rate in synchronization with the visual image that is to be displayed. The security light sources 120 project the security light 121 from the light dump 118 onto the micromirrors 1 14 of the digital micromirror devices 1 13a, 1 13b, 1 13c. When the micromirrors 14 are in the off position OFF, the security light 121 is reflected from the micromirrors 1 14 through the color splitting prisms 124a, 124b, 124c where the security light 121 from each of the digital micromirror devices 1 13a, 1 13b, 1 13c is recombined and is reflected through the total internal reflection prism assembly 1 1 1 onto the projection lens 1 17 and onto the screen 23. In an embodiment, the off position can be an intermediate off position at a slope between the on position ON and the off position OFF

|0020| Although generally undetectable by a viewer directly watching the visual image on the screen 123, the security light 121 will be detected by a camera or other device recording the visual image from the screen 123. The security light 121 thereby generates watermarks in the visuai image that are captured by the camera or other device. The watermarks can be just markings or actual message patterns that contain warning messages that explicitly indicate that the recording of the visual image is unauthorized. When the security light 121 is emitted at a high frequency, such as about 50 Hz or greater, or when the security light 121 is emitted at a frame rate in synchronization with the visual image that is to be displayed, the viewer has even less ability to detect the watermarks due to the natural tendency of the viewer's eyes to integrate the visual image being displayed. Thus, the watermarks can be only visible to the camera or other device recording the visual image from the screen 123. The imaging system 100 therefore provides a security system that is easily adaptable to different types of imaging systems. Additionally, the watermarks according to the imaging system 100 are capable of being flexibly and temporally controlled. Examples of how the security light can be intentionally made undetectable to humans can include the use of metamerism, light at invisible wavelengths, and/or imperceptable flash rates. |002i I The concept of the imaging system 1 according to the invention can also be used in other applications. For example, in the field of biology or medicine, digital micromirror devices are currently used to remove, kill, or burn a particular protein, cell or other chemical component using ultraviolet light. This action is recorded with an advanced microscopic recording system. If there is a demand to identify a certain protein, cell, or chemical components marked, for example, with an infrared ink or infrared pigment, infrared illumination would be needed. A light source arrangement, similar to the security light source arrangement in the imaging system 1 according to the invention could therefore be used to identify the desired protein, cell, or chemical components. |0022] In sum, the invention can be characterized as a method including the steps: modulating a micromirror of at least one micromirror device between on and off positions responsive to an image signal; reflecting a first light from a first location off the micromirror to an image display when the micromirror is in the on position; and reflecting the first light from the first location off the micromirror to another location when the micromirror by tilting the micromirror to a position toward the off position. Further, the second light can be formulated from a second location to form a watermark on the displayed image, wherein the another location and second location can be the same location. The second light can be visible light or infrared light and the first and second lights can be subjected to total internal prismatic reflection prior to being reflected by the micromirror. Further, the invention can include the step of emitting the second light on a pixel by pixel basis in synchronization with a visually perceptible image on the image display and can include the step of emitting the second light at a frame rate in synchronization with a visually perceptible image on the image display. |0023| The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents. For example, although there is the advantage of reducing the space needed when the security light source (or second light source) and light dump are located together, the security light source and light dump can be in separate locations. Also, embodiments of the invention include having the watermarks visible to a viewing audience.

Claims

1. An imaging system, comprising: at least one digital micromirror device provided with a least one micromirror; the micromirror being rotatable about at least one axis between an off position and an on position; a light source projecting a light onto the micromirror, the micromirror reflecting the light to a screen when the micromirror is in the on position and the micromirror reflecting the light to a light dump when the micromirror is tilted toward the off position; and a security light source arranged in the light dump, the security light source projecting a security light onto the rnicrornirror, the micromirror reflecting the security iight to the screen when the micromirror is in the off position.

2. The imaging system of claim 1 , wherein the security light is visible or infrared light.

3. The imaging system of claim 1 , further comprising a total internal reflection prism, the light and the security light entering the total internal reflection prism prior to reflection by the micromirror.

4. The imaging system of claim 1 , wherein the security light is emitted pixel by pixel in synchronization with a visual image to be displayed on the screen.

5. The imaging system of claim 1 , wherein the security light is emitted by frame rate in synchronization with a visual image to be displayed on the screen.

6. The imaging system of claim 1 , wherein the security light forms a watermark on the screen.

7. The imaging system of claim 1 , wherein the security light forms a message pattern on the screen.

8. The imaging system of claim 1. further comprising at least one color splitting prism that separates and recombines the light.

9. A method comprising: projecting a light onto a micromirror of at least one digital micromirror device from a light source, the micromirror being rotatable about at least one axis between an off position and an on position; reflecting the light from the micromirror to a screen when the micromirror is in the on position and to a light dump when the micromirror tilted toward the off position; projecting a security light onto the micromirror from a security light source arranged in the light dump; and reflecting the security light to the screen when the micromirror is in the off position.

10. The method of claim 9, wherein the security light is visible or infrared light.

1 1. The method of claim 9, wherein the light and the security light enter a total internal reflection prism prior to reflection by the micromirror.

12. The method of claim 9, further comprising emitting the security light pixel by pixel in synchronization with a visual image to be displayed on the screen.

13. The method of claim 9, further comprising emitting the security light by frame rate in synchronization with a visual image to be displayed on the screen.

14. The method of claim 9, further comprising forming a watermark on the screen with the security light.

15. A method comprising: modulating a micromirror of at least one micromirror device between on and off positions responsive to an image signal; reflecting a first light from a first location off said micromirror to an image display when said micromirror is in said on position; reflecting said first light from said first location off said micromirror to another location when said micromirror is tilted toward said off position; and reflecting a second light from a second location off said micromirror to said image display when said micromirror is in said off position.

16.. The method of claim 15, further comprising the step of formulating said second light from said second location to form a watermark on said displayed image.

17. The method of claim 15, comprising the step of generating said second light as visible light or infrared light, wherein the another location and second position are the same position.

18. The method of claim 15, comprising the step of subjecting said first and second lights to total internal prismatic reflection prior to said reflecting by said micromirror.

19. The method of claim 15, further comprising the step of emitting said second light on a pixel by pixel basis in synchronization with a visually perceptible image on said image display.

20. The method of claim 15, further comprising the step of emitting said second light at a frame rate in synchronization with a visually perceptible image on said image display.