JP2012068649A - Reduction of rainbow artifact in digital light projection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection system employing a DMD technique which reduces perceivable visual artifacts, in particular, rainbow artifacts.SOLUTION: The projection system includes a color wheel and at least one digital micromirror device. The color wheel generates light of different colors from a light source. The respective colors are sequentially generated with respect to a predetermined color phase. The each digital micromirror device has a plurality of micromirrors. At least one of the plurality of micromirrors is activated in respective different parts of two consecutive color phases in response to a control signal. The projection system further includes a lens configured to project light reflected from at least one of the digital micromirror devices onto a projection surface.

Description

  The present invention relates generally to projection systems, and more particularly to reducing visual artifacts in such systems.

  Digital light processing (registered trademark) technology shows the use of an optical periodic circuit to operate a light source. The optical semiconductor is called a digital micromirror device (DMD) and can be incorporated into a large projection system. Products incorporating DMD technology are manufactured for a variety of different applications, including home and commercial theater use.

  The DMD includes a rectangular array of approximately 1.3 million microscope mirrors called micromirrors. Each micromirror is extremely small and measures a width that is narrower than about one fifth of human hair. Each micromirror is mounted on a hinge that allows the micromirror to tilt toward or away from the light source under the control of a driver circuit. When tilted towards the light source, the mirror is said to be in the “on” position because light from the light source reflects. When tilting away from the light source, the light from the light source does not reflect, so the mirror is said to be in the off position.

  A control signal supplied from the driver circuit to the DMD instructs each micromirror to switch on and off up to several thousand times per second. When the micromirror is switched on more frequently than off, the micromirror reflects bright gray pixels. Conversely, micromirrors that are switched off more frequently than on reflect dark play pixels. Thus, when a light source that emits white light combines the DMD and the lens, a gray scale projection system is formed.

  A color projection system can be constructed by inserting a color wheel in the optical path between the DMD and the light source, or by inserting a color wheel in the optical path between the DMD and the projection lens. At the edge of the color wheel are light filters that produce red, green and blue. White light emitted from the light source passes through these filters as the color wheel rotates. The resulting color light is input to the projection lens for display on the screen.

  The rotation of the color wheel is adjusted by a control signal supplied to the DMD. Thus, each micromirror is switched on and off at a specific rate or switched at a selected time, which selected light filter of the color wheel will turn off the light source at a given time. It can vary according to what is being used to filter. In other words, the on and off states of the respective micromirrors are adjusted by the rotation of the three color light filters of the color wheel.

  In the illustration, micromirrors intended to generate purple pixels are turned on to cause red and blue light reflections. That is, the micromirror is switched on more frequently than off when the red and blue filters are used to filter the light. Red and blue reflected light is perceived as a specific shadow of purple when displayed in rapid succession in the same projection space. Thus, each micromirror can project what is perceived as a color pixel of the image. As explained, the switching of the micromirrors, the percentage of time each micromirror is on or off, is adjusted according to the color light filter used to filter the light source. The human visual system integrates continuous color images and sees multicolor images.

  The color wheel passes only a single color of light corresponding to a particular one of the filters aligned with the light incident on the wheel. This leads to a situation where red, green and blue images do not occur simultaneously on the projection surface. The time delay between successive color images causes perceptible visual artifacts in the resulting image. If the viewer's eyes move too quickly, the viewer may perceive individual red, green, and blue images. This is true even when the object is assumed to be white. This is perceived as a rainbow artifact, meaning that different color images are not perceived as a single blended image.

  It would be desirable to provide a projection system using DMD technology that reduces perceptible visual artifacts, particularly rainbow artifacts.

  One aspect of the present invention includes a projection system. The projection system includes means for sequentially generating color light from the light source. Each color light is generated for a predetermined color phase or period. One or more digital micromirror devices are included in the optical path of the color light generating means and the light source. Each digital micromirror device includes a plurality of micromirrors. At least one of the plurality of micromirrors is activated in response to a control signal starting during a different respective portion within each of two successive color phases, and the color light from the means for sequentially generating color light Cause reflection. The projection system also includes a lens configured to project the color light reflected from the one or more digital micromirror devices onto the projection surface.

  The one or more micromirrors generate at least one composite color pixel. A composite color pixel is a pixel having a color that is generated using more than one color filter from a color wheel. Similarly, a composite pixel or image is a picture or image that contains a composite color.

  In one embodiment, the control signal can activate one or more micromirrors at an intermediate portion or end portion within the first color phase of the two color phases. In another embodiment, the control signal can activate one or more of the plurality of micromirrors at the beginning or middle portion within the second color phase of the two color phases. In particular, the control signal is turned on to at least a part of the second color phase of the two color phases from the middle part of the first color phase of the two color phases to one or more micromirrors. Let it remain.

  The means for sequentially generating color light includes a color wheel having blue, green and red light filters. In response, one or more of the plurality of micromirrors generates one or more composite images from sequentially ordered blue, green, and red images. The color wheel also includes a clear filter for generating white light. The white image generated using the clear filter is generated after the blue image and before the red image. The white color phase generated using the clear filter is shorter in time than the other color phases.

  Another aspect of the invention includes a projection system having means for generating blue, green, white, and red light from a light source. Each color is generated in sequential order for a predetermined color phase. The projection system also includes at least one digital micromirror device for causing reflection of different colors of light, a lens configured to project different colors of light onto the projection surface. In particular, the color phase of white light is shorter than the color phase of other colors. Furthermore, the color phase of white light is arranged between the color phases for blue and red light.

  Another aspect of the invention includes means for generating a composite color in a projection system. The method includes: (a) sequentially generating different light colors for each predetermined color phase; and (b) at least one starting at each different respective portion of two successive color phases. Activating the micromirror. Each color phase can correspond to a different color, thereby producing at least a portion of a composite color picture.

  In one embodiment, the step of activating the at least one micromirror includes (c) intermediate part of the first color phase of two successive color phases, and at least part of the image in the first color. Activating at least one micromirror for generation. In particular, the intermediate part is at least one of the intermediate or the end of the first color phase. In another embodiment, the activating step includes (d) at least one micro to generate a portion of the image in the second color, approximately at the beginning of the next color phase for the second color. Activating the mirror.

  Step (b) is repeated for different ones of the micromirrors. The method also includes generating a composite image by generating a color image that is a component ordered as blue, green, and red. The white image is generated using a clear filter that does not give a specific hue to the light. A white image is generated between the blue and red images.

1 is a conceptual diagram illustrating an embodiment of a projection system according to the configuration of the invention disclosed in this specification. FIG. It is a conceptual diagram explaining the color wheel comprised according to another embodiment of this invention. FIG. 6 is a signal flow diagram illustrating a conventional method for generating a composite color in a projection system. It is a signal flow figure explaining the method to produce | generate the composite color which concerns on one embodiment of this invention. 5A to 5E are signal flow diagrams illustrating a method for generating various composite colors according to another embodiment of the present invention.

Preferred embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
The present invention relates to a projection system and method related to the present invention. In accordance with the arrangement of the present invention, a projection system is disclosed that can reduce visible artifacts, such as rainbow artifacts. In today's projection system, a multi-color image is generated by displaying a continuous color image as an element. That is, a green image is displayed, and a red image and then a blue image are displayed. When displayed one after another, human vision perceives a single multicolor image.

  Rainbow artifacts are perceived by the viewer when the amount of time between elemental images is increased. The viewer begins to visually sense the individual or elemental color images that form the multicolor image. This can be exacerbated when the viewer momentarily loses focus, for example from vibrations caused by meals or simply by moving the head.

  According to the arrangement of the invention disclosed herein, visual artifacts, including rainbow artifacts, are reduced by displaying the images of the elements of the multicolor image in a specific order that depends on the intensity of each color. Can do. Also, the time between elemental color images or portions thereof that form a multi-color image can be reduced and / or minimized.

  FIG. 1 is a conceptual diagram illustrating an embodiment of a projection system 100 according to the arrangement of the present invention disclosed in this specification. As shown, the system 100 includes a light source 105, a color wheel 110, a digital micromirror device (DMD) 115 and a projection lens 120. The light source 105 provides a source of white light that is directed to the color wheel 110. One or more control processors (not shown) are included to generate and supply control signals to the DMD 115 and to coordinate the rotation of the color wheel 110 with the operation of the DMD 115.

  According to one embodiment, the color wheel 110 includes three different light filters. The color wheel 110 includes a blue light filter 125, a green light filter 130, and a red light filter 135. The color wheel 110 rotates so that each color filter 125-135 is exposed to the light source 105 for a predetermined period of time called the color phase. The color wheel 110 rotates in the clockwise direction indicated by the arrow 155, for example. In response, the sequence of color light that passes through DMD 115 is blue, green, and red, and repeats as color wheel 110 continues to rotate. However, it should be understood that the color wheel 110 can rotate in a counterclockwise direction. In that case, the color filters 125-135 are configured such that the color sequence is blue, green, red.

  Other color sequences can also be used. With reference to the embodiment where blue, green and red form a sequence, high quality pictures can be retained. Green has a higher luminous intensity than both blue and red. By placing a high intensity color such as green between low intensity colors such as red and blue, visual artifacts can be reduced, thereby leading to high quality pictures.

  Although the present invention is described in large part with reference to a color wheel, it should be understood that other mechanisms that generate light of different colors can be used. Therefore, the present invention should not be limited only to the use of a color wheel. Rather, a mechanism capable of generating sequentially ordered color light as described herein can be used. Further, although the exemplary embodiment shows the color wheel 110 as being in the light path between the light source 105 and the DMD 115, the color wheel is in the light path between the DMD and the projection lens 150.

  As is known, DMD 115 includes a micromirror array 140. The micromirror array includes approximately 1.3 million micromirrors, each mounted on a hinged mechanism. Each micromirror can be tilted using a hinged mechanism toward or away from the light source 105. When tilted towards the light source 105, the micromirror is said to be in an “on” or “activated” state. When tilted away from the light source 105, the micromirror is said to be in an “off” or “deactivated” state.

  Projection lens 120 receives the light reflected from micromirror array 140. This light forms a series of color images, resulting in a perceived multicolor image 145 that is projected onto the projection surface 150.

  In operation, the color wheel 110 is at several fixed rotational speeds so that the beam 160 of light from the light source 105 passes through the respective color light filters 125-135 for a predetermined period of time called the color phase. It is made to rotate. Color light 165 emitted from the color wheel 110 continues to the micromirror array 140 of the DMD 115.

  The control signal is supplied to the DMD 115 to control the individual micromirrors of the micromirror array 140. Micromirrors are activated and deactivated during successive color phases, each color phase corresponding to a specific color. That is, during the blue color phase, one or more selected micromirrors are activated while blue light is incident on the micromirror array 140. Thereby, a blue image 170 sent to the lens 120 is obtained. During the green color phase, when green light is incident on the micromirror array 140, one or more selected micromirrors of another grouping are activated, thereby producing a green image 175. The same is performed during the color phase when red light is incident on the micromirror array 140, thereby producing a red image 180.

  During each color phase, each individual micromirror is activated for an amount of time corresponding to the intensity of the color being reflected within that color phase. As stated, each micromirror corresponds to an individual pixel in the color image 170, 175 and / or 180, as well as the resulting image 145. Thus, the blue image 170 has different blue tone pixels corresponding to the individual micromirrors that are activated for varying times. The green image 175 has a fluctuating green tone, and the red image 180 has a fluctuating red tone. By displaying continuous color images 170 to 180, a multi-color image 145 displayed on the display screen 150 is obtained.

  Conventional display systems operate by activating individual micromirrors of a micromirror display. That is, the control signal is synchronized with the rotation of the color wheel 110 so that the DMD 115 begins activating individual micromirrors at the beginning of each color phase. For example, to generate a cyan color formed from blue and green, a blue image needs to be generated followed by a green image. Thus, at the beginning of the blue color phase, the conventional projection system activates the micromirrors necessary to produce a blue image at the beginning of the blue color phase. Individual micromirrors are deactivated during the blue color phase according to the intensity of the respective pixel to which each micromirror corresponds.

  At the start of the green color phase, the selected micromirrors that are required to produce a green image are activated. Individual micromirrors are deactivated during the green color phase according to the intensity of the pixels to which each micromirror corresponds. The resulting image is a cyan image with a gradation that depends on the intensity of each blue and green image or part thereof. The resulting image is called a composite image in that the image contains colors that are generated using two or more color filters of the color wheel 110. In particular, the example described above is applicable at the pixel level, where the same micromirror is activated at the start of successive blue and green color phases. In any case, it should be understood that the cycle described in this embodiment is repeated as necessary to generate a series of composite images to render motion.

  FIG. 2 is a conceptual diagram illustrating a color wheel 200 configured according to another embodiment of the present invention. The color wheel 200 includes four light filters. In addition to the blue light filter 205, the green light filter 210 and the red light filter 215, a clear filter 220 is included. The clear filter 220 allows the white light of the light source to pass freely. In one embodiment, the clear filter 220 is positioned between the green light filter 210 and the red light filter 215 as shown. In another embodiment, the clear filter 220 can be located between the blue light filter 205 and the green light filter 210.

  The introduction of the clear filter 220 reduces the length of the color phase of other colors. This slightly reduces the brightness available to project a fully saturated color. This reveals itself as a loss in brightness available for fully saturated colors. For a more general partially saturated color, the available brightness is when the clear filter 220 projects white light containing blue, green and red light components rather than a single color component. To increase. In any case, the blue light filter 205, the green light filter 210 and the red light filter 215 adjust the tone of the image as needed and are fed between the clear filter 220 portions of the wheel. It continues to be used to produce the required white intensity beyond that.

  In FIG. 2, the clear filter 220 is shown to be approximately the same size as the other color light filters 205-215. In other embodiments, the clear filter 220 is made smaller than the other color filters 205-215. That is, the portion of the color wheel 200 situation occupied by the clear filter 220, represented by line 225, is shorter in length than the other color light filters 205-215. As a result, a color phase of white light that is shorter in duration than the color phases of other colors generated by the color wheel 200 is generated.

  FIG. 3 is a signal flow diagram illustrating a conventional method for generating a composite color. This signal flow diagram illustrates the state of the control signal with respect to repeating the color phase sequence. The signal flow graph thus describes the activation and deactivation states corresponding to a given micromirror in the micromirror array during successive color phases. The color produced in FIG. 3 is a fully saturated intermediate yellow consisting of red and green. As shown, the color phase sequence is red, green, then blue. Traditionally, micromirrors are activated at the beginning of both the red and green color phases and remain on for some or all of the respective color phases. As a result, the time between red and green image generation, which in this case is a single pixel, is maximized when the micromirror is activated at the start of the red and green color phases. Thereby, a large time “t” is obtained.

  FIG. 4 is a signal flow diagram illustrating a method for generating a composite color according to an embodiment of the present invention. As shown, the sequence of color phases is changed to blue, green and then red. Furthermore, the control signal no longer activates the micromirrors only at the beginning of each color phase. Rather, the control signal activates the micromirror at the beginning or middle of the color phase as shown. The midpoint corresponds to the portion of the color phase excluding the start. For example, the midpoint corresponds to the middle of the color phase, or the portion in the color phase that precedes the end portion.

  In order to produce a fully saturated intermediate yellow consisting of green and red, the control signal causes the micromirror to be activated during both color phases. In particular, the micromirror is activated towards the middle or end of the green color phase, ie in the middle part. The micromirror is activated or remains activated at the beginning of the red color phase.

  The time between successive activations of the micromirror for the green and red color phases is reduced and / or minimized. This reduces the time between the green and red pixels forming a fully saturated intermediate yellow. When a large scale is realized for a large number of micromirrors, the time between successive color images, in this case green and red images, is reduced and / or minimized. By reducing the time between these pixels and / or images, the number and size of rainbow artifacts perceived from the system can be reduced.

  5A to 5E are signal flow diagrams illustrating a method for generating various composite colors according to another embodiment of the present invention. As shown, the white color is included in the color phase sequence to accommodate the case where the clear filter is included in the color wheel. As described in the present embodiment and shown in FIGS. 5A to 5E, the period of the white color phase is shorter in time than the other color phases. In any case, as in the case of FIG. 4, the colors shown are a complete list of composite colors that may be generated using the embodiments disclosed herein. Is not intended. Rather, the selected composite color is given as an example that is intended to broaden the scope of the present invention.

  FIG. 5A illustrates a method for generating a dark gray color according to one embodiment of the present invention. The control signal causes the micromirror to be activated during the white color phase. In particular, the control signal switches to the on state during the white color phase. That is, the control signal does not need to go on at the start of the white color phase.

  FIG. 5B illustrates a method for producing a dark yellow color (dark yellow color) according to the arrangement of the present invention disclosed herein. Dark yellow is generated from green, white and red light. The control signal is turned on approximately halfway between the green color phases, i.e. the midpoint portion. The signal returns to the on state during the white color phase at the midpoint portion. The control signal is again turned on near or at the beginning of the red color phase. In this way, by moving the pulse for the green color phase later in time, holding the white pulse near the middle of the white color phase, and moving the pulse for the red color phase towards the start, The time “t” between each on state can be reduced and / or minimized.

  FIG. 5C illustrates a method for producing a perfect white color (full white color) according to the arrangement of the invention disclosed herein. Full white color is generated by keeping the micromirror active during each of the color phases, as shown. Since the clear (transparent) section of the color wheel is used to generate all color components simultaneously, this full white color is brighter than the full white from the color wheel without the clear segment.

  FIG. 5D illustrates a method for producing a full yellow color according to the arrangement of the invention disclosed herein. The full yellow color is formed from green, white and red light. Thus, as shown, the control signal is turned on during each of the green, white, and red color phases. The control signal is turned off during the blue color phase.

  FIG. 5E illustrates a method for producing a light yellow color according to the arrangement of the present invention disclosed herein. The light yellow color is formed from green, white and red light. The control signal is turned on at the midpoint through the green color phase at the midpoint portion. The control signal remains on to the midpoint through the white color phase, which is turned off at that point. The control signal then returns to the on state at or near the beginning of the red color phase. Continuous micromirror activation of different color phases by shifting the pulses of the green color phase back in time and holding both the white and red color phases at or near the start of each color phase The amount of time is reduced and / or minimized. As explained, this reduces perceptible rainbow artifacts in the projection system.

  To maximize the effect of the clear segment of the color wheel, the following techniques can be used. First, for a given pixel color, the desired amplitudes of red, green and blue are calculated. The clear segment is then used for a time equivalent to the shortest activation time of the three color phases. If the shortest red, green or blue activation time is longer than the clear segment color phase, the entire time of the clear segment color phase is used. Each red, green and blue activation time is reduced by the time the clear color segment is activated. However, it should be understood that other methods using a clear segment of a color wheel can be used and the present invention is not limited to the techniques described above.

  While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the present invention is determined by the claims.

100: System 105: Light source 110: Color wheel 115: Digital micromirror device (DMD)
120: Projection lens 125: Blue light filter 130: Green light filter 135: Red light filter 140: Micro mirror array 145: Multi-color image 150: Projection surface 155: Arrow 160: Light beam 165: Color light

Claims (24)

Means for sequentially generating light of three or four colors from a light source, and light of each color is generated for a predetermined period called a color phase;
At least one digital micromirror device having a plurality of micromirrors and at least one of the plurality of micromirrors reflects the color light from the means for sequentially generating color light, so that the control signal In response to each of two successive color phases, activated at a position intermediate each color face, the two successive color phases being a first color phase consisting of green and a second color consisting of red. It is composed sequentially from the color phase,
A lens configured to project light reflected from the at least one digital micromirror device onto a projection surface;
A video projection system. The at least one of the plurality of micromirrors generates at least one composite color pixel;
The video projection system according to claim 1. The control signal activates the at least one of the plurality of micromirrors at an intermediate position in the first color phase of the two color phases;
The video projection system according to claim 1. The control signal activates the at least one of the plurality of micromirrors at an end position in the first color phase of the two color phases;
The video projection system according to claim 1. The control signal activates the at least one of the plurality of micromirrors at a starting position in the second color phase of the two color phases;
The video projection system according to claim 1. The control signal activates the at least one of the plurality of micromirrors at an intermediate position in the second color phase of the two color phases;
The video projection system according to claim 1. The control signal is transmitted to the at least one of the plurality of micromirrors from an intermediate point of the first color phase of the two color phases to a second color phase of the two color phases. Leave at least one part of the
The video projection system according to claim 1. Further comprising a light source,
The video projection system according to claim 1. The means for sequentially generating colored light includes a color wheel having blue, green and red light filters;
The video projection system according to claim 1. The at least one micromirror device generates at least one composite image from sequentially ordered blue, green, and red images;
The video projection system according to claim 1. The color wheel further includes a clear filter for obtaining white light,
The video projection system according to claim 9. The white image generated using the clear filter is generated after the blue image and before the red image.
The video projection system according to claim 11. The white color phase generated using the clear filter is shorter in time than the other color phases.
The video projection system according to claim 11. Means for generating blue, green, white and red light from the light source, and the respective colors are generated in a sequential order for a predetermined period of time called the color phase;
At least one digital micromirror device that reflects light of different colors and activates the digital micromirror device at a position intermediate each color face in each of two successive color phases; and the two successive color phases Consists of a first color phase consisting of green light and a second color phase consisting of red light,
A lens configured to project light of different colors onto the projection surface;
A video projection system. The color phase of white light is shorter than the color phase of other colors,
The video projection system according to claim 14. The white light color phase is arranged between the blue light color phase and the red light color phase,
The video projection system according to claim 14. A method for generating a composite color in a projection system, comprising:
(A) sequentially generating light of three or four different colors, each color being generated for a predetermined period called a color phase;
(B) activating at least one micromirror at each intermediate position of each color face in each of two successive color phases;
The two consecutive color phases are sequentially composed of a first color phase consisting of green and a second color phase consisting of red, thereby generating at least a part of a composite color picture. The step of activating the at least one micromirror includes (c) generating at least a portion of the green image at a midpoint position in the first color phase of the two consecutive color phases. Activating at least one micromirror to:
The method of claim 17. The position of the intermediate point is located in the middle or end of the first color phase;
The method of claim 18. The step of activating the at least one micromirror comprises (d) at least one micromirror to produce a portion of the image in the red, approximately at the beginning of the second color phase of the red. Including the step of activating
The method of claim 18. Repeating the step (b) for different micromirrors of the micromirrors;
The method of claim 17. Generating a composite image by generating a color image with elements ordered as blue, green and red;
The method of claim 17. Further comprising generating a white image using a clear filter;
The method of claim 22. The white image is generated between a blue image and a red image.
24. The method of claim 23.

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