Patent Publication Number: US-11044447-B2

Title: Projection display system, controlling method thereof, and projection display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Bypass Continuation-in-Part Application of PCT/CN2020/086588 filed Apr. 24, 2020, which claims priority to Chinese Patent Application No. 201910892459.X filed Sep. 20, 2019, which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relates to a projection display system, a controlling method thereof, and a projection display device. 
     BACKGROUND 
     At present, the resolution of a projection display system is determined by the number of micromirrors included in a digital micromirror device (DMD), and each micromirror may correspond to one pixel in an image to be projected. 
     SUMMARY 
     In one aspect, a projection display system is provided. The projection display system includes a control assembly, a light source assembly, a digital micromirror device, an optical path changing device and a projection lens. The control assembly is configured to: determine whether a resolution of an image to be projected is greater than a preset resolution; and divide the image to be projected into N sub-images in response to a determination that the resolution of the image to be projected is greater than the preset resolution, where N is an integer greater than or equal to 2. For each frame of sub-image, the control assembly is further configured to determine a light source control signal, a digital micromirror signal, and an optical path changing signal according to the sub-image, send the light source control signal to the light source assembly, send the digital micromirror signal to the digital micromirror device, and send the optical path changing signal to the optical path changing device; the light source assembly is configured to sequentially emit light of a plurality of primary colors to the digital micromirror device based on a timing indicated by the light source control signal; the digital micromirror device is configured to reflect at least a portion of the light of the plurality of primary colors toward the optical path changing device according to the digital micromirror signal; the optical path changing device is configured to rotate under control of the optical path changing signal, so that light reflected by the digital micromirror device to the optical path changing device is directed to the projection lens. The projection lens is configured to project the N sub-images at different times. 
     In another aspect, a controlling method of the projection display system is provided. The projection display system includes an optical path changing device, a light source assembly, a digital micromirror device, a control assembly and a projection lens. The controlling method includes: determining, by the control assembly, whether a resolution of the image to be projected is greater than a preset resolution; dividing, by the control assembly, the image to be projected into N sub-images in response to a determination that the resolution of the image to be projected is greater than the preset resolution, wherein N is an integer greater than or equal to 2; for each frame of sub-image: determining, by the control assembly, a light source control signal, a digital micromirror signal, and an optical path changing signal according to the sub-image; sending, by the control assembly, the light source control signal to the light source assembly to control a timing of the light source assembly to emit light of a plurality of primary colors to the digital micromirror device; sending, by the control assembly, the digital micromirror signal to the digital micromirror device to control a plurality of micromirrors in the digital micromirror device to rotate, so that the digital micromirror device reflects at least a portion of the light of the plurality of primary colors toward the optical path changing device, and sending, by the control assembly, the optical path changing signal to the optical path changing device to control the optical path changing device to rotate, so that the optical path changing device directs light reflected by the digital micromirror device toward the projection lens. 
     In yet another aspect, a projection display device is provided. The projection display device includes a communication interface configured to receive an image to be projected and a processor configured to execute one or more steps in the controlling method of the projection display system. 
     In yet another aspect, a non-transitory computer-readable storage medium is provided. The computer-readable storage medium stores computer program instructions that, when executed by a computer, cause the computer to perform one or more steps in the controlling method of the projection display system as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe technical solutions in embodiments of the present disclosure more clearly, the accompanying drawings used in the description of embodiments will be introduced briefly below. Obviously, the accompanying drawings to be described below are merely some embodiments of the present disclosure, and a person of ordinary skill in the art may obtain other drawings according to these drawings. In addition, the drawings in the following description may be regarded as schematic diagrams, and are not intended to limit the actual size of the product, the actual process of the method, the actual timing of the signals, etc., involved in the embodiments of the present disclosure. 
         FIG. 1  is a block diagram of a projection display system, in accordance with some embodiments; 
         FIG. 2  is a diagram of a partial structure of a projection display system, in accordance with some embodiments; 
         FIG. 3  is a schematic diagram of an image to be projected, in accordance with some embodiments; 
         FIG. 4  is a schematic diagram showing a plurality of sub-images, in accordance with some embodiments; 
         FIG. 5  is a schematic diagram of dividing an image to be projected into a plurality of sub-images, in accordance with some embodiments; 
         FIG. 6  is a schematic diagram of another image to be projected, in accordance with some embodiments; 
         FIG. 7  is a schematic diagram showing a plurality of sub-images, in accordance with some embodiments; 
         FIG. 8  is a timing diagram of displaying a plurality of sub-images, in accordance with some embodiments; 
         FIG. 9  is a schematic diagram of a projection of two sub-images, in accordance with some embodiments; 
         FIG. 10  is a schematic diagram of displaying two sub-images projected in  FIG. 9 , in accordance with some embodiments; 
         FIG. 11  is a schematic diagram of a projection of two sub-images, in accordance with some embodiments; 
         FIG. 12  is a schematic diagram of displaying two sub-images projected in  FIG. 11 , in accordance with some embodiments; 
         FIG. 13  is a schematic diagram showing a plurality of sub-images displayed as one image, in accordance with some embodiments; 
         FIG. 14  is a schematic diagram of an optical path changing device driving assembly, in accordance with some embodiments; 
         FIG. 15  is a flow diagram of a controlling method of a projection display system, in accordance with some embodiments; 
         FIG. 16  is a flow diagram of another controlling method of a projection display system, in accordance with some embodiments; 
         FIG. 17  is a flow diagram of yet another controlling method of a projection display system, in accordance with some embodiments; and 
         FIG. 18  is a schematic diagram of a projection display device, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the present disclosure will be described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some but not all of embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure shall be included in the protection scope of the present disclosure. 
     Unless the context requires otherwise, throughout the description and the claims, the terms “comprise” and other forms thereof, such as the third-person singular forms “comprises” and the present participle form “comprising”, are to be construed in an open, inclusive sense, that is as “including, but not limited to”. 
     In the description and the claims, terms other than those expressly stated may have nuanced meanings implied in the context. Similarly, phrase “in one embodiment” or “in some embodiments” does not necessarily refer to same embodiment(s), and phrase “in another embodiment” or “in some other embodiments” does not necessarily refer to different embodiment(s). Similarly, phrase “in one example” or “in some examples” does not necessarily refer to same example(s), and phrase “in another example” or “in some other examples” does not necessarily refer to different example(s). For example, a subject that is requested to be protected is intended to include, in whole or in part, exemplary embodiments or a combination of examples. 
     Generally, a term may be understood at least in part from its use in the context. For example, terms such as “and”, “or”, “and/or” as used herein may include a variety of meanings, which may depend at least in part on the context in which these terms are used. In general, if the term “or” is used to connect several objects, such as A, B, or C, it intends to mean A, B, and C (meaning included) and A, B, or C (meaning separate). If the term “and/or” is used to connect several objects, such as “A and/or B”, it should be understood as only A, only B, or A and B. That is, “A and/or B” includes three kinds of relationships. In addition, the terms “one or more” or “at least one” as used herein depends at least in part on the context, may be used to describe any feature, structure, or characteristic in the singular, or may be used to describe features, structures, or a combination of characteristics in the plural. 
     Generally, if “at least one” is used to connect several objects, such as “at least one of A and B”, it should be understood as “only A, only B, or both A and B”. Similarly, based at least in part on context, terms such as “a” or “the” can be understood to mean singular or plural. 
     In addition, based at least in part on the context, the term “based on” or “determined by” may be understood as not necessarily intended to express a set of exclusive elements, but may allow for the existence of other elements that are not necessarily explicitly described. 
     In describing some embodiments, the expression “connected” and its extensions may be used. For example, the term “connected” may be used in describing some embodiments to indicate that two or more assemblies are in direct physical or electrical contact with each other. However, the term “connected” may also mean that two or more assemblies are not in direct contact with each other, but still cooperate or interact with each other. The embodiments disclosed herein are not necessarily limited to the content herein. 
       FIG. 1  is a block diagram of a projection display system, in accordance with some embodiments. As shown in  FIG. 1 , the projection display system  10  includes a control assembly  120 , an optical path changing device  130 , a light source assembly  140 , a digital micromirror device  150  and a projection lens  160 . The control assembly  120  is connected to the optical path changing device  130 , the light source assembly  140 , and the digital micromirror device  150 . 
     For example, the projection display system  10  is a projector, a holographic projector, a laser projection television, or the like. 
     The control assembly  120  is configured to receive an image to be projected, determine a light source control signal, a digital micromirror signal and an optical path changing signal according to the image to be projected, send the light source control signal to the light source assembly  140 , send the digital micromirror signal to the digital micromirror device  150  and send the optical path changing signal to the optical path changing device  130 . In one example, the controller assembly  120  may be configured as a controller. 
     In some embodiments, the control assembly  120  includes or can be a microprocessor or a processor programmed to perform one or more of the operations and/or functions described herein. In some other embodiments, the control assembly  120  is implemented in whole or in part with specially configured hardware (for example, by one or more application-specific integrated circuits (ASIC(s)). In one example, the control assembly  120  may further include, or be connected to, a storage such as a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium), which stores software, program, or codes. When the microprocessor or the processor reads and executes the software, program, or codes, the microprocessor or the processor is configured to perform one or more of the operations and/or functions described herein. 
     In some embodiments, as shown in  FIG. 1 , the projection display system  10  further includes a decoding assembly  110 . The decoding assembly  110  is configured to receive or retrieve image information and decode the image information to obtain the image to be projected (i.e., the decoded image information), and send the image to be projected to the control assembly  120 . In this case, the control assembly  120  is configured to receive the image to be projected from the decoding assembly  110 . 
     The light source assembly  140  is configured to sequentially emit light of a plurality of primary colors, such as, blue light, red light and green light, to the digital micromirror device  150  based on a timing indicated by the light source control signal. 
     In some embodiments, the light source assembly  140  includes a laser driving module and a plurality of lasers. The light driving module is configured to receive the light source control signal and control the plurality of lasers to emit laser beams of different colors (e.g., blue, red, and green) according to the timing indicated by the light source control signal, so that the light source assembly  140  sequentially emits the light of the plurality of primary colors. The laser driving module, for example, includes one or more application specific integrated circuits, and is configured to control the plurality of lasers based on information indicated by the light source control signal. 
     In some other embodiments, the light source assembly  140  includes a laser driving module, a single laser, and a phosphor wheel. The laser driving module is configured to receive the light source control signal and control the laser to emit a laser beam (such as a blue laser beam) according to the light source control signal. The phosphor wheel includes different regions, such as fluorescent regions, a laser transmissive region and a laser reflecting region. The laser driving module is further configured to, according to the timing indicated by the light source control signal, control the phosphor wheel such that different regions of the phosphor wheel rotate successively and periodically to a propagation path of the laser beam. When the light beam is incident on a fluorescent region, the light beam excites fluorescent powder on the fluorescent region to generate fluorescence with a corresponding color (for example, red or green fluorescence). When the light beam is incident on the laser transmissive region or the laser reflecting region (the regions are not provided with fluorescent powder), the laser transmissive region may transmit the light beam, or the light may be reflected by the laser reflecting region. Therefore, the light source assembly  140  sequentially emits light of the plurality of primary colors. 
     In order to improve a color purity of the fluorescence, for example, the light source assembly  140  further includes a color filter wheel disposed behind the phosphor wheel. The color filter wheel includes color filter regions and a laser transmissive region. Each color filter region of the color filter wheel and a corresponding fluorescent region of the phosphor wheel have a same shape and a same size. The laser transmissive region of the color filter wheel and the laser transmissive region (or the laser reflecting region) of the phosphor wheel have a same shape and a same size. The laser driving module is further configured to control the color filter wheel according to the timing indicated by the light source control signal, so that the color filter wheel and the phosphor wheel rotate synchronously to filter the fluorescence, and the color purity is improved. The laser transmissive region of the color filter wheel is configured to allow a laser beam to pass through. Therefore, the light source assembly  140  sequentially emits light of the plurality of primary colors. For example, the laser emits a blue laser beam to the phosphor wheel and then to the color filter wheel, thereby obtaining the light of the plurality of primary colors. 
     The digital micromirror device  150  is configured to reflect at least a portion of the light of the plurality of primary colors toward the optical path changing device  130  according to the digital micromirror signal. 
     The digital micromirror device  150  includes or can be a spatial light modulator composed of a plurality of micromirrors (precision, micro-mirrors). In one example, the spatial light modulator is composed thousands of micromirrors, although the number of micromirrors is not limited thereto. Each micromirror corresponds to one pixel in the image to be projected. By controlling a tilting state of each micromirror, such as individually controlling a tilting angle and dwell duration of each micromirror, a gray-scale modulation of a corresponding pixel may be achieved. It will be noted that the projection display system  10  may include one or more digital micromirror devices  150 . For clarity, the embodiments of the present disclosure are described by taking a projection display system including one digital micromirror device  150  as an example in  FIG. 1 . 
     The optical path changing device  130  is configured to rotate under control of the optical path changing signal, so that the light reflected by the digital micromirror device  150  to the optical path changing device  130  is directed toward the projection lens  160 . 
     In some embodiments, the optical path changing device  130  includes an optical member having a plate face for changing an optical path, an application specific integrated circuit, and actuators. The optical member is, for example, a disc plate glass. The actuators are connected to the peripheral edge of the optical member. The actuators are evenly spaced, for example. The application specific integrated circuit may send a signal to an actuator, and the actuator may drive the optical member forward and backward (such as, drive a lower portion of the optical member forward, as shown in  FIG. 9 ) based on the signal from the application specific integrated circuit, thereby changing the optical path of light entering the optical member. Of course, the optical path changing device  130  may have other structures, as long as the optical path can be changed. For example, the optical member includes or can be a mirror. 
     In some embodiments, the optical path changing signal includes a synchronization signal and a rotation signal. The control assembly  120  is configured to send the synchronization signal and the rotation signal to the optical path changing device  130 . The synchronization signal is used for indicating a rotation moment of the optical path changing device (i.e., the optical member, for simplicity, the optical path changing device and the optical member are not distinguished). The rotation signal is used for indicating a rotation direction and a rotation angle of the optical path changing device  130 . The optical path changing device  130  is configured to rotate under control of the synchronization signal and the rotation signal to transmit or reflect the light reflected to the optical path changing device  130  (i.e., the optical member) by the digital micromirror device  150  toward the projection lens  160 . 
     In the projection display system  10  provided by the embodiments of the present disclosure, through the signal transmissions between the control assembly  10  and all of the light source assembly  140 , the digital micromirror device  150  and the optical path changing device  130 , the projection display system  10  may realize the projection of the image to be projected. 
     In some embodiments, as shown in  FIG. 2 , the projection display system  10  further includes a light absorber  170 . Through rotation of a plurality of micromirrors included in the digital micromirror device  150 , effective light (i.e., light used to form a projected image) of the light of the plurality of primary colors emitted from the light source assembly  140  may be reflected to the optical path changing device  130 , and ineffective light (i.e, light other than light used to form the projected image) of the light of the plurality of primary colors may be reflected to the light absorber  170 . The light absorber  170  is configured to block and absorb the ineffective light to prevent the ineffective light from affecting the quality of the projected image. In some examples, a surface of the light absorber  170  facing the digital micromirror device  150  is provided with a light-absorbing material. The light-absorbing material can be referred to related technologies, and details thereof are not described herein. 
     For convenience of description, two micromirrors of the digital micromirror device  150  are illustrated in  FIG. 2 , as an example. Referring to  FIG. 2 , the two micromirrors include a first micromirror  151  and a second micromirror  152 , and each of the first micromirror  151  and the second micromirror  152  corresponds to a corresponding pixel in the image to be projected. The light source assembly  140  sequentially emits light of a plurality of primary colors to the digital micromirror device  150 , such as the first micromirror  151  and the second micromirror  152 . If the first micromirror  151  is tilted to a first angle under driving of the digital micromirror signal sent by the control assembly  120 , the first micromirror  151  reflects the received light of a primary color to the light absorber  170 . If the second micromirror  152  is tilted to a second angle under driving of the digital micromirror signal sent by the control assembly  120 , the second micromirror  152  reflects the received light of the primary color to the optical path changing device  130 . The optical path changing device  130  transmits or reflects the light of the primary color to the projection lens  160  to realize the projection of the corresponding pixel. For example, the first angle is negative 12 degrees with respect to a reference plane, and the second angle is positive 12 degrees with respect to the reference plane. The amount of light entering the projection lens  160  may be determined by the tilting angle and the dwell duration of each micromirror. The light of the primary color is blue light, red light, or green light. 
     In a case where the resolution of the projection display system  10  is smaller than the resolution of the image to be projected, in the related art, some of pixels in the image to be projected are usually removed, and the processed image to be projected is displayed to ensure that the digital micromirror device in the projection display system may realize the projection of all the pixels remaining in the processed image to be projected. 
     In some embodiments of the present disclosure, the control assembly  120  is configured to determine whether the resolution of the image to be projected is greater than a preset resolution, divide the image to be projected into N sub-images if the resolution of the image to be projected is greater than the preset resolution, and determine a light source control signal, a digital micromirror signal and an optical path changing signal according to each sub-image. Herein, N is an integer greater than or equal to two. 
     For each sub-image, the control assembly  120  is further configured to send the light source control signal to the light source assembly  140 ; the light source assembly  140  is configured to emit light of a plurality of primary colors to the digital micromirror device  150  based on the timing indicated by the light source control signal; the control assembly  120  is further configured to send the digital micromirror signal to the digital micromirror device  150 ; the digital micromirror device  150  is configured to reflect at least a portion of the light of the plurality of primary colors to the optical path changing device  130  according to the digital micromirror signal; the control assembly  120  is further configured to send the optical path changing signal to the optical path changing device  130 ; and the optical path changing device  130  is configured to rotate under the control of the optical path changing signal so that the light reflected by the digital micromirror device  150  to the optical path changing device  130  is directed toward the projection lens  160 . The projection lens  160  is configured to project the N sub-images at different times. The N sub-images are superimposed to form a projected image. 
     In this case, based on the movement (such as rotation) of the optical path changing device, the projection display system  10  may project the N sub-images constituting the image to be projected at different times. Based on the visual persistence effect of the human eyes, a time-sharing projection of the N sub-images is equivalent to a projection of an image with a pixel information carried by the image to be projected, thereby realizing a projection display of the original pixel information of the image to be projected without loss of high resolution, and overcoming the shortcomings of easily losing pixels when displaying high-resolution images in the related art. 
     For example, the preset resolution is the resolution of the projection display system  10 , and the resolution of each sub-image is less than or equal to the resolution of the projection display system  10 . In this way, for a case where the resolution of the projection display system  10  is smaller than the resolution of the image to be projected, the pixel information carried by the image to be projected may be retained during projection display, thereby reducing or even avoiding the loss of pixel information. 
     For example, during a display of a specified sub-image in the plurality of sub-images, the control assembly  120  determines a light source control signal, a digital micromirror signal, and an optical path changing signal corresponding to the specified sub-image according to the specified sub-image. The specified sub-image may be any one of the plurality of sub-images. The optical path changing signal includes a synchronization signal and a rotation signal. The control assembly  120  sends the light source control signal to the light source control assembly  140 , so that the light source assembly  140  emits light of a plurality of primary colors to the digital micromirror device  150  based on the timing indicated by the light source control signal. The control assembly  120  sends the digital micromirror signal to the digital micromirror device  150 , so that the digital micromirror device  150  reflects at least a portion of the light of the plurality of primary colors toward the optical path changing device  130  according to the digital micromirror signal. The control assembly  120  sends the synchronization signal and the rotation signal to the optical path changing device  130 , so that the optical path changing device  130  transmits or reflects the light toward the projection lens  160  according to the synchronization signal and the rotation signal. Thereby, display of the specified sub-image is realized. 
     After the display of the specified sub-image is completed, the control assembly  120  generates a light source control signal, a digital micromirror signal, and an optical path changing signal corresponding to a next sub-image of the specified sub-image in the plurality of sub-images. The optical path changing signal includes a synchronization signal and a rotation signal. The control assembly  120  sends the light source control signal to the light source control assembly  140 , so that the light source assembly  140  emits light of a plurality of primary colors to the digital micromirror device  150  based on the timing indicated by the light source control signal. The control assembly  120  sends the digital micromirror signal to the digital micromirror device  150 , so that the digital micromirror device  150  reflects at least a portion of the light of the plurality of primary colors toward the optical path changing device  130  according to the digital micromirror signal. The control assembly  120  sends the synchronization signal and the rotation signal to the optical path changing device  130 , so that the optical path changing device  130  transmits or reflects the light toward the projection lens  160  according to the synchronization signal and the rotation signal. Thereby, display of the next sub-image of the specified sub-image is realized. And so on, until the N sub-images are displayed, and the image to be projected is displayed. 
     In some embodiments, the optical path changing device  130  is configured to rotate in response to receiving the synchronization signal in the optical path changing signal, and the synchronization signal is used to control the optical path changing device  130  to rotate within a time period in which the optical path changing device  130  receives light of a target primary color in the light of the plurality of primary colors during display of each sub-image. For example, the synchronization signal is used to control the optical path changing device  130  to rotate when the optical path changing device  130  receives the light of the target primary color in the light of the primary colors during the display of each sub-image. 
     The light of the target primary color is, for example, blue light. Since the human eyes are not sensitive to blue, if the optical path changing device  130  rotates during a period of receiving the blue light, the human eyes do not obviously see the rotation of the optical path changing device  130 , thereby further ensuring the display effect of the image. 
     In some examples, for any sub-image, the optical path changing device  130  rotates when receiving the light of the target primary color, and then the optical path changing device  130  remains stationary, that is, the optical path changing device  130  remains stationary in a case where the received light of the primary color is light of a primary color other than the light of the target primary color, and transmits or reflects the light of the primary color other than the light of the target primary color to the projection lens  160 , and so on, until light of the plurality of primary colors is directed to the projection lens  160 , thereby realizing the display of the sub-image. For example, during a display of any sub-image, the light source assembly  140  first emits the light of the target primary color, and then emits the light of primary colors other than the light of the target primary colors. 
     A method for the control assembly  120  to divide the image to be projected into N sub-images is exemplified below. 
     The control assembly  120  is configured to divide the image to be projected into a plurality of image blocks, each of which includes N pixels; and select one pixel from each image block of the plurality of image blocks to form a sub-image to obtain the N sub-images. A position of any pixel of the sub-image in a corresponding image block is the same as a position of another pixel of the sub-image in a corresponding image block. Two pixels in any two sub-images disposed in a same image block have different positions in the image block. Relative positions of pixels included in the sub-image on the sub-image are the same as relative positions of the pixels on the image to be projected. 
     For example, as shown in  FIG. 3 , if a resolution of the image to be projected  00  is 12×16 and N is 4, the control assembly  120  may divide the image to be projected  00  into 48 image blocks  01 . Each image block  01  includes 4 pixels, and the image block  01  includes 2 pixels in a row direction and 2 pixels in a column direction. The control assembly  120  may select a pixel at a first position in each image block  01  to form a sub-image A, select a pixel at a second position in each image block  01  to form a sub-image B, select a pixel at a third position in each image block  01  to form a sub-image C, and select a pixel at a fourth position in each image block  01  to form a sub-image D, so that the sub-image A, the sub-image B, the sub-image C, and the sub-image D shown in  FIG. 4  are obtained. For example, the first position is a position on which the pixel  02  in an upper left corner of the image block  01  is located, the second position is a position on which the pixel  05  in an upper right corner of the image block  01  is located, the third position is a position on which the pixel  06  in a lower left corner of the image block  01  is located, and the fourth position is a position on which the pixel  07  in a lower right corner of the image block  01  is located. 
     As shown in  FIGS. 3 and 4 , a position of a pixel  02  of the sub-image A in the image block  01  is the same as a position of a pixel  03  of the sub-image A in a corresponding image block, which are located at their respective first positions in their respective image blocks. The pixel  02  of the sub-image A and a pixel  05  of the sub-image B are located in the image block  01 . The two pixels have different positions in the image block  01 . 
     Referring to  FIG. 4 , taking the pixel  02 , the pixel  03 , and the pixel  04  in the sub-image A as an example, in the sub-image A, the pixel  03  is located directly to the right of the pixel  02 , and the pixel  04  is located directly below the pixel  02 . Referring to  FIG. 3 , in the image to be projected  00 , the pixel  03  is also located to the right of the pixel  02 , and the pixel  04  is also located below the pixel  02 . That is, relative positions of pixels included in the sub-image A on the sub-image A are the same as relative positions of the pixels on the image to be projected  00 . With regard to the pixels  05 ,  06  and  07 , reference may be made to the pixel  02 . 
     In some examples, each image block includes X pixels in the row direction and Y pixels in the column direction, and the product of X and Y is N. 
     In some embodiments, the resolution of the image to be projected is 3840×2160 (3840 is a number of pixels in a horizontal direction and 2160 is a number of pixels in a vertical direction), that is, the amount of information stored in the image to be projected is 4K. The resolution of the projection display system  10  is 1920×1080, that is, the projection display system  10  displays an image with an amount of information of 1K. In this case, the digital micromirror device  150  in the projection display system  10  includes 1920×1080 micromirrors. As shown in  FIG. 5 , resolutions of the obtained sub-image A, sub-image B, sub-image C and sub-image D are all 1920×1080. 
     In some embodiments, as shown in  FIG. 6 , if the image to be projected includes K columns of pixels (K is an integer greater than or equal to 6), and N is 4, the control assembly  120  may obtain the sub-image A, the sub-image B, the sub-image C and the sub-image D as shown in  FIG. 7  according to the position information of the pixels in the image to be projected. 
     On the basis of the embodiments described above, in some examples, for a rotation signal in the optical path changing signal corresponding to the specified sub-image, the control assembly  120  determines the rotation direction and the rotation angle of the optical path changing device  130  according to the position of any pixel of the specified sub-image in a corresponding image block, and generates the rotation signal according to the rotation direction and rotation angle. 
     In some embodiments, the control assembly  120  is configured to pre-store a corresponding relationship between a position of any pixel of each sub-image in a corresponding image block and both the rotation direction and the rotation angle of the optical path changing device  130 . In a case where the specified sub-image is displayed, the control assembly  120  may determine the rotation direction and the rotation angle of the optical path changing device  130  according to a position of any pixel of the specified sub-image in the corresponding image block and the corresponding relationship. 
     For example, as shown in  FIGS. 6 and 7 , each pixel in the sub-image A is located at the first position in a corresponding image block, each pixel in the sub-image B is located at the second position in a corresponding image block, each pixel in the sub-image C is located at the third position in a corresponding image block, and each pixel in the sub-image D is located at the fourth position in a corresponding image block. 
     If the specified sub-image is the sub-image A, the control assembly  120  determines that the rotation direction of the optical path changing device  130  is a first rotation direction and the rotation angle is a first rotation angle according to the first position of each pixel of the sub-image A in the corresponding image block and the pre-stored corresponding relationship. If the specified sub-image is the sub-image B, the control assembly  120  determines that the rotation direction of the optical path changing device  130  is a second rotation direction and the rotation angle is a second rotation angle according to the second position of each pixel of the sub-image B in the corresponding image block and the pre-stored corresponding relationship. If the specified sub-image is the sub-image C, the control assembly  120  determines that the rotation direction of the optical path changing device  130  is a third rotation direction and the rotation angle is a third rotation angle according to the third position of each pixel of the sub-image C in the corresponding image block and the pre-stored corresponding relationship. If the specified sub-image is the sub-image D, the control assembly  120  determines that the rotation direction of the optical path changing device  130  is a fourth rotation direction and the rotation angle is a fourth rotation angle according to the fourth position of each pixel of the sub-image D in the corresponding image block and the pre-stored corresponding relationship. For example, the control assembly  120  may drive the optical path changing device  130  to rotate in a two-dimensional direction. The first rotation direction refers to a rotation to the upper left, the second rotation direction refers to a rotation to the upper right, the third rotation direction refers to a rotation to the lower left, and the fourth rotation direction refers to a rotation to the lower right. 
     Next, the control assembly  120  generates the rotation signal according to the rotation direction and the rotation angle. For example, if the specified sub-image is the sub-image A, the control assembly  120  generates a rotation signal according to the first rotation direction and the first rotation angle. 
     It will be noted that, in the process of displaying different sub-images, the digital micromirror signals sent by the control assembly  120  to the digital micromirror device  150  are different, and the rotation signals sent to the optical path changing device  130  are also different. 
     In the following, rotations of the optical path changing device  130  under control of the synchronization signals and the rotation signals during the display of the sub-image A, the sub-image B, the sub-image C and the sub-image D respectively are illustrated with reference to  FIG. 8 . 
     If the specified sub-image is the sub-image A, the control assembly  120  determines the rotation direction and the rotation angle of the optical path changing device  130  according to the position of a pixel of the sub-image A in a corresponding image block, and generates the rotation signal according to the rotation direction and the rotation angle. Then, the control assembly  120  sends a synchronization signal Vs and the rotation signal to the optical path changing device  130 . The optical path changing device  130  rotates during the time period t 1  under control of the synchronization signal Vs and the rotation signal, and then remains stationary during a time period t 2 . For example, the optical path changing device  130  reflects blue light towards the projection lens  160  after rotation. Then, the optical path changing device  130  remains stationary, and reflects the received light of primary colors other than the blue light toward the projection lens  160 , and so on, until light of the plurality of primary colors are reflected toward the projection lens  160 , thereby achieving display of the sub-image A. 
     After that, if the sub-image B is displayed, the control assembly  120  is configured to perform the above steps again, and in a time period t 3 , the control assembly  120  sends the synchronization signal Vs and the rotation signal to the optical path changing device  130  again, so that the optical path changing device  130  rotates under the control of the synchronization signal Vs and the rotation signal when the light of a primary color sent to the digital micromirror device  150  by the light source assembly  140  is changed into the light of the target primary color again, thereby realizing the display of the sub-image B. 
     If the sub-image C is displayed, the control assembly  120  is configured to perform the above steps again, and in a time period t 4 , the control assembly  120  sends the synchronization signal Vs and the rotation signal to the optical path changing device  130  again, so that the optical path changing device  130  rotates under the control of the synchronization signal Vs and the rotation signal when light of a primary color sent to the digital micromirror device  150  by the light source assembly  140  is changed into the light of the target primary color again, thereby realizing the display of the sub-image C. 
     If the sub-image D is displayed, the control assembly  120  is configured to perform the above steps again, and in a time period t 5 , the control assembly  120  sends the synchronization signal Vs and the rotation signal to the optical path changing device  130  again, so that the optical path changing device  130  rotates under the control of the synchronization signal Vs and the rotation signal when the light of a primary color sent to the digital micromirror device  150  by the light source assembly  140  is changed into the light of the target primary color again, thereby realizing the display of the sub-image D. The display of the image to be projected is finished. 
     For example, referring to  FIGS. 9 and 10 , in a case where the sub-image A and the sub-image C are displayed, the control assembly  120  drives the lower portion of the optical path changing device  130  to rotate forward and backward respectively, so that the later displayed sub-image C is located below the sub-image A. Referring to  FIGS. 11 and 12 , in a case where the sub-image B is displayed, the control assembly  120  may drive the left portion of the optical path changing device  130  to rotate forward after driving the lower portion of the optical path changing device  130  to rotate forward, so that the finally displayed sub-image B is located to the right of the sub-image A. In a case where the sub-image D is displayed, the control assembly  120  may drive the lower portion of the optical path changing device  130  to rotate backward after driving the left portion of the optical path changing device  130  to rotate forward, or drive the left portion of the optical path changing device  130  to rotate backward after driving the lower portion of the optical path changing device  130  to rotate backward, and then the displayed sub-image D is located below the sub-image B and to the right of the sub-image C. After the sub-image A, the sub-image B, the sub-image C, and the sub-image D are displayed, the image shown in  FIG. 13  may be obtained. 
     In some embodiments, referring to  FIG. 14 , the projection display system  10  further includes another driving assembly for driving the optical path changing device  130 , and the driving assembly includes an analog to digital converter (ADC)  181 , an amplifier  182 , a coil  183 , and a voltage dividing sub-module  184 . For example, the voltage dividing sub-module  184  includes and can be a resistor R. 
     In the embodiments, the control assembly  120  may send the synchronization signal Vs and a rotation signal S to the driving assembly. The synchronization signal Vs and the rotation signal S are converted into digital signals through the ADC  181 , and the converted rotation signal S is output to the amplifier  182  for amplification, so as to control the vibration of the coil  183  and further control the rotation of the optical path changing device  130 . The voltage dividing sub-module  184  may increase a threshold voltage input to the amplifier  182 , thereby enhancing an interference resistance of the amplifier  182 . 
     In some examples, in the process of displaying the plurality of sub-images, the decoding assembly  110  may send the decoded image to be projected to the control assembly  120  at a frequency of 60 hertz (Hz). The sub-images may be displayed at a frequency of N×60 Hz. For example, if N is 4, the sub-images may be displayed at a frequency of 240 Hz. 
     In summary, in the projection display system  10  provided by the embodiments of the present disclosure, since the image to be projected is divided into a plurality of sub-images, the digital micromirror device  150  may project all the pixels of the image to be projected. Compared with the digital micromirror device in the related art that may only project some of pixels in the image to be projected, the system does not lose pixel information and ensures the display effect of the displayed image. In addition, the low-resolution projection display system may also completely display all pixels of the high-resolution image to be projected, which improves the flexibility of the projection display system to display images. 
       FIG. 15  is a flow chart of a controlling method of a projection display system according to some embodiments of the present disclosure. The controlling method may be performed by the control assembly  120  in the projection display system  10  shown in  FIG. 1 . The projection display system  10  may further include an optical path changing device  130 , a light source assembly  140 , a digital micromirror device  150 , and a projection lens  160 . As shown in  FIG. 15 , the method may include steps  301  to  304 . 
     In step  301 , the control assembly  120  determines a light source control signal, a digital micromirror signal, and an optical path changing signal according to an image to be projected. 
     In some examples, as shown in  FIG. 1 , the projection display system  10  includes a decoding assembly  110 . During the process of displaying the image to be projected, the decoding assembly  110  may decode image information to obtain the image to be projected (i.e., the decoded image) and send the image to be projected to the control assembly  120 . The image to be projected may be any frame of image to be displayed in a video played by the projection display system  10 . In this way, the control assembly  120  may receive the image to be projected from the decoding assembly  110 . 
     In step  302 , the control assembly  120  sends the light source control signal to the light source assembly  140 . The light source control signal is used to control the light source assembly  140  to sequentially emit light of a plurality of primary colors to the digital micromirror device  150  according to a timing indicated by the light source control signal. 
     For example, the light source control signal is a control signal corresponding to a specified sub-image in a plurality of sub-images obtained by dividing the image to be projected. The specified sub-image is any sub-image among the plurality of sub-images. 
     In step  303 , the control assembly  120  sends the digital micromirror signal to the digital micromirror device  150 . The digital micromirror signal is used to control a plurality of micromirrors in the digital micromirror device  150  to rotate, so as to reflect effective light for imaging among the light of the plurality of primary colors to the optical path changing device  130 . 
     In step  304 , the control assembly  120  sends the optical path changing signal to the optical path changing device  130 . The optical path changing signal is used to control the optical path changing device  130  to rotate. 
     For example, the optical path changing signal includes a synchronization signal and a rotation signal. The synchronization signal is used for indicating a rotation moment of the optical path changing device  130 , and the rotation signal is used for indicating a rotation direction and a rotation angle of the optical path changing device  130 . The optical path changing device  130  rotates under control of the synchronization signal and the rotation signal to transmit or reflect the received light of a primary color to the projection lens  160 . 
     It will be noted that the sequence of steps of the controlling method of the projection display system in the embodiments of the present disclosure is not limited to the sequence of above  301  to  304 . For example, the controlling method of the projection display system performed, for example, by the control assembly  120 , may also include: first, determining the light source control signal according to the image to be projected, and sending the light source control signal to the light source assembly  140 ; second, determining the digital micromirror signal according to the image to be projected, and sending the digital micromirror signal to the digital micromirror device  150 ; finally, determining the optical path changing signal according to the image to be projected, and sending the optical path changing signal to the optical path changing device  130 . 
     In some embodiments, referring to  FIG. 16 , the step  301 , in which the light source control signal, the digital micromirror signal, and the optical path changing signal are determined according to the image to be projected, includes steps  401  to  403 . 
     In step  401 , the control assembly  120  determines whether the resolution of the image to be projected is greater than a preset resolution, and if so, step  402 , dividing the image to be projected into N sub-images, is performed, wherein N is an integer greater than or equal to 2. 
     For example, the preset resolution is a resolution of the projection display system  10 , and a resolution of each sub-image is less than or equal to the resolution of the projection display system  10 . For example, after receiving the image to be projected, the control assembly  120  obtains the resolution of the image to be projected, and determines whether the resolution of the image to be projected is greater than the resolution of the projection display system  10 . If the control assembly  120  determines that the resolution of the image to be projected is greater than the resolution of the projection display system  10 , the control assembly  120  divides the image to be projected into N sub-images to ensure that each micromirror of the digital micromirror device  150  in the projection display system  10  may project a pixel in each sub-image. 
     If the control assembly  120  determines that the resolution of the image to be projected is not greater than (e.g., less than or equal to) the resolution of the projection display system  10  (e.g., No in step  401 ), the image to be projected may be displayed directly based on step  404 . 
     In some embodiments, the step  402  includes: dividing the image to be projected into a plurality of image blocks, and selecting one pixel from each image block of the plurality of image blocks to form a sub-image to obtain N sub-images. A position of any pixel of the sub-image in a corresponding image block is the same as a position of another pixel of the sub-image in a corresponding image block. That is, in the N sub-images, each sub-image is composed of pixels at the same position in a plurality of image blocks into which the image to be projected is divided. In addition, two pixels of any two sub-images in a same image block have different positions in the image block. Relative positions of pixels included in the sub-image on the sub-image are the same as relative positions of the pixels on the image to be projected. Each image block includes N pixels. For example, each image block includes X pixels in the row direction and Y pixels in the column direction, and the product of X and Y is N. 
     In step  403 , the control assembly  120  determines the light source control signal, the digital micromirror signal, and the optical path changing signal according to each sub-image of the N sub-images. 
     Since the image to be projected is divided into a plurality of sub-images, the digital micromirror device may project all the pixels of the image to be projected. Compared with the digital micromirror device in the related art that may only project some of pixels in the image to be projected, the system does not lose pixel information and ensures the display effect of the displayed image. In addition, the low-resolution projection display system may also completely display all pixels of the high-resolution image to be projected, which improves the flexibility of the projection display system to display images. 
     In some embodiments, the optical path changing signal includes a synchronization signal and a rotation signal. Referring to  FIG. 17 , the controlling method further includes steps  501  and  502 . 
     In step  501 , a rotation direction and a rotation angle of the optical path changing device are determined according to a position of each pixel of the sub-image in the image block. 
     For example, the control assembly  120  pre-stores, in a storage such as a transitory computer readable medium or a non-transitory computer readable medium, a corresponding relationship between the position of any pixel of each sub-image in a corresponding image block and both the rotation direction and the rotation angle of the optical path changing device. In a case where the specified sub-image is displayed, the control assembly  120  may determine the rotation direction and the rotation angle of the optical path changing device according to the position of any pixel of the specified sub-image in the image block and the corresponding relationship. 
     In step  502 , the control assembly  120  generates a rotation signal according to the rotation direction and the rotation angle. 
     For example, the control assembly  120  generates the rotation signal according to the rotation direction and the rotation angle. The control assembly  120  sends the synchronization signal and the rotation signal to the optical path changing device  130  after generating the rotation signal, so that the optical path changing device  130  rotates under the control of the synchronization signal and the rotation signal and reflect the received light of a primary color to the projection lens  160 . The synchronization signal is used for indicating a rotation moment of the optical path changing device  130 , and the rotation signal is used for indicating the rotation direction and the rotation angle of the optical path changing device  130 . 
     In some examples, the synchronization signal is used to control the optical path changing device  130  to rotate during a period in which the optical path changing device  130  receives the light of the target primary color in the light of the plurality of primary colors. For example, the synchronization signal is used to control the optical path changing device  130  to rotate when the light of a primary color emitted by the light source assembly  140  is changed into the light of the target primary color. The light of the target primary color is, for example, blue light. Since the human eyes are not sensitive to blue, when the light of the primary color travelling to the digital micromirror device is blue light, the optical path changing device  130  is driven to rotate, and the human eyes do not obviously see the rotation of the optical path changing device  130 , which further ensures the display effect of images. 
     In some examples, the control assembly  120  may send the synchronization signal and the rotation signal to the optical path changing device  130 , so that the optical path changing device  130  rotates under control of the rotation signal when the light of a primary color sent from the light source assembly  140  to the digital micromirror device  150  is changed into the light of the target primary color, and then the optical path changing device  130  remains stationary. For example, the optical path changing device  130  reflects the received light of the target primary color to the projection lens  160  after rotation. Thereafter, when the light of the primary color sent to the digital micromirror device  150  by the light source assembly  140  becomes light of primary colors other than the light of the target primary color, the optical path changing device  130  remains stationary, and transmits or reflects the light of the primary colors other than the light of the target primary color toward the projection lens  160 , and so on until the light of the plurality of primary colors is transmitted through or reflected toward the projection lens  160  to achieve display of the specified sub-image. 
     Thereafter, the control assembly  120  performs the above steps again to display a next sub-image of the specified sub-image in the plurality of sub-images, and so on until the display of the N sub-images are completed, and the display of the image to be projected is finished. 
     It will be noted that the sequence of the steps of the controlling method of the projection display system provided by the embodiments of the present disclosure may be appropriately adjusted and the steps may be deleted according to circumstances. Any person skilled in the art could readily conceive of changes or replacements within the technical scope of the present disclosure, which shall all be included in the protection scope of the present disclosure, and will not be described in detail herein. 
     Some embodiments of the present disclosure provide a control device for projecting an image. The control device may be the control assembly  120  in the projection display system  10  shown in  FIG. 1 . The projection display system  10  may include the decoding assembly  110 , the optical path changing device  130 , the light source assembly  140 , the digital micromirror device  150 , and the projection lens  160  shown in  FIG. 1  The structure and function of the control device may be described with reference to the control assembly  120  in the above embodiments and will not be described in detail herein. 
     The beneficial effects of the control device of the projection display system provided by the embodiments of the present disclosure are the same as the beneficial effects of the control assembly described in any of the foregoing embodiments, and will not be described in detail herein. 
     Some embodiments of the present disclosure provide a projection display device. As shown in  FIG. 18 , the projection display device  60  includes a communication interface  601  and a processor  602 . The communication interface  601  is configured to receive an image to be projected. The processor  602  is configured to implement one or more steps in the controlling method of the projection display system as in any of the above embodiments. 
     For example, the above-mentioned projection display device is a projector, a holographic projector, a light projection television, or the like. 
     In some embodiments, as shown in  FIG. 18 , the projection display device  60  further includes a memory  603  that stores computer program instructions. The memory  603  is, for example, a computer-readable storage medium. In some examples, the memory  603  also pre-stores a corresponding relationship between the position of any pixel included in each sub-image in a corresponding image block and both the rotation direction and the rotation angle of the optical path changing device. In a case where the specified sub-image is displayed, the control assembly  120  may determine the rotation direction and the rotation angle of the optical path changing device according to the position of each pixel of the specified sub-image in the corresponding image block and the corresponding relationship. 
     Some embodiments of the present disclosure provide a computer-readable storage medium (e.g., a non-transitory computer-readable storage medium). The computer-readable storage medium stores computer program instructions that, when executed by a computer, cause the computer to perform one or more steps in the controlling method of the projection display system as in any of the embodiments described above. 
     For example, the computer-readable storage medium described above may include, but is not limited to: a magnetic storage device (e.g., a hard disk, a floppy disk, or a magnetic tape, etc.), a compact disk (CD) a digital versatile disk (DVD), a smart card and a flash memory device (e.g., an erasable programmable read-only memory (EPROM), a card, a stick or a key drive, etc.). The computer-readable storage mediums described in the embodiments of the present disclosure may represent one or more devices and/or other machine-readable storage mediums used to store information. The term “machine-readable storage medium” may include, but is not limited to, wireless channels and a plurality of other mediums capable of storing, containing, and/or carrying instruction(s) and/or data. 
     Some embodiments of the present disclosure provide a computer program product. The computer program product includes computer program instructions that, when run on a computer, cause the computer to perform one or more steps in the controlling method of the projection display system described in any of the embodiments described above. 
     Some embodiments of the present disclosure provide a computer program. When the computer program is executed on a computer, the computer program causes the computer to execute one or more steps in the controlling method of the projection display system described in any of the embodiments described above. 
     The beneficial effects of the projection display device, the computer-readable storage medium, the computer program product, and the computer program are the same as the beneficial effects of the controlling method of the projection display system in any of the embodiments described above, and will not be described in detail herein. 
     The above descriptions are merely exemplary implementation of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacement, improvements made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.