Patent Publication Number: US-2015084986-A1

Title: Compositor, system-on-chip having the same, and method of driving system-on-chip

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2013-0112791 filed on Sep. 23, 2013, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field 
     Exemplary embodiments in accordance with principles of inventive concepts relate to a compositor, and more particularly, to a hardware compositor. 
     2. Description of Related Art 
     A compositor combines visual elements from separate sources into a single image. An early example of compositing is the use in television broadcasting of “blue screen” to combine the image of a weatherman with that of a weather map, allowing the combined image to give the appearance of having the weatherman interact with the weather map. Compositing has evolved to a substantially digital process, employing computer-generated imagery. Such imagery may be used in any of a variety of applications, including, not only more conventional entertainment (for example, television broadcasting, motion pictures, animation, etc.) applications, but graphics used in computers, smart televisions, and entertainments systems for everything from word processing to computer gaming, to sophisticated simulation processes, to user interfaces in mobile electronic devices. As such applications have increased in complexity, more and more image layers may be incorporated in a single image, each image may be increasingly complex and of greater resolution, and management of all image components from a variety of applications and user interfaces has become a daunting task. Processors referred to as hardware compositors may be employed to accelerate the compositing process. Such compositors may be two-dimensional or three-dimensional (that is, may be employed to produce two- or three-dimensional images), and may employ a variety of technologies, including hardware, firmware, software, application specific, graphics processing, digital signal processing, or other technologies, for example. 
     Conventional compositors typically compose a single image by operating on two image layers to produce a resultant image (for example, combing a weatherman and weather map). In order to compose an image having more than two image layers (think of adding an exterior storm shot, for example) such a compositor must repeat the process for each additional image layer. 
     SUMMARY 
     Exemplary embodiments in accordance with principles of inventive concepts provide a compositor capable of generating an intermediate image based on update information regarding each of a plurality of image layers, and generating a resultant image using the intermediate image. 
     Exemplary embodiments in accordance with principles of inventive concepts also provide a system-on-chip (SoC) including the compositor and a method of driving the SoC. 
     Exemplary embodiments in accordance with principles of inventive concepts also provide a mobile device including the SoC. 
     The technical objectives of the inventive concept are not limited to the above disclosure; other objectives may become apparent to those of ordinary skill in the art based on the following descriptions. 
     In accordance with an aspect of the inventive concept, a compositor includes a sorter configured to sort first, second, and third image layers based on update information thereof and select the first and second image layers according to a result of sorting the first to third image layers; and an intermediate image generator configured to generate an intermediate image by performing composition on the selected first and second image layers. 
     In exemplary embodiments, the compositor may further include a resultant image generator configured to generate a resultant image by performing composition on the intermediate image and the third image layer. 
     In exemplary embodiments, the intermediate image generator generates the intermediate image in consideration of an alpha blending rule. 
     In exemplary embodiments, the intermediate image generator does not generate the intermediate image when the first and second image layers satisfy the alpha blending rule. 
     In exemplary embodiments, the update information may include information indicating whether the first to third image layers are updated; update rates of the first to third image layers; or a composition rule. 
     In exemplary embodiments, the update rates may include information regarding frames per second (FPS). 
     In exemplary embodiments, an FPS of each of the first and second image layers may be less than an FPS of the third image layer. 
     In exemplary embodiments, the composition rule may include a blend function. 
     In exemplary embodiments, the composition may include blending. 
     In accordance with another aspect of the inventive concept, a system-on-chip (SoC) includes a compositor configured to sort first to third image layers based on update information thereof, select the first and second image layers according to a result of sorting the first to third image layers, generate an intermediate image by performing composition on the selected first and second image layers, and generate a resultant image by performing composition on the intermediate image and the third image layer; and a memory configured to store the resultant image generated by the compositor. 
     In exemplary embodiments, the compositor generates the intermediate image in consideration of an alpha blending rule, and does not generate the intermediate image when the first and second image layers satisfy the alpha blending rule. 
     In exemplary embodiments, the update information may include information indicating whether the first to third image layers are updated; update rates of the first to third image layers; or a composition rule. 
     In exemplary embodiments, the update rate may include information regarding frames per second (FPS), and an FPS of each of the first and second image layers may be less than an FPS of the third image layer. 
     In exemplary embodiments, the composition rule may include a blend function. 
     In accordance with another aspect of the inventive concept, a mobile device includes a system-on-chip (SoC), and a display device configured to receive the resultant image from the memory and display the resultant image thereon. The SoC includes a compositor configured to sort first to third image layers based on update information thereof, select the first and second image layers according to a result of sorting the first to third image layers, generate an intermediate image by performing composition on the selected first and second image layers, and generate a resultant image by performing composition on the intermediate image and the third image layer; and a memory configured to store the resultant image generated by the compositor; and 
     In exemplary embodiments, the compositor may generate the intermediate image in consideration of an alpha blending rule, and may not generate the intermediate image when the first and second image layers satisfy the alpha blending rule. 
     In exemplary embodiments, the update information may include information indicating whether the first to third image layers are updated; update rates of the first to third image layers; and a composition rule. 
     In exemplary embodiments, the update rate may include information regarding frames per second (FPS), and an FPS of each of the first and second image layers may be less than an FPS of the third image layer. 
     In exemplary embodiments, the compositor may decrease a bandwidth of the SoC by reading the intermediate image. 
     In accordance with another aspect of the inventive concept, a method of driving a system-on-chip (SoC) includes sorting first to third image layers based on update information thereof, and generating an intermediate image by performing composition on the first and second image layers, based on a result of sorting the first to third image layers. 
     In exemplary embodiments, the method may further include generating a resultant image by performing composition on the intermediate image and the third image layer. 
     In exemplary embodiments, the sorting of the first to third image layers based on the update information thereof may include sorting the first to third image layers based on information indicating whether the first to third image layers are updated, update rates of the first to third image layers, and a composition rule. 
     In exemplary embodiments, the sorting of the first to third image layers based on the update information thereof may include selecting the first and second image layers 
     In exemplary embodiments, the generating of the intermediate image may include generating the intermediate image in consideration of an alpha blending rule. In exemplary embodiments, the method may further include preventing the intermediate image from being generated when the first and second image layers satisfy the alpha blending rule. In exemplary embodiments, the method may further include storing the resultant image in a memory, and transmitting the resultant image from the memory to a display device. 
     A compositor in accordance with principles of inventive concepts may include a sorter configured to sort a plurality of image layers based on update information thereof and select first and second image layers according to a result of sorting the first to third image layers; and an intermediate image generator configured to generate an intermediate image by performing composition on the selected first and second image layers. 
     A compositor in accordance with principles of inventive concepts may include a resultant image generator configured to generate a resultant image by performing composition on the intermediate image and the third image layer. 
     A compositor in accordance with principles of inventive concepts may include an intermediate image generator, wherein the intermediate image generator generates the intermediate image according to an alpha blending rule. 
     A compositor in accordance with principles of inventive concepts may include intermediate image generator wherein the intermediate image generator does not generate an intermediate image when the first and second image layers satisfy the alpha blending rule. 
     In accordance with principles of inventive concepts update information comprises any one of: information indicating whether any image layers are updated; update rates of the image layers; and a composition rule. 
     In accordance with principles of inventive concepts update rates comprise information regarding frame per second (FPS). 
     In accordance with principles of inventive concepts FPS of each of the selected image layers is less than an FPS of the remaining image layer. 
     In accordance with principles of inventive concepts a composition rule comprises a blend function. 
     In accordance with principles of inventive concepts a composition comprises blending. 
     In accordance with principles of inventive concepts a system-on-chip (SoC) includes a compositor configured to sort a plurality of image layers based on update information thereof, select a subset of the layers according to a result of sorting the image layers, generate an intermediate image by performing composition on the selected image layers, and generate a resultant image by performing composition on the intermediate image and a remaining image layer; and a memory configured to store the resultant image generated by the compositor. 
     In accordance with principles of inventive concepts a compositor generates the intermediate image in consideration of an alpha blending rule, and does not generate the intermediate image when the selected image layers satisfy the alpha blending rule. 
     In accordance with principles of inventive concepts the update information comprises any one of: information indicating whether the selected image layers are updated; update rates of the image layers; and a composition rule. 
     In accordance with principles of inventive concepts the update rate comprises information regarding frame per second (FPS), wherein the FPS of each of the selected image layers is less than the FPS of the remaining image layer. 
     In accordance with principles of inventive concepts the composition rule comprises a blend function. 
     In accordance with principles of inventive concepts a mobile device includes a system-on-chip (SoC) that includes a compositor configured to sort a plurality of image layers based on update information thereof, select a subset of the image layers according to a result of sorting the image layers, generate an intermediate image by performing composition on the selected image layers, and generate a resultant image by performing composition on the intermediate image and a remaining image layer; and a memory configured to store the resultant image generated by the compositor; and a display device configured to receive the resultant image from the memory and display the resultant image thereon. 
     In accordance with principles of inventive concepts a compositor generates the intermediate image in consideration of an alpha blending rule, and does not generate the intermediate image when the selected image layers satisfy the alpha blending rule. 
     In accordance with principles of inventive concepts update information comprises any one of: information indicating whether the selected image layers are updated; update rates of the image layers; and a composition rule. 
     In accordance with principles of inventive concepts the update rate comprises information regarding frame per second (FPS), wherein the FPS of each of the selected image layers is less than the FPS of the third image layer. 
     In accordance with principles of inventive concepts the compositor decreases a bandwidth required of the SoC by reading the intermediate image. 
     In accordance with principles of inventive concepts a method of a system on a chip includes sorting a plurality of image layers based on update information thereof; selecting a subset of the image layers according to a result of the sorting; and generating an intermediate image by performing composition on the selected image layers. 
     A method in accordance with principles of inventive concepts includes generating a resultant image by performing composition on the intermediate image and a remaining image layer. 
     In accordance with principles of inventive concepts the sorting of image layers based on the update information thereof comprises sorting the image layers based on information indicating whether the image layers are updated, update rates of the image layers, and a composition rule. 
     In accordance with principles of inventive concepts the generating of the intermediate image comprises generating the intermediate image in consideration of an alpha blending rule. 
     A method in accordance with principles of inventive concepts includes preventing the intermediate image from being generated when the selected image layers satisfy the alpha blending rule. 
     A method in accordance with principles of inventive concepts includes storing the resultant image in a memory; and transmitting the resultant image from the memory to a display device. 
     An apparatus in accordance with principles of inventive concepts includes a processor configured to receive a plurality of image layers; the processor configured to composite a subset of the plurality of image layers to form an intermediate image; and the processor configure to composite the intermediate image and a remaining image layer to form a resultant image frame. 
     An apparatus in accordance with principles of inventive concepts a processor is configured to select the subset of the plurality of image layers with which to form the intermediate image based on the frame rates of the associated image layers. 
     An apparatus in accordance with principles of inventive concepts the processor is configured to select image layers having frame rates below a threshold value for compositing the intermediate image. 
     An apparatus in accordance with principles of inventive concepts the processor is configured to form an intermediate image layer according to a blending rule. 
     In accordance with principles of inventive concepts a smartphone includes a processor configured to receive a plurality of image layers; the processor configured to composite a subset of the plurality of image layers to form an intermediate image; and the processor configure to composite the intermediate image and a remaining image layer to form a resultant image frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the inventive concepts will be apparent from the more particular description of preferred exemplary embodiments in accordance with principles of inventive concepts, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the inventive concepts. In the drawings: 
         FIG. 1  is a block diagram of a mobile device in accordance with principles of inventive concepts; 
         FIG. 2  is a block diagram of a conventional compositor; 
         FIGS. 3A and 3B  are conceptual diagrams illustrating composition operations of the conventional compositor of  FIG. 2 ; 
         FIGS. 4A to 4C  are conceptual diagrams illustrating operations of the conventional compositor of  FIG. 2 ; 
         FIGS. 5A and 5B  are block diagrams of compositors in accordance with principles of inventive concepts; 
         FIG. 6  is a detailed block diagram of the compositor illustrated in  FIG. 5A ; 
         FIGS. 7A to 7C  illustrate a first image layer to a third image layer, respectively; 
         FIGS. 8A to 8C  are conceptual diagrams illustrating operations of the compositor of  FIG. 5A ; 
         FIG. 9  is a conceptual diagram illustrating driving of a compositor in accordance with principles of inventive concepts; 
         FIG. 10  illustrates a result of driving the compositor of  FIG. 9 ; 
         FIGS. 11A and 11B  are conceptual diagrams illustrating composition performed according to an alpha blending rule; 
         FIG. 12  is a flowchart illustrating a method of driving a compositor in accordance with principles of inventive concepts; 
         FIG. 13  is a block diagram of a computer system including a compositor illustrated in  FIG. 1  in accordance with principles of inventive concepts; 
         FIG. 14  is a block diagram of a computer system including the compositor of  FIG. 1  in accordance with another embodiment of the inventive concept; and 
         FIG. 15  is a block diagram of a computer system including the compositor of  FIG. 1  in accordance with another embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. Exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough, and will convey the scope of exemplary embodiments to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The teen “or” is used in an inclusive sense unless otherwise indicated. 
     It will be understood that, although the terms first, second, third, for example. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. In this manner, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of exemplary embodiments. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. In this manner, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of exemplary embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized exemplary embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. In this manner, exemplary embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. In this manner, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of exemplary embodiments. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which exemplary embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, exemplary embodiments in accordance with principles of inventive concepts will be explained in detail with reference to the accompanying drawings. 
     When an embodiment in accordance with principles of inventive concepts may be accomplished in different ways, a function or an operation specified in a particular block may be performed in an order that is different from that illustrated in a flowchart. For example, functions or operations specified in continuous two blocks may be actually substantially simultaneously performed or may be performed in a reverse order according to a related function or operation. 
     A compositor produces an image that combines image layers, each of which may have a different update rate. A moving weatherman in one image layer may be updated much more frequently than a relatively static weather map in another image layer or an external weathercam image from another image layer, for example. A compositor may employ a composition rule, such as a blend function. A blend function may control various mixing factors when image layers are overlapped. A blend function may include a variety of modes, such as a normal blend mode, a dissolve mode, multiply, screen, overlay, hard light, soft light, dodge and burn, arithmetic blend modes, including: divide, add, subtract, difference, darken only, lighten only, Boolean blend modes, a color burn mode, and a linear burn mode, for example. Blend modes are known and described, for example, at: http://en.wikipedia.org/wiki/Blend_modes. 
     Exemplary embodiments of a compositor in accordance with principles of inventive concepts may consider one or more image layer update rates in the process of compositing. For example, such a compositor may generate an intermediate image from a plurality of image layers of relatively low update rates and generate a resultant image from the intermediate image and a relatively high update-rate image layer. By compositing an intermediate image at a relatively low rate and then compositing the intermediate image with another, higher-rate image layer, a compositor in accordance with principles of inventive concepts may reduce overhead and increase bandwidth. An exemplary embodiment of a compositor in accordance with principles of inventive concepts will be described with reference to  FIGS. 5A to 12  below. 
     In exemplary embodiments of a system-on-chip (SoC) and a method of driving the same a compositor is employed in accordance with principles of inventive concepts. Exemplary embodiments of a SoC and a method of driving the same will be described with reference to  FIGS. 1 and 12  below. 
       FIG. 1  is a block diagram of an exemplary embodiment of a mobile device  1  in accordance with principles of inventive concepts. Mobile device  1  may include a SoC  10  and a display device  20 . In exemplary embodiments mobile device  1  may include a smart-phone, a tablet personal computer (PC), a net-book, an e-reader, a personal digital assistant (PDA), a portable multimedia player (PMP), etc. 
     The SoC  10  may include a compositor  11  configured to perform composition on a plurality of image layers, and a frame buffer/on-screen-display (OSD)  12  configured to store a result of performing composition on the plurality of image layers, the result may also referred to herein as a “composition,” “composite image,” or “composed image.” In exemplary embodiments, frame buffer/OSD  12  transmits a final composite image, also referred to herein as a resultant image, to the display device  20 . The frame buffer/on-screen-display (OSD)  12  may be embodied using a memory. That is, the memory may be used as a frame buffer. 
     In exemplary embodiments in accordance with principles of inventive concepts, compositor  11  may select one or more of a plurality of received image layers and generates an intermediate image using the selected images, with the selection of image layers based, for example, on update information related to the layers. For example, image layers with relatively low update rates (that is, those in which images are relatively static) may be combined to form an intermediate image, or image layer. The intermediate image may then be combined with a relatively high update rate image layer to produce another image, which may be the ultimate, resultant image, or another intermediate image layer, for example. By producing intermediate image layers only so often as is required by the update rates of slower-update image layers (the faster of two slower update rates, for example) and compositing the thus-formed intermediate image with a higher update-rate image layer, at the rate required by that higher update-rate layer a compositor in accordance with principles of inventive concepts avoids substantial processing that would otherwise be performed if, for example, every image layer, including the lower update-rate layers, were composited at the rate of the highest update-rate image layer. The compositor  11  may use an intermediate image to generate a resultant image. 
     Compositor  11  in accordance with principles of inventive concepts may avoid generating an intermediate image according to an alpha blending rule. An alpha blending rule may be a rule related to the combination of an alpha channel with other layers in an image in order to show translucency, for example. In accordance with principles of inventive concepts, because the compositor  11  may generate a resultant image from an intermediate image, the number of times that each of the plurality of image layers is read and composited may be reduced and, as a result, the bandwidth of the SoC  10  in accordance with principles of inventive concepts may be improved. Compositor  11  in accordance with principles of inventive concepts will be described with reference to  FIGS. 5A to 12  below. A conventional compositor  110  will described with reference to  FIGS. 2 to 4C  below in order to better illustrate some differences that may be employed by a compositor in accordance with principles of inventive concepts. 
       FIG. 2  is a block diagram of a conventional compositor  110 , which receives first to third image layers IL 1  to IL 3  and performs composition on the first to third image layer IL 1  to IL 3  to generate a resultant image. That is, all image layers are employed to form a composite image at the rate required by the highest update-rate of all the image layers IL 1  to IL 3 . 
     The term composition may be used herein to mean, in this context, arranging the first to third image layers IL 1  to IL 3  in a predetermined order. For example, the conventional compositor  110  may arrange the first to third image layers IL 1  to IL 3  such that the second image layer IL 2 , the third image layer IL 3 , and the first image layer IL 1  are sequentially disposed. Composition may include blending, which refers to determining the way that an upper image layer and a lower image layer are viewed in an overlapping manner. That is, blending means changing the way that image layers are viewed without “causing damage to,” eliminating, or completely obstructing the image layers or portions thereof. 
     The conventional compositor  110  receives and employs all image layers each time a resultant image is generated. 
       FIGS. 3A and 3B  are conceptual diagrams illustrating composition operations of the conventional compositor  110  of  FIG. 2 . 
     Referring to  FIG. 3A , the conventional compositor  110  performs composition on a first image layer IL 1  and a second image layer IL 2 . For example, if it is assumed that the first image layer IL 1  is located above (in the sense of being closer to the viewer of the image) the second image layer IL 2 , the conventional compositor  110  generates a first resultant image R 1 , with a portion of image IL 1  obstructing a portion of image layer IL 2 , as would occur if the object of image layer IL 1  were lain on top of (“above”) image layer IL 2 . 
     Referring to  FIG. 3B , the conventional compositor  110  performs composition on the first image layer IL 1  and the second image layer IL 2 . For example, if it is assumed that the first image layer IL 1  is located below (in the sense of being farther from the view of the image) the second image layer IL 2 , the conventional compositor  110  generates a second resultant image R 2 . 
       FIGS. 4A to 4C  are conceptual diagrams illustrating operations of the conventional compositor  110  of  FIG. 2 . 
       FIG. 4A  illustrates an operation of the conventional compositor  110  during a period of a first frame.  FIG. 4B  illustrates an operation of the conventional compositor  110  during a period of a second frame.  FIG. 4C  illustrates an operation of the conventional compositor  110  during a period of a third frame. Each frame may, for example, be a frame for display in sequence to thereby form the illusion of motion, as in motion pictures, for example. 
     Referring to  FIG. 4A , the conventional compositor  110  receives first to third image layers IL 1  to IL 3  during the period of the first frame then generates a first resultant image R 1  using the received first to third image layers IL 1  to IL 3 . During the period of the first frame, the conventional compositor  110  reads the three image layers IL 1  to IL 3  and writes one resultant image R 1 . 
     Referring to  FIG. 4B , the conventional compositor  110  receives first to third image layer IL 1  to IL 3  during the period of the second frame then generates a second resultant image R 2  using the received first to third image layers IL 1  to IL 3 . During the period of the second frame, the conventional compositor  110  reads the three image layers IL 1  to IL 3  and writes one resultant image R 2 . 
     Referring to  FIG. 4C , the conventional compositor  110  receives first to third image layers IL 1  to IL 3  during the period of the third frame then generates a third resultant image R 3  from the first to third image layers IL 1  to IL 3 . During the period of the third frame, the conventional compositor  110  reads the three image layers IL 1  to IL 3  and writes one resultant image R 3 . 
     Referring to  FIGS. 4A to 4C , in this example, the conventional compositor  110  reads nine image layers and writes three resultant images during the periods of the first through third frames. 
       FIGS. 5A and 5B  are block diagrams of exemplary embodiments of compositors in accordance with principles of inventive concepts. Compositor  11  in accordance with principles of inventive concepts may consider one or more image layer update rates in the process of compositing. For example, such a compositor may generate an intermediate image from a plurality of image layers of relatively low update rates and generate a resultant image from the intermediate image and a relatively high update-rate image layer. By compositing an intermediate image at a relatively low rate and then compositing the intermediate image with another, higher-rate image layer, a compositor in accordance with principles of inventive concepts may reduce overhead and increase bandwidth. In an exemplary embodiment employing three image layers, compositor  11  in accordance with principles of invent receives first to third image layers IL 1  to IL 3 . The compositor  11  sorts the first to third image layers IL 1  to IL 3  according to update information thereof. In exemplary embodiment, the update information of each of the first to third image layers IL 1  to IL 3  may include information indicating whether each of the first to third image layers IL 1  to IL 3  is updated, an update rate of the each of the first to third image layers Il 1  to IL 3 , or a composition rule. 
     The compositor  11  selects at least two image layers based on a result of sorting the first to third image layers IL 1  to IL 3 . For example, when the first to third image layers IL 1  to IL 3  are sorted according to the update rates (i.e., update speeds) thereof, the compositor  11  may generate an intermediate image IM by performing composition on two image layers of relatively low update rates among the first to third image layers IL 1  to IL 3 . Then the compositor  11  may generate a resultant image R by performing composition on the intermediate image IM and the other image layer of a highest update rate. In accordance with principles of inventive concepts, the compositing of the plurality of lower update-rate image layers may be performed at a rate that satisfies requirements for the highest update rate of those layers, which rate may still be lower than that of the highest overall update rate. The intermediate image layer may then be composited with the highest update rate image layer(s) to produce resultant images at the rate required for such image layer 
     In exemplary embodiments, the update rate includes information regarding a frame per second (FPS) and, in accordance with principles of inventive concepts, a composition rule may include a blend function. A blend function may control various mixing factors when image layers are overlapped. A blend function may include a variety of modes, such as a normal blend mode, a dissolve mode, multiply, screen, overlay, hard light, soft light, dodge and burn, arithmetic blend modes, including: divide, add, subtract, difference, darken only, lighten only, Boolean blend modes, a color burn mode, and a linear burn mode, for example. 
     The blend function is a function of producing various effects by controlling various mixing factors when image layers overlap. For example, the blend function may include a normal mode in which mixed image layers are directly displayed, a dissolved mode in which an image is displayed by dividing the image in units of pixels and a pixel that is to be displayed is randomly selected among blend pixels and base pixels, a darken mode in which a color that is lighter than blend colors is replaced with another color and a color that is darker than a blend colors is not replaced with another color, a multiply mode in a blend color and a base color are expressed by multiplying them, a color burn mode in which a base color is controlled to be darker and a blend color is reflected by increasing a contrast, and a linear burn mode in which a base color is controlled to be darker and a blend color is reflected by decreasing brightness, etc. 
     For example, if the first image layer IL 1  has 1 FPS, the second image layer IL 2  has 20 FPS, and the third image layer IL 3  has 60 FPS, the compositor  11  generates an intermediate image IM using the first and second image layers IL 1  and IL 2  at a rate of 20 FPS (or at a slightly higher rate, 21 FPS, for example, in order to provide margin). The compositor  11  generates the resultant image R by compositing the intermediate image IM and the third image layer IL 3  at a rate of 60 FPS. A compositor  11  reads image layer Il 1  once per second, reads image layer IL 2  twenty times per second and composites the two layers twenty times per second to form an intermediate layer twenty times per second. Then it reads intermediate layer twenty times per second and image layer IL 3  sixty times per second and composites the two layers to form resultant images sixty times per second. In contrast, a conventional compositor  110  generates a resultant image, using all layers each time, at the highest image layer update rate. For example, if the first image layer IL 1  has 1 FPS, the second image layer IL 2  has 20 FPS, and the third image layer IL 3  has 60 FPS, the conventional compositor  110  reads each of the first to third image layers IL 1  to IL 3  sixty times per second and composites all layers to form a resultant image layer sixty times per second. 
     In contrast, the compositor  11  in accordance with principles of inventive concepts generates the intermediate image IM using image layers, the update rates of which are less than a threshold value, e.g., 21 FPS (as previously indicated, although the highest frame update rate of the lower update rate image layers is 20 FPS, one or more additional compositing operations may be executed per frame, for margin). Because the compositor  11  generates the resultant image R using the intermediate image IM, the number of times that the first and second image layers IL 1  and IL 2  are read may be relatively low and, as a result, the bandwidth required of a compositor  11  in accordance with principles of inventive concepts may be reduced and performance increased. Exemplary embodiments of a compositor  11  in accordance with principles of inventive concepts will be described in greater detail with reference to  FIG. 6  below. 
     Referring to  FIG. 5B , a compositor  11  in accordance with principles of inventive concepts may receive N image layers IL 1  to ILN and may generate M intermediate images IM 1  to IMM using a plurality of the N image layers IL 1  to ILN. In exemplary embodiments in accordance with principles of inventive concepts, the compositor  11  may be embodied as one functional block included in an application processor. Additionally, a compositor  11  in accordance with principles of inventive concepts may be embodied as one semiconductor chip that constitutes a mobile electronic device, such as a mobile phone, smartphone, tablet computer, or notebook computer, for example. 
       FIG. 6  is a detailed block diagram of an exemplary embodiment of compositor  11  illustrated in  FIG. 5A . Compositor  11  may include a sorter  111 , an intermediate image generator  112 , and a resultant image generator  113 . 
     The sorter  111  selects image layers to be used to generate an intermediate image IM, based on an update rate of each image layer (first to third image layers IL 1  to IL 3  in this exemplary embodiment), whether each of first to third image layers IL 1  to IL 3  is updated, and a composition rule. In exemplary embodiments, the sorter  111  may be embodied as hardware, software, firmware, or a combination, such as software employed by a processor, for example, the ARM™ processor. 
     In accordance with principles of inventive concepts a compositor may employ image layers having update rates less than a threshold update rate to produce an intermediate image. For example, when image layers are selected based on the update rate of each of first to third image layers IL 1  to IL 3 , the sorter  111  arbitrarily sets a threshold value to 21 FPS. With the first image layer IL 1  at 1 FPS, the second image layer IL 2  at 20 FPS, and the third image layer IL 3  at 60 FPS, sorter  111  selects the first and second image layers IL 1  and IL 2 , the FPSs of which are less than the threshold value to generate an intermediate image IM. 
     The intermediate image generator  112  generates the intermediate image IM using the first and second image layers IL 1  and IL 2  selected by the sorter  111 . The resultant image generator  113  generates a resultant image R by performing composition on the intermediate image IM and the third image layer IL 3 . 
       FIGS. 7A to 7C  illustrate a first image layer IL 1  to a third image layer IL 3 , respectively. 
     Referring to  FIG. 7A , the first image layer IL 1  in this exemplary embodiment is a status bar indicating the state of a mobile device. The status bar represents time information, the sensitivity of a transmission/reception signal, battery state information, etc. Thus, an update rate of the status bar may be relatively low. If the first image layer IL 1  representing the status bar is updated by one frame for a second, the first image layer IL 1  has an update rate of 1 FPS. 
     Referring to  FIG. 7B , the second image layer IL 2  in this exemplary embodiment is a background image of the mobile device. Examples of the background image may include a still image, a moving wallpaper image, etc. In general, the update rate of the moving wallpaper image may be lower than a video reproducing speed. If the second image layer IL 2  is updated by 20 frames for a second, the second image layer IL 2  has an update rate of 20 FPS. 
     Referring to  FIG. 7C , the third image layer IL 3  in this exemplary embodiment is video displayed on a screen of the mobile device. If the video is updated by 60 frames for a second, the third image layer IL 3  has an update rate of 60 FPS. 
       FIGS. 8A to 8C  are conceptual diagrams illustrating operations of exemplary embodiments compositor  11  in accordance with principles of inventive concepts of  FIG. 5A .  FIG. 8A  illustrates an operation of the compositor  11  during a period of a first frame.  FIG. 8B  illustrates an operation of the compositor  11  during a period of a second frame.  FIG. 8C  illustrates an operation of the compositor  11  during a period of a third frame. 
     Referring to  FIG. 8A , during the period of the first frame, the compositor  11  receives first to third image layers IL 1  to IL 3 . The compositor  11  generates an intermediate image IM and a first resultant image R 1  using the first to third image layers IL 1  to IL 3 . During the period of the first frame, the compositor  11  reads the three image layers IL 1  to IL 3  and writes one resultant image R 1  and one intermediate image IM. 
     Referring to  FIG. 8B , during the period of the second frame, the compositor  11  receives the intermediate image IM and the third image layer IL 3 . The compositor  11  generates a second resultant image R 2  using the intermediate image IM and the third image layer IL 3 . During the period of the second frame, the compositor  11  reads the two images, IM and IL 3 , and writes one resultant image R 2 . 
     Referring to  FIG. 8C , during the period of the third frame, the compositor  11  receives the intermediate image IM and the third image layer IL 3 . The compositor  11  generates a third resultant image R 3  using the intermediate image IM and the third image layer IL 3 . During the period of the third frame, the compositor  11  reads the two image layers, IM and IL 3 , and writes one resultant image R 3 . 
     Referring to  FIGS. 1 and 8A  to  8 C, the compositor  11  reads seven image layers and writes four resultant images during the periods of the first to third frames. As illustrated by this example, the compositor  11  in accordance with principles of inventive concepts may decrease the number of times that the image layers IL 1  to IL 3  are read (during the periods of the three frames in this exemplary embodiment). Additionally, the greater the number of frames, the greater the savings in the number of image layers read by the compositor  11 . Accordingly, the bandwidth required of the SoC  10  of the compositor  11  may be reduced. 
       FIG. 9  is a conceptual diagram illustrating driving of a compositor in accordance with principles of inventive concepts. 
     In this exemplary embodiment first image layer IL 1  is a status bar having an update rate of 1 FPS, a second image layer IL 2  is a moving background image having an update rate of 20 FPS, and a third image layer IL 3  is video having an update rate of 60 FPS. 
     The compositor  11  sorts the first to third image layers IL 1  to IL 3  according to a threshold value. If it is assumed that the threshold value is 21 FPS, the compositor  11  selects the first and second image layers IL 1  and IL 2 , the FPSs of which are less than threshold value to composite an intermediate image IM. The compositor  11  generates the intermediate image IM using the first and second image layers IL 1  and IL 2 . Additionally, the compositor  11  generates a resultant image R using the intermediate image IM and the third image layer IL 3 . 
       FIG. 10  illustrates a result of driving the compositor  11  of  FIG. 9 . 
     Referring to  FIGS. 1 and 10 , the mobile device  1  includes the SoC  10  including the compositor  11 . The compositor  11  generates a resultant image R by performing composition on first to third image layers IL 1  to IL 3 . The mobile device  1  displays the resultant image R on a screen thereof. 
     The mobile device  1  is capable of decreasing a bandwidth thereof by reducing the number of times that image layers are to be read. Accordingly, a decrease in the bandwidth dedicated to compositing by the mobile device  1  may result in an improvement in the performance of the mobile device  1 . 
       FIGS. 11A and 11B  are conceptual diagrams illustrating composition performed according to an alpha blending rule. Alpha blending is a general method used to mix two images, in which the two images are mixed at an appropriate degree such that these images are viewed in an overlapping manner. 
     Referring to  FIG. 11A , a compositor  11  performs composition on a first image layer IL 1  and a second image layer IL 2 . For example, if it is assumed that the first image layer IL 1  is located above, or, in front of, the second image layer IL 2 , the compositor  11  generates a first intermediate image IM 1 . 
     Referring to  FIG. 11B , the compositor  11  performs composition on the first image layer IL 1  and the second image layer IL 2 . For example, if it is assumed that the first image layer IL 1  is located below, or, behind, the second image layer IL 2 , the conventional compositor  110  generates a second intermediate image IM 2 . 
     That is, when the second image layer IL 2  is located above the first image layer ILL and the second image layer IL 2  would totally obstruct the first image layer ILL the second intermediate image IM 2  need not be generated. Thus, the compositor  11  in accordance with principles of inventive concepts generates the intermediate image IM in consideration of the alpha blending rule (e.g., the relationship between the locations of the first and second image layers IL 1  and IL 2 ). 
     For example, when the first and second image layers IL 1  and IL 2  used to generate the intermediate image IM satisfy the alpha blending rule in a manner in which one of the layers would be totally obstructed, the compositor  11  does not generate the intermediate image IM, or may use the image layer IL 2  as the intermediate image IM. 
       FIG. 12  is a flowchart illustrating a method of driving a compositor in accordance with principles of inventive concepts. 
     Referring to  FIGS. 9 and 12 , in operation S 11 , the compositor  11  may sort a plurality of image layers according to update information (e.g., update rates) thereof. 
     In exemplary embodiments, the update rates may be set in the unit of a frame per second (FPS). For example, when a first image layer IL 1  is an upper status bar, an update rate of the first image layer IL 1  may be 1 FPS. When a second image layer IL 2  is a moving background image, an update rate of the second image layer IL 2  may be 20 FPS. When a third image layer IL 3  is video, an update rate of the third image layer IL 3  may be 60 FPS. 
     In operation S 12 , the compositor  11  determines whether the update rates of the first to third image layers IL 1  to IL 3  are less than a threshold value. Image layers, the update rates of which are less than the threshold value among the first to third image layers IL 1  to IL 3 , are processed in operation S 13 . When the update rate of any one of the first to third image layers IL 1  to IL 3  is not less than the threshold value, operation S 15  is performed. 
     In operation S 13 , the compositor  11  determines whether image layers, the update rates of which are less than the threshold value satisfy the alpha blending rule; in particular, in exemplary embodiments in accordance with principles of inventive concepts, an alpha blending rule in which one layer may be obscured by another when composited. Operation S 15  is performed when these layers satisfy the alpha blending rule, and operation S 14  is performed when these layers do not satisfy the alpha blending rule. 
     In operation S 14 , the compositor  11  generates an intermediate image IM using the image layers, the update rates of which are less than the threshold value. For example, when the threshold value is set to 21 FPS, the compositor  111  may generate the intermediate image IM by performing composition on the first image layer IL 1  and the second image layer IL 2 . 
     In operation S 15 , the compositor  11  does not generate the intermediate image IM. For example, when the second image layer IL 2  is an opaque image layer and the first image layer IL 1  is completely covered with the second image layer IL 2 , the compositor  11  need not generate the intermediate image IM (that is, when the layer IL 2  satisfies the alpha blending rule referred to above). 
     In operation S 16 , the compositor  11  generates a resultant image R using the intermediate image IM. That is, the compositor  11  generates the resultant image R by performing composition on the intermediate image IM and the third image layer IL 3 . 
     In operation S 17 , the compositor  11  determines whether any more image layers are to be composited. The method of driving the compositor  11  is completed when no more image layers are to be composited, otherwise the process returns to operation S 11 . 
       FIG. 13  is a block diagram of a computer system  210  including the compositor  11  illustrated in  FIG. 1  in accordance with principles of inventive concepts. Computer system  210  includes a memory device  211 , a memory controller  212  configured to control the memory device  211 , a radio transceiver  213 , an antenna  214 , an application processor  215 , an input device  216 , and a display device  217 . 
     The radio transceiver  213  may transmit or receive a radio signal via the antenna  214 . For example, the radio transceiver  213  may convert the radio signal received via the antenna  214  into a signal that is to be processed by the application processor  215 . 
     Thus, the application processor  215  may process a signal output from the radio transceiver  213  and transmit the processed signal to the display device  217 . Also, the radio transceiver  213  may convert a signal output from the application processor  215  into a radio signal and output the radio signal to an external device via the antenna  214 . 
     The input device  216  is a device via which a control signal for controlling an operation of the application processor  215  or data that is to be processed by the application processor  215  may be input, and may be embodied as a pointing device such as a touch pad and a computer mouse, a keypad, or a keyboard. 
     In exemplary embodiments in accordance with principles of inventive concepts, the memory controller  212  configured to control an operation of the memory device  211  may be embodied as a part of the application processor  215  or a chip installed separately from the application processor  215 . Application processor  215  may be embodied to include the compositor  11  of  FIG. 1 . 
       FIG. 14  is a block diagram of an exemplary embodiment of a computer system  220  including the compositor  11  of  FIG. 1  in accordance with principles of inventive concepts. Computer system  220  may be embodied as a personal computer (PC), a network server, a tablet PC, a net-book, an e-reader, a PDA, a PMP, an MP3 player, or an MP4 player, for example. Computer system  220  includes a memory device  221 , a memory controller  222  configured to control a data processing operation of the memory device  221 , an application processor  223 , an input device  224 , and a display device  225 . 
     The application processor  223  may display data stored in the memory device  221  on the display device  225  based on data received via the input device  224 . For example, the input device  224  may be embodied as a pointing device such as a touch pad and a computer mouse, a keypad, or a keyboard. The application processor  223  may control overall operations of the computer system  220  and an operation of memory controller  222 . 
     In exemplary embodiments, the memory controller  222  configured to control an operation of the memory device  221  may be embodied as a part of the application processor  223  or a chip installed separately from the application processor  223 . Application processor  223  may be embodied to include a compositor in accordance with principles of inventive concepts, such as the compositor  11  described in the discussion related to  FIG. 1 . 
       FIG. 15  is a block diagram of a computer system  230  including compositor  11  of  FIG. 1  in accordance with principles of inventive concepts. Computer system  230  may be embodied as an image process device, e.g., a digital camera or a cellular phone with a built-in digital camera, a smart phone, or a tablet PC, for example. 
     The computer system  230  includes a memory controller  232  capable of controlling the memory device  231  and a data processing operation (e.g., a write operation or a read operation) of the memory device  231 . The computer system  230  may further include an application processor  233 , an image sensor  234 , and a display device  235 . 
     The image sensor  234  of the computer system  230  converts an optical image into digital signals and transmits the digital signals to the application processor  233  or the memory controller  232 . Under control of the application processor  233 , the digital signals may be displayed on the display device  235  or stored in the memory device  231  via the memory controller  232 . 
     The data stored in the memory device  231  may be displayed on the display device  235 , under control of the application processor  233  or the memory controller  232 . 
     In exemplary embodiments, the memory controller configured to control an operation of the memory device  231  may be embodied as a part of the application processor  233  or a chip installed separately from the application processor  233 . Application processor  233  may be embodied to include a compositor in accordance with principles of inventive concepts, such as compositor  11  of  FIG. 1 . 
     Compositors in accordance with exemplary embodiments in accordance with principles of inventive concepts generate a resultant image using an intermediate image, thereby reducing the number of times that a plurality of image layers are read. Thus, a bandwidth required of a SoC including such as compositor may be reduced. 
     The foregoing is illustrative of embodiments and is not to be construed as limiting thereof. Although a few embodiments have been described, it will readily be appreciated that many modifications are possible in embodiments without materially departing from the novel teachings and advantages. It is to be understood that the foregoing is illustrative of various embodiments and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims.