Patent Publication Number: US-2012038672-A1

Title: Mobile device having projector module and method for outputting images in the mobile device

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. §119(a) of a Korean patent application filed on Aug. 11, 2010 in the Korean Intellectual Property Office and assigned Serial No. 10-2010-0077182, the entire disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to image output technology for a mobile device having a projector module. More particularly, the present invention relates to a mobile device and method for efficiently outputting images through a projector module. 
     2. Description of the Related Art 
     With the remarkable growth of related technologies, a great variety of mobile devices are becoming increasingly popular. Mobile devices not only provide a voice call service, but also may optionally offer a data transmission service as well as other various additional services, thereby evolving into multimedia communication devices. 
     Recently, mobile devices with a built-in projector module have been developed. This mobile device can project images onto a surface such as a projection screen or a wall through the projector module, thus allowing many persons to simultaneously view image contents (e.g., photo contents, video contents, etc.) stored in the mobile device. 
     This type of mobile device drives a dedicated player (e.g., a DivX player) equipped therein and then outputs image contents through the projector module. At this time, the mobile device updates and outputs real-time image frames. However, since the mobile device has restricted hardware in comparison with a typical stand-alone projector, the mobile device is relatively poor at updating image frames to the projector module. Therefore, there is a need for improving the performance of the mobile device in connection with a function to output images through the projector module. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a method for improving the performance of a mobile device with relatively restricted hardware in connection with a function to output images through the projector module. 
     Another aspect of the present invention is to provide a mobile device supporting the above method. 
     According to one aspect of the present invention, a mobile device is provided. The mobile device includes a projector module for outputting image frames that constitute image content, a display unit for outputting a manipulation User Interface (UI) for manipulating the image content, a display driver for updating the image frames through the projector module, and for updating the manipulation UI through the display unit whenever a UI update command is received, and a control unit for sending an image frame update command and the UI update command to the display driver, and for controlling the display driver such that a process of updating the manipulation UI through the display unit is stopped when a turn-off command for the display unit is inputted. 
     According to another aspect of the present invention, a mobile device is provided. The mobile device includes a projector module for outputting image frames and captions, both of which constitute image content, a display driver for receiving a plurality of layers, and for updating a frame layer among the received layers or for merging and updating the frame layer and a caption layer among the received layers, and a control unit for determining whether the caption is contained in a selected image to be outputted through the projector module, for sending a merging update command for the caption layer and the frame layer to the display driver when the caption is contained, and for sending a frame layer update command to the display driver when the caption is not contained. 
     According to still another aspect of the present invention, a method of outputting images in a mobile device that includes a projector module, a display unit and a display driver is provided. The method includes sending update commands when recognizing a play command for a selected image content, the sending of the update commands including sending image frames constituting the selected image content, an image frame update command, a manipulation UI, and a UI update command to the display driver, performing an update process at the display driver, the performing of the update process including updating the image frame by controlling the projector module, and updating the manipulation UI by controlling the display unit whenever the UI update command is received, and when recognizing a turn-off command for the display unit, stopping the updating of the manipulation UI through the display unit by controlling the display driver. 
     According to yet another aspect of the present invention, a method of outputting images in a mobile device that includes a projector module and a display driver is provided. The method includes determining whether a caption is contained in a selected image to be outputted through the projector module, sending a merging update command for a caption layer and a frame layer to the display driver when the caption is contained, or sending a frame layer update command to the display driver when the caption is not contained, and at the display driver, merging and updating the frame layer and the caption layer through the projector module when the merging update command is received, or updating the frame layer only through the projector module when the frame layer update command is received. 
     Aspects of the present invention may not only improve the output performance of the projector module, but also improve the decoding performance of the content playback controller. Additionally, aspects of the present invention may reduce undesirable load when the display driver outputs images through the display unit and the projector module, thus wholly enhancing the content playback performance of the mobile device. Therefore, aspects of the present invention may improve the image output performance of the mobile device with relatively restricted hardware. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating an external appearance of a mobile device having a projector module in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating a configuration of a mobile device having a projector module in accordance with an exemplary embodiment of the present invention. 
         FIG. 3  is a block diagram illustrating a method for outputting images by means of related elements of a mobile device in accordance with an exemplary embodiment of the present invention. 
         FIG. 4  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. 
         FIG. 5  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. 
         FIG. 6  is a schematic diagram illustrating a method for outputting images with four layers by means of a display driver of a mobile device in accordance with an exemplary embodiment of the present invention. 
         FIG. 7  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. 
         FIG. 8  is a schematic diagram illustrating a method for outputting images with four layers by means of a display driver of a mobile device in accordance with an exemplary embodiment of the present invention. 
     
    
    
     Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skilled in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention is provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     Although a mobile device will be exemplarily described hereinafter, the present invention is not always limited to the mobile device. Alternatively, exemplary embodiments of the present invention may be applied to any other electronic device that has a projector module and a display unit. The mobile device according to exemplary embodiments of the present invention may include a mobile communication terminal, a Portable Multimedia Player (PMP), a Personal Digital Assistant (PDA), a smart phone, a Moving Picture Experts Group (MPEG)-1 or MPEG-2 Audio Layer 3 (MP3) player, and the like. Additionally, the mobile device of exemplary embodiments of the present invention may include an International Mobile Telecommunication 2000 (IMT-2000) device, a Wideband Code Division Multiple Access (WCDMA) device, a Global System for Mobile communication (GSM) device, a General Packet Radio Service (GPRS) device, a Universal Mobile Telecommunication Service (UMTS) device, and the like. 
     A disclosure set forth herein will be based on a mobile device that can output images, each of which is composed of at least one layer including a basic layer for offering backgrounds, a frame layer for offering image frames of image content, a caption layer for offering captions of image content, and a User Interface (UI) layer for offering UIs suitable for manipulating the playback of image content. The number of such layers may be determined depending on the performance of a processor. Parts of layers may be outputted through a projector module, whereas the others may be outputted through a display unit. 
       FIG. 1  is a perspective view illustrating an external appearance of a mobile device having a projector module according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , a mobile device  100  includes a display unit  150  and a projector module  160 . The mobile device  100  shown in  FIG. 1  is a touch screen based mobile device in which a touch panel is completely overlapped on the display unit  150 . Preferably, the projector module  160  is disposed at the top side of the mobile device  100  so that a user can see a projected image while alternately seeing the display unit  150 . In  FIG. 1 , the mobile device  100  is executing a ‘Movie Player’ application, for example, and hence the display unit  150  displays thereon an execution screen of the ‘Movie Player’ application. This execution screen offers a UI for manipulating the playback of image content, including a progress bar, a volume control bar, a play icon, a pause icon, a stop icon, a seek icon, etc. Now, respective elements of the mobile device  100  will be described in detail. 
       FIG. 2  is a block diagram illustrating a configuration of a mobile device having a projector module in accordance with an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the mobile device  100  includes a Radio Frequency (RF) unit  110 , an audio processing unit  120 , an input unit  130 , a memory unit  140 , a display unit  150 , a projector module  160 , a display driver  170 , and a control unit  180 . 
     The RF unit  110  performs a function of transmitting and receiving data for a wireless communication of the mobile device  100 . Normally the RF unit  110  may include an RF transmitter that up-converts the frequency of an outgoing signal and then amplifies the signal, an RF receiver that amplifies with low-noise an incoming signal and down-converts the frequency of the signal, and the like. Additionally, the RF unit  110  may receive data through a wireless channel and then output the data received through the wireless channel to the control unit  180 , and also receive data from the control unit  180  and then transmit the data received from the control unit  180  through a wireless channel. 
     The audio processing unit  120  may include a codec which may be composed of a data codec for processing packet data and an audio codec for processing an audio signal such as voice. The audio processing unit  120  converts a digital audio signal into an analog audio signal through the audio codec and then outputs the analog audio signal through a speaker (SPK), and also convents an analog audio signal received from a microphone (MIC) into a digital audio signal through the audio codec. 
     The input unit  130  receives a user&#39;s key manipulation for controlling the mobile device  100 , creates a corresponding input signal, and then delivers the corresponding input signal to the control unit  180 . The input unit  130  may be formed of a keypad based on the 3*4 or QWERTY key layout and having alphanumeric keys and navigation keys. Alternatively or additionally, the input unit  130  may be formed of a touch panel. Depending on a user&#39;s input action, the input unit  130  creates various input signals for performing particular functions (e.g., a call function, a video or music playback function, an image display function, a broadcast receiving function, a camera function, a voice recording function, a function to execute a selected application such as a calculator or a scheduler) of the mobile device  100  and then sends the various input signals to the control unit  180 . A disclosure set forth herein is based on the assumption that the input unit  130  is formed of a touch panel. In this case, the input unit  130  may further have a button key, a jog key, a wheel key, etc. 
     The memory unit  140  stores programs and data required for operations of the mobile device  100  and may consist of a program region and a data region. The memory unit  140  may be formed of a volatile memory such as a Random Access Memory (RAM), a non-volatile memory such as a flash memory or a hard disk, and their combinations. 
     The display unit  150  may be formed of a Liquid Crystal Display (LCD) or any equivalent, and visually offers a menu, input data, function setting information and any other various information of the mobile device  100  to a user. For instance, the display unit  150  performs a function to output a booting screen, an idle screen, a menu screen, a call screen, or any application execution screens of the mobile device  100 . In particular, the display unit  150  displays a UI suitable for manipulating the playback of image content. While selected image content is played, the display unit  150  updates and shows a specific UI for manipulating the playback of the selected image content under the control of the control unit  180  and the display driver  170 . 
     The projector module  160  projects an image, such as a picture, a photo, a video, etc. together with text, onto a surface such as a projection screen or a wall. More particularly, the projector module  160  of exemplary embodiments of the present invention outputs image frames that constitute image content. While any image content is played, the projector module  160  updates and outputs real-time image frames under the control of the control unit  180  and the display driver  170 . 
     The display driver  170  performs a function to control the outputs of the display unit  150  and the projector module  160 . The display driver  170  receives image data and a command to output the image data from the control unit  180  and then controls the display unit  150  and the projector module  160  to output the image data. If the control unit  180  is composed of a single processor chip, the display driver  170  may be equipped in the processor chip. More particularly, the mobile device  100  of exemplary embodiments of the present invention has only one display driver  170 . Additionally, the display driver  170  has a single output unit, which is connected to both the display unit  150  and the projector module  160 . Therefore, while outputting image data through the display unit  150 , the display driver  170  may not output any image data through the projector module  160 . When image content is played, the display driver  170  updates image frames of the image content by controlling the projector module  160 . Also, when receiving a command for a UI update such as an execution time update, the display driver  170  updates a manipulation UI by controlling the display unit  150 . 
     Furthermore, if receiving an image composed of several layers, the display driver  170  may merge all or parts of the received layers under the control of the control unit  180  and then output the merged layers by controlling the display unit  150  or the projector module  160 . Also, under the control of the control unit  180 , the display driver  170  may output parts of the received layers through the display unit  150  and output the other parts of the received layers through the projector module  160 . 
     The control unit  180  performs a function to control operations of the mobile device  100 . The control unit  180  may be composed of a single processor chip or alternatively composed of two or more processor chips (e.g., a main processor chip and an application processor chip). Hereinafter, the operation of the control unit  180  that controls the display driver  170  will be described. 
     The control unit  180  includes a content playback controller  181  and a UI controller  182 . In another exemplary embodiment of the present invention, the control unit  180  may include the content playback controller  181  only. 
     The content playback controller  181  controls the operations in connection with the playback of image contents. The content playback controller  181  reads data related to image contents stored in the memory unit  140 , performs a decoding, and then sends decoded image content data together with an image content output command to the display driver  170 . If any image content with a frame rate of 30 frames per second (fps) is to be played, the content playback controller  181  sends a command to update thirty frames per second to the display driver  170 . 
     When a content play command is inputted, the content playback controller  181  sends a UI update start command to the UI controller  182 . Then the UI controller  182  receives the UI update start command from the content playback controller  181  and sends a UI update command to the display driver  170 . In this exemplary embodiment, when a command to turn off the display unit  150  is inputted, the content playback controller  181  sends a UI update stop command to the UI controller  182 . 
     The UI controller  182  controls the operation in connection with a manipulation UI. While image content is played, the UI controller  182  controls a Graphic User Interface (GUI) for manipulating the image content displayed in the display unit  150 . In an exemplary embodiment, such a GUI may be formed of a flash UI, and the UI controller  182  may be formed of a flash engine. 
     In this exemplary embodiment, the UI controller  182  receives the UI update start command or UI update stop command from the content playback controller  181  and then, based on the received command, sends the UI update command to the display driver  170  or temporarily stops sending the UI update command. 
     Now, an image output method for the above-discussed mobile device  100  will be described. 
       FIG. 3  is a block diagram illustrating a method for outputting images by means of related elements of a mobile device in accordance with an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , a stage [a] shows the operations of the display unit  150 , the projector module  160 , the display driver  170 , the content playback controller  181  and the UI controller  182  when the display unit  150  is in a turned-on state. 
     At stage [a] of  FIG. 3 , when receiving an image content play command by a user&#39;s input, the content playback controller  181  sends an image frame update command to the display driver  170  and also sends a UI update start command to the UI controller  182 . 
     More specifically, when a user inputs instructions to play selected image content through the input unit  130 , the content playback controller  181  receives the image content play command from the input unit  130 . Then the content playback controller  181  retrieves selected image content from the memory unit  140 , performs a decoding process, and sends image frames of the selected image content to the display driver  170 . At this time, the content playback controller  181  further sends the image frame update command to the display driver  170 . 
     Additionally, the content playback controller  181  sends the UI update start command to the UI controller  182 . When receiving the UI update start command, the UI controller  182  sends a UI update command together with graphic data of a manipulation UI to the display driver  170 . This sending process may be performed periodically after the UI controller  182  receives the UI update start command from the content playback controller  181 . 
     The display driver  170  receives the image frames and the image frame update command from the content playback controller  181  and then updates the received image frames through the projector module  160 . Also, whenever receiving the UI update command from the UI controller  182 , the display driver  170  updates the manipulation UI by controlling the display unit  150 . If the selected image content requires an update of thirty frames per second (i.e., a 30 fps frame rate), the display driver  170  updates thirty frames per second and then outputs them through the projector module  160  or the display unit  150 . In this process, since the display driver  170  has the only output unit as discussed above, the display driver  170  cannot simultaneously update both the image frames and the manipulation UI. Therefore, when updating the manipulation UI through the display unit  150 , the display driver  170  cannot update the image frames through the projector module  160 . If two frames are required for updating the manipulation UI, the display driver  170  outputs only twenty-eight frames among thirty frames in total through the projector module  160  while dropping the remaining two frames. 
     A stage [b] of  FIG. 3  shows the operations of the display unit  150 , the projector module  160 , the display driver  170 , the content playback controller  181  and the UI controller  182  when the display unit  150  is in a turned-off state. 
     Referring to the stage [b] of  FIG. 3 , when a given time elapses during the playback of selected image content or when a user inputs a display unit turn-off command, the content playback controller  181  sends the display unit turn-off command to the display driver  170 . Then the display driver  170  controls the display unit  150  to be turned off. On the one hand, the content playback controller  181  sends a UI update stop command to the UI controller  182 . The UI update stop command may correspond to a UI update pause command. On the other hand, the content playback controller  181  continues to send the image frames and the image frame update command to the display driver  170 . 
     The UI controller  182  receives the UI update stop command from the content playback controller  181  and then stops sending the UI update command and graphic data of the manipulation UI to the display driver  170 . 
     The display driver  170  receives the image frame update command and the image frames from the content playback controller  181  and then updates the received image frames by controlling the projector module  160 . At this time, since failing to receive the UI update command from the UI controller  182 , the display driver  170  does not perform a process of updating the manipulation UI by controlling the display unit  150 . Therefore, the display driver  170  performs only a process of updating the image frames through the projector module  160 . 
     Typically, even while the display unit  150  is turned off, the UI controller  182  continuously sends the UI update command to the display driver  170 . Thus, the display driver  170  continues a process of updating the manipulation UI even though the display unit  150  is turned off. However, the UI controller  182  of an exemplary embodiment of the present invention temporarily stops a process of sending the UI update command to the display driver  170  when the display unit  150  is turned off. Therefore, the display driver  170  outputs images to only the projector module  160 . Namely, since some frames required for the display unit  150  are used for the projector module  160  in the turned-off state of the display unit  150 , the performance of outputting images through the projector module  160  can be improved. 
     When a user inputs a display unit turn-on command in the display turned-off state, the content playback controller  181  sends the UI update start command to the UI controller  182 . Then the UI controller  182  sends the UI update command and graphic data of the manipulation UI to the display driver  170 . Meanwhile, the display driver  170  receives the image frames and the image frame update command from the content playback controller  181  and then updates the image frames through the projector module  160 . Also, whenever receiving the UI update command from the UI controller  182 , the display driver  170  updates the manipulation UI through the display unit  150 . 
       FIG. 4  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the content playback controller  181  recognizes the image content play command inputted through the input unit  130  in step  401 . Namely, when a user inputs instructions to execute selected image content through the input unit  130 , the content playback controller  181  receives the image content play command from the input unit  130 . 
     Then the content playback controller  181  sends the UI update start command to the UI controller  182  in step  402 . The UI update start command corresponds to a command to enable the UI controller  182  to start a process of sending the UI update command to the display driver  170 . 
     Next, the content playback controller  181  sends image frames and the image frame update command to the display driver  170  in step  403 . More specifically, the content playback controller  181  retrieves selected image content from the memory unit  140 , performs a decoding process, and sends image frames of the selected image content and the image frame update command to the display driver  170 . In another exemplary embodiment, the order of the steps  402  and  403  may be changed. Namely, in this case, the content playback controller  181  sends image frames and the image frame update command to the display driver  170  and then sends the UI update start command to the UI controller  182 . 
     After receiving the UI update start command from the content playback controller  181 , the UI controller  182  periodically sends the UI update command and graphic data of the manipulation UI to the display driver  170 . 
     The display driver  170  receives the image frames and the image frame update command from the content playback controller  181  and then updates the received image frames through the projector module  160 . Also, whenever receiving the UI update command from the UI controller  182 , the display driver  170  updates the manipulation UI by controlling the display unit  150 . For instance, the display driver  170  may update a playback time of image content through the display unit  150 . 
     Next, the content playback controller  181  determines whether the display unit turn-off command is inputted in step  404 . More specifically, in order to perform the above determination step  404 , the content playback controller  181  may determine whether a given time elapses or not in the turned-on state of the display unit  150  or receive user&#39;s instructions to turn off the display unit  150  from the input unit  130 . In another exemplary embodiment, step  404  may be performed by some element in the control unit  180  other than the content playback controller  181 . 
     If there is no input for the display unit turn-off command, the content playback controller  181  returns to step  403 . At this time, the UI controller  182  periodically sends the UI update command and graphic data of the manipulation UI to the display driver  170 . Then the display driver  170  updates the received image frames by controlling the projector module  160  and also, whenever receiving the UI update command from the UI controller  182 , updates the manipulation UI through the display unit  150 . 
     If the display unit turn-off command is inputted in the above step  404 , the content playback controller  181  sends the UI update stop command to the UI controller  182  in step  405 . Additionally, the content playback controller  181  continues to send the image frames and the image frame update command to the display driver  170  in step  406 . 
     The UI controller  182  receives the UI update stop command from the content playback controller  181  and then stops a process of sending the UI update command and graphic data of the manipulation UI to the display driver  170 . The display driver  170  receives the image frame update command and the image frames from the content playback controller  181  and then updates the received image frames by controlling the projector module  160 . Since failing to receive the UI update command from the UI controller  182 , the display driver  170  does not perform a process of updating the manipulation UI by controlling the display unit  150  and therefore performs only a process of updating the image frames through the projector module  160 . 
     Next, the content playback controller  181  determines whether the display unit turn-on command is inputted in step  407 . In step  407 , the content playback controller  181  may receive a user&#39;s instructions to turn on the display unit  150  from the input unit  130 . If there is no input for the display unit turn-on command, the content playback controller  181  returns to step  406 . 
     If the display unit turn-on command is inputted in step  407 , the content playback controller  181  returns to step  402 . Therefore, the UI controller  182  again starts to periodically send the UI update command and graphic data of the manipulation UI to the display driver  170 . Meanwhile, the display driver  170  continues to update the received image frames by controlling the projector module  160  and also, whenever receiving the UI update command from the UI controller  182 , updates the manipulation UI through the display unit  150 . 
       FIG. 5  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. The exemplary embodiment of the present invention shown in  FIG. 5  relates to a case of merging layers when a selected image composed of such layers is outputted. 
     Referring to  FIG. 5 , at the outset, the content playback controller  181  recognizes the image content play command inputted through the input unit  130  in step  501 . Namely, when a user inputs instructions to execute selected image content through the input unit  130 , the content playback controller  181  receives the image content play command from the input unit  130 . 
     Next, the content playback controller  181  determines whether there is a caption file linked to selected image content in step  502 . Normally, image content with superimposed captions contains a caption file (with an smi extension format, for example). If there is no caption file linked to selected image content, the content playback controller  181  determines that there is no caption file to be outputted, and sends a frame layer update command to the display driver  170  in step  505 . Then the display driver  170  updates a frame layer only through the projector module  160  even though a plurality of layers is received. 
     If it is determined in step  502  that a caption file is linked to selected image content, the content playback controller  181  further determines whether any caption is contained in a current frame to be outputted in step  503 . Even though image content has a caption file, each individual frame may or may not have captions. According to an exemplary embodiment of the present invention, each image frame of image content may have an identifier for indicating whether or not captions are present. In this exemplary embodiment, the content playback controller  181  may perform the above determination step  503  by checking for such identifiers. In another exemplary embodiment, the content playback controller  181  may perform the above determination step  503  by comparing a playback time of each image frame with that of the caption file. For instance, the content playback controller  181  finds a time stamp of a current image frame to be outputted, determines whether there is a caption in a corresponding time stamp of a caption file, and then determines whether the current frame contains a caption. If it is determined in the step  503  that there is no caption to be outputted, the content playback controller  181  performs the above-discussed step  505 . Namely, the content playback controller  181  sends a frame layer update command to the display driver  170 , which updates a frame layer only through the projector module  160 . 
     If it is determined in the step  503  that the current frame to be outputted contains a caption, the content playback controller  181  sends a merging update command to the display driver  170  in step  504 . Namely, when there is a caption to be outputted, the content playback controller  181  sends instructions to merge and update a caption layer and a frame layer to the display driver  170 . Then the display driver  170  merges the caption layer and the frame layer and also updates them through the projector module  160 . 
     Typically, the display driver  170  does not selectively merge layers, but merges all layers. For instance, even when updating image content with no caption through the projector module  160 , the typical display driver  170  merges the caption layer and the frame layer. Unfortunately, a load of this merging process in the display driver  170  may deteriorate the image output performance of the projector module  160  and may consequently cause the degradation in the performance of the mobile device  100 . 
     Exemplary embodiments of the present invention allow the display driver  170  to selectively perform a layer merging process, depending on whether or not captions are present. Therefore, exemplary embodiments of the present invention may reduce undesirable load caused by the layer merging process and may also improve the image output performance of the projector module  160  and the content playback performance of the mobile device  100 . 
       FIG. 6  is a schematic diagram illustrating a method for outputting images with four layers by means of a display driver of a mobile device in accordance with an exemplary embodiment of the present invention. 
     Although  FIG. 6  shows four layers that constitute an image, this is exemplary only and not to be considered as a limitation of the present invention. The number of layers may be varied according to the performance of a processor of the mobile device  100 . 
     Referring to  FIG. 6 , an image is composed of a layer  1  (i.e., a basic layer), a layer  2  (i.e., a frame layer), a layer  3  (i.e., a caption layer), and a layer  4  (i.e., a UI layer). 
     The layer  1  is a basic layer that offers the background screen, indicators, etc. in the display unit  150  of the mobile device  100 . The layer  2  is a frame layer that offers image frames of image content. The layer  3  is a caption layer that offers captions of image content. The layer  4  is a UI layer that offers the manipulation UI used for manipulating image content and representing a playback time, etc. 
     A stage [a] of  FIG. 6  shows a layer merging form of the display driver  170  when an image with captions is outputted. The display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 . Also, the display driver  170  merges the layers  2  and  3  and then outputs the merged layers  2  and  3  through the projector module  160 . Referring to  FIG. 2  as well, when receiving the UI update command from the UI controller  182 , the display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 . Meanwhile, when receiving image frames and the image frame update command from the content playback controller  181 , the display driver  170  merges the layers  2  and  3  and then outputs the merged layers  2  and  3  through the projector module  160 . 
     A stage [b] of  FIG. 6  shows a layer merging form of the display driver  170  when an image with no caption is outputted. The display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 , and also outputs the layer  2  only through the projector module  160 . Referring to  FIG. 2  as well, when receiving the UI update command from the UI controller  182 , the display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 . Meanwhile, when receiving image frames and the image frame update command from the content playback controller  181 , the display driver  170  outputs the layer  2  only through the projector module  160 . 
       FIG. 7  is a flow diagram illustrating a method for outputting images by means of a content playback controller of a mobile device in accordance with an exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , at the outset, the content playback controller  181  recognizes the image content play command inputted through the input unit  130  in step  701 . Namely, when a user inputs instructions to execute selected image content through the input unit  130 , the content playback controller  181  receives the image content play command from the input unit  130 . 
     Then the content playback controller  181  sends the UI update start command to the UI controller  182  in step  702 . Next, the content playback controller  181  sends image frames and the image frame update command to the display driver  170  in step  703 . More specifically, the content playback controller  181  retrieves selected image content from the memory unit  140 , performs a decoding process, and sends image frames of the selected image content and the image frame update command to the display driver  170 . 
     After receiving the UI update start command from the content playback controller  181 , the UI controller  182  periodically sends the UI update command and graphic data of the manipulation UI to the display driver  170 . The display driver  170  receives the image frames and the image frame update command from the content playback controller  181  and then updates the received image frames through the projector module  160 . Also, whenever receiving the UI update command from the UI controller  182 , the display driver  170  updates the manipulation UI by controlling the display unit  150 . For instance, the display driver  170  may update a playback time of image content through the display unit  150 . 
     Next, the content playback controller  181  determines whether the display unit turn-off command is inputted in step  704 . More specifically, in order to perform the above determination step  704 , the content playback controller  181  may determine whether a given time elapses or not in the turned-on state of the display unit  150  or receive a user&#39;s instructions to turn off the display unit  150  from the input unit  130 . 
     If there is no input for the display unit turn-off command, the content playback controller  181  returns to step  703 . At this time, the UI controller  182  periodically sends the UI update command and graphic data of the manipulation UI to the display driver  170 . Then the display driver  170  updates the received image frames by controlling the projector module  160  and also, whenever receiving the UI update command from the UI controller  182 , updates the manipulation UI through the display unit  150 . 
     If the display unit turn-off command is inputted in step  704 , the content playback controller  181  sends the UI update stop command to the UI controller  182  in step  705 . Additionally, the content playback controller  181  continues to send the image frames and the image frame update command to the display driver  170 . The UI controller  182  receives the UI update stop command from the content playback controller  181  and then stops a process of sending the UI update command and graphic data of the manipulation UI to the display driver  170 . The display driver  170  receives the image frame update command and the image frames from the content playback controller  181  and then updates the received image frames by controlling the projector module  160 . 
     Next, the content playback controller  181  determines whether there is a caption file linked to selected image content in step  706 . If there is no caption file linked to selected image content, the content playback controller  181  determines that there is no caption file to be outputted, and sends a frame layer update command to the display driver  170  in step  710 . 
     If it is determined in the step  706  that a caption file is linked to selected image content, the content playback controller  181  further determines whether any caption is contained in a current frame to be outputted in step  707 . If it is determined that there is no caption to be outputted, the content playback controller  181  performs the above-discussed step  710 . Namely, the content playback controller  181  sends a frame layer update command to the display driver  170 , which updates a frame layer only through the projector module  160 . 
     If it is determined in the step  707  that the current frame to be outputted contains a caption, the content playback controller  181  sends a merging update command to the display driver  170  in step  708 . Namely, when there is a caption to be outputted, the content playback controller  181  sends instructions to merge and update a caption layer and a frame layer to the display driver  170 . Then the display driver  170  merges the caption layer and the frame layer and also updates them through the projector module  160 . 
     Next, the content playback controller  181  determines whether the display unit turn-on command is inputted in step  709 . In step  709 , the content playback controller  181  may receive a user&#39;s instructions to turn on the display unit  150  from the input unit  130 . If there is no input for the display unit turn-on command, the content playback controller  181  returns to step  706  while continuing to send image frames and the image frame update command to the display driver  170 . 
     If the display unit turn-on command is inputted in step  709 , the content playback controller  181  returns to step  702 . Therefore, the UI controller  182  starts again to periodically send the UI update command and graphic data of the manipulation UI to the display driver  170 . Meanwhile, the display driver  170  continues to update the received image frames by controlling the projector module  160  and also, whenever receiving the UI update command from the UI controller  182 , updates the manipulation UI through the display unit  150 . 
       FIG. 8  is a schematic diagram illustrating a method for outputting images with four layers by means of a display driver of a mobile device in accordance with an exemplary embodiment of the present invention. 
     Like the aforesaid  FIG. 6 ,  FIG. 8  exemplarily shows four layers that constitute an image. 
     Referring to  FIG. 8 , an image is composed of a layer  1  (i.e., a basic layer), a layer  2  (i.e., a frame layer), a layer  3  (i.e., a caption layer), and a layer  4  (i.e., a UI layer). 
     A stage [a] of  FIG. 8  shows a layer merging form of the display driver  170  when an image with captions is outputted in the turned-on state of the display unit  150 . The display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 . Also, the display driver  170  merges the layers  2  and  3  and then outputs the merged layers  2  and  3  through the projector module  160 . Referring to  FIG. 2  as well, when receiving the UI update command from the UI controller  182 , the display driver  170  merges the layers  1  and  4  and then outputs the merged layers  1  and  4  through the display unit  150 . Meanwhile, when receiving image frames and the image frame update command from the content playback controller  181 , the display driver  170  merges the layers  2  and  3  and then outputs the merged layers  2  and  3  through the projector module  160 . 
     A stage [b] of  FIG. 8  shows a layer merging form of the display driver  170  when an image with no caption is outputted in the turned-off state of the display unit  150 . The display driver  170  outputs only the layer  2  through the projector module  160 . Referring to  FIG. 2  as well, when receiving image frames and the image frame update command from the content playback controller  181 , the display driver  170  outputs only the layer  2  through the projector module  160 . The image frame update command contains instructions to output only the frame layer. 
     Table 1 given below shows the results of image output executed by a mobile device according the conventional art and the mobile device  100  according to an exemplary embodiment of the present invention. The following results were obtained when image content with a frame rate of 30 fps and no caption was executed for one minute. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conventional 
                 Mobile device according to 
               
               
                   
                 mobile device 
                 exemplary embodiment 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 skippedDisplay 
                  311 
                 116 
               
               
                 avsyncDrops 
                 1486 
                 433 
               
               
                 Decoding Frame Rate 
                 25/30 
                 29/30 
               
               
                 Display Frame Rate 
                 24/30 
                 29/30 
               
               
                   
               
            
           
         
       
     
     In Table 1, ‘skippedDisplay’ indicates the number of frames dropped when the content playback controller  181  performs a decoding process, and ‘aysyncDrops’ indicates the number of frames dropped without synchronization of audio and video. As shown in Table 1, the number of frames dropped in the mobile device of the exemplary embodiment of the present invention was remarkably reduced in comparison with a case of a conventional mobile device. 
     Additionally, ‘decoding frame rate’ indicates the number of frames decoded for one second by the content playback controller  181 , and ‘display frame rate’ indicates the number of frames outputted through the projector module  160 . While twenty-five frames among thirty frames were decoded and twenty-four frames only were outputted in a conventional mobile device, twenty-nine frames among thirty frames were decoded and outputted in the mobile device of the exemplary embodiment of the present invention. 
     As seen from Table 1, not only the output performance of the projector module  160  but also the decoding performance of the content playback controller  181  was improved. Namely, exemplary embodiments of the present invention may reduce undesirable load when the display driver  170  outputs images through the display unit  150  and the projector module  160 , thus wholly enhancing the content playback performance of the mobile device  100 . Therefore, exemplary embodiments of the present invention may improve the image output performance of the mobile device  100  with relatively restricted hardware. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.