Abstract:
Apparatus and method for providing thumbnail image data on a mobile terminal are provided. The apparatus and method comprise determining whether an image management mode is selected when the mobile terminal is in a standby mode; analyzing bit streams of a plurality of stored actual images to obtain picture sizes and compression ratios of the actual images upon selection of the image management mode; extracting Discrete Cosine Transform (DCT) coefficients at certain blocks of the bit streams of the actual images based on the obtained picture sizes and compression ratios; and partially decoding the extracted DCT coefficients, reducing the partially decoded DCT coefficients at a predetermined rate for generating thumbnail images of the plurality of actual images and displaying the generated thumbnail images.

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. 119(a) of an application entitled “Method for Providing Thumbnail Image Data on Mobile Terminal” filed with the Korean Intellectual Property Office on Dec. 6, 2003 and assigned Serial No. 2003-88386, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and method for providing thumbnail image data on a mobile terminal. More particularly, the present invention relates to an apparatus and method for generating thumbnails from image data stored in a mobile terminal. 
     2. Description of the Related Art 
     Mobile terminals have become integrated with cameras and now provide wireless communication as well as photography as an option and offer the convenience of allowing a user to take photographs anywhere and at any time. Image data of the pictures taken through the camera of a mobile terminal can be stored and reproduced whenever needed. The image data may include still images and moving images. Still images are compressed in a Joint Picture Experts Group (JPEG) format, while moving images are compressed in an Moving Picture Experts Group (MPEG) format. The compressed still and moving images are stored in the memory of the mobile terminal. 
     Specifically, the actual images photographed and their smaller images (hereinafter referred to as “thumbnails”) reduced in size to be easily managed by the user are both stored in memory. 
     The user can display multiple thumbnail images simultaneously on a screen display using a multi-function capability available in the actual image data management mode. 
     Since conventional mobile terminals store both actual images and reduced-size thumbnail images, they have a limitation in storing all data (such as images and ringtone melodies/bell sounds) given the finite memory resources available. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an apparatus and method for providing thumbnail images on a mobile terminal only in a mode requiring thumbnail image data, without storing the thumbnail images with actual images in a memory. 
     Another object of the present invention is to provide an apparatus and method for providing thumbnail image data on a mobile terminal which can effectively utilize finite memory resources. 
     In order to accomplish the above objects of the present invention, an apparatus and method for providing thumbnail image data on a mobile terminal are used, comprising determining whether an image management mode is selected when the mobile terminal is in a standby mode; analyzing bit streams of a plurality of actual images stored to obtain picture sizes and compression ratios of the actual images upon selection of the image management mode; extracting Discrete Cosine Transform (DCT) coefficients at certain blocks of the bit streams of the actual images based on the obtained picture sizes and compression ratios; partially decoding the extracted DCT coefficients; and reducing the partially decoded DCT coefficients at a predetermined rate for generating thumbnail images of the plurality of actual images and displaying the generated thumbnail images. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a view illustrating a mobile terminal according to an embodiment of the present invention; 
         FIG. 2  is a flow chart illustrating a process of providing a thumbnail image on a mobile terminal according to an embodiment of the present invention; and 
         FIG. 3  is a view illustrating a bit stream of a Joint Picture Experts Group (JPEG) image for providing thumbnail image data according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when for conciseness. 
     Image data includes still images compressed in Joint Picture Experts Group (JPEG) format and moving images compressed in Moving Picture Experts Group (MPEG) format. In this embodiment of the present invention, still images will be described as being image data. Also, the term “Discrete Cosine Transform (DCT) coefficient” will refer to both DC and AC coefficients. 
       FIG. 1  illustrates a mobile terminal according to an embodiment of the present invention. 
     Referring to  FIG. 1 , a radio frequency (RF) section  21  performs a wireless communication function for the mobile terminal. The RF section  21  comprises a RF transmitter (not shown) for performing upward conversion and amplification of the frequency of a transmitted signal and a RF receiver (not shown) for amplifying a received signal with low noise and performing downward conversion of the frequency of the signal. 
     A data processor  23  comprises a transmitter for coding and modulating a signal which is being transmitted and a receiver for demodulating and decoding a signal which is being received. The data processor  23  may comprise a modem and a codec. 
     An audio processor  25  reproduces an audio signal output from the data processor  23  to a speaker or transmits an audio signal generated from a microphone to the data processor  23 . Also, the audio processor  25  reproduces audio data stored with moving images and outputs the audio data through the speaker. 
     A keypad  27  is provided with keys for inputting numbers and characters and function keys for setting up various functions. The key input section  27  may also include a menu key, an OK key and an image management key according to an embodiment of the present invention. 
     A memory  29  may comprise a program memory and a data memory. The program memory stores programs for controlling general operations of the mobile terminal and programs for compressing still images in JPEG format and moving images in MPEG format and storing the images. The data memory temporarily stores data generated during implementation of the above programs. 
     A control section  10  controls the overall operations of the mobile terminal. The control section  10  may include the data processor  23 . When a multi-mode option is selected by an input from the keypad  27  during an image management mode, the control section  10  outputs image data stored in the memory  29  and controls the display of thumbnail images. 
     A camera  50  comprises a camera sensor for converting a photographed optical signal into an electrical signal. The camera sensor can be a charge coupled device (CCD) sensor. A signal processor  60  converts an image signal output from the camera  50  into digital data. The signal processor  60  can be a digital signal processor (DSP). 
     An image processor  70  generates picture data for displaying an image signal output from the signal processor  60 . The image processor  70  adjusts image signals received under the control of the control section  10  or image data photographed through the camera  50  to conform to the size of a display section  80  and outputs the adjusted signals or data. In addition, the image processor  70  compresses the image data into a JPEG or MPEG format or reconstructs the compressed image data. 
     The display section  80  displays messages generated during the implementation of a program under the control of the control section  10 . The display section  80  also displays image signals output from the image processor  70  in a camera mode or user data output from the control section  10 . In addition, the display section  80  displays multiple thumbnail images generated from the image data stored in the memory  29  under the control of the control section  10 . The display section  80  can be a Liquid Crystal Display (LCD) comprising a LCD controller, a memory for storing image data and a LCD device. When the LCD is a touch screen, it can serve as an input means like the keypad  27 . 
     Referring to  FIG. 1 , if a user (caller) sets an outgoing call mode after dialing by using the keypad  27 , the control section  10  will detect the mode and will process the dialed information received through the data processor  23 . The control section  10  converts the dialed information into a RF signal through the RF section  21  and outputs the RF signal. A reply signal generated from a recipient is detected by the RF section  21  and the data processor  23 . The audio processor  25  then forms a voice communication path so that the user can communicate with the recipient. 
     In contrast, when detecting an incoming call, the control section  10  controls the audio processor  25  to generate a ringing signal. When the user replies to the incoming call, the control section  10  detects the reply and controls the audio processor  25  to form a voice communication path so that the user can receive the incoming call. Although voice communications in the incoming or outgoing call mode have been described as examples, the control section  10  can also perform data communication functions for receiving or transmitting packet data or image data. In a standby mode or a messaging mode, the control section  10  displays text data processed by the data processor  23  on the display section  80 . 
     The mobile terminal also enables the user to photograph an object or a scene in order to display or send the photographed image. The camera  50  can be embedded in the mobile terminal or mounted on the exterior of the mobile terminal. In other words, the camera  50  can be either an external or an internal component. The camera  50  may use a charge coupled device (CCD) sensor. An image photographed by the camera  50  is converted into an electrical signal in the CCD sensor and applied to the signal processor  60 . Then the signal processor  60  converts the received electrical signal to a digital image data and outputs the digital image data to the image processor  70 . 
     Hereinafter, a process of providing thumbnail images on the mobile terminal will be explained in detail. Images photographed or downloaded in the multi-mode of the image management mode are compressed and stored in the memory  29 . The control section  10  analyzes the picture size and positions of DCT coefficients of each image stored in the memory  29 . The control section  10  partially decodes the DCT coefficients located at different positions according to the picture size and compression format of each stored image and generates a thumbnail image to display on the display section  80 . 
     Partial decoding is a process of decoding part of a bit stream of a stored image for generating one thumbnail image, without decoding the bit stream as a whole. 
       FIG. 2  is a flow chart illustrating a process of providing a thumbnail image on a mobile terminal according to an embodiment of the present invention. 
     Referring to  FIG. 2 , the control section in standby mode at step  211  determines whether the image management mode is selected at step  212 . Upon selection of the image management mode, the control section  10  reconstructs one of images compressed and stored in the memory  29  and displays the reconstructed image on the display section  80  at step  213 . 
     Image data stored in the memory  29  include still images and moving images. Still images are compressed in a JPEG format, while moving images are compressed in a MPEG format. The compression of still or moving images will be briefly explained below. 
     A still image of an object photographed through the camera  50  is divided into 8×8 pixel blocks by the image processor  70 . The DCT transforms the 64 pixels in each 8×8 block into two-dimensional spatial frequency values to obtain DCT coefficients. After quantization and entropy coding of the DCT coefficients, the still image is compressed and stored in the memory  29 . Moving images in MPEG can be compressed and stored in the same manner. For moving images, however, compression ratios need be increased by effectively exploiting the correlation between frames. In other words, the compression of moving images further involves increasing compression ratios by discarding any redundant information in adjacent frames (“motion compensation”) and using the displacement of the macroblock in the previous frame with respect to the macroblock in the current frame (“motion vector”). 
     While a still image is displayed on the display section  80  at step  213 , the control section  10  determines whether a multi-mode is selected at step  214 . If a multi-mode is not selected at step  214 , the mobile terminal performs other functions at step  218 . If the multi-mode is selected at step  214 , the control section  10  analyzes a picture size and a compression ratio of each image stored in the memory  29  at step  215 . 
     Hereinafter, a bit stream of a JPEG image which varies according to the picture size and compression ratio of the image will be explained in detail with reference to  FIG. 3 . 
       FIG. 3  shows a bit stream of a JPEG image for providing thumbnail image data services according to an embodiment of the present invention. 
     Referring to  FIG. 3 , a bit stream of a JPEG still image comprises a header  301  including information representing the JPEG still image such as a picture size and a compression ratio, a block header  302  representing a sequential number of each 8×8 pixel block, DCT coefficients (DC, AC)  303  and  304  positioned next to the block header  302  and an end stream  305  indicating the end of the JPEG bit stream. The DCT coefficients  303  and  304  comprise a DC coefficient  303  representing the average value of the 8×8 pixel blocks and AC coefficients  304  representing the remaining pixel information. In an embodiment of the present invention, thumbnail image data is generated using the DCT coefficient  303 . 
     Assuming that a photographed image can have one of four picture sizes specified by rows by columns of pixels (640×480, 352×288, 176×176 and 176×144) and a compression ratio in one of three levels (high, middle and low), the control section  10  will analyze DCT coefficients corresponding to the twelve cases according to the possible picture sizes and compression ratios of the image. 
     At step  216 , the control section  10  detects the positions of the DCT DC coefficients  303  located at different positions according to the picture size and compression ratio of the image and outputs the DCT DC coefficients  303 . 
     For example, in order to generate a thumbnail of a JPEG still image stored in a picture size of 176×144 pixels, the JPEG image is divided into a total of 396 8×8 pixel blocks (22×18 blocks). The DCT DC coefficient  303  of the first block can be read out from the JPEG bit stream based on a JPEG standard format. Since the positions of the rest 395 DCT DC coefficients  303  vary according to the picture size and compression ratio of the image, the positional information of the block headers ( 0  to  395 )  302  is obtained to extract the DCT DC coefficients  303  positioned next to the block headers  302 . The extraction of DCT DC coefficients  303  is performed up to the number of times corresponding to the number of 8×8 pixel blocks which is in proportion to the picture size of an image. 
     The control section  10  applies the DCT DC coefficients  303  obtained by the above process and a multi-mode control signal in the image management mode to the image processor  70 . The image processor  70  partially decodes the received DCT DC coefficients  303 . Also, the image processor  70  reduces the partially decoded DC coefficients  303  to ⅛ and outputs pixel information of thumbnail image data to the display section  80 . 
     At step  217 , the display section  80  displays a thumbnail image having a 22×18 size based on the pixel information received from the image processor  70 . 
     The above process as shown in  FIG. 2  is repeated up to the number of times corresponding to the number of actual images stored in the memory  29 , thereby generating multiple thumbnail images in realtime and displaying the thumbnail images. 
     Although a certain embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the accompanying claims including the full scope of equivalents thereof. Accordingly, the present invention is equally applicable to JPEG still images and MPEG moving images comprising frames of JPEG still images. 
     As explained above, the present invention partially decodes DCT coefficients of multiple actual images stored in the memory and generates corresponding multiple thumbnail images in real-time. Thus, it is possible to provide thumbnail images on a mobile terminal without the need to store them in the memory, thereby effectively utilizing finite memory resources.