Abstract:
Video encoding methods and video encoders that provide improved performance while reducing power consumption. In one aspect, a video encoding method comprises the steps of outputting a parameter for a slice of a current frame, wherein the slice comprises a plurality of macroblocks, and the parameter comprises an address of a first macroblock of the slice, an address of a search area on a previous frame, a search area corresponding to a current macroblock, and a number of macroblocks comprising the slice; processing the slice by consecutively encoding and decoding each macroblock of the slice in response to the parameter; and outputting an interrupt signal for the current frame, when encoding and decoding for each macroblock of the all slices is consecutively performed so that encoding for the current frame is completed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a Continuation-in-Part of application Ser. No. 10/359,410, filed on Feb. 6, 2003, the contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to video encoding methods and video encoders, and more particularly, to video encoding methods and video encoders for providing a system on chip (SOC) with improved performance by generating one interrupt signal per slice. Further, the present invention relates to a video encoding methods and video encoders that are used in international standards such as H.261, H.263 or Moving Picture Expert GROUP (MPEG).  
       BACKGROUND  
       [0003]      FIG. 1  is a block diagram of a conventional video encoder. Referring to  FIG. 1 , a conventional video encoder  10  includes a main control unit (MCU)  20 , a motion estimation processor (MEP)  30 , a motion compensation processor (MCP)  40 , an internal bus system  50 , a memory  60 , a memory controller  70 , and a camera system  80 .  
         [0004]     The MEP  30  estimates the motion of a macroblock using the difference between a previous frame and a current frame. Based on the motion estimated by the MEP  30 , the MCP  40  reads from the memory  60 , 16×16 blocks that are the most perfectly matched with a current macroblock on the previous frame, that is, a motion-compensated macroblock.  
         [0005]     The memory  60  is a data storage device, such as a synchronous dynamic random access memory (SDRAM), and stores previous and present frames. The memory controller  70  controls all of the operations of the memory  50 , that is, reading of a previous frame, a current frame, or a motion-compensated macroblock from the memory  60  or writing of a previous frame, a current frame, or a restored image to the memory  60 .  
         [0006]     The camera system  80  captures an image and transfers the captured image to the memory  60 . Each of the MCU  20 , the MEP  30 , the MCP  40 , the memory controller  70 , and the camera system  80  is connected to the internal bus system  50  and transceives predetermined data to/from the internal bus system  50 .  
         [0007]      FIG. 2  is a flowchart illustrating a conventional image encoding method that is performed by the video encoder of  FIG. 1 . Referring to  FIGS. 1 and 2 , when an image frame captured by the camera system  80  has been stored in the memory  60 , the MCU  20  produces a picture header for the image frame to be encoded and encodes the image frame a macroblock at a time. Here, a macroblock is composed of 16×16 pixels. The picture header includes data regarding the image size, the image type (e.g., intra type (I) or predicted type (P)), and the like.  
         [0008]     The MCU  20  transfers an MEP parameter via the internal bus system  50  to the MEP  30 . The MEP parameter denotes information required to calculate a moving vector, and includes the address of a current macroblock on a current frame and the address of a search area on its previous frame, the search area corresponding to the current macroblock.  
         [0009]     The MEP  30  receives the MEP parameter and estimates a motion vector. The MEP  30  can perform another operation, such as quantization coefficient calculation, while estimating a motion vector. The time for the MEP  30  to estimate a motion vector varies. Accordingly, when motion vector estimation is completed, the MEP  30  produces an interrupt signal IRQ and transfers the same to the MCU  20 . The interrupt signal IRQ interrupts the operation of the MCU  20 .  
         [0010]     In response to the interrupt signal IRQ, the MCU  20  stops calculating a quantization coefficient and outputs an MCP parameter to the MCP  40 . The MCP parameter includes the motion vector estimated by the MEP  30  and the start address of the search area on the previous frame.  
         [0011]     The MCP  40  reads a motion-compensated macroblock from the memory  60  in response to the MCP parameter. When the data reading is completed, the MCP  40  outputs the interrupt signal IRQ to the MCU  20 .  
         [0012]     In response to the interrupt signal IRQ, the MCU  20  reads the motion-compensated macroblock from the MCP  40  and calculates a difference signal. The difference signal represents the difference between the current macroblock and the motion-compensated macroblock.  
         [0013]     The MCU  20  determines whether to process the current macroblock in an intermode or in an intramode. If it is determined to process the current macroblock in an intermode, the MCU  20  performs discrete cosine transformation (DCT) and quantization (Q) with respect to the difference between the current macroblock and the motion-compensated macroblock.  
         [0014]     On the other hand, if it is determined to process the current macroblock in an intramode, the MCU  20  performs discrete cosine transformation (DCT) and quantization (Q) with respect to the current macroblock.  
         [0015]     After the discrete cosine transformation (DCT) and quantization (Q), the MCU  20  produces a header for the current macroblock and performs variable length encoding with respect to a quantized coefficient. When the variable length encoding is completed, the MCU  20  performs inverse quantization (IQ) and inverse discrete cosine transformation (IDCT) with respect to the quantized coefficient.  
         [0016]     If the current macroblock is in an intramode, the MCU  20  transfers the image restored or decoded by IQ and IDCT to the memory  60 .  
         [0017]     However, if the current macroblock is in an intermode, the MCU  20  transfers the motion vector estimated by the MEP  30  and the start address of the search area on the previous frame to the MCP  40 . In response to the motion vector estimated by the MEP  30  and the start address of the search area on the previous frame, the MCP  40  reads a motion-compensated image from the memory  60  and an interrupt signal IRQ to the MCU  20 .  
         [0018]     In response to the interrupt signal IRQ, the MCU  20  adds the motion-compensated image stored in the MCP  40  to a dequantized image to produce a restored or decoded image, and stores the restored image in the memory  60 . If encoding and decoding with respect to one macroblock are completed through the above-described process, the conventional video encoder  10  encodes and decodes the next macroblock.  
         [0019]     The conventional video encoder  10  generates an interrupt signal IRQ three times to encode and decode one macroblock. Accordingly, in order to process 30 352×288 images per second, the conventional video encoder  10  generates an interrupt signal IRQ 35640 times (35640=352×288×3×30/16×16). Since the conventional video encoder  10  performs other operations during image encoding, frequent generation of the interrupt signal IRQ degrades the performance of the video encoder.  
         [0020]     Since the MCU  20  requires tens to hundreds of cycles to process one interrupt signal IRQ, the operations of the MCU  20  other than image encoding are significantly hindered by the IRQ signal. When the MCU  20  performs DCT and Q, a significant amount of power is consumed.  
       SUMMARY OF THE INVENTION  
       [0021]     To solve the above-described problems, it is an object of the present invention to provide video encoding methods and video encoders that are capable of improving performance while significantly reducing the frequency at which internal IRQ signals are generated.  
         [0022]     Another object of the present invention is to provide video encoding methods and video encoders that are capable of reducing power consumption.  
         [0023]     According to an aspect of the present invention, there is provided a video encoder including: a main control unit for outputting a parameter for a slice of a current frame, wherein the slice comprise a plurality of macroblocks, wherein the parameter comprises an address of a first macroblock of the slice, an address of a search area in a previous frame, the search area corresponding to a current macroblock in a current frame, and a number of macroblocks of the slice; a motion estimator for consecutively encoding and decoding each macroblock of the slice in response to the parameter and outputting an interrupt signal to the main control unit when the encoding and decoding for the slice is complete, wherein the motion estimator estimates a motion vector in response to the parameter, determines whether a current macroblock of the slice is to be processed in an intermode or intramode, and produces data required for DCT (discrete cosine transformation) and quantization depending on a determined mode; and a digital signal processor for executing the DCT and quantization on the produced data, outputting a quantized coefficient, executing VLC (variable length coding) on the quantized coefficient, executing IDCT (inverse DCT) and IQ (inverse quantization) on the quantized coefficient when the VLC is completed, and decoding the current macroblock in the determined mode.  
         [0024]     If it is determined that the macroblocks are to be processed in an intermode, the motion estimator calculates a difference between the macroblocks and motion-compensated macroblocks. The digital signal processor executes DCT and quantization on the difference, forms a quantized coefficient and a coded block pattern based on the quantized coefficient, and produces headers for the macroblocks in response to the determined mode, the coded block pattern, and the difference between the macroblock and a motion-compensated macroblock.  
         [0025]     If it is determined that the macroblocks are to be processed in an intramode, the digital signal processor executes DCT and quantization on the macroblocks, forms a quantized coefficient and a coded block pattern based on the quantized coefficient, and produces headers for the macroblocks in response to the determined mode and the coded block pattern.  
         [0026]     According to another aspect of the present invention, there is provided a video encoder including: a digital signal processor for outputting a parameter for a slice of a current frame, wherein the slice comprise a plurality of macroblocks, wherein the parameter comprises an address of a first macroblock of the slice, an address of a search area in a previous frame, the search area corresponding to a current macroblock in a current frame, and a number of macroblocks of the slice; and a motion estimator for consecutively encoding and decoding each macroblock of the slice in response to the parameter and outputting an interrupt signal to the main control unit when the encoding and decoding for the slice is complete, wherein the motion estimator estimates a motion vector in response to the parameter, determines whether a current macroblock of the slice is to be processed in an intermode or intramode, and produces data required for DCT (discrete cosine transformation) and quantization depending on a determined mode, wherein the digital signal processor executes the DCT and quantization on the produced data, outputs a quantized coefficient, executes VLC on the quantized coefficient, executes IDCT and IQ on the quantized coefficient when the VLC is completed, and decodes the current macroblock in the determined mode.  
         [0027]     If it is determined that the macroblocks are to be processed in an intermode, the digital signal processor calculates a difference between the macroblocks and motion-compensated macroblocks, executes DCT and quantization on the difference, forms a quantized coefficient and a coded block pattern based on the quantized coefficient, and produces headers for the macroblocks in response to the determined mode, the coded block pattern, and the difference between the macroblock and a motion-compensated macroblock.  
         [0028]     If it is determined that the macroblocks are to be processed in an intramode, the digital signal processor executes DCT and quantization on the macroblocks, forms a quantized coefficient and a coded block pattern based on the quantized coefficient, and produces headers for the macroblocks in response to the determined mode and the coded block pattern.  
         [0029]     According to another aspect of the present invention, there is provided a video encoding method, comprising the steps of outputting a parameter for a slice of a current frame, wherein the slice comprises a plurality of macroblocks, and the parameter comprises an address of a first macroblock of the slice, an address of a search area on a previous frame, a search area corresponding to a current macroblock, and a number of macroblocks comprising the slice; processing the slice by consecutively encoding and decoding each macroblock of the slice in response to the parameter; and outputting an interrupt signal for the current frame, when encoding and decoding for each macroblock of the all slices is consecutively performed so that encoding for the current frame is completed.  
         [0030]     According to another aspect of the present invention, the step of processing the slice comprises the steps of estimating a motion vector in response to the parameter; determining whether a current macroblock of the slice is to be processed in an intermode or intramode; producing data required for discrete cosine transform (DCT) and quantization depending on a determined mode, DCT transforming and quantizing the produced data, and outputting a quantization coefficient; performing variable length coding (VLC) on the quantization coefficient; and performing inverse DCT (IDCT) and inverse quantization (IQ) on the quantized coefficient and decoding the current macroblock in the determined mode.  
         [0031]     According to another aspect of the present invention, the step of processing the slice comprises the steps of estimating a motion vector in response to the parameter; determining whether the macroblocks comprising the slice are to be processed in an intermode or intramode; calculating a difference between the macroblocks and motion-compensated macroblocks, DCT transforming and quantizing the difference, and forming a quantized coefficient and a coded block pattern based on the quantized coefficient, if it is determined that the macroblocks are to be processed in an intermode, and DCT transforming and quantizing the macroblocks and forming a quantized coefficient and a coded block pattern based on the quantized coefficient, if it is determined that the macroblocks are to be processed in an intramode; producing headers for the macroblocks in response to the determined mode, the coded block pattern, and the quantized coefficient and VLC coding the quantized coefficient; and IDCT transforming and IQ quantizing the quantization coefficient and decoding the macroblocks in the determined mode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0033]      FIG. 1  is a block diagram of a conventional video encoder;  
         [0034]      FIG. 2  is a flowchart illustrating a conventional image encoding method performed in the video encoder of  FIG. 1 ;  
         [0035]      FIG. 3  is a block diagram of a video encoder according to an embodiment of the present invention;  
         [0036]      FIG. 4  is a flowchart illustrating an image encoding method according to one aspect of the invention, which is preferably performed in the video encoder of  FIG. 3 ;  
         [0037]      FIG. 5  is a block diagram of a video encoder according to another embodiment of the present invention;  
         [0038]      FIG. 6  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder of  FIG. 5 ;  
         [0039]      FIG. 7  is a block diagram of a video encoder according to another embodiment of the present invention;  
         [0040]      FIG. 8  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder of  FIG. 7 ;  
         [0041]      FIG. 9  is a block diagram of a video encoder according to another embodiment of the present invention;  
         [0042]      FIG. 10  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder of  FIG. 9 ;  
         [0043]      FIG. 11  is a block diagram of a video encoder according to another embodiment of the present invention;  
         [0044]      FIG. 12  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder of  FIG. 11 ;  
         [0045]      FIG. 13  is a block diagram of a video encoder according to another embodiment of the present invention; and  
         [0046]      FIG. 14  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder of  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0047]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown, wherein the same reference numbers denote the same or similar elements.  
         [0048]     Referring to  FIG. 3 , a video encoder  100  according to an embodiment of the present invention comprises a main control unit (MCU)  110 , a motion estimation processor (MEP)  120 , a variable length coder (VLC)  140 , an internal bus system  150 , a memory  160 , a memory controller  170 , and a camera system  180 . The video encoder  100  can be implemented on a semiconductor chip.  
         [0049]      FIG. 4  is a flowchart illustrating a video encoding method according to one aspect of the invention, which is preferably performed in the video encoder  100  of  FIG. 3 . Referring to  FIGS. 3 and 4 , process steps of a mode of operation of the video encoder  100  will be described in chronological order. To begin, the camera system  180  captures a video or image frame and outputs the captured video or image frame via the internal bus system  150  to the memory  160 . The memory  160  receives and stores the video or image frame output from the camera system  180 .  
         [0050]     The MCU  110  starts encoding while producing a picture header for the video or image frame to be encoded. The MCU  110  transfers the picture header to the VLC  140 . The VLC  140  performs variable length coding (VLC) on the picture header and outputs the result to the memory  160 .  
         [0051]     The MCU  110  divides the video or image frame to be encoded into slices, divides each of the slices into macroblocks, and performs encoding while dividing each of the macroblocks into blocks.  
         [0052]     The MCU  110  transfers an MEP parameter to the MEP  120 . The MEP parameter denotes data required for the MEP  120  to calculate a motion vector. The MEP parameter includes the address of the first macroblock of a slice, the address of a search area on a previous frame, the search area corresponding to the current macroblock of the current frame, and the number of macroblocks constituting a slice.  
         [0053]     After transferring the MEP parameter to the MEP  120 , the MCU  110  performs several operations including quantization coefficient calculation until a slice is encoded and decoded.  
         [0054]     The MEP  120  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode.  
         [0055]     The MEP  120  prepares data required for discrete cosine transformation (DCT) and quantization depending on a determined mode. If the current macroblock is processed in an intermode, the MEP  120  calculates the difference between the current macroblock and a motion-compensated macroblock, DCT transforms and quantizes the difference, and outputs a quantized DCT coefficient to the VLC  140 . The MEP  120  also produces a coded block pattern (CBP) based on the quantized DCT coefficient and outputs the CBP to the VLC  140 .  
         [0056]     The MEP  120  can calculate the difference between the motion vector of the current macroblock and a predicted motion vector by a motion vector prediction method used in international standards such as H.263 or MPEG4 (Moving Picture Expert Group 4).  
         [0057]     On the other hand, if the current macroblock is processed in an intramode, the MEP  120  DCT transforms and quantizes the current macroblock and outputs a quantized DCT coefficient to the VLC  140 .  
         [0058]     The VLC  140  receives the mode data (whether intramode or intermode), the CBP, and the quantized DCT coefficient from the MEP  120 , produces a macroblock header using the received data, and outputs the macroblock header to the memory  160 . The VLC  140  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 .  
         [0059]     After VLC encoding on the quantized DCT coefficient is completed, the MEP  120  performs inverse quantization (IQ) and inverse DCT (IDCT) on the quantized DCT coefficient. In an intramode, the MEP  120  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, the MEP  120  obtains the decoded original macroblock by adding the motion-compensated macroblock to the IQ-quantized macroblock and outputs the decoded original macroblock to the memory  160 .  
         [0060]     As described above, when encoding and decoding for one macroblock in a slice is completed, its adjacent macroblock within the same slice is subsequently encoded and decoded.  
         [0061]     Thereafter, the MEP  120  generates an interrupt signal IRQ, which indicates the point in time when encoding and decoding for a slice has been completed, and outputs the same to the MCU  110 . The MCU  110  transfers an MEP parameter to the MEP  120  in response to the interrupt signal IRQ. The following encoding and decoding process is the same as described above.  
         [0062]     The video encoder  100  according to the present invention generates an interrupt signal IRQ once for each slice. Consequently, in order to process 30 frames (each frame is 352×288 pixels) per second, the video encoder  100  generates the interrupt signal IRQ 540 times (540 288×30/16) per second.  
         [0063]     Accordingly, the frequency of IRQ generations by the video encoder  100  according to the present invention is reduced to a maximum of one sixty-sixth ( 1/66) of the frequency of IRQ generations by the conventional video encoder  10 . Therefore, the burden upon the MCU  110  to process the interrupt signal IRQ is reduced, leading to an improvement in the entire system of the video encoder  100 .  
         [0064]      FIG. 5  is a block diagram of a video encoder  200  according to another embodiment of the present invention. The video encoder  200  comprises an MCU  110 , an MEP  121 , a digital signal processor  130 , a VLC  140 , an internal bus system  150 , a memory  160 , a memory controller  170 , and a camera system  180 . In addition, the MEP  121  is directly connected to the VLC  140  by a dedicated bus  151 . Each of the VLC  140 , the memory  160 , the memory controller  170 , and the camera system  180  is connected to the internal bus system  150  and transceives predetermined data.  
         [0065]      FIG. 6  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder  200  of  FIG. 5 . The operation of the video encoder  200  is similar to the operation of the video encoder  100 .  
         [0066]     Referring to  FIGS. 5 and 6 , process steps of a mode of operation of the video encoder  200  will be described in chronological order. To begin, when a video frame to be encoded is prepared, the MCU  110  starts encoding while producing a picture header for the video frame. The MCU  110  transfers the picture header to the VLC  140 .  
         [0067]     The VLC  140  VLC encodes the received picture header and outputs the result to the memory  160 . The memory  160  receives and stores the output signal of the VLC  140 .  
         [0068]     The MCU  110  transfers an MEP parameter to the MEP  121 . The MEP parameter includes the address of the first macroblock of a slice, the address of a search area on a previous frame, the search area corresponding to the current macroblock of the current frame, and the number of macroblocks constituting a slice.  
         [0069]     After transferring the MEP parameter to the MEP  121 , the MCU  110  performs several operations including quantization coefficient calculation until a slice is encoded and decoded.  
         [0070]     The MEP  121  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode.  
         [0071]     The MEP  121  prepares data required for discrete cosine transformation (DCT) and quantization depending on a determined mode. If the current macroblock is processed in an intermode, the MEP  121  calculates the difference between the current macroblock and a motion-compensated macroblock and outputs the same to the DSP  130 .  
         [0072]     The MEP  121  can calculate the difference between the motion vector of the current macroblock and a predicted motion vector by a motion vector prediction method used in international standards such as H.263 or MPEG4.  
         [0073]     On the other hand, if the current macroblock is processed in an intramode, the MEP  121  outputs the current macroblock to the DSP  130 .  
         [0074]     The MEP  121  outputs the data regarding the determined mode and the difference between the motion vector of the current macroblock and a predicted motion vector directly to the VLC  140  via bus  151 . Here, the data regarding the determined mode is referred to as mode data.  
         [0075]     The DSP  130  receives the current macroblock or the difference between the current macroblock and a motion-compensated macroblock, DCT-transforms and quantizes them, and outputs a quantized DCT coefficient to the VLC  140 . The DSP  130  also produces a CBP based on the produced quantized DCT coefficient and outputs the same to the VLC  140 .  
         [0076]     The VLC  140  receives the mode data, the CBP, and the quantized DCT coefficient from the MEP  121 , produces a macroblock header using the received data, and outputs the macroblock header to the memory  160 . The VLC  140  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 .  
         [0077]     After VLC encoding on the quantized DCT coefficient is completed, the DSP  130  performs IQ and IDCT on the quantized DCT coefficient. In an intramode, the MEP  121  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, the MEP  121  obtains the decoded original macroblock by adding the motion-compensated macroblock to the IQ-quantized macroblock and then outputs the decoded original macroblock to the memory  160 .  
         [0078]     As described above, if encoding and decoding for one macroblock in a slice is completed, its adjacent macroblock within the same slice is subsequently encoded and decoded. Thereafter, the MEP  121  generates an interrupt signal IRQ, which indicates the point in time when encoding and decoding for a slice has been completed, and outputs the same to the MCU  110 .  
         [0079]      FIG. 7  is a block diagram of a video encoder  300  according to another embodiment of the present invention. The video encoder  300  comprises an MCU  110 , an MEP  220 , a VLC  240 , an internal bus system  150 , a memory  160 , a memory controller  170 , an MCP  270 , and a camera system  180 .  
         [0080]     Referring to  FIGS. 7 and 8 , a video encoding method according to another aspect of the present invention, which is preferably performed in the video encoder  300 , will be described. To begin, when a video frame to be encoded is prepared, the MCU  110  starts encoding while producing a picture header for the video or image frame to be encoded. The MCU  110  transfers the picture header to the VLC  240  via the internal bus system  150 . The VLC  240  performs variable length coding (VLC) on the picture header and outputs the result to the memory  160 .  
         [0081]     The MCU  110  transfers an MEP parameter to the MEP  220 . The MEP parameter includes the address of the first macroblock in a current frame, the address of a search area on its previous frame, the search area corresponding to a current macroblock in the current frame, and the number of macroblocks constituting a slice.  
         [0082]     After transferring the MEP parameter to the MEP  220 , the MCU  110  performs several operations including quantization coefficient calculation until a slice is encoded and decoded.  
         [0083]     The MEP  220  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode.  
         [0084]     The MEP  220  prepares data required for DCT and quantization depending on the data regarding the determined mode. If the current macroblock is processed in an intermode, the MEP  220  calculates the difference between the current macroblock and a motion-compensated macroblock, DCT transforms and quantizes the difference, and outputs a quantized DCT coefficient to the VLC  240 . The MEP  220  also produces a CBP based on the quantized DCT coefficient and outputs the CBP to the VLC  240 .  
         [0085]     The MEP  220  can calculate the difference between the motion vector of the current macroblock and a predicted motion vector by a motion vector prediction method used in international standards such as H.263 or MPEG4.  
         [0086]     On the other hand, if the current macroblock is processed in an intramode, the MEP  220  DCT transforms and quantizes the current macroblock and outputs a quantized DCT coefficient to the VLC  240 .  
         [0087]     The MEP  220  also produces an interrupt signal IRQ for indicating the point in time when encoding for a slice has been completed, and outputs the same to the MCU  110 .  
         [0088]     The VLC  240  receives the data regarding the determined mode, the CBP, and the quantized DCT coefficient from the MEP  220 , produces a macroblock header using the received data, and outputs the same to the memory  160 .  
         [0089]     The VLC  240  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 . The memory  160  successively stores the VLC-coded macroblock header and the VLC-coded quantized DCT coefficient.  
         [0090]     After VLC encoding on the quantized DCT coefficient is completed, the MEP  220  performs IQ and IDCT on the quantized DCT coefficient. In an intramode, the MEP  220  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, after the IQ and IDCT performed on the quantized DCT coefficient by the MEP  220 , the MCP  270  adds the motion-compensated macroblock to the IQ-quantized macroblock to obtain the decoded original macroblock and outputs the decoded original macroblock to the memory  160 .  
         [0091]     As described above, when encoding and decoding for one macroblock in a slice is completed, its adjacent macroblock within the same slice is subsequently encoded and decoded.  
         [0092]      FIG. 9  is a block diagram of a video encoder  400  according to another embodiment of the present invention. The video encoder  400  comprises an MCU  110 , an MEP  221 , a digital signal processor  230 , a VLC  240 , an internal bus system  150 , a memory  160 , a memory controller  170 , an MCP  270 , and a camera system  180 . In addition, the MEP  221  is directly connected to the VLC  240  by a dedicated bus  151 .  
         [0093]      FIG. 10  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder  400  of  FIG. 9 . Referring to  FIGS. 9 and 10 , process steps of a mode of operation of the video encoder  400  will be described in chronological order. To begin, when a video frame to be encoded is prepared, the MCU  110  starts encoding while producing a picture header for the video frame. The MCU  110  transfers the picture header to the VLC  240  via the internal bus system  150 .  
         [0094]     The VLC  240  VLC encodes the received picture header and outputs the result to the memory  160 . The memory  160  receives and stores the output signal of the VLC  240 .  
         [0095]     The MCU  110  transfers an MEP parameter to the MEP  221 . The MEP parameter includes the address of the first macroblock of a slice, the address of a search area on a previous frame, the search area corresponding to the current macroblock of the current frame, and the number of macroblocks constituting a slice.  
         [0096]     After transferring the MEP parameter to the MEP  221 , the MCU  110  performs several operations including quantization coefficient calculation until a slice is encoded and decoded.  
         [0097]     The MEP  221  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode. Data regarding the determined mode is transferred directly to the VLC  240  via the bus  151 .  
         [0098]     Depending on the data regarding the determined mode, the MEP  221  prepares data required for discrete cosine transformation (DCT) and quantization. If the current macroblock is processed in an intermode, the MEP  221  calculates the difference between the motion vector of the current macroblock and a predicted motion vector using a motion vector prediction method used in international standards such as H.263 or MPEG4 and outputs the same directly to the VLC  240  via the bus  151 .  
         [0099]     On the other hand, if the current macroblock is processed in an intramode, the MEP  221  outputs the current macroblock directly to the DSP  230 . The MEP  221  generates an interrupt signal IRQ that indicates the point in time when encoding for a slice has been completed, and outputs the interrupt signal IRQ to the MCU  110 .  
         [0100]     The DSP  230  receives the current macroblock or the difference between the current macroblock and a motion-compensated macroblock, DCT-transforms and quantizes them, and outputs a quantized DCT coefficient to the VLC  240 . The DSP  230  also produces a CBP based on the produced quantized DCT coefficient and outputs the same to the VLC  240 .  
         [0101]     The VLC  240  receives the mode data, the CBP, and the quantized DCT coefficient from the MEP  221 , produces a macroblock header using the received data, and outputs the macroblock header to the memory  160 . The VLC  240  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 .  
         [0102]     After VLC encoding on the quantized DCT coefficient is completed, the MEP  221  performs IQ and IDCT on the quantized DCT coefficient. In an intramode, the MEP  221  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, the MEP  221  obtains the decoded original macroblock by adding the motion-compensated macroblock to the IQ-quantized macroblock and then outputs the decoded original macroblock to the memory  160 .  
         [0103]     As described above, when encoding and decoding for one macroblock in a slice is completed, its adjacent macroblock within the same slice is subsequently encoded and decoded.  
         [0104]      FIG. 11  is a block diagram of a video encoder  500  according to another embodiment of the present invention. In contrast with the previous embodiments, the video encoder  500  includes a dedicated DSP for performing DCT, IDCT, Q, IQ, and VLC.  
         [0105]     The video encoder  500  comprises an MCU  110 , an MEP  121 , a DSP  330 , an internal bus system  150 , a memory  160 , a memory controller  170 , and a camera system  180 . Each of the MCU  110 , the MEP  121 , the DSP  330 , the memory  160 , the memory controller  170 , and the camera system  180  is connected to the internal bus system  150  and transceives predetermined data.  
         [0106]      FIG. 12  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder  500  of  FIG. 11 . Referring to  FIGS. 11 and 12 , process steps of a mode of operation of the video encoder  500  will be described in chronological order.  
         [0107]     To begin, when a video frame to be encoded is prepared, the MCU  110  starts encoding while producing a picture header for the video frame. The MCU  110  transfers the picture header to the DSP  330 . The DSP  330  VLC encodes the received picture header and outputs the result to the memory  160 . The memory  160  receives and stores the output signal of the DSP  330 .  
         [0108]     The MCU  110  transfers an MEP parameter to the MEP  121 . The MEP parameter includes the address of the first macroblock of a slice, the address of a search area on a previous frame, the search area corresponding to the current macroblock of the current frame, and the number of macroblocks constituting a slice.  
         [0109]     After transferring the MEP parameter to the MEP  121 , the MCU  110  performs several operations including quantization coefficient calculation until a slice is encoded and decoded.  
         [0110]     The MEP  121  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode.  
         [0111]     The MEP  121  prepares data required for discrete cosine transformation (DCT) and quantization (Q) depending on a determined mode. If the current macroblock is processed in an intermode, the MEP  121  calculates the difference between the current macroblock and a motion-compensated macroblock and outputs the same to the DSP  330 .  
         [0112]     The MEP  121  can calculate the difference between the motion vector of the current macroblock and a predicted motion vector by a motion vector prediction method used in international standards such as H.263 or MPEG4.  
         [0113]     On the other hand, if the current macroblock is processed in an intramode, the MEP  121  outputs the current macroblock to the DSP  330 .  
         [0114]     The MEP  121  outputs the data regarding the determined mode and the difference between the motion vector of the current macroblock and a predicted motion vector directly to the DSP  330 . Hereinafter, the data regarding the determined mode is referred to as mode data.  
         [0115]     The DSP  330  receives the current macroblock or the difference between the current macroblock and a motion-compensated macroblock, DCT-transforms and quantizes them, and outputs a quantized DCT coefficient. The DSP  330  also produces a CBP based on the produced quantized DCT coefficient.  
         [0116]     The DSP  330  produces a macroblock header using the mode data received from the MEP  121 , the CBP, and the quantized DCT coefficient and outputs the macroblock header to the memory  160 . The DSP  330  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 .  
         [0117]     After VLC encoding on the quantized DCT coefficient is completed, the DSP  330  performs IQ and IDCT on the quantized DCT coefficient. In an intramode, the MEP  121  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, the MEP  121  obtains the decoded original macroblock by adding the motion-compensated macroblock to the IQ-quantized macroblock and then outputs the decoded original macroblock to the memory  160 .  
         [0118]     As described above, if encoding and decoding for one macroblock in a slice is completed, its adjacent macroblock within the same slice is subsequently encoded and decoded. Thereafter, the MEP  121  generates an interrupt signal IRQ, which indicates the point in time when encoding and decoding for a slice has been completed, and outputs the same to the MCU  110 .  
         [0119]      FIG. 13  is a block diagram of a video encoder  600  according to another embodiment of the present invention. In contrast with the embodiment of  FIG. 11 , the video encoder  600  starts encoding by using a DSP instead of a MCU (not shown), and the DSP performs the operations that the MCU perform in order to achieve the encoding. The MCU indicates the point in time when encoding for frame is started to the DSP  331 , and DSP  331  indicate the point in time when encoding for a frame has been completed.  
         [0120]     The video encoder  600  comprises an MEP  121 , a DSP  331 , an internal bus system  150 , a memory  160 , a memory controller  170 , and a camera system  180 . Each of the MEP  121 , the DSP  331 , the memory  160 , the memory controller  170 , and the camera system  180  is connected to the internal bus system  150  and transceives predetermined data.  
         [0121]      FIG. 14  is a flowchart illustrating an image encoding method according to another aspect of the invention, which is preferably performed in the video encoder  600  of  FIG. 13 . Referring to  FIGS. 13 and 14 , process steps of a mode of operation of the video encoder  600  will be described in chronological order.  
         [0122]     To begin, when a video frame to be encoded is prepared, the DSP  331  starts encoding while producing a picture header for the video frame in response to an instruction of the MCU to start encoding. In other words, the DSP  331  VLC encodes the produced picture header and outputs the result to the memory  160 . The memory  160  receives and stores the output signal of the DSP  331 .  
         [0123]     The DSP  331  transfers an MEP parameter to the MEP  121 . The MEP parameter includes the address of the first macroblock of a slice, the address of a search area on a previous frame, the search area corresponding to the current macroblock of the current frame, and the number of macroblocks constituting a slice.  
         [0124]     After transferring the MEP parameter to the MEP  121 , the DSP  331  calculates a quantization coefficient until data required for encoding is received from the MEP  121 .  
         [0125]     The MEP  121  estimates a motion vector in response to the MEP parameter and determines whether a current macroblock is to be processed in an intermode or an intramode.  
         [0126]     The MEP  121  prepares data required for discrete cosine transformation (DCT) and quantization (Q) depending on a determined mode. If the current macroblock is processed in an intermode, the MEP  121  calculates the difference between the current macroblock and a motion-compensated macroblock and outputs the same to the DSP  331 .  
         [0127]     The MEP  121  can calculate the difference between the motion vector of the current macroblock and a predicted motion vector by a motion vector prediction method used in international standards such as H.263 or MPEG4.  
         [0128]     On the other hand, if the current macroblock is processed in an intramode, the MEP  121  outputs the current macroblock to the DSP  331 .  
         [0129]     The MEP  121  outputs the data regarding the determined mode and the difference between the motion vector of the current macroblock and a predicted motion vector directly to the DSP  331 . Hereinafter, the data regarding the determined mode is referred to as mode data.  
         [0130]     The DSP  331  receives the current macroblock or the difference between the current macroblock and a motion-compensated macroblock, DCT-transforms and quantizes them, and outputs a quantized DCT coefficient. The DSP  331  also produces a CBP based on the produced quantized DCT coefficient.  
         [0131]     The DSP  331  produces a macroblock header using the mode data received from the MEP  121 , the CBP, and the quantized DCT coefficient and outputs the macroblock header to the memory  160 . The DSP  331  also VLC-encodes the quantized DCT coefficient and outputs the encoding result to the memory  160 .  
         [0132]     After VLC encoding on the quantized DCT coefficient is completed, the DSP  331  performs IQ and IDCT on the quantized DCT coefficient.  
         [0133]     In an intramode, the MEP  121  outputs the decoded original macroblock to the memory  160  without any intervening process. However, in an intermode, the MEP  121  obtains the decoded original macroblock by adding the motion-compensated macroblock to the IQ-quantized macroblock and then outputs the decoded original macroblock to the memory  160 .  
         [0134]     As described above, the DSP  331  performs not only encoding and decoding the macroblocks but also generating and encoding the picture header of the frame. Therefore, MEP  121  need not generate an interrupt signal IRQ, which indicates the point in time when encoding and decoding for a slice has been completed, and outputs the same to the DSP  331 . Instead, the DSP  331  generates an interrupt signal IRQ, which indicates the point in time when encoding for a frame has been completed, and outputs the same to the MCU (not shown).  
         [0135]     Accordingly, each of the video encoders  100 ,  200 ,  300 ,  400 , and  500  according to the present invention generates an interrupt signal IRQ once for each slice. Consequently, in order to process 30 frames (each frame is 352×288 pixels) per second, each of the video encoders  100 ,  200 ,  300 , and  400  generates the interrupt signal IRQ 540 times (540=288×30/16) per second.  
         [0136]     In addition, the video encoders  600  according to the present invention generates an interrupt signal IRQ once for each frame. Consequently, in order to process 30 frames (each frame is 352×288 pixels) per second, the video encoder  600  generates the interrupt signal IRQ 30 times per second.  
         [0137]     Accordingly, the frequency of generations of IRQ by each of the video encoders  100 ,  200 ,  300 ,  400 , and  500  according to the present invention is reduced to a maximum of one sixty-sixth ( 1/66) of the frequency at which IRQ signals are generated by the conventional video encoder  10 . In addition, the frequency of generations of IRQ by the video encoders  600  according to the present invention is reduced to a maximum of one over one thousand and one hundred eighty-eight ( 1/1188) of the frequency at which IRQ signals are generated by the conventional video encoder  10 . Therefore, the burden upon the MCU  110  to process the interrupt signal IRQ is reduced, leading to an improvement in the entire system of each of the video encoders  100 ,  200 ,  300 ,  400 ,  500 , and  600 .  
         [0138]     While this invention has been particularly shown and described with reference to preferred 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.