KR20030091134A - Apparatus and method for generating thumbnail image - Google Patents

Abstract

PURPOSE: A system and method for generating thumbnail images are provided to generate thumbnail images having the same size irrespective of the format of a video stream. CONSTITUTION: A system for generating thumbnail images includes a DC decoder(101), a buffer(103), and a buffer controller(102). The DC decoder parses only the DC value of I-picture from an inputted video stream. The buffer stores the DC value output from the DC decoder. The buffer controller reduces DC values of sub-blocks included in a macro-block including the DC value output from the DC decoder by 1/N (N is more than 2) and stores the reduced DC values in the buffer when the macro-block is HD grade. The buffer controller outputs the DC values stored in the buffer to a system memory in order to generate a thumbnail image.

Description

Apparatus and method for generating thumbnail image}

The present invention relates to an apparatus and method for generating thumbnail images having a consistent size from moving images having different formats among additional functions provided by a personal video recorder (PVR) installed in a digital TV.

In general, a thumbnail image represents a specific frame of a video smaller than the original size for the purpose of browsing or searching. These thumbnail images are program guides, story boards, content summary functions, and keys for the stored video media, among the additional functions provided by personal video recorders (PVRs), which are mainly equipped with digital TVs. Used to provide functions such as key frame generation. In particular, there are various fields of use, such as the ability to display multiple thumbnail images on one screen in order to implicitly display the contents of recorded videos in an additional function such as a storyboard in a personal video recorder, or to create a representative image for use in a program guide. Do.

A conventional method of generating a thumbnail image is a method using a DC value of an I picture among frames of video encoded by MPEG. This method does not require a variable length decoder (VLD) for playing the entire video frame, and does not require scaling operations for further reduction to generate thumbnail images, greatly reducing the hardware burden and reducing the horizontal. And an image reduced by 1/8 in the vertical direction, respectively. That is, a relatively simple method has the advantage of generating a thumbnail image corresponding to the size of 1/64 of the original image without burden on the hardware.

In general, however, MPEG video streams that can be viewed on a digital TV have various formats such as HD (High Definition) and SD (Standard Definition), and the resolution of each frame of the video also varies according to the various formats.

Therefore, the existing thumbnail image generation method using the DC value generates a thumbnail corresponding to the size of 1/64 of the original image regardless of the format of the input video. For example, thumbnail images of HD video having a resolution of 1920x1088 and SD video having a resolution of 720x480 have a resolution of 240x136 and 90x60, respectively. That is, the size of the thumbnail image may be more than six times different depending on the format of the video. This difference leads to the problem that the layout of thumbnail images must be defined differently depending on the video format in applications such as storyboard composition. Also, when displaying thumbnail images for videos of different formats on one screen, the size of each thumbnail The difference may cause a visual inconvenience to the user. That is, the display map for displaying several thumbnail images on the screen should be defined differently for each format, and the device that stores the thumbnails, for example, the memory map that defines the storage space in the memory, may also have different sizes. There is a problem that needs to be defined differently according to the video format. In addition, there are hardware problems such as complex computations, computational complexity, and additional memory burden in order to perform post-processing such as scaling or interpolation to solve the size mismatch.

In addition, the conventional method of generating a thumbnail image generates a thumbnail image for only one field in the case of a video stream in which each field is independently encoded, and as a result, thumbnails reduced by 1/2 in the vertical direction may occur. In order to solve this problem, the conventional method generates a thumbnail frame by interlacing each of the thumbnail fields obtained from the top field and the bottom field. However, in the case of an interlaced sequence, a thumbnail image obtained by this method has a problem in that flickering occurs due to a time difference between an odd scan line and an even scan line and movement between fields.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a thumbnail image generating apparatus and method for generating a thumbnail image of a consistent size regardless of the format of the video stream.

Another object of the present invention is to generate a thumbnail image using only one field in the case of an interlace sequence, and in the process, a thumbnail image generating apparatus and method for generating a thumbnail image having the same size as a frame by duplication of each line In providing.

1 is a block diagram showing an embodiment of a thumbnail image generating apparatus according to the present invention

2 is a flowchart illustrating an embodiment of a decimation mode during operation of a thumbnail image generating apparatus according to the present invention.

3 is a flowchart illustrating an embodiment of an average mode during operation of a thumbnail image generating apparatus according to the present invention;

4A and 4B illustrate an embodiment of an internal buffer configuration for an HD picture and an SD picture of the thumbnail image generating device according to the present invention.

FIG. 5 is a flowchart illustrating an exemplary embodiment of performing redundancy with respect to an HD field picture during the operation of a thumbnail image generating apparatus according to the present invention; FIG.

FIG. 6 is a flowchart illustrating an exemplary embodiment of performing redundancy with respect to an SD field picture during an operation of a thumbnail image generating apparatus according to the present invention; FIG.

Explanation of symbols for main parts of the drawings

101: DC decoder 102: buffer controller

103: buffer 104: system memory interface

An apparatus and method for generating a thumbnail image according to the present invention for achieving the above object generates a thumbnail image using a DC value of an I picture, but additionally 1 / N for an HD video stream (eg, N is 4). It includes two modes for generating thumbnail images further reduced. The first mode is a decimation mode, in which a 4: 1 decimation technique is applied to store only a DC value of one luminance block among four luminance blocks included in one macroblock in a buffer. The second mode is an average mode, in which an average value of DC values of four luminance blocks included in one macro block is calculated, and the average value is stored in a buffer.

In addition, the present invention is characterized by generating a thumbnail image using only one field of the top, bottom field for the field sequence, and outputs by overlapping each line of the thumbnail image in order to have the same size as the frame. .

To this end, a thumbnail image generating apparatus according to the present invention includes a DC decoder for parsing only a DC value of an I picture from an input video stream, a buffer for storing a DC value output from the DC decoder, and a DC output from the DC decoder. If the macroblock including the value is HD, the DC value of the subblocks included in the macroblock is reduced to 1 / N (N is a natural number of 2 or more) and controlled to be stored in the buffer, and the DC value stored in the buffer is thumbnailed. And a buffer controller which outputs to the system memory to generate an image.

The buffer controller controls the DC value of any one of the four luminance blocks included in the macro block and the DC values of the Cb and Cr blocks to be stored in the buffer when the macro block to be input is HD. It is done.

The buffer controller obtains an average of the DC values of the four luminance blocks included in the macro block if the input macro block is HD, and controls the average value and the DC values of the Cb and Cr blocks to be stored in the buffer. It features.

The buffer controller is characterized in that if the input macro block is SD class, the DC values for the four luminance blocks included in the macro block and the DC values for the Cb and Cr blocks are stored in the buffer.

When the input bit stream is a field picture, the buffer controller controls only the DC value of any one of the top and bottom fields to be stored in the buffer, and the read point of the buffer when transferring the data stored in the buffer to the system memory. The control may overlap and transmit data corresponding to one thumbnail image line from the buffer.

The method for generating a thumbnail image according to the present invention includes parsing only a DC value of an I picture from an input video stream, and if the macro block including the DC value input in the parsing step is HD, the sub block is included in the macro block. Reducing DC values of the blocks by 1 / N (N is a natural number of 2 or more) and storing them in the buffer; and if the macro block including the DC value input in the parsing step is SD, all subs included in the macro block are And storing the DC values for the blocks in the buffer, and outputting the DC values stored in the buffer to the system memory when the slice including the macro block ends.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the preferred embodiment of the present invention, the configuration and operation of the invention shown in the drawings and described by it are described as at least one embodiment, which By the technical spirit of the present invention described above and its core configuration and operation is not limited.

The present invention is a minimal hardware without undergoing complex processes such as interpolation or size conversion, and the size of thumbnail images generated from video having different formats such as HD and SD video and field / frame video To have a consistent size. In addition, the present invention generates a thumbnail image using only one field in the case of an interlaced sequence, and in this process, by generating a thumbnail image having the same size as a frame by overlapping each line, This is to prevent flickering that can occur by interlacing a field.

1 is a block diagram illustrating an embodiment of a thumbnail image generating apparatus according to an embodiment of the present invention, a DC decoder 101 for parsing only a DC value of an I picture from a video input, and a buffer for storing the parsed DC value ( 103, and a buffer controller 102 for storing the DC value in the buffer 103 and for transmitting the DC value stored in the buffer 103 to the system memory through the system memory interface 104, and controlling the overall flow. It is composed of

That is, the buffer controller 102 allows the data stored in the buffer 102 to be stored at a specific location in the system memory through the system memory interface 104.

The DC decoder 101 has a structure that can parse only the DC value of the I picture in a very simple structure compared to the VLD of a general MPEG video decoder. That is, since the purpose is to generate a thumbnail image, there is no need to decode the P picture and the B picture, and the structure of the variable decoding table and hardware required to obtain other AC values is removed.

The buffer 103 is composed of two buffers 103a and 103b, and the two buffers 103a and 103b are controlled by the double-buffering technique in the buffer control unit 102. . That is, when a DC value is filled in one buffer, the DC value is transferred from the buffer to the system memory, and the newly input DC value is stored in another buffer.

In this case, each buffer has a size enough to store one slice, and in the thumbnail image generating apparatus according to the present invention, each buffer is set to have a size of 360 bytes. This size is based on an HD-quality image with a resolution of 1920x1088, which has the largest amount of data among the inputtable video formats, and a total of three DC values per macro block (i.e., one Y, one Cb, and one Cr per DC block). Value), so it is set to 360 bytes to store 120x3 DC values per slice.

When each slice ends, the DC value stored in the buffer 103 is transferred to the system memory or the hard disk. The end of the slice is generated in the buffer controller 102 when the last DC value of the slice is input. When the slice ends, the buffer controller 102 requests a memory access through the system memory interface 104, and the slice data is transmitted to the system memory through a series of control processes. At this time, the buffer controller 102 calculates and transmits address information for storing the current thumbnail image on the system memory. In other words, if the start address is increased by the size of slice data each time a DC value corresponding to each slice is transmitted, the current slice data is automatically stored in the system memory by being continuously connected to previously stored slice data.

Thus, through this process, a full-scale thumbnail image is stored in the system memory. The thumbnail image stored in the system memory may be stored in a storage device such as a hard disk, and the present invention is not limited to an interface with the storage device because the present invention is limited to a device for generating a thumbnail image.

The thumbnail image generating apparatus according to the present invention generates four thumbnail image pixels per macroblock for an SD class video, and one thumbnail image pixel per macroblock for an HD class video.

In this case, when generating HD video thumbnail image pixels, two different modes exist, and are classified into a decimation mode and an averaging mode. The control of the decimation mode and the average mode is made in the buffer controller 102.

According to an embodiment of the present invention, the size of the thumbnail image to be generated is based on an SD class image having a resolution of 720x480. The reason is to minimize the simplification and complexity of the hardware, which is the object of the present invention, and to minimize the inconsistency of the size of the thumbnail image due to the difference in the input format. In other words, in the case of HD-based video, a circuit for performing size conversion on the SD-based video is required, which requires computation such as image conversion and interpolation, and thus has a large memory and hardware complexity. In addition, when thumbnails of 720x480 size images are generated, thumbnail images having a resolution of 90x60 are generated, which is large enough to provide a user with functions such as browsing and searching.

Therefore, in the case of an HD image having a size of 1920x1088 by the thumbnail generation device according to the present invention, one thumbnail pixel is generated per macroblock, and as a result, a thumbnail image having a size of 120x68 is generated, which is only 1.5 compared to the SD level. The size difference is about twice. As a result, the maximum size conversion effect can be achieved with minimum complexity.

As a result, the thumbnail generating apparatus according to the present invention generates four thumbnail pixels per macroblock for the SD video, and generates four Y components and one Cb and Cr component for each macroblock. : Thumbnail pictures having a 0 color format are generated. On the other hand, one thumbnail pixel is generated per macroblock for HD video, and one Y, Cb, and Cr component is generated for each macroblock, resulting in a thumbnail image having a 4: 4: 4 color format. .

2 is a flowchart according to an embodiment of a decimation mode during operation of a thumbnail image generating apparatus according to the present invention, wherein an input image is limited to an I picture of an MPEG encoded video stream and is controlled by the buffer controller 102. The DC value of each I picture is stored in the buffer 103 accordingly. Each DC value has a value from 0 to 255, which is represented by 1 byte of data. In general, in an MPEG video having a 4: 2: 0 format, a DC value means an average value of each block, and since there are six blocks per macroblock, six DC values are input from one macroblock. The DC values of the first four (blocks 0 to 3) are the DC values of the Y component corresponding to the luminance signal, and the remaining two (blocks 4 and 5) correspond to the DC values of the Cb and Cr components, respectively.

That is, when the macro block is started (step 201), it is determined whether the input macro block is HD class or SD class (step 202). If it is determined in step 202 that the HD level, the DC value corresponding to one Y block among the four Y blocks per macroblock and the DC value of the Cb and Cr blocks are stored in the buffer 103 (step 203). That is, only one Y component is stored in the buffer 103 for each macroblock for the HD video stream.

Then, it is determined whether the slice including the macroblock is finished (step 205). Since the slice end determination has been described above, a detailed description thereof will be omitted.

If it is determined in step 205 that the slice is not finished, the process returns to the step of determining whether the slice is HD or SD by receiving the next macro block, and when it is determined that the slice is finished, the DC value stored in the buffer 103 is transferred to the system memory. Transmit (step 207).

When the input macro block is HD, the present invention is an embodiment in which the DC value of block 0 is stored among four Y blocks. This is an embodiment, and in some cases, any one of blocks 1, 2, and 3 may be stored, which does not significantly affect the overall performance. As a result, in the case of HD-quality video, one thumbnail pixel becomes data corresponding to a macroblock of the original video.

Thus, in the case of 1920x1088, one slice is composed of 120 macroblocks, and 120 thumbnail pixels are stored in each of the buffers 103a and 103b. As a result, by generating one thumbnail pixel per macroblock, size reduction of 1/16 is performed in the horizontal and vertical directions, respectively.

On the other hand, if it is determined in the step 202 to the SD class, the DC value of all blocks existing in the macro block, that is, the DC values for four Y blocks and one Cb, Cr block are stored in the buffer 103 (step 204). . Then, it is determined whether the slice is finished (step 205). Similarly, if it is determined in step 205 that the slice is not finished, the process returns to the step of determining whether it is HD or SD class by receiving the next macro block, and if it is determined that the slice is finished, the system stores the DC value stored in the buffer 103. Transfer to memory (step 207).

3 is a flowchart illustrating an average mode of an operation of a thumbnail image generating apparatus according to an embodiment of the present invention. When an input video is HD, an image outputs one thumbnail pixel per macroblock like a decimation mode. . However, the Y component of the thumbnail pixel is set to an average value of all blocks corresponding to the Y component, that is, the blocks 0 to 3, instead of one representative value.

That is, when the macro block is started (step 301), it is determined whether the input macro block is HD class or SD class (step 302). If it is determined in step 302 that the HD level, the average of the DC values of the four Y blocks per macro block and then the average value and the DC value of the Cb, Cr blocks are stored in the buffer 103 (step 303).

Then, it is determined whether the slice in which the macroblock is included is finished (step 305). If it is determined in step 305 that the slice is not finished, the process returns to the step of determining whether the slice is HD or SD by receiving the next macro block, and when the slice is finished, the DC value stored in the buffer 103 is transferred to the system memory. Transmit (step 307).

In the average mode as described above, a smoothing effect can be obtained when a high frequency component is obtained. However, when applied to a general image, there is a slight blur. exist. Therefore, when the system determines the characteristics of the input image and uses a high frequency component, the average mode can generate a thumbnail image more effectively.

On the other hand, in the case of decimation and average mode, the generation method of the thumbnail image for the SD video is the same. That is, if it is determined in the step 302 as the SD class, the DC values of all blocks existing in the macro block, that is, the DC values of four Y blocks and one Cb and Cr block are stored in the buffer 103 (step 304). . Then, it is determined whether the slice is finished (step 205). If it is determined that the slice is not finished, it returns to the step of determining whether it is HD or SD class by receiving the next macro block, and when it is determined that the slice is finished, the buffer ( The DC value stored in 103 is transferred to the system memory (step 307).

As such, for the SD video stream, a thumbnail image is generated using all DC values of the macro block regardless of the decimation mode and the average mode, and as a result, four thumbnail pixels are generated per macroblock.

FIG. 4 is a view showing an embodiment of a configuration or a buffer map of the internal buffers 103a and 103b of the thumbnail image generating apparatus according to the present invention. FIG. 4A is a map of a buffer in which an HD image is stored, and FIG. 4B is an SD. It shows the map of the buffer where the high quality image is stored.

That is, video data corresponding to one slice is stored in each buffer. In this case, when thumbnail images are used as reference, two thumbnail lines are stored for the Y signal in the case of SD video, and one thumbnail line is stored in the case of HD video. Referring to the configuration of the buffer for the SD video of Figure 4b based on the first 90 bytes of data stored in one line is configured as {DC0, DC1, DC0, DC1, DC0, DC1, ...} DC0 and DC1 represent DC values obtained from blocks 0 and 1, respectively. Further, the 91th to 180th bytes stored in the second line are configured as {DC2, DC3, DC2, DC3, DC2, DC3, ...}. DC2 and DC3 represent DC values obtained from blocks 2 and 3, respectively. That is, in case of SD class, one buffer storage area is composed of four (Y1, Y2, Cb, Cr), and the DC value extracted from blocks 0 and 1 in slice units is stored in the Y1 storage area, and Y2 is stored. In the region, DC values extracted from blocks 2 and 3 in slice units are stored. In the Cb and Cr storage regions, DC values of the Cb and Cr blocks are stored in units of slices.

On the other hand, for HD-quality video, up to 120 Y, Cb, Cr thumbnail pixels are generated per slice, and the same number of Y component thumbnail pixels is generated regardless of decimation and average modes, so the two modes are the same. It has a buffer diagram. That is, in the case of HD class, one buffer storage area is composed of three Y, Cb, and Cr, DC values for the Y component are stored in the Y storage area in slice units, and Cb, Cb, and Cb in the Cb, Cr storage areas. Each DC value of the Cr block is stored.

5 and 6 are flowcharts of performing a duplication mode when the input video stream is a field picture, FIG. 5 is a flowchart of a field picture of HD level, and FIG. 6 is a flowchart of a field picture of SD level. to be.

That is, when the input video is a field picture, a thumbnail image is generated for the first decoded field regardless of the top or bottom field. In this case, a thumbnail image is not generated for the second input field. The redundancy mode is performed by the buffer controller 102, and in particular, by transferring data corresponding to one thumbnail line from the buffer 103 when the thumbnail data is transmitted to the system memory.

Therefore, the configuration of the buffer or the buffer map does not change, and by controlling the read point of reading the buffer, the thumbnail image may be enlarged twice in the vertical direction. In FIG. 5 and FIG. 6, a block denoted as performing a buffer read is used to include both an operation of reading data from the buffer 103 and transferring the read data to the system memory. In addition, the control of the read point adjusts the data corresponding to one thumbnail line to be repeatedly transmitted for each color component. As a result, the duplicated thumbnail image is stored in the system memory.

Assuming that the configuration diagram of the buffer 103 is the same as that of FIG. 4A, in the case of an HD video stream, data is transmitted in duplicate by 120 bytes as shown in FIG. 5. First, for the Y component, the first to 120th bytes of the buffer 103 are read and transferred to the system memory. Then, the buffer read pointer is moved to the first byte, and the 120 bytes are read again and transferred to the system memory. 504). After the above steps 501 to 504 are performed, the buffer read for the Cb component is started. That is, for the Cb component, the 121th to 240th bytes are read and transferred to the system memory. Then, the buffer read pointer is moved to the 121th byte, and 240 bytes are read again and duplicated to the system memory (steps 505 to 508). For the Cr component, the 241 th to 360 th bytes are read and transferred to the system memory. Then, the buffer read pointer is moved to the 241 th byte, and the 360 bytes are read again and transferred back to the system memory (steps 509 to 512).

As a result, if 360 bytes of data are stored in the buffer 103, in the case of a field picture, 720 bytes of data, which is twice that number, are transferred to the system memory by performing redundancy.

On the other hand, assuming that the configuration diagram of the buffer 103 is the same as that of Fig. 4B, two Y component thumbnail data and one Cb and Cr component thumbnail data exist in the SD video stream.

Therefore, when the input video stream is a field picture and an SD video stream, one thumbnail line is repeatedly transmitted as shown in FIG. 6, so that the first 90 bytes are duplicated and the next 90 bytes are repeatedly transmitted. Redundant transfer is performed byte by byte. That is, first, the first to the 90th bytes are read and transferred to the system memory for the Y1 storage area of the buffer 103, and then the buffer read pointer is moved to the first byte to read the 90 bytes again and redundantly transferred to the system memory ( Steps 601 to 604). After the above steps 601 to 604 are performed, the buffer read for the Y2 storage area is repeatedly performed (steps 605 to 608). That is, in steps 605 to 608, the buffer read pointer is moved to the 91 th byte to transfer the 90 bytes of data to the system memory, and then the buffer read pointer is moved to the 91 th byte again and the 90 bytes of data are repeatedly transferred to the system memory. do. This means that each 90 bytes is one thumbnail line. Subsequently, in the case of the Cb and Cr components, duplication of 45 bytes may be performed (steps 609 to 612 and steps 613 to 616).

Therefore, a thumbnail image having a 4: 2: 0 color format is stored in the system memory. As in the case of HD-quality video, up to 270 bytes of data are required for field pictures to store slice data of SD-quality video, and the size of data transmitted to system memory becomes 540 bytes due to redundancy.

In this case, the unit for transmitting data to the system memory at one time is determined by the specification of the data bus between the thumbnail image generating device, the memory interface, and the system memory. Generally, 8 or 16 bytes may be used, but considering the efficiency of the entire system, It may have a different value. In addition, the data storage unit of the buffer may also be determined by the transmission unit in consideration of the transmission efficiency.

Therefore, in the thumbnail generating apparatus according to the present invention, the enlargement of the thumbnail image in the vertical direction may be achieved by only controlling the buffer read pointer without adding the buffer capacity or modifying the configuration of the buffer for the field picture.

As described above, the present invention is applied to a format of a video stream to a user by applying it to a program guide, a storyboard, a summary of contents, and other applications related to implicit information transmission of a video in a personal video recorder or a video retrieval device of a digital TV. Regardless, it is possible to provide thumbnail images of a consistent size.

As described above, according to the apparatus and method for generating a thumbnail image according to the present invention, a thumbnail image having a relatively consistent size can be solved by resolving an inconsistency of a thumbnail image due to a difference in resolution of an image of an HD and SD video stream. Has the effect of generating

In addition, there is an effect of reducing the size of the thumbnail image of the HD-level video to 1/4 by decimation or averaging without complicated operations such as scale calculation and image pixel interpolation required for the size conversion of the thumbnail image. That is, a thumbnail image is generated by using the DC value of the I picture of the MPEG encoded video stream, but a SD image is generated by applying decimation or averaging technique to the HD-quality video stream, without further scaling. It is possible to generate a thumbnail image of a size similar to the thumbnail of the stream.

In addition, the present invention has an effect of generating a thumbnail image having the same size as a frame picture by controlling a simple buffer read pointer without applying a resizing algorithm of an image to a field picture.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (13)

A DC decoder for parsing only a DC value of an I picture from an input video stream; A buffer to store a DC value output from the DC decoder; And If the macroblock including the DC value output from the DC decoder is HD, the DC value of the subblocks included in the macroblock is reduced to 1 / N (N is a natural number of 2 or more) and controlled to be stored in the buffer. And a buffer controller for outputting a DC value stored in the buffer to a system memory to generate a thumbnail image. The method of claim 1, wherein the buffer controller If the input macro block is HD, a thumbnail image, characterized in that the DC value for any one of the four luminance blocks included in the macro block and the DC value for the Cb, Cr blocks are controlled to be stored in the buffer. Generating device. The method of claim 1, wherein the buffer controller If the input macro block is HD, the average of the DC values of the four luminance blocks included in the macro block after obtaining the average and the DC value for the Cb, Cr blocks are controlled to be stored in the buffer Video generation device. The method of claim 1, wherein the buffer is And a DC value input in units of slices. The method of claim 1, wherein the buffer controller And a DC value for four luminance blocks included in the macro block and a DC value for Cb and Cr blocks are stored in a buffer if the input macro block is SD. The method of claim 1, wherein the buffer is And two buffers, wherein the two buffers perform double buffering under the control of the buffer controller. The method of claim 6, Each buffer is composed of three storage areas, each of which corresponds to one thumbnail image line in the case of HD class, one storage area includes a DC value for the Y component, and the other storage area has a DC value for the Cb component. And the DC value for the Cr component is stored in each slice unit in another storage area. The method of claim 6, Each buffer is composed of four storage areas, each of which corresponds to one thumbnail image line in the case of SD class, in which one DC is parsed from two luminance blocks in one storage area, and the other two in another storage area. And a DC value parsed from the luminance block, and the DC values for the Cb and Cr blocks are stored in slice units in the remaining two storage regions. The method of claim 1, wherein the buffer controller When the input bit stream is a field picture, only the DC value of one of the top and bottom fields is stored in the buffer, and when the data stored in the buffer is transferred to the system memory, the read point of the buffer is controlled. And transmitting data corresponding to one thumbnail image line by overlapping the buffer. In the method for generating a thumbnail using a buffer for storing the input DC value, Parsing only the DC value of the I picture from the input video stream; If the macroblock including the DC value input in the parsing step is HD, reducing the DC values of the subblocks included in the macroblock by 1 / N (N is a natural number of 2 or more) and storing them in the buffer; If the macro block including the DC value input in the parsing step is SD, storing the DC values of all sub-blocks included in the macro block in the buffer; And And outputting DC values stored in the buffer to a system memory when the slice including the macro block ends. The method of claim 10, wherein the HD storage step And storing the DC value of any one of the four luminance blocks included in the macro block and the DC value of the Cb and Cr blocks in the buffer in thumbnail image lines. The method of claim 10, wherein the HD storage step And obtaining the average of the DC values of the four luminance blocks included in the macro block, and storing the average value and the DC values of the Cb and Cr blocks in the buffer on a thumbnail image line basis. The method of claim 10, When the input bit stream is a field picture, only the DC value of any one of the top and bottom fields is stored in the buffer, and the data stored in the buffer is transferred from the buffer by the read point control of the buffer when the data stored in the buffer is transferred to the system memory. And transmitting data by overlapping data corresponding to one thumbnail image line.