KR19990019198A - Slice Position Compensation Method for Address Generation of Predicted Macroblock in Frame Memory - Google Patents

Abstract

The present invention relates to a slice position compensation method when an address is generated for a predictive macroblock in a frame memory.

In the method of the present invention, in the frame memory mapped to the macroblock of the field structure, the row address and the column of the macroblock predicted by using the slice position value, the macroblock position value and the motion vector of the current picture to be motion compensated. When generating an address, it is determined whether the original field position (field _i ) is odd or even.If the field position is even, the original field position is divided into two so that the modified field position (field _{i + 1} ) points to the upper field. If the field position is odd, calculate the equation so that the modified field position (field _{i + 1} ) points to the lower field, and multiply the slice position in the macroblock of the frame structure by 16 to determine the slice position in the field structure. Row address due to a difference between a picture type for mapping a frame memory and a picture type of an input image for motion compensation. The error of and column address can be reduced.

Description

Method for compensating a slice position during an address generation of a predicted macroblock in a frame memory

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frame memory for a motion compensation device, and more particularly to generate a row address (RA) and a column address (CA) for reading a macroblock predicted by motion compensation from a frame memory. The present invention relates to a method and circuit for compensating slice position according to a motion type.

The motion compensation technique used in the Moving Picture Experts Group (MPEG) -2 standard is to reduce temporal redundancy by estimating and compensating for motion between two adjacent temporal pictures in macroblock units. That is, in the motion estimation and compensation process, a neighboring image is compared with the current image to detect a motion vector, which is information about an object's motion, and the current image is predicted using the motion vector.

In an MPEG-2 video encoder using such a motion compensation technique, the P picture performs forward motion compensation on the basis of the I picture or P picture of the previous picture with respect to the current picture, and the B picture performs the current picture. The best one is selected from among motion compensation blocks obtained by performing forward motion compensation, reverse motion compensation, and interpolated motion compensation based on the I picture or P picture of the previous picture and the I picture or P picture of the next picture.

Methods for motion estimation and compensation include frame motion estimation and compensation mode, field motion estimation and compensation mode, dual prime motion estimation and compensation mode, and basically all motion estimation and compensation are half pixel. It is specified to have a half-pel unit.

Among these, frame motion estimation and compensation mode has been used since MPEG-1, and motion estimation and compensation are performed in a frame structure without distinguishing a top field or even field and a bottom field or odd field. do. To this end, a full search is performed on the macroblock MB to be encoded of the current frame up to half-pixel precision in the search region of the reference frame, thereby obtaining the smallest mean absolute error (MAE). The position to generate is determined as a motion vector for the macroblock. In fact, since data is given in units of pixels, a pixel-by-pixel motion vector is obtained through the first-order full search in pixel units, and then a half-pixel motion vector is obtained through interpolation and a second full search in half-pixel units. In the case of frame motion estimation, one motion vector is transmitted per one macroblock for a P picture, and one or two motion vectors are transmitted per one macroblock for a B picture. The number of bits required for transmission is small.

Next, the field motion estimation and compensation mode performs motion estimation and compensation for each field in the picture of the frame structure. For this purpose, the upper and lower, upper and upper, lower and upper, lower and lower positions in the unit of 16 * 8 (pixels) sub macroblocks between upper and lower fields of the current frame and upper and lower fields of the reference frame, respectively. After four motion vectors are obtained, one motion vector is generated to generate a minimum motion compensation error for each of the upper and lower fields of the current frame. Therefore, two motion vectors per macroblock for a P picture and two or four motion vectors per macroblock for a B picture are transmitted. The MPEG-2 image encoder applies all the frame / field prediction modes to all macroblocks, and then uses the prediction mode having the smaller prediction error. Meanwhile, since the prediction mode used by the encoder is transmitted in the MPEG-2 image decoder, motion compensation is performed to restore the image.

On the other hand, there is a 16 * 8 (pixels) motion estimation and compensation mode as a deformation mode of the field motion estimation and compensation mode, in which two motion vectors are used for each macroblock, and the first motion vector is the top 16. For the * 8 region, the second motion vector is used for the lower 16 * 8 region. In the case of a bidirectional predicted macroblock, four motion vectors are used, two for forward prediction and two for backward prediction.

Next, the dual prime motion estimation and compensation mode transmits only one motion vector and differential motion vector (dmv) per macroblock, and is known to be effective for sequences with relatively slow motion. This mode is specified to be used only when the B picture is not used. That is, when the B picture is allowed, a better picture quality can be obtained using the B picture. However, when the B picture is not allowed, the dual prime prediction mode can be used to improve the picture quality with as little bit generation as possible. . In the dual prime prediction mode, first, the motion vectors of the upper, upper, and lower part of the four motion vectors obtained from the field prediction mode from upper to lower, upper to upper, lower to upper, lower to lower are used as the basic motion vectors. The upper and lower motion vectors and upper and lower motion vectors are scaled (* 2, * 2/3) and truncated, respectively, to form a basic motion vector. Next, each of the four basic motion vectors thus created is fine-tuned by -1, 0, and 1 in the horizontal and vertical directions to minimize the motion compensation error for the two 16 * 8 (pixels) sub macroblocks. A motion vector and a differential motion vector are transmitted. Since the dual prime prediction mode has a large amount of computation in the image encoder, it is necessary to calculate nine prediction candidate values per one basic motion vector. Therefore, the basic motion vector and the differential motion vector of one of 36 candidates must be calculated. Meanwhile, the image decoder can be implemented relatively simply because only two field motion vectors need to be calculated from the transmitted basic motion vector and the differential motion vector.

The frame memory is used to store the I picture or P picture of the previous picture and the I picture or P picture of the next picture as the reference picture for motion compensation. In addition, the frame memory is used to temporarily store a decoded picture and fetch it according to the display order since the decoding order and the display order are different in the MPEG-2 video decoder.

However, the frame memory as described above must have a capacity to store at least three frames of image data according to the I picture and the P picture or the distance M between the P picture and the P picture, and thus the price thereof is expensive, and therefore, the entire picture. In addition to raising the price of the decoder, there is a problem that the delay time from the completion of decoding to the display increases.

Accordingly, the present invention has been made to solve the above problems, and includes a region for storing reference image data, a region for storing decoded image data for display, and an encoded bitstream input to an image decoder. In a frame memory in which an area to be stored is implemented on one memory module, when a row address and a column address are generated to read a macroblock predicted by motion compensation from the frame memory, the slice position is determined according to the motion type. The purpose is to provide a method for compensation.

The method of the present invention for providing the above object, in the frame memory mapped to the macroblock of the field structure, predicted using the slice position value, the macroblock position value and the motion vector of the current picture to be motion compensated In the case of generating the row address and column address of the macroblock, determining whether the original field position (field _i ) is odd or even. If the field position is even, the field position modified by a predetermined equation is determined. _{i + 1} ) to point to the upper field, and if the field position is odd as a result of the determination, the field position (field _{i + 1} ) modified by a predetermined equation to point to the lower field. It is characterized by.

1 is a diagram showing the structure of a frame memory adopted in the present invention;

2 is a diagram illustrating a scheduling order of the frame memory shown in FIG. 1;

3 is a diagram illustrating an example of a method for setting a RAS box for one frame in the frame memory shown in FIG. 1;

4 is a view showing an example of a macroblock structure in the RAS box shown in FIG.

5 is a flowchart illustrating a slice position compensation method according to the present invention;

6 is an exemplary diagram illustrating a conversion from a frame structure to a field structure according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 illustrates a structure of a frame memory adopted in the present invention, in which the frame memory 100 includes a restored image data write operation, a data read operation for motion compensation, and a data read operation for display to a memory controller (not shown). Synchronous-DRAM (SDRAM) controlled by a burst length of 8 will be taken as an example. The frame memory 100 has two memory banks, bank 1 and bank 2, bank 1 has first and second frame storage areas 100-1 and 100-2, and bank 2 stores third and fourth frames. There are regions 100-3 and 100-4. Here, the first to fourth frame storage areas 100-1, 100-2, 100-3, and 100-4 have a capacity for storing pixel data of one frame, respectively, and the first to fourth frame storage areas 100-1, 100-. 2,100-3 and 100-4 each have 1,024 row addresses, and have a column address of 256 words (where 1 word is 8 bits). One address stores eight Y pixels, two Cr pixels, two Cb pixels, and a total of 12 pixel data. Here, 1,024 row addresses mean the number of RAS boxes. And the 256-word column address comes from (8 macroblocks per RAS box * 32 boxes per macroblock = 256 boxes).

The actual physical row address of the frame memory 100 is 000 _H to 3FF _H , 400 _H to 7FF _H for the first to fourth frame storage areas 100-1 to 100-4, respectively. , 800 _H to BFF _H and C00 _H to FFF _H. However, the first to fourth frame storage regions 100-1 to 100-4 exist independently, and the second and fourth frames corresponding to the macroblocks located at predetermined row addresses of the first frame storage region 100-1 are respectively provided. The macroblocks of the third frame storage areas 100-2 and 100-3 have the same row address. As such, the row address in the first to third frame storage areas 100-1 to 100-3 is referred to as a virtual row address. Then, based on the scheduling order of the frame memory 100 as shown in FIG. 2 during motion compensation, an address used to convert a virtual row address in a corresponding storage area in which a reference image is located into a physical row address is framed. It is called the frame offset address and is called RA [11:10]. That is, if RA [11:10] is '00', the first frame storage area 100-1, if '01', the second frame storage area 100-2, and if the '10', the third frame storage area 100 -3) and '11' indicate the fourth frame storage areas 100-4, respectively.

Here, the first and second frame storage areas 100-1 and 100-2 are used to store reconstructed I-picture or motion-compensated P-picture image data for use as a reference image for motion compensation and simultaneously for display. The three-frame storage area 100-3 is used to store the motion compensated B-picture image data, and the fourth frame storage area 100-4 stores the encoded bitstream input to the image decoder in units of predetermined bits. Used to save.

FIG. 2 shows a scheduling order of the frame memory 100 shown in FIG. 1, and the decoding order is I, P, B, B, P, B, B, P, B, B, P, B, B, I. , P, B, B, ... and the display order is I, B, B, P, B, B, P, B, B, P, B, B, P, I, B, B, ... For example, the display latency is 2 pictures. Here, the underlined portion indicates the picture currently being decoded, the arrow indicates the picture to be referred for motion compensation, and the storage area to which 'D' is added indicates that image data is fetched for display.

FIG. 3 shows an example of a method for setting a RAS box for one frame in the frame memory 100 shown in FIG. 1. For example, when one frame includes 1,920 pixels * 1,088 pixels, 15 RAS boxes * 68 It is divided into RAS boxes, a total of 1,020 Row Address Strobe (RAS) boxes. That is, the number of the RAS box is the row address (RA) of the frame memory 100. Here, one RAS box is composed of 8 macroblocks * 1 macroblocks and a total of 8 macroblocks MB0 to MB7. Each macroblock is divided into four blocks b0 to b3 when the luminance Y block is taken as an example.

FIG. 4 shows an example of a macroblock structure in the RAS box shown in FIG. 3, with four luminance (Y) blocks b0 to b3, one color difference (Cr) block, and one color difference (Cb) block. Four luminance (Y) blocks are composed of eight boxes (b0-0 to b0-7, b1-0 to b1-7, b2-0 to b2-7, and b3-0 to b3-7), respectively. Each of the two color difference (Cr, Cb) blocks has eight sub boxes (sb0-0 to sb0-7, sb1-0 to sb1-7, sb2-0 to sb2-7, and sb3-0 to sb3-7). It consists of. Then, 8 pixel data in 8 * 1 format for each box constituting the Y block, 2 pixel data in 2 * 1 format for each box constituting the Cr block, and 2 * 1 format for each box constituting the Cb block. There are two pixel data of.

3 and 4, when the open dress CA [7: 0] is examined, the position of the macro block in one RAS box is CA [7: 5] and the position of the block in the macro block. CA [4: 3], the position of the box in the block is called CA [2: 0], and the position of the pixel in the box is called the pixel address PA [2: 0]. In addition, a line in which the row address is changed in one frame is called a RAS line, and a line in which the open address is changed is called a CAS (Column Address Strobe) line.

5 is a flowchart illustrating a slice position compensation method according to the present invention when an address for a prediction macroblock is generated in a frame memory.

Then, the slice position compensation method according to the present invention will be described with reference to FIGS. 1 to 5.

3 and 4, in the method for generating an address of a macroblock predicted by motion compensation, first, a frame offset address (frame) based on the scheduling order of the frame memory 100 as shown in FIG. offset address), that is, RA [11:10]. For example, as in the second step of FIG. 2, motion compensation is performed on a B picture stored in the second frame storage area 100-2 with reference to an I picture stored in the first frame storage area 100-1. In this case RA [11:10] is '00'.

Second, a start address of a current macroblock MB to be compensated for motion, that is, a slice position slice_pos and a macroblock position mb_pos, and a motion vector mv_v and mv_h are input.

Third, match the scale of the input variables. Among the input variables, the slice position (slice_pos) and the macroblock position (mb_pos) each have 7 bits and have a macroblock scale, while the motion vector has a half pixel scale. Therefore, the horizontal motion vector mv_h [12: 0] and the vertical motion vector mv_v [8: 0] are divided by 16 to fit the macroblock scale, that is, mv_h [11: 5] and mv_v [ 7: 5] and put them as 'mv_h_mb' and 'mv_v_mb', respectively.

Fourth, the linear transformation of the horizontal and vertical coordinate systems is performed as in Equation 1 below to determine the predicted macroblock position (predict_MB_v, predict_MB_h).

mb_position ± mv_h_mb = predict_MB_h

Here, 'predict_MB_h' indicates a horizontal position of the predicted macroblock, and 'predict_MB_v' indicates a vertical position of the predicted macroblock.

Fifth, a linear address (LA) indicating a macroblock position in one frame is generated by the following Equation 2, and RA [9: 0] and CA [7: 5] are determined from the linear address. .

Here, since there are 120 macroblocks in the horizontal direction in one frame (1920 pixels * 1088 pixels), 'predict_MB_v' is multiplied by 120. Since 'predict_MB_v' is 7 bits, '120' is 7 bits, and 'predict_MB_h' is 7 bits, the calculation result of Equation 2 is 14 bits. That is, LA [12: 3] becomes RA [9: 0] indicating the position of the RAS box in the storage pointed to by RA [11:10] determined in the first step, and LA [2: 0] is the corresponding RAS box. Is CA [7: 5] indicating the position of the macroblock in Eq.

Sixth, CA [4: 0] and PA [2: 0] are determined by the following equation.

That is, the lower four bits are taken from the horizontal and vertical motion vectors mv_h and mv_v, respectively, to determine the block position in the macroblock, the box position in the block, and the pixel position in the box. In MA [7: 0], MA [7: 6] becomes CA [4: 3], which indicates the block position in the macroblock, and MA [5: 3] represents CA [2: 0], which indicates the box position in the block. MA [2: 0] becomes PA [2: 0] indicating the pixel position in the box. Here, PA [2: 0] is used to determine the reference point (R.P) of the predicted macroblock.

However, the frame memory 100 (see FIG. 1) used in the present invention is mapped to a macroblock having a field structure, whereas in MPEG-2, an encoded bitstream input to an image decoder by supporting both a field picture and a frame picture is It may be a macroblock of a field structure or a macroblock of a frame structure. Therefore, compensation for mismatching of a picture type of the frame memory 100 and a picture type of an image input to the image decoder when an address is generated for the predicted macroblock is required.

Referring to the slice position compensation method according to the present invention with reference to Figure 5, it is first determined whether the original field position (field _i ) is even or odd (501). If the original field position (field _i ) is an even number as a result of the determination of step 501, the field is divided into two to obtain a modified field position (field _{i + 1} ). When the result of the determination of step 501 is an odd number, a lower field (bottom field or odd field) is represented, and a modified field position (field _{i + 1} ) is obtained by Equation 4 below (503).

In Equation 4, 543 divides 1088 into 2 in consideration of the field being divided into upper and lower parts, and subtracts 1 in consideration of starting from 0 in the field position.

6 is an exemplary view illustrating conversion of a macroblock of a frame structure into a field structure by the slice position compensation method according to the present invention. Since slices are a sequence of macroblocks, as shown in FIGS. 3 to 4, one frame includes 68 slices. In the macroblock of the frame structure, the slice position may be multiplied by 16 to obtain the slice position in the field structure. . The slice position therefore always points to the higher field.

On the other hand, the above detailed description is intended to describe particular embodiments presented herein and is not intended to limit the present invention. Those skilled in the art will be able to make various modifications and modifications according to the type of memory constituting the frame memory, the structure of the RAS box, and the structure of the macroblock with reference to the above description and drawings.

As described above, in the method of the present invention, in order to read a macroblock predicted by motion compensation from a frame memory in a frame memory in which the first to fourth frame storage areas are implemented on one memory module, By generating the row address and the column address using the slice position compensated according to the type, the error between the row address and the column address due to the difference between the picture type mapping the frame memory and the picture type of the image input for motion compensation can be reduced. have.

Claims (2)

In a frame memory mapped to a macroblock of a field structure, when generating a row address and a column address of a macroblock predicted by using a slice position value, a macroblock position value, and a motion vector of a current picture to be motion compensated, Determining whether the original field position field _i is odd or even (501); If the field position is an even number as a result of the determination, dividing the original field position (field _i ) into two so that the modified field position (field _{i + 1} ) indicates the upper field; And If the field position is odd as a result of the determination, the modified field position points to the lower field. Where field _{i + 1} represents the modified field position and field _i represents the original field position Calculating a slice position when generating an address for a predicted macroblock in a frame memory. In a frame memory mapped to a macroblock of a field structure, when generating a row address and a column address of a macroblock predicted by using a slice position value, a macroblock position value, and a motion vector of a current picture to be motion compensated, And a slice position in the field structure is obtained by multiplying the slice position in the macroblock of the frame structure by 16 to obtain a slice position compensation method when an address is generated for the predicted macroblock in the frame memory.