Abstract:
A novel method and structure for the implementation of Half Pixel Filtering and Block Averaging that are efficient for implementation on a general purpose CPU. The number of required operations are reduced by operating on multiple pixels simultaneously using sliced arithmetic, while maintaining full accuracy. In certain embodiments, the number of operations are further reduced by compromising full accuracy. This approximation is applicable to decoding of bi-directional frames.

Description:
This is a continuation of application Ser. No. 08/526,533 filed Sep. 11, 1995 now abandoned. 
    
    
     INTRODUCTION 
     1. Technical Field 
     This invention pertains to the storage and transmission of video information in a digital format, and more specifically to novel methods and structures for decompressing digital video in a highly efficient manner. 
     2. Background 
     The CCITT/ISO committee has standardized a set of compression algorithms for full motion digital video. These compression standards are popularly known as MPEG-1 (ISO/IEC 11170-2), and MPEG-2 (ISO/IEC 13818-2). Applications of these standards include CD-ROM based interactive video for edutainment, and digital video transmission for home entertainment. Both these standards as well emerging HDTV standards are based on motion compensated predictive coding techniques. A simplified video decoding process based on such a scheme is shown in FIG. 1. 
     The processing steps shown in FIG. 1 are for decoding full motion video according to the MPEG standard. Processor 1 converts hierarchically encoded fixed length and variable length encoded data into a sequence of fixed length control data and coefficient data. Fixed length control data such as quantization scale is sent to Inverse Quantizer 2, block type is sent to Block Adder processor 4, and motion vectors are sent to Frame Buffer 6. Inverse quantization is applied to coefficient data by inverse quantizer 2. Inverse quantized coefficient data is passed through Inverse DCT Processor 3 to produce in an 8×8 block of pixel data. Motion Vectors are sent to Frame Buffer 6, which contains three frames, namely Forward Frame, Backward Frame, and a Bi-directional Frame. A block of data is fetched from one or both of Forward Frame and Backward Frame, addressed by the motion vectors. Fetched blocks are passed through Half Pixel Filter 5 for two-dimensional filtering. These filtered blocks are combined with the pixel block from Inverse DCT processor 3 according to the block type to make the reconstructed block. This reconstructed block is sent to Frame Buffer 6 along with the destination vector to be written into the destination frame. 
     Software implementations of decoders on a general purpose computer is attractive because of its low cost. However, prior art software decoder implementations of these standards (MPEG-1), such as one available from UC Berkeley, for use on general purpose computers tend to be slow in terms of number of decoded frames per second. One of the time-consuming tasks in decompressing video is the arithmetic required for Half Pixel Filtering and Motion Compensation. 
     FIG. 2 is a diagram depicting video frame 21 including a plurality of pixel blocks, such as pixel block 22. Pixel blocks are a subset of pixels contained within the video frame, and the size of a pixel block is determined for easy manipulation, and typically contains an 8×8 or 9×9 block of pixel data. 
     FIG. 3 is a diagram depicting a typical 9×9 pixel block, including a plurality of pixels P00 through P88. 
     FIG. 4 is a diagram depicting an 8×8 filter pixel block 41 which is derived from the 9×9 pixel block of FIG. 3, utilized in the following manipulations: 
     Horizontal One Dimensional Filter 
     U 00  =(P 00  +P 01  +1)&gt;&gt;1, U 01  =(P 01  +P 02  +1)&gt;&gt;1, U 02  =(P 02  +P 03  +1)&gt;&gt;1, 
     U 10  =(p 10  +p 11  +1)&gt;&gt;1, U 11  =(p 11  +p 12  +1)&gt;&gt;1, U 12  =(P 12  +P 13  +1)&gt;&gt;1, 
     U 70  =(P 70  +P 71  +1)&gt;&gt;1, U 71  =(P 71  +P 72  +1)&gt;&gt;1, U 72  =(P 72  +P 73  +1)&gt;&gt;1, 
     Vertical One Dimensional Filter 
     U 00  =(P 00  +P 10  +1)&gt;&gt;1, U 01  =(P 01  +P 11  +1)&gt;&gt;1, U 02  =(P 02  +P 12  +1)&gt;&gt;1, 
     U 10  =(P 10  +P 20  +1)&gt;&gt;1, U 11  =(P 11  +P 21  +1)&gt;&gt;1, U 12  =(P 12  +P 22  +1)&gt;&gt;1, 
     U 70  =(P 70  +P 80  +1)&gt;&gt;1, U 71  =(P 71  +P 81  +1)&gt;&gt;1, U 72  =(P 72  +P 82  +1)&gt;&gt;1, 
     Two Dimensional Filter 
     U 00  =(P 00  +P 01  +P 10  +P 11  +2)&gt;&gt;9, U 01  =(P 01  +P 02  +P 11  +P 12  +2)&gt;&gt;9, U 02  =(P 02  +P 03  +P 12  +P 13  +2)&gt;&gt;9, 
     U 10  =(P 10  +P 11  +P 20  +P 21  +2)&gt;&gt;9, U 11  =(P 11  +p 12  +P 21  +P 22  +2)&gt;&gt;9 
     U 70  =(U 77  +U 78  +U 87  +U 88  +2)&gt;&gt;4 
     The present invention is concerned with Half Pixel Filter 5, and Motion Compensation Processor 4, which permits efficient implementation of Half Pixel Filter and Block Reconstruction Arithmetic on a general purpose CPU. In accordance with the teachings of this invention, novel methods and structures are taught for implementing Half Pixel Filtering and Block Averaging procedures, that require significantly fewer numbers of operations, thereby greatly enhancing speed. 
     SUMMARY 
     In accordance with the teachings of this invention, novel method and structure are taught for the implementation of Half Pixel Filtering and Block Averaging that are efficient for implementation on a general purpose CPU. In accordance with this invention, the number of required operations are reduced by operating on multiple pixels simultaneously using sliced arithmetic, while maintaining full accuracy. In certain embodiments of this invention, the number of operations are further reduced by compromising full accuracy. This approximation is applicable to decoding of bi-directional frames. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram depicting a typical prior art video decoding structure; 
     FIG. 2 is a diagram depicting a typical video frame containing a plurality of pixel blocks; 
     FIG. 3 is a more detailed view of a typical pixel block; 
     FIG. 4 is a diagram depicting a filter pixel block derived from the pixel block of FIG. 3; and 
     FIG. 5 depicts a computer that stores and executes the procedures for performing one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     In accordance with the teachings of this invention, a novel method and structure are taught for implementation of half pixel filtering and block averaging utilizing sliced arithmetic. Thus, in accordance with the teachings of this invention, two eight bit sets of pixels are treated as a single 16 bit word, for example, when the CPU bus is a 16 bit bus. Obviously, for 32 bit buses, four eight bit sets of pixels can be manipulated simultaneously, for a 64 bit CPU bus eight sets of eight pixels can be manipulated simultaneously, etc. The following example shows how two sets of eight pixel bits are processed simultaneously. 
     i) A prior art software implementation of a one Dimensional Half Pixel Filter in horizontal direction: 
     
         ______________________________________     for (i = 0; i &lt; 8; i++) {      for (j = 0; j &lt; 8; j++) {       a = in.sub.-- block i! j!       b = in.sub.-- block i! j+1!;       o = (a + b + 1) &gt;&gt; 1;       out.sub.-- block i! j! = o;      }     }______________________________________ 
    
     In accordance with this prior art software implementation, the total number of operations for an 8×8 block of pixels is 384. 
     A typical prior art software implementation for a two dimensional half pixel filter operating on an 8×8 block of pixels is as follows. 
     ii) Two Dimensional Half Pixel Filter: 
     
         ______________________________________   for (i = 0; i &lt; 8; i++) {    for (j = 0; j &lt; 8; j++) {     a = in.sub.-- block i! j!     b = in.sub.-- block i! j+1!;     c = in.sub.-- block i+1! j!;     d = in.sub.--block i+1!  j+1!;     o = (a + b + c + d + 2) &gt;&gt; 2;     out.sub.-- block i! j! = o;     }    }______________________________________ 
    
     In accordance with this prior art software implementation of a two dimensional half pixel filter on an 8×8 block of pixels, the total number of operations per block is 640. 
     A typical prior art software only implementation for a block average for a bi-directional block of 8×8 pixels is as follows. 
     iii) Block Average for Bi-directional Block 
     
         ______________________________________     for (i = 0; i &lt; 8; i++) {      for (j = 0; j &lt; 8; j++) {       a = f.sub.-- in.sub.-- block i! j!       b = b.sub.-- in.sub.-- block i! j+1!;       o = (a  + b + 1) &gt;&gt; 1;       out.sub.-- block i! j! = o;      }     }______________________________________ 
    
     As can be seen from the above, for a typical prior art software only block average for bi-directional block of 8×8 pixels requires a total of 384 operations per block. 
     The following embodiment shows two pixels processed simultaneously on a 16 bit data path, in accordance with this invention. As will be described later, the teachings of this invention are equally applicable to other sizes of pixel blocks, and other sizes of data paths, allowing a bit sliced operation for enhanced performance. The operation performed is: 
     
         J=(Z+Y+1)&gt;&gt;1 
    
     
         K=(Y+X+1)&gt;&gt;1 
    
     
         __________________________________________________________________________Step   8 MSBs                    8 LSBs                              Operation__________________________________________________________________________1  Z7Z6  Z5    Z4      Z3        Z2          Z1            Z0              Y7                Y6                  Y5                    Y4                      Y3                        Y2                          Y1                            Y0                              ZY2  Y7Y6  Y5    Y4      Y3        Y2          Y1            Y0              X7                X6                  X5                    X4                      X3                        X2                          X1                            X0                              YX3  Z7Z6  Z5    Z4      Z3        Z2          Z1            00              Y7                Y6                  Y5                    Y4                      Y3                        Y2                          Y1                            00                              ZY &amp; OXFEFE4  00Z7  Z6    Z5      Z4        Z3          Z2            Z1              00                Y7                  Y6                    Y5                      Y4                        Y3                          Y2                            Y1                              ZY.sub.-- MSB=(ZY &amp; OXFEFE) &gt;&gt;15  0000  00    00      00        00          00            Z0              00                00                  00                    00                      00                        00                          00                            Y0                              ZY.sub.-- LSB = (ZY &amp; 0X0101)6  Y7Y6  Y5    Y4      Y3        Y2          Y1            00              X7                X6                  X5                    X4                      X3                        X2                          X1                            00                              YX &amp; OXFEFE7  00Y7  Y6    Y5      Y4        Y3          Y2            Y1              00                X7                  X6                    X5                      X4                        X3                          X2                            X1                              YX.sub.-- MSB=(YX &amp; OXFEFE) &gt;&gt;18  0000  00    00      00        00          00            Y0              00                00                  00                    00                      00                        00                          00                            00                              YX.sub.-- LSB=(YX &amp; 0X0101)9  00Z7  Z6    Z5      Z4        Z3          Z2            Z1              00                Y7                  Y6                    Y5                      Y4                        Y3                          Y2                            Y1   +10 00Y7  Y6    Y5      Y4        Y3          Y2            Y1              00                X7                  X6                    X5                      X4                        X3                          X2                            X1   ==11 U7U6  U5    U4      U3        U2          U1            U0              V7                V6                  V5                    V4                      V3                        V2                          V1                            V0                              UV.sub.-- MSB=(ZY.sub.-- MSB+YX.sub.--                              MSB)12 0000  00    00      00        00          00            Z0              00                00                  00                    00                      00                        00                          00                            Y0   OR13 0000  00    00      00        00          00            Y0              00                00                  00                    00                      00                        00                          00                            X0   =14 0000  00    00      00        00          00            E0              00                00                  00                    00                      00                        00                          00                            F0                              EF.sub.-- LSB = (ZY.sub.-- LSB.vertline                              .YX.sub.-- LSB)15 U7U6  U5    U4      U3        U2          U1            U0              V7                V6                  V5                    V4                      V3                        V2                          V1                            V0   +16 0000  00    00      00        00          00            E0              00                00                  00                    00                      00                        00                          00                            F0   =17 J7J6  J5    J4      J3        J2          J1            J0              K7                K6                  K5                    K4                      K3                        K2                          K1                            K0__________________________________________________________________________ 
    
     As shown in step 1, a 16 bit word is filled such that its eight most significant bits are the eight pixel bits Z0 through Z7 of pixel Z, and its eight least significant bits are filled with the eight pixels Y0 through Y7 of pixel Y. In step 2, another 16 bit word is filled such that its eight most significant bits are filled with the Y0 through Y7 pixels of pixel Y, and its eight least significant bits are filled with the eight pixel bits X0-X7 of pixel X. In step 3, 16 bit word ZY is ANDed with digital word OXFEFE such that the least significant bits of the Z and Y pixel blocks are set to 0. In step 4, the ZY word from step 3 is shifted one position to the right, with the most significant bit being filled with 00, thereby forming a ZY --  MSB word containing the most significant bits of the Z and Y pixel blocks. 
     As shown in Step 5, a new word ZY --  LSB is created such that the least significant pixels Y0 and Z0 are maintained for later use in order to ensure full accuracy of the final result. 
     In step 6, 7 and 8, the same operations are performed on the YX word of step 2 as was performed in steps 3, 4 and 5 for the ZY word of step 1. This results in a YX --  MSB word (7) and a YX --  LSB word (step 8). In step 11, the ZY --  MSB word is added with the YX --  MSB word to provide a UV --  MSB word as shown in step 11. In step 14, the ZY --  LSB word is logically ORed with the YX --  LSB word to provide an EF --  SB word as shown in step 14. 
     Then, as shown in steps 15 through 17, the UV --  MSB word from step 11 and the EF --  LSB word from step 14 are ANDed together to provide pixels J and K. 
     As shown in step 17, in accordance with the teachings of this invention a plurality of pixel blocks are operated on simultaneously in bit sliced fashion while retaining full accuracy because the operations include manipulation and inclusion of the LSBs. 
     Having now demonstrated the above exemplary embodiment for processing simultaneously two 8 bit pixels in a 16 bit data path, the following equation describes one embodiment of this invention for the basic procedure required for one-dimensional half pixel filter and bi-directional block averaging operation of a single 8 bit pixel on an 8 bit data path. ##EQU1## 
     Since this operation is performed on 8 bit data path without any carry propagation to the most significant bits, it is extensible to processing multiple pixels on a wider data path. For example, two 8 bit pixels processed simultaneously on a 16 bit data path; four 8 bit pixels processed simultaneously on a 32 bit data path; eight 8 bit pixels can be processed on a 64 bit data path, and the like. 
     Implementation of H=(A+B+1)&gt;&gt;1 on 8 bit Data Path 
     A is an 8 bit number of bits a7 (MSB) to a0 (LSB); 
     B is an 8 bit number of bits b7 (MSB) to b0 (LSB); and 
     H is an 8 bit number of bits h7 (MSB) to h0 (LSB). 
     H=(a7, . . . 0+b7, . . . 0+1)&gt;&gt;1 
     H=(a7, . . . 1+b7, . . . 1)+(a0+b0+1)&gt;&gt;1 
     a7, . . . 1=(A&amp;0×fe)&gt;&gt;1 
     b7, . . . 1=(B&amp;0×fe)&gt;&gt;1 
     a0=A&amp;0×1 
     b0+B&amp;0×1 
     (a0+b0+1)&gt;&gt;1=a0|b0 
     H=((A&amp;0×fe)&gt;&gt;1)+((B&amp;0×fe)&gt;&gt;1+((A&amp;0×1)|(B&amp;0.times.1)) 
     The following equation describes one embodiment for the basic procedure required for a two-dimensional half pixel filter and bi-directional block averaging operation of a single 8 bit pixel on an 8 bit data path. Since this operation is performed on 8 bit data path without any carry propagation to the most significant bits, it is extensible to processing multiple pixels on a wider data path. For example, two 8 bit pixels processed simultaneously on a 16 bit data path; four 8 bit pixels can be processed simultaneously on a 32 bit data path; eight 8 bit pixels can be processed simultaneously on a 64 bit data path; and the like. ##EQU2## Implementation of H=(A+B+C+D+2)&gt;&gt;2, on 8 bit Data Path A is an 8 bit number of bits a7 (MSB) to a0 (LSB), a7 being 
     MSB and a0 LSB 
     B is an 8 bit number of bits b7 (MSB) to b0 (LSB); 
     A is an 8 bit number of bits c7 (MSB) to c0 (LSB); 
     D is an 8 bit number of bits d7 (MSB) to d0 (LSB); and 
     H is an 8 bit number of bits h7 (MSB) to h0 (LSB). 
     H=(a7, . . . 0+b7, . . . 0+c7, . . . 0+d7, . . . 0+2)&gt;&gt;2 
     H=(a7, . . . 2+b7, . . . 2+c7, . . . 2+d7, . . . 2 
     )+(a1·0+b1, 0+d1, 0+2)&gt;&gt;2 
     a7, . . . 2=(A&amp;0×fc)&gt;&gt;2 
     b7, . . . 2=(B&amp;0×fc)&gt;&gt;2 
     c7, . . . 2=(C&amp;0×fc)&gt;&gt;2 
     d7, . . . 2=(D&amp;0×fc)&gt;&gt;2 
     a1,0=A&amp;0×3 
     b1,0=B&amp;0×3 
     c1,0=C&amp;0×3 
     d1,0=D&amp;0×3 
     H=((A&amp;0×fc)&gt;&gt;2)+((B&amp;0×fc)&gt;&gt;2)+((C&amp;0×fc)&gt;&gt;2)+((D&amp;0fc)&gt;&gt;2+((A&amp;0×3)+(B&amp;0×3)+(C&amp;0×3)+(D&amp;0×3)+2)&gt;&gt;2 
     Given the above general description of the present invention, the following is an exemplary embodiment of this invention for use with a 64 bit processor for performing a one dimensional half pixel filter in the horizontal direction on two adjacent eight bit pixel blocks is as follows. 
     i) One Dimensional Half Pixel Filter in horizontal direction: 
     
         ______________________________________for (i = 0; i &lt; 8; i++) {  A = (int64*) (in.sub.-- block i! 0!);  B = (int64*) (in.sub.-- block i! 0!);  A.sub.-- MSB = (A &amp; 0xfefefefefefefefe) &gt;&gt; 1;  B.sub.-- MSB = (B &amp; 0xfefefefefefefefe) &gt;&gt; 1;  A.sub.-- LSB = A &amp; 0x0101010101010101;  B.sub.-- LSB = B &amp; 0x0101010101010101;  MSB = A.sub.-- MSB + B.sub.-- MSB;  LSB = A.sub.-- LSB | B.sub.-- LSB );  0 = MSB + LSB;  (int64*) (out.sub.-- block i! j!) = O;  }______________________________________ 
    
     As shown, in accordance with the teachings of this invention, a software only implementation of a one dimensional half pixel filter in the horizontal direction requires only 96 operations per 8×8 pixel block, as compared with the 384 operations previously described with respect to the prior art. 
     Also, in accordance with the teachings of this invention, a software procedure that performs a two dimensional half pixel filter is as follows. 
     ii) Two Dimensional Half Pixel Filter: 
     
         ______________________________________for (i = 0; i &lt; 8; i++) {  A = (int64*) (in.sub.-- block i! 0!);  B = (int64*) (in.sub.-- block i! 0!);  C = (int64*) (in.sub.-- block{i! 0!);  D = (int64*) (in.sub.-- block i! 0!);  A.sub.-- MSB = (A &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;  B.sub.-- MSB = (B &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;  C.sub.-- MSB = (C &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;  D.sub.-- MSB = (D &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;  A.sub.-- LSB = A &amp; 0x0303030303030303;  B.sub.-- LSB = B &amp; 0x0303030303030303;  C.sub.-- LSB = C &amp; 0x0303030303030303;  D.sub.-- LSB = D &amp; 0x0303030303030303;  MSB = A.sub.-- MSB + B.sub.-- MSB C.sub.-- MSB + D.sub.-- MSB;  LSB = A.sub.-- LSB + B.sub.-- LSB C.sub.-- LSB + D.sub.-- LSB);  LSB = (LSB + 0x0303030303030303) &gt;&gt; 2;  O = MSB + LSB;  (int64*) (out.sub.-- block i! j!) = O;  }______________________________________ 
    
     As shown, the total number of operations per 8×8 pixel block is 208, as compared with the 640 described above with respect to the prior art. 
     Also, in accordance with this invention, a software procedure that performs a block average for a bi-directional block is as follows. 
     iii) Block Average for BiDirectional Block 
     
         ______________________________________for      (i = 0; i &lt; 8; i++) {    A = (int64*) (f.sub.-- in.sub.-- block i! 0!);    B = (int64*) (b.sub.-- in.sub.-- block i! 0!);    A.sub.-- MSB = (A &amp; 0xfefefefefefefefe) &gt;&gt; 1;    B.sub.-- MSB = (B &amp; 0xfefefefefefefefe) &gt;&gt; 1;    A.sub.-- LSB = A &amp; 0x0101010101010101;    B.sub.-- LSB = B &amp; 0x0101010101010101;    MSB = A.sub.-- MSB + B.sub.-- MSB;    LSB = (A.sub.-- LSB | B.sub.-- LSB);    O = MSB + LSB;    (int64*) (out.sub.-- block i! j!) = O;    }______________________________________ 
    
     As shown, the total number of operations to manipulate an 8×8 block of pixels is 96, as compared with the 384 operations required in the prior art. 
     In alternative embodiments of this invention, greater speed is achieved at the sake of a small amount of accuracy by ignoring the LSB words (ZY --  LSB and YX --  LSB). In these embodiments, an example of a one dimensional half pixel filter, which requires only 64 operations per 8×8 block of pixels is as follows. 
     i) One Dimensional Half Pixel Filter in horizontal direction: 
     
         ______________________________________for      (i = 0; i &lt; 8; i++) {    A = (int64*) (in.sub.-- block i! 0!);    B = (int64*) (in.sub.-- block i! 1!);    A.sub.-- MSB = (A &amp; 0xfefefefefefefefe) &gt;&gt; 1;    B.sub.-- MSB = (B &amp; 0xfefefefefefefefe) &gt;&gt; 1;    O = A.sub.-- MSB + B.sub.-- MSB;    (int64*) (out.sub.-- block i! j! = O;    }______________________________________ 
    
     In accordance with this embodiment in which the LSBs are ignored with a small amount of inaccuracy being tolerated for the sake of speed, a two dimensional half pixel filter is achieved which requires only 128 operations per 8×8 block of pixels, for example as follows. 
     ii) Two Dimensional Half Pixel Filter: 
     
         ______________________________________for      (i = 0; i &lt; 8; i++) {    A = (int64*) (in.sub.-- block i! 0!);    B = (int64*) (in.sub.-- block i! 1!);    C = (int64*) (in.sub.-- block i+1! 0!);    D = (int64*) (in.sub.-- block i+1! 1!);    A.sub.-- MSB = (A &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;    B.sub.-- MSB = (B &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;    C.sub.-- MSB = (C &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;    D.sub.-- MSB = (D &amp; 0xfcfcfcfcfcfcfcfc) &gt;&gt; 2;    O = A.sub.-- MSB + B.sub.-- MSB + C.sub.-- MSB + D.sub.-- MSB;    (int64*) (out.sub.-- block i! j!) = O;    }______________________________________ 
    
     Furthermore, in accordance with this embodiment in which the LSBs are ignored, a block average for bi-directional block is achieved utilizing only 64 operations per block of 8×8 pixels as follows. 
     iii) Block Average for BiDirectional Block 
     
         ______________________________________for      (i = 0; i &lt; 8; i++) {    A = (int64*) (f.sub.-- in.sub.-- block i! 0!);    B = (int64*) (f.sub.-- in.sub.-- block i! 0!);    A.sub.-- MSB = (A &amp; 0xfefefefefefefefe) &gt;&gt; 1;    B.sub.-- MSB = (B &amp; 0xfefefefefefefefe) &gt;&gt; 1;    O = A.sub.-- MSB + B.sub.-- MSB;    (int64*) (out.sub.-- block i! j! = O;    }______________________________________ 
    
     FIG. 5 depicts a computer 50 that stores and executes the procedures for performing one embodiment of the invention. A user can interact with computer 50 via user interface 52 that is connected through data bus 53. Data bus 53 is an n bit data bus, for example a 16 bit data bus. The user can control the procedure operations and interact with the computer to design and implement various embodiments of the invention. A CPU 54 is provided to execute the various procedures involved in the invention, as described above. A RAM memory 56 is provided to store procedures and various other information that is needed for the CPU 54 and other elements of computer 50. A disk memory 58 is provided to store large amounts of information and to serve as an archive to store various procedures and operations that are needed by the processor from time to time. A network interface 60 permits computer 50 to communicate with other computers and to receive and transmit various information that may include other procedures for performing the invention. A spare interface 62 is provided to accommodate various storage devices, test equipment, video equipment, or other elements that may be needed from time to time. 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     The invention now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims.