Coding of a plurality of binary input data words into one codeword

0001The present invention relates to a method of encoding a first and second data word to obtain a coded third data word. More particularly, the invention relates to a method of encoding two data words, each representing differential data values, such as differential luminance values ​​and differential chrominance values.

0002In image processing, it is well known to define individual pixels of an image in each case by a plurality of image information values, for example a luminance value (brightness value) and two chrominance values ​​(color values). The transmission or storage of such images takes place in that the image information values ​​of the individual pixels of the image are mapped in a predetermined sequence to a serial data stream which is stored or transmitted. For images in the so-called YUV format, the individual pixels are assigned a Y value as a luminance value and a U value and a V value as chrominance values, the number of Y, U and V associated with an image being dependent on the specific format Values ​​varies. In the so-called 4: 4: 4 format, the same number of Y, U and V values ​​are available to display an image, so each pixel is assigned a Y value, a U value and a V value. In 4: 2: 2 format, there are twice as many Y values ​​as U and V values. The transmission or storage of the values ​​of an image takes place as a serial data sequence such that every other transmitted data value is a Y value, followed alternately by a U value and a V value (Y1-U1-Y2-V1-Y3-U2 ...).

0003In order to reduce the data transmission rate in the transmission of image or sound data, various coding methods are known. Such a coding method for reducing the data rate in the transmission of image or sound data is the so-called DPCM method (DPCM = differential pulse-code modulation), for example, in Ohm, Jens-Rainer: "Digital image coding: representation, compression and Transmission ", Springer, 1995, ISBN 3-540,58579-6, pages 246-261.

0004In the DPCM method, differences of respectively successive values ​​of a data sequence are quantized and coded instead of absolute values. Assuming that in the transmission of audio data or image data at successive values, i. H. If values ​​representing brightness data representing values ​​or color data represent small signal jumps occur more frequently from value to value than large signal jumps and that the eye is more tolerant in quantizing the jumps at large jumps than at smaller signal jumps, in the DPCM Method large difference values ​​coarser quantized, while smaller difference values ​​are finely quantized. The reduction of the transmission rate is adjustable via the accuracy of the quantization.

0005The DPCM method will be explained below for encoding a luminance difference value and a chrominance difference value with reference to FIG. By means of this method, luminance difference values ​​and chrominance difference values ​​are coded, which can each assume amplitudes between -255 and +255. For an error-free coding of these values, 9 bits each, namely 1 sign bit and 8 data bits would be required. However, in order to reduce the transmission rate, the known luminance difference value method provides only 7 bits, 1 sign bit and 6 data bits, and only 5 bits, 1 sign bit and 4 data bit for transmission of the chrominance difference values. This results in a reduction of the required transmission rate or the required transmission bandwidth, but inevitably also a loss of information or an error resulting from the coding.

0006The difference values ​​are quantized non-linearly with reference to the coding tables shown in FIG. 1b, whereby the quantization becomes coarser with increasing amplitude of the difference value to be coded. For the luminance difference values, the quantization is carried out for amplitude values ​​between 0 and 10 in steps of one step, and thus without quantization error. From an amplitude value of 10, the quantization takes place in two steps, from an amplitude value 44 in four steps and from an amplitude value of 128 in steps of eight. Does it apply z. B. To transmit a luminance difference value having an amplitude of 247, the value 240 is encoded and transmitted for this purpose, resulting in a quantization error of 7. When applying the quantization or The coding table for chrominance difference values, which provides only 4 data bits for the transmission of chrominance difference values, the maximum quantization error for amplitude values ​​greater than 128 is even 63, since 128 is quantized from an amplitude value 128 in 64-bit steps.

0007The conversion of a luminance difference value and a chrominance difference value to a data word of length 12 bits is shown for a luminance difference value dY = 60 and a chrominance difference value dC = 19 in FIG. 1c. In the method, in addition to the two sign bit, namely the sign bit Sgn_y the luminance difference value dY and the sign bit Sgn_c of the chrominance difference value, the codewords dY 'and dC' to be taken from the coding table are mapped onto the codeword to be transmitted. The transmission of the luminance difference value dY is performed in the example without quantization error, since the luminance difference value dY = 60 coincidentally corresponds to just one of the interval limit value indicated in the luminance coding table. For the chrominance difference value dC = 19, which is between the thresholds 16 and 20 indicated in the chrominance coding table, the difference value dC '= 16 is transmitted, resulting in a quantization error of 3 for the chrominance difference value dC.

0008A disadvantage of the known method, in which two image information values, namely a luminance difference value and a chrominance difference value, are mapped onto a common coded data word, is that the quantization accuracy depends on the coding tables used, whereby the method is rigid and inflexible.

0009DE 100 07 171 describes a method for coding a plurality of data words in a common coded data word. In this method, the number of significant digits is first determined for each data word, and each data word is assigned a significance information that depends on the number of digits. The significance information is then stored in a coded data word and the individual data bits of the data words are mapped to the coded data word, taking account of the significance information.

0010The aim of the present invention is a method of coding at least one, a number of data bits comprising the first data word and a provide a number of data bits comprising the second data word in a coded data word comprising a number of data bits, which ensures a more flexible coding, that ensures at least for some value pairs of the first and second data words lower quantization errors in the coding and that is easy to implement.

0011This object is achieved by a method according to claim 1. Advantageous embodiments of this method are the subject of the dependent claims.

0012The invention relates to a method for coding a first data value and at least one second data value into a coded data word, comprising the following method steps:<ul id="ul0001" list-style="dash"><li>Determining a first approximation value, which is assigned a first code word, for the first data value, and a second approximation value, which is assigned a second code word, for the second data value,</li><li>Mapping the first codeword to a first data portion of the coded data word and mapping the second codeword to a second data portion of the coded data word,</li><li>Determining a first difference between the first data value and the first approximation value and determining a second difference between the second data value and the second approximation value and at least partially mapping a first difference value word representing the first difference value and / or a second difference data word representing the second difference value to at least one additional data portion of the coded data word.</li></ul>

0013Preferably, the first data value is represented by a first data word comprising a number of data bits, and the second data value is represented by a second data word comprising a number of data bits. A first approximation value is then preferably formed by determining the position of the highest relevant data bit for the value of the first data word and forming the power of two of this bit position. Accordingly, a second is preferably formed by determining the position of the highest relevant data bit for the value of the second data word and forming the power of two of this bit position.

0014Preferably, each data bit position of the first data word is assigned at least one first codeword and each data bit position of a second data word at least one second codeword individual for that bit position, and a first rank order number is assigned to each bit position of the first data word and a second rank order number is assigned to each bit position of the second data word , The method comprises the following further method steps:<ul id="ul0002" list-style="none"><li>a) determining the highest relevant bit position for the value of the first data word and mapping the first code word assigned to this bit position to a first data section of the coded data word,</li><li>b) determining the highest relevant bit position for the value of the second data word and mapping the second code word assigned to this bit position to a second data section of the coded data word,</li><li>c) mapping the data bit of at least one lower bit position of the first or second data word relative to the highest relevant bit position to at least one additional data section of the coded data word.</li></ul>

0015The mapping of the data bit at least one lower bit position relative to the highest relevant bit position corresponds to the mapping of the first and / or second difference to the additional data section of the coded data word.

0016Preferably, in this method, the ranking numbers of the highest relevant bit positions of the first and second data word are compared, and depending on this comparison, a data bit of the first or second data word is mapped to the additional data section. The rank order numbers of the individual bit positions can be selected in particular depending on a fictitious quantization error which would be present if only the information about the highest relevant bit position was coded respectively for the first and second data word. would transfer. Preferably, the next relevant data bit of that of the first and second data words is encoded next for which the quantization error would be greater.

0017Of course, the first and / or second data word may also include a sign in addition to the data bits. These Vörzeichenbits can be mapped to the coded data word in addition to the first and second codewords. In addition, it is also possible to consider the sign bit in the generation of the first and second codewords that are mapped to the coded data word. Thus, each bit position of the first data word can be assigned two first codewords and each bit position of the second data word can have two second codewords, which respectively take into account the bit position and the sign.

0018Preferably, the coded data word comprises, in addition to the first and second codewords and possibly the sign bits, a plurality of additional data sections to which data bits of the first and / or second data word are assigned according to the following method steps:<ul id="ul0003" list-style="none"><li>c1) determining the rank order number of the bit position of the data bit of the first data word last copied to the coded data word and determining the rank order number of the data bit of the second data word last copied onto the coded data word,</li><li>c2) comparing the ranking numbers,</li><li>c3) selecting one of the first and second data words as a function of the comparison of the ranking numbers and mapping a data bit from this selected data word to the coded data word,</li><li>c4) repeating the method steps c1) to c3) until all additional data bits of the coded data word are occupied.</li></ul>

0019Preferably, in this method, the data word is selected in each case, whose last data bit or bit mapped onto the coded data word is selected. most relevant of which is the data bit previously mapped to the encoded data word having the higher ranking number. If the ranking numbers are equal, a data bit of a fixed one of the two data words is mapped to the additional data section of the coded data word. For example, if the first and second data words to be encoded are a data word representing a luminance value and a data word representing a chrominance value, a data bit of the luminance value is preferably mapped to the coded data word to reduce the coding error of the luminance value. This is based on the finding that coding errors of the luminance value are of greater importance for the viewer than coding errors of the chrominance value and therefore are preferably to be reduced.

0020In particular, there is the possibility of assigning one of the first and second data words an encoding priority, wherein in method step c3) the data word with the coding priority is always selected in order to code a further data bit of this data word, if the difference between the ranking number of the most recently mapped from this data word Data bits and the last bit of data mapped from the other data word is less than a predetermined value.

0021The ranking numbers of the bit positions of the individual data words are selected, for example, such that they are dependent on the number of the bit position and form an ascending number sequence starting with the least significant bit (LSB = Least Significant Bit) of the respective data word.

0022The data words encoded by the method according to the invention represent, in particular, differential data values, in particular a luminance difference value and a chrominance difference value.

0023The codewords associated with the individual bit positions of the first and second data words may be selected to each include an equal number of codebits. Of course, however, it is also possible to select the codewords so that the individual codewords are of different lengths, whereby depending on the highest relevant bit position of the individual data words to be coded, different numbers of additional data portions are available for the coding of further data bits.

0024The present method will be explained in more detail with reference to figures.<dl id="dl0001" compact="compact"><dt>FIG. 1</dt><dd>illustrates a DPCM method for encoding two differential data words to a coded data word in the prior art.</dd><dt>FIG. 2</dt><dd>illustrates the data length of the first and second data word and the coded data word.</dd><dt>FIG. 3</dt><dd>illustrates an encoding table with first codewords each associated with a bit position of the first data word.</dd><dt>FIG. 4</dt><dd>illustrates an encoding table with second codewords each associated with a bit position of the second data word.</dd><dt>FIG. 5</dt><dd>illustrates the coding of a first and second data word to the coded data word using the encoding tables shown in Figures 3 and 4 according to the inventive method.</dd><dt>FIG. 6</dt><dd>discusses the receiver-side reconstruction of transmitted data words and the error resulting from the coding.</dd><dt>FIG. 7</dt><dd>illustrates another example for encoding two data words to a coded data word (Figure 7a) and the receiver-side reconstruction (Figure 7b).</dd><dt>FIG. 8</dt><dd>illustrates the encoding of signed first and second data words to a coded data word.</dd><dt>FIG. 9</dt><dd>shows a data value sequence comprising several consecutive data values.</dd><dt>FIG. 10</dt><dd>summarizes a coding of two differential data words to a coded data word.</dd><dt>FIG. 11</dt><dd>summarizes a coding of two data words to a coded data word in a further embodiment of the method according to the invention.</dd><dt>FIG. 12</dt><dd>shows another table with approximation values, their order number and their associated code word.</dd></dl>

0025In the figures, unless otherwise indicated, like reference numerals designate like signals and variables of like meaning.

0026The aim of the present invention is to map a first and at least one second data value to a coded data word in order to transmit the coded data word.

0027In the example according to FIG. 2, the first data value is represented by a first data word d1 having a first number of m1 data bits, and the second data value by a second data word d2 having a second word length m2. The coded data word d3 has a word length n, wherein the word length n of this coded data word d3 is preferably smaller than the sum of the first and second word lengths m1, m2, so that n &lt;m1 + m2.

0028In the example chosen in FIG. 2, m1 = m2 = 7 for the first and second word lengths, so that the first and the second data word d1, d2 each have decimal values ​​between 0 and 127 (= 2⁷-1). The word length of coded data word d3 is n = 10 in the example.

0029Referring to FIG. 3, each of the seven bit positions k1 of the first data word d1 is assigned a first code word c1 which is stored in a first code table 11. FIG. 3 illustrates the assignment of the individual first code words c1 (1) to c1 (7) to the individual bit positions. The first bit position, which in the example comprises the least relevant data bit (LSB) of the first data word d1, is assigned the first code word c1 (1) = 001 in the example. The individual codewords comprise three data bits and are chosen in the exemplary embodiment so that the numerical value of the binary codeword corresponds in each case to the bit position k1. Of course, the binary code words 001 to 111 could also be assigned to the individual bit positions as desired. It is only important here that each bit position k1 is assigned by the coding table 11 an individual, that is to say unique, first code word c1. For a better understanding of the coding method which will be explained below, in addition to the code table, FIG. 3 also indicates which decimal numerical value is represented by the respective bit position of the first data word D1.

0030With reference to FIG. 4, it is further provided in the method according to the invention to associate with each bit position k2 of the second data word d2 an individual code word c2 which is stored in a second coding table 12. In the example, the second codewords assigned to the individual bit positions k2 of the second data word d2 correspond to the first codewords c1 assigned to the respective bit positions of the first data word d1. Of course, however, the second codewords c2 of the individual bit positions k2 of the second data word d2 can be selected completely independently of the first codewords c1 of the bit positions k1 of the first data word d1.

0031The inventive method for coding a first and second data word d1, d2 using the coding tables shown in Figures 3 and 4 will be explained below with reference to Figure 5 for a first binary data word d1 = 0111100 and a second binary data word d2 = 0010011. In decimal representation, the first data word d1 corresponds to the value 60 and the second data word to the value 19.

0032The method first approximates the data values ​​represented by the data words by approximation values. For this purpose, the most relevant data bits for the value of the first and second data words d1, d2 are first determined in the example.

0033In the example in which the data bits starting with the least significant data bit (LSB) of the data words d1, d2 are numbered 1 through 7 and the most relevant data bit (MSB) of the data words d1, d2 is bit position 7, these are the data bits k1 = 6 for the first data word d1 and k2 = 5 for the second data word d2. The higher-order data bits of these two data words d1, d2 are each 0 and thus do not provide a relevant proportion to the values ​​of the two data words d1 = 0111100₂ = 60₁₀ and d2 = 0010011₂ = 19₁₀,

0034The method further provides for mapping the bit positions of the highest relevant bit positions k1 = 6 and k2 = 5 to first and second data sections of the coded data word d3. The first code word c1 (6) = 110 assigned to the bit position k1 = 6 of the first data word d1 can be taken from the first code table 11 and is mapped in the example to the first data section of the coded data word d3, which contains the three bit positions k3 = 8 to k3 = 10 of coded data word d3. The second code word c2 (5) = 101 assigned to the bit position k2 = 5 of the second data word d2 is shown in the second code table 12 and is mapped to a second data portion of the coded data word d3, which comprises the bit positions k3 = 5 to k3 = 7 ,

0035The information about the highest relevant bit position contained in the coded data word in the first and second data words d1, d2 makes possible a first approximation to the data values ​​represented by the first and second data word d1, d2. It is evident from the information in the first and second data word d1, d2 contained in the first and second code words c1 (6), c2 (5) that the first data word d1 has a value greater than or equal to 2⁵= 32 and that the second data word d2 has a value greater than or equal to 2⁴= 16 owns.

0036Generally, in the illustrated example, the approximation values ​​for the first and second data values ​​correspond to a power of two of the bit positions of the highest relevant data bits when the bit positions are numbered such that bit position 0 is assigned to the LSB. The first approximation value for the first data value is 2 in the example^k1-1= 2⁵= 32 and the second approximation value for the second data is 2^K2-1= 2⁴= Sixteenth

0037For a further approximation to the data words d1, d2 to be transmitted, additional bit positions, in the example the bit positions k3 = 1 to k3 = 4, of the coded data word d3, which are used to transmit information portions of the first and second data word, are available are less relevant than the information contained in the first and second data word c1 (6), c2 (5) on the position of the most relevant data bits. Each additional information component mapped to the coded data word d3, in the example each additional data bit, of the first and second data word d1, d2 enables a more precise approximation to the respective data word d1, d2 on the receiver side and reduces the error resulting from the coding.

0038The mapping of further data bits of the first and second data word to the coded data word corresponds to an encoding of the differences between the respective data value and the approximation values ​​represented by the first and second code words.

0039In the illustrated example, in which both the data words d1, d2 to be transmitted and the coded data word d3 are binary data words, individual data bits of the data words d1, d2 are mapped according to a predetermined scheme directly to the additional bit positions k3 to k4.

0040This mapping is done with the aim of minimizing the coding error caused by the data reduction from m1 + m2 = 14 bits to n = 10 bits. Each bit position of the first and second data word is assigned a ranking number which is a measure of how large a maximum error would be if, starting from this respective bit position, the values ​​of all the next smaller positions would not be coded. In the simplest case, these rank order numbers r1, r2 correspond to the number of the respective bit positions. The rank order number of a given bit position is greater, the greater the coding error would be, if starting from this predetermined bit position, all smaller bit positions would not be coded or set to zero. If only the highest relevant bit position k1 = 6 were transmitted from the first data word d1, which corresponds to the above-explained first approximation to the value of the first data word d1, neglecting or zeroing the bit positions k1 = 5 to k1 = 1 would result in the maximum Coding error Emaxl = 11111₂ = 31₁₀ be. If only the bit position of the highest relevant bit k2 = 5 was transmitted from the second data word d2 in the example, which corresponds to the above-explained first approximation to the value of the second data word d2, the maximum error would be Emax2 = 1111₂ = 15₁₀ be.

0041For the mapping of further data bits of the first and second data word to the additional bit positions of the coded data word d3 is now determined which is the highest bit position of the first and second data word d1, d2, the data bit is mapped to the coded data word d3. At the beginning of the process, these are the bit positions of the highest relevant data bits, namely the bit position k1 = 6 of the first data word d1, which is assigned the ranking number r1 = 6, and the bit position k2 = 5 of the second data word d2, which is the rank sequence number r2 = 5 assigned.

0042These ranking numbers r1 = 6 and r2 = 5 are compared to decide from which of the two data words d1, d2 the first additional data bit at the bit position k3 = 4 of the coded data word d3 should originate. The selection is made in the example such that the data bit at the additional bit position of coded data word d3 is selected from among the first and second data words d1, d2 whose highest bit position already mapped to the coded data word has the greater rank order number. In the case of equal ranking numbers of the last coded bit positions, in each case the data bit of the next smaller bit position of the first data word d1 is mapped to the coded data word d3 in the example.

0043In the concrete example, this means that after coding the bit positions k1 = 6 and k2 = 5 with the ranking numbers r1 = 6 and r2 = 5 to the first and second data section to the first additional bit position k3 = 4 of the coded data word d3, the data bit d1 (5) the bit position k1 = 5 of the first data word d1 is mapped. After this step, r1 = 5 applies to the rank order number of the highest bit position of the first data word d1 already mapped to the coded data word d3, while r2 = 5 still applies. At the second additional bit position k3 = 3 of the coded data word d3, the data bit d1 (4) of the bit position k1 = 4 of the first data word d1 is mapped next. After this step, r1 = 4 and r2 = 5, so that in a next step the data bit d2 (4) of the second data word d2 is mapped to the third additional bit position k3 (= 2) of the coded data word d3. After this method step, r1 = 4 and r2 = 4, so that in the next method step a data bit from the first data word is coded, namely the data bit of the bit position k1 = 3 next to the bit position k1 = 4 next relevant bit position, the data bit d1 (3).

0044The remaining data bits at the bit positions k1 = 2 and k1 = 1 of the first data word d1 and the remaining data bits of the bit positions k2 = 3 to k2 = 1 of the second data word d2 are no longer taken into account in the coding, so that the maximum error in the coding emax1 = 11₂ = 3₁₀ for the first data word d1 and emax2 = 111₂ = 7₁₀ for the second data word d2.

0045Referring to Fig. 5, in the embodiment, data bits d1 (6), d1 (5), d1 (4), and d1 (3) are mapped and transmitted to the encoded data word d3 by the first data word d1. On the receiver side, a transmitted data bit d1 '= 111100 is from these transmitted data bits with reference to FIG. 6a₂ = 60₁₀ reconstructed. In this case, the data bits of the first data word d1, to which no information is transmitted, are set to 0, for example. In the example, d1 = d1 '= 60, so that there is no coding error since, coincidentally, the two non-transmitted data bits d1 (2), d1 (1) of the first data word d1 are 0.

0046Of the second data word d2, the data bits d2 (5) and d2 (4) are transmitted, the non-transmitted data bits d2 (3), d2 (2) and d2 (1) are set to 0, respectively. From this the data word d2 '= 10000₂ = 16₁₀ reconstructed. The coding error is d2 to d2 '= 011₂ = 3₁₀since the data bits d2 '(2) and d2' (1) set to 0 in the reconstruction of the data word are not equal to the data bits d2 (2), d2 (1).

0047FIG. 7a illustrates the coding method according to the invention with reference to a further example for the transmission of a first data word d1 = 110₂ = 61₀ and a second data word d2 = 10011₂ = 19₁₀ ,

0048The highest relevant data bit of the first data word d1 is the data bit at the bit position k1 = 3, with reference to the table in Figure 3, the first code word cl (3) = 011 assigned, and which is mapped to a first data portion of the coded data word d3 , The highest relevant data bit of the second data word d2 is the data bit of the bit position k2 = 5, to which referring to FIG. 4 the second codeword c1 (5) = 101 is assigned, which is mapped to the second data portion of the coded data word d3.

0049After these first process steps, the rank order number r1 = 3 for the bit position is the highest relevant data bit of the first data word d1 and r2 = 5 of the highest relevant data bit of the second data word d2. In a next method step, the data bit of the bit position k2 = 4 of the second data word d2 is mapped to the first additional bit position of the third data word d3. Since the ranking sequence number r1 = 4 of this data bit d2 (4) last mapped from the second data word d2 is still greater than the rank sequence number of the highest bit position of the first data word already mapped to the coded data word, a data bit of the second one is again used in a next method step Data word, namely the data bit d2 (3) of the bit position k2 = 3 of the second data bit d2. Thereafter, r1 = 3 for the rank order number of the highest bit position already coded from the first data word d1 and r2 = 3 for the rank order number of the highest bit position already coded from the second data word d2, so that the ranking numbers of the last from the respective data words d1, d2 the coded data word d3 overmatched data bits. In a next method step, therefore, the data bit d1 (2) of the position k1 = 2 of the first data word d1 is mapped to the third additional data portion of the coded data word d3. In the fourth additional data section at the bit position k3 = 1 of the coded data word d3, the data bit d2 (2) of the bit position k2 = 2 of the second data word d2 is mapped in a last method step.

0050In this specific numerical example, the data bits d1 (3) and d1 (2) are encoded by the first data word d1, so that for the data word reconstructed from the encoded data word d1 '= 110 after the transmission according to FIG₂ = 6₁₀ applies. Of the second data word d2, the four data bits d2 (5) to d2 (1) are transmitted in this example-in contrast to the only three data bits in the example according to FIGS. 5 and 6-for the reconstructed data word d2 '= 10010₂ = 18₁₀ applies. The coding error is in this case only 1.

0051As is clear from the concrete numerical examples in FIGS. 5 to 7, the coding method according to the invention does not use a rigid assignment of individual bit positions of the coded data word to individual bit positions of the two data words d1, d2 to be transmitted, but these bit positions adaptively depend, inter alia, on the specific ones assigned values, always with the aim of minimizing the maximum coding error.

0052The case in which one of the two data words or both data words are 0 has not yet been considered. In this case, in which there is no highest relevant position, a special first or second code word is taken into account on the first or second data section of the coded data word, taking this case into account. With reference to FIGS. 3 and 4, this code word is denoted by c1 (0) or c2 (0) and has, for example, the value 000₂, This code word, for example, the ranking number 0 is assigned, with the effect that only data bits of the other data word are mapped to the additional data sections of the coded data word. If both data words are equal to 0, then, for example, a coded data word d3 is transmitted, which also includes only zeros.

0053If, when mapping the data bits of the first and second data word d1, d2 to the coded data word, the case is reached that the LSB bits of the two data words d1, d2 are already mapped to the coded data word d3, then still available data portions of the coded data word, for example, filled with zeros.

0054In a manner not shown in the method explained with reference to Figures 2 to 7, of course, the possibility of signed data words, ie data words that contain an amount and a sign to transfer. In this case, in addition to the data bits for the amount, additional bits are to be provided in the coded data word to which the sign bits of the first and second data words are then each mapped.

0055In addition, however, it is also possible to consider the sign in the individual bit positions assigned first or second code words c1, c2 of the first and second data word d1, d2, as explained below with reference to FIG.

0056FIG. 8a illustrates a first data word d1 with a word length of 8 bits, which comprises a sign bit v1 and m1 = 7 data bits. In addition, a second data word d2 with an 8-bit length is shown which comprises a sign bit v2 and m2 = 7 data bits. These two data words d1, d2 are to be mapped according to the inventive method to a coded data word d3 of the word length 12 bits.

0057Referring to FIG. 8b, each bit position of the first and second data words d1, d2 is assigned two codewords, ie each bit position of the first data word d1 has to be assigned two first codewords and two codewords assigned to each bit position of the second data word d2. Without restricting generality, it has been assumed in the exemplary embodiment according to FIG. 8b that corresponding codewords are assigned to corresponding bit positions of the first and second data word.

0058The codewords assigned to a bit position, for example the codewords 1001 and 0001, which are assigned to the first bit position, differ in at least one bit position, one of the codewords representing the respective bit position and a positive sign of the respective data word and the other the one bit position associated codewords for the respective bit position and a negative sign of the respective data word is. In the example according to FIG. 8b, the codewords assigned to a bit position differ at exactly one bit position, in the example of the MSB position of the codewords. Of course, the codewords associated with a bit position may however differ as desired. It is essential that, as in any coding method, the coding rule, that is to say the code words assigned to the individual bit positions, are known on the receiver side.

0059The table in FIG. 8b also shows, in addition to the code words associated with individual bit positions, the respective ranking numbers, which in the example of the bit position are reduced by one.

0060Of the 4-bit representable 2⁴= 16 codewords are used in the table according to FIG. 8b 14 in order to be able to take account of the 7-bit positions and in each case two different signs of the data word. In the example, the code words 0000 and 1000 are not used for the bit positions. The code word 0000 is used, for example, to code a data word which comprises only zeros at its seven data bit positions and possibly at its sign bit position.

0061In general, with a code word of length k, the sign of a data word and one of i = 2^k-1 allows positions of the highest non-relevant data bit to be transmitted. The codeword is thus suitable for the coding of the sign and the position of the highest relevant data bit for data values ​​between - (2ⁱ-1) ... 2ⁱ-1.

0062By means of a data word d1, d2 comprising seven data bits and one sign bit, decimal data values ​​between -127 and +127 can be represented. In order to transmit the position of the highest relevant data bit of the seven data bits and the sign information, codewords having four code bits, one sign bit bit, and three code bits for the highest relevant bit position are required.

0063In order to transfer the position of the highest relevant data bit and sign for data values ​​between -255 and +255, codewords require five code bits, one sign bit code and four code bits for the highest relevant data bit position.

0064In one embodiment of the invention, data values ​​whose magnitude is above a predetermined value are coded without sign information, ie to map to the coded data word. This procedure is suitable when differential values ​​between two successive data values ​​of a data sequence are to be transmitted as data values, since for signatures above a predetermined value the sign information can be reconstructed on the basis of previously transmitted data, as will be explained below.

0065In the example explained with reference to FIG. 8, in which code words with 4 code bits are available, it is provided that difference values ​​with values ​​greater than or equal to 128 (= 2⁷) without sign. The codeword 1000 is used in the example to transmit the information that the difference value to be transmitted is greater than or equal to 128, ie in an interval [128,255]. The transmission of the codeword corresponds to a transmission of a sign-independent approximation value of 128. In order to additionally transmit a sign information, an additional bit of the code word would be required, which however can be saved for the reasons set forth below.

0066If, in this embodiment of the method, the transmission of a difference amplitude value greater than or equal to 128 for one of the first and second data words is detected on the receiver side, then the sign information can be determined on the basis of the previously transmitted information.

0067It is assumed that the data values ​​transmitted by means of the method according to the invention, which may be between -255 and +255, represent differences between in each case two successive data values ​​of a data value sequence, absolute values ​​of these data values ​​lying between 0 and 255. For clarification, such a data sequence with data values ​​Y-2... Y1 is shown schematically in FIG. A difference value between a data Y0 and a previous data Y-1 is denoted by dY in FIG.

0068In order to transfer a jump from the value 0 of the first value Y-1 to a value 255 of the subsequent value Y0, a difference value +255 must be coded and transmitted, while for a jump from 255 to 0 a difference value -255 is to be coded and transmitted. The absolute values ​​of the values ​​of the data sequence are reconstructed on the receiver side by adding a received difference value to the absolute value determined immediately before. For the reconstruction of the data value Y0, the sum of the value Y-1 and the difference value dY is thus formed.

0069If in the method according to the invention a sign-independent difference value dY greater than or equal to 128 is received, it is determined which value the preceding absolute value Y-1 of the data sequence has. If this value lies in the interval [0, 128 [then the currently received difference value dY is assumed to be a positive difference value, since a negative difference value dY having an amount greater than or equal to 128 in addition to the previous absolute value Y-1 of the interval [0, 128 would result in an invalid current data value Y0 value less than zero. If, on the other hand, the previous value Y-1 is in the interval [128,255] and a difference value greater than or equal to 128 is received, the difference value is assumed to be the negative difference value since a positive difference value dY equal to or greater than 128 is added to the previous one Absolute value Y-1 of the interval [128,255] would result in an invalid current data value Y0 value greater than 255.

0070In summary, difference values ​​with an amount greater than 128 can be transmitted without a sign since the sign information can be reconstructed on the receiver side based on the respectively preceding value of the data sequence. Difference values ​​with an amount greater than 128 are thus transmitted without sign information.

0071An encoding method using an encoding table explained with reference to FIG. 8b is explained in summary with reference to FIG. 10 for the coding of two difference values ​​dY, dC. These difference values ​​dY, dC each represent a difference between a current data value and a preceding data value of two data sequences Y-2... Y1 or C-2... C1. As numerical examples, dY = 60 in FIG₁₀= 00111100₂ and dC = 19₁₀= 00010011₂ selected.

0072In a first method step, a first approximation is performed to the difference value dY, dC to be coded using the coding table in which approximation values ​​for the difference values ​​to be transmitted are stored. Each approximation value is a codeword, in the example, a codeword 4 bits long, stored. The approximation values ​​are chosen in the coding tables shown in FIG. 10b such that they are each powers of two. The coding table is used to select the approximation value which comes closest to the data value to be transmitted, but which is smaller in magnitude than the data value to be transmitted. In the example shown, the first approximation value dY '= 32 to which the code word 0110 is assigned is selected for the data value dY = 60 to be transmitted from the coding table. For the data value dC = 19 to be transmitted, the first approximation value from the coding table dC '= 16 is selected, to which the code word 0101 is assigned. In the example, approximation values ​​with values ​​between 1 and 64 are distinguished according to sign, whereas for differential values ​​with values ​​greater than or equal to 128, the first approximation value is coded and transmitted independent of sign.

0073The codewords associated with the first approximation values ​​dY 'and dC' are then mapped onto the coded data word d3. The remaining data bits of the coded data word d3, four data bits in the illustrated example, are used to represent and transmit as precisely as possible the difference between the data value to be transmitted and the first approximation value. For the data value dY = 60 and its first approximation value dY '= 32, this difference is 28₁₀= 11100_2, and for the data value dC = 19 and its first approximation value dC '= 16 this difference is 3₁₀= 0011₂,

0074The coding of these differences, ie the mapping of the data bits of these differences to the additional data bits of the coded data word d3, takes place in the example with the aim of minimizing the absolute error for the transmission of each data word as far as possible. This is done in the example in that data bits of the binary data words 11100₂ or 0011₂representing the difference values ​​mapped to the available additional bits of coded data word d3. The mapping takes place with the aim of obtaining an identically large maximum coding error for both data values ​​dY, dC. In the example, the highest data bits Y are used for this purpose₄, Y₃, Y₂ of the first difference value and the data bit C₃ of the second difference value mapped to the coded data word. Not considered by the first difference value while the data bits Y₁ and Y₀ of the first difference value and the data bits C₂, C₁ and C₀ of the second difference value, resulting in a maximum coding error of 11 for the first data word₂= 3₁₀ and for the second data dC, a maximum coding error of 111₂= 8₁₀ results.

0075In summary, in the transmission method according to the invention, a first approximation to the data value dY, dC to be transmitted first takes place, wherein the approximation value, optionally including a sign information, is encoded by a codeword stored in an encoding table. A further successive approximation to the data values ​​dY, dC to be transmitted takes place by at least partial coding of the remaining differences, the coding error being greater, the more data bits of the difference value can not be mapped onto the coded data word.

0076Although the inventive method was previously explained for the mapping of a first and second data word to a coded data word, it should be noted that the inventive method is of course also suitable for mapping more than two data words to a coded data word.

0077In the methods explained so far, the coded data word c3 each has a predetermined length. The possible coding error that results in the coding of two data words on the coded data word, in particular depends on the value of the first and second data word and increases in the previously explained examples with increasing amplitude of the value represented by the respective data word.

0078In order to reduce the coding error, it is provided in another embodiment to make the length of the coded data word variable, in that the number of additionally available data sections can vary. Thus, it is possible to provide so many additional data sections in the coded data word that predetermined data bits of the first data word d1 and of the second data word are securely coded. This will be explained below with reference to FIG.

0079As explained, the maximum coding error of the first data word d1 in the method explained with reference to FIG. 5 is 11₂ = 3₁₀while the maximum error of the second data word d2 111₂ = 7₁₀ is. With the aim of the coding error for both data words d1, d2 certainly not greater than 11₂ = 3₁₀ It is therefore provided in one embodiment of the method to continue the mapping of data bits of these data words until the data bit at both k1 = 3 and k2 = 3 is securely coded by both data words. In order to achieve this for the numerical example in FIG. 5, an additional coding step is required in which the data bit d2 (FIG. 3) of the second data word d2 is mapped onto the coded data word, which is shown in dashed lines in FIG. The data word transmitted in this case then has a length of 11 bits in the example.

0080A "lossless coding" can be achieved by means of this method if the mapping of the data bits of the data words d1, d2 to the coded data word d3 is continued until, of the two data words, the least significant bit (LSB), namely the bit dl (1) and the bit d2 (1) is mapped to the coded data word.

0081Of course, the maximum allowable coding errors for the first and second data word d1, d2 may also be chosen differently.

0082In the embodiments explained above, the approximation values ​​are each chosen such that they are a power of two of the bit position of the highest relevant data bit, that is, dC '= 2^MSB or dY '= 2^MSB, MSB designates the bit position of the respective highest relevant data bit, assuming MSB = 0 for the lowest relevant data bit (LSB). However, the invention is not limited to powers of the number 2 as approximation values, but almost arbitrary approximation values ​​can be provided, as will be explained below with reference to FIG.

0083FIG. 11a shows an encoding table which comprises approximation values ​​in the left column, ranking numbers of the individual approximation values ​​in the middle column and the codewords assigned to the individual approximation values ​​in the right column. The approximation values ​​contained in this table differ from the approximation values ​​given in the table in FIG. 10b in that there are approximation values, such as ± 12, ± 24, ± 48, which are not integer powers of the number 2. Preferably, the individual approximation values ​​are chosen such that the differences between an approximation value and the next larger or next smallest approximation value are in each case integer powers of the number 2. For example, for the difference between the approximation value 32 and the next larger approximation value 48: 48-32 = 16 = 2⁴, This procedure of choosing the differences between the individual approximation values ​​as integer powers of the number 2 makes sense with regard to effective coding, but is not necessary with regard to the functionality of the coding method. Also not required in terms of the operability of the method is that there are approximate values ​​in the table which are integer powers of the number 2.

0084The implementation of the method according to the invention using the table shown in FIG. 11a is explained below for an encoding of the data values ​​dY = 60 and dC = 19:

0085For each of the data values ​​dY, dC to be coded, the first step is to use the table to determine the approximation value which corresponds to the respective data value or which is smaller in magnitude than the respective data value and which, in terms of amount, is the least different from the respective data value in comparison to the other approximation values. For the data value dY = 60, this procedure leads to a first approximation value 48 to which the code word dY '= 11010 is assigned. For a first difference between the first data value and the first approximation value, 60-48 = 12 = 1100₂, The binary representation 1100 of this difference is referred to below as the first differential data word.

0086For the data value dC = 19, a second approximation value 16 results, to which the code word dC '= 10100 is assigned. For the difference between the second data value dC and the first approximation value, the following applies: 19-16 = 3 = 011₂, The binary representation 011 of this difference is referred to below as the second differential data word.

0087Each of the approximation values ​​of the coding table is assigned a ranking number. These ranking numbers are each an integer in the example and are dependent on the maximum size of an error which can occur when approximating a data value by an approximation value. This maximum error corresponds to the amount of the difference between the respective approximation value and the next larger approximation value minus one. For the first approximation value 48 whose next largest approximation value is the approximation value 64, this maximum error is 15 (= 64-48-1). For the second approximation value 16 whose next largest approximation value in the table is the approximation value 24, this maximum error is 7 (= 24-16-1). This error is hereinafter referred to as the maximum error associated with an approximation value.

0088The ranking number to an approximation value can thereby correspond to this maximum error . Preferably, however, the ranking number depends on how the difference between the determined approximation value and the data value is mapped to the coded data word.

0089In one embodiment, it is provided to represent the difference between the approximation value and the data value in the manner already explained above as a binary data word and to map individual data bits of this data word to the coded data word in each case starting with the data bit of the highest relevant bit position and taking into account conditions yet to be explained , The rank order number of an approximation value corresponds to the number of bit positions that are required in order to represent the maximum error associated with the approximation value in binary form. For the first approximation value 48 with the maximum error 15 assigned to it, the ranking sequence number 4 is obtained, and for the second approximation value 16 with the maximum error 7 assigned to it, the ranking sequence number 3 is obtained. In general, the rank order number r can be represented as: <maths id="math0001" num="(1)"><math display="block"><mrow><mi mathvariant="normal">r</mi><mo>=</mo><mi mathvariant="normal">rd</mi><mrow><mo>(</mo><mi mathvariant="normal">ld</mi><mrow><mo>(</mo><mi mathvariant="normal">Emax</mi><mo>)</mo></mrow><mo>)</mo></mrow></mrow></math><img file="EP1631091A1_D0001.tif" /></maths> ld (.) denotes the function of the base 2 logarithm, Emax denotes the maximum error associated with an approximation value, and rd (.) denotes a rounding function which rounds up a numerical value to the next largest integer numerical value, ie an integer numerical value is incremented by one and a non-integer value is rounded up to the next largest integer number.

0090In the example, the approximation values ​​are chosen such that the differences between several adjacent approximation values ​​are equal in each case, so that the same ranking numbers r are assigned to some approximation values. The rank order number 7 of the approximation value ± 128 results from the amount of the difference (127) to the largest possible data value ± 255 in terms of value, for the representation of which 7 bit positions are required.

0091The table of the approximation values ​​is preferably generated as a function of a signal statistic of the data values ​​to be transmitted by generating more approximation values ​​or approximation values ​​with smaller distances to adjacent approximation values ​​for ranges of values ​​in which the data values ​​are particularly frequent.

0092For encoding signed values, the approximation values ​​with reference to FIG. 11a are preferably selected to be "symmetrical" to zero, so that a negative approximation value of equal magnitude is present for each positive approximation value.

0093The codewords associated with the first approximation value and the at least one second approximation value are mapped onto the coded data word in the method. Subsequently, taking into account the ranking numbers of the approximation values, the differences between the respective data value and the approximation value determined for the respective data value are coded. This can be done by representing these differences as binary data words and by mapping individual data bits of these data words onto the coded data word. The number of bit positions of such a difference data word, which represents a difference between a data value and an approximation value, corresponds to the number of bit positions that are required in order to represent the maximum error associated with the approximation value in binary form. In a determination of the ranking number according to equation (1), the number of bit positions of a data word representing a difference between a data value and an approximation value corresponds to the ranking number of the approximation value.

0094The difference data words, which each represent a difference between a data value and an approximation value, are first assigned the rank order number of the corresponding approximation value. The mapping of the data bits of these difference data words then takes place depending on the ranking sequence number. Thus, first the highest relevant data bit of the difference data word whose approximation value has the highest rank order number is mapped onto the coded data word. The rank order number of the difference data word whose data bit has been mapped is then reduced by a predetermined value, preferably 1. In the case of equal ranking numbers, it is determined in advance which difference data word is to be preferred, ie from which difference data word a data bit is mapped onto the coded data word.

0095For the mapping of a next data bit, the ranking numbers of the difference data words are again determined and the highest relevant data bit of the difference data word with the highest ranking number is mapped to the coded data word.

0096With reference to an encoding of the values ​​dY = 60 and dC = 19 using the code table in FIG. 11a, this means that, due to the larger ranking number of the first approximation value dY ', first the highest relevant data bit Y₃= 1 of the first difference value or first difference data word 1100₂ is shown. This difference data word has the rank sequence number 4, the highest relevant data bit mapped has the bit position 4. The remainder after the mapping remains the difference data word 100₂ with the rank order number 3 (= 4-1), which corresponds to the number of bit positions. Assuming that, with an equal number of bit positions of the difference data words to be coded, the difference data word of the value dY to be coded is preferred, the data bit Y will be next₂= 1 of the difference value 1100₂that has the bit position 3 mapped. The remaining difference data word 00₂ receives the rank order number 2. Now the difference data word 00 stands₂ of dY with the rank number 3 or with two bit positions and the difference data word 100₂ of dC with the rank number 3 or with three bit positions, respectively, so that next the bit at the highest bit position of this value is 100₂ is coded.

0097This procedure for encoding the difference values ​​between the data value to be coded and the respective approximation value is continued until one of the above-explained conditions is reached, ie until all data bits of the differences have been mapped, or a predetermined number of data bits of the coded word have been reached or respectively a minimum coding error is achieved for each data value. Assuming the end condition that all data bits of the first and second data values ​​are coded, the coding method is summarized in FIG. 11b.

0098Of course, it is also possible in this method, one of the data words to be coded or assign a coding priority to one of the difference data words to be coded after encoding the approximation value and to select the prioritized difference data word and to code its respective data bit as long as its order number is less than a predetermined value, the order number of the at least one other difference Data word exceeds.

0099With reference to the table in FIG. 11a, the individual approximation values ​​can be selected such that the maximum error associated therewith remains the same or increases with increasing magnitude of the approximation values, which means that the difference to the respectively next larger approximation value remains the same with increasing amounts of the approximation values or gets bigger.

0100However, there is also the possibility that the distances between individual approximation values ​​become smaller for increasing approximation values.

0101Furthermore, it is possible to choose the distance between individual approximation values ​​of a group with at least two approximation values ​​smaller than the distance between the absolute minimum of the approximation values ​​of this group and the next smaller approximation value and the distance between the largest of the approximation values ​​of this group and the next larger approximation value , This procedure is particularly useful if it is to be expected that the data values ​​to be coded frequently assume values ​​which are in the range of the approximation values ​​of this group. In the method according to the invention, such values ​​are already approximated with a small error in the first step, in which an approximation value from the table is selected. FIG. 12 shows by way of a table an example of such a sequence with approximation values. In the left-hand column, the approximation values ​​(0, ± 32, ± 64, ± 80, ± 96, ± 112, ± 144) are assigned in the middle column, and in the right column, the codewords assigned to the approximation values ​​are indicated, each unique to the individual approximation values.

0102The table contains a group of four approximation values ​​± 64, ± 72, ± 80, ± 88 of which two adjacent ones each differ by 8 and are assigned the rank sequence number 3. The distance, ie the amount of the difference, between the absolute smallest approximation value ± 64 and the next smallest approximate value ± 32, is 32, which means that this next smaller approximation value ± 32 has the order number 5. The distance between the next closest to this group approximation value ± 96 and its magnitude greater approximation value ± 112 is 16 whereby this approximation value ± 96 has the rank order number 4.

0103This choice of approximation values ​​is particularly useful if it is to be expected that the amounts of the data values ​​to be coded frequently assume values ​​in the range between 64 and 88.

0104In the methods explained above, the first codewords associated with the bit positions of the first data word each have a same word length, and the first codewords associated with the bit positions of the second data word each have the same word length. In a further embodiment of the method is provided to select the first and / or second code words so that they have a different word length. The codewords which are assigned to the individual bit positions are preferably selected depending on the frequency with which the individual bit positions are occupied by the respectively highest relevant data bit of a data word. Bit positions which form the highest relevant bit position more frequently than other bit positions are assigned shorter code words than the other bit positions in order to obtain a shorter coded data word overall for the coding of frequently occurring data words. Such a procedure to use different lengths of codewords for the transmission of information depending on the probability of occurrence of the information to be transmitted is well known and, for example, in Proakis, John G.: "Digital Communications", 3rd Edition, Mc Graw-Hill, ISBN 0-07-051726-6, pages 95-103. This type of coding is called variable length coding.

0105In the previous explanation, various coding tables for coding the most relevant signal component have been explained. It should be noted that it is also possible to provide different coding tables and, depending on the signal statistics, ie depending on the frequency of occurrence of certain values ​​to be coded in the signal sequence, to select one of the coding tables for the coding.

0106It should also be noted that the method is not limited to the coding of two data values ​​but is applicable to any number of data values ​​to be coded. In the encoding of the difference data words is to determine which of the difference data words is preferably coded for the same ranking numbers.

0107The method for the receiver-side decoding of a coded data word generated by the method according to the invention, comprising at least a first data portion, a second data portion and at least one additional data portion to obtain a first and second decoded data word results directly from the coding algorithm. Here, data words decoded on the receiver side are reconstructed from the transmitted approximation values ​​and the data bits of the difference data words.