Video coding apparatus

Abstract: A highly efficient coding apparatus for coding digital video signal according to a first standard having a resolution substantially N times higher than that of a second standard, comprising, averaging circuit (3) for averaging the digital video data N picture elements and for generating the averaged data, block encoding circuit (4) for encoding the averaged data in a block format allowing data compression, and subtracting circuit (10) for generating the subtracted data representing the difference between a plurality of video data of the N picture elements and the averaged data, encoding circuit (12) for encoding the subtracted data to generate an additional data, and transmitting circuit for transmitting the output of the block encoding circuit and the additional data in a predetermined order.

Description: This invention relates to a highly efficient coding apparatus for a digital video signal capable of providing compatibility in coding of digital video signals of two systems with different resolution. For a television system, a higher resolution, for example, high vision system as compared with the NTSC system put into practical use has been proposed. Also, research and development of peripheral equipment such as VTR and video camera have been done with respect to the former system. For example, the recording of a high resolution video signal in the form of digital data has also been proposed. In even the existing standard system, a digital video signal requires much information, and there is a need to record/reproduce much more information in the case of a digital video signal. For this purpose, it is common to adopt highly efficient coding for compression of the recording data at the time of recording a high resolution digital video signal. US-A-4 845 560 discloses an example of such a coding which uses separate branches for the still and moving parts of the image. The picture elements of the still blocks are averaged, coded and transmitted. Conventionally, highly efficient coding applicable to a digital video signal with high resolution and that applicable to a standard digital video signal are independent of each other and have no compatibility with each other. However, considering the use of a digital VTR in a period where plural systems are mixed, it is desirable that a tape recorded by a digital VTR for high resolution (called HD VTR) should be reproducible by a digital VTR for standard resolution (called SD VTR). Also, conversely, it is desirable that a tape recorded by the SD VTR should be reproducible by the HD VTR. For not only VTR but also transmission and reception of a digital video signal, the above mentioned bidirectional compatibility with common coding and decoding equipment is desirable for sales as well as to reduce the hardware size. An object of the invention is, therefore, to provide a highly efficient coding apparatus with bidirectional compatibility between a high resolution digital video signal and a standard resolution digital video signal. Another object of the invention is to provide a highly efficient coding apparatus which is capable of increasing efficiency of coding. According to the present invention, there is provided a highly efficient coding apparatus for coding digital video signals according to a first standard having a resolution substantially N times higher than that of a second standard, the apparatus comprising: averaging means for averaging the digital video data of N picture elements to generate averaged data, subtracting means for generating subtracted data representing the difference between a plurality of video data of said N picture elements and said averaged data, encoding means for encoding said subtracted data to generate additional data, and transmitting means for transmitting the averaged data and said additional data in a predetermined order. Block encoding means may be provided including block segmentation means supplied with said digital video data and for generating block data, and orthogonal transformation means supplied with said block data and for generating coefficient data including a DC component and a plurality of AC components for each block. The present invention will be better understood from the following detailed description of illustrative examples, which is to be read in connection with the accompanying drawings, in which:- Fig. 1 is a block diagram of one embodiment of the invention; Fig. 2 is a schematic diagram showing a part of a picture to be processed; Fig. 3 is a schematic diagram showing an average value of a part of the picture to be processed; Fig. 4 is a schematic diagram for describing the development of additional information and a reproduced value; Fig. 5 is a block diagram showing a specific structure of a distribution detecting circuit and an additional information generating circuit; Fig. 6 is a schematic diagram showing a first example of frequency distribution; Fig. 7 is a schematic diagram showing a second example of frequency distribution; Fig. 8 is a schematic diagram showing a third example of frequency distribution; Fig. 9 is a schematic diagram showing a fourth example of frequency distribution; Fig. 10 is a schematic diagram showing a structure of recording data; Fig. 11 is a schematic diagram showing an arrangement of rotary heads for VTR for a high resolution video signal; Fig. 12 is a schematic diagram showing a recording pattern of a tape; and Fig. 13 is a schematic diagram showing an arrangement of rotary heads for VTR for a standard resolution video signal. Hereunder, one embodiment of this invention will be described referring to the drawings. This one embodiment is the one for a digital video signal recording apparatus where a video signal with high resolution, for example, a high vision signal is recorded onto a magnetic tape by a rotary head. In Fig. 1, 1 is an input terminal for a high resolution digital video signal to be recorded, and each picture element of the video signal has been digitized into eight bits. 2 indicates a block segmentation circuit, and picture element data in the sequence of raster scanning is converted into data having a subblock structure of (2 picture elements × 2 lines) by the block segmentation circuit 2. As shown in Fig. 2, in the case where the subblock of (2 picture elements × 2 lines) is composed of picture element data x11, x21, x12 and x22, the picture element data is output in the order of x11, x12, x21 and x22 from the block segmentation circuit 2. The size of the subblock corresponds to the proportion of the resolution of a high resolution digital video signal and that of a standard digital video signal or the proportion of their data amount. A high vision signal has picture elements in the horizontal direction and lines in the vertical direction which are almost twice as compared with those in the existing NTSC system and the resolution of the high vision signal is nearly four times that in the latter system. Therefore, the subblock is composed of four picture elements. The output of the block segmentation circuit 2 is supplied to an average value generating circuit 3, a 4-sample delay circuit 9 and a distribution detection circuit 13, respectively. In an average value generating circuit 3, the average value y of each subblock picture elements is developed. As shown in Fig. 3, for example, an average value y11 (= x11 + x12 + x21 + x22/4) corresponding to the picture element data x11, x12, x21 and x22 is developed. For other subblocks, average values y12, y13, ..., y44 are developed similarly. As a result, (4 × 4 = 16) average values of Fig. 3 are formed from the area of (8 picture element × 8 lines). Data of the average values is given to an ADRC encoder 4 and a latch 11. A clock with a sampling frequency synchronized with an input digital video signal is supplied to an input terminal 5. The clock is given to a frequency divider 6 to form a clock with one-fourth of the frequency. The clock from the frequency divider 6 is fed to the average value generating circuit 3, the latch 11 and the ADRC encoder 4. These circuits operate in synchronism with the divided clock. Average values of each subblock are taken into the latch 11. ADRC coding has been proposed by the present applicant and is coding adaptive to a dynamic range DR which is the difference a maximum value MAX and a minimum value MIN of picture element data within an ADRC block. In this example, average value data of (4 × 4) of Fig. 3 is taken as the ADRC block. At the ADRC encoder 4, the maximum value MAX and a minimum value MIN in the average values y11 to y44 are detected, the dynamic range DR is calculated, each average value is quantized into a code signal of 4-bit length to be adaptive to the dynamic range DR. The quantization is the processing where the average data is divided by a quantized step obtained by (DR/2 4 ) and from its quotient an integer is developed. The bit number of the code signal developed at the ADRC encoder is not limited to four bits and the code signal may have the bit number of variable length. The coded output of the average value from the ADRC encoder 4 is supplied to a rate converting circuit 7. A clock from the input terminal 5 is given to the rate converting circuit 7 so that the data rate of the coded output of the average value data is converted into the original rate, i.e., the sampling rate of a high resolution digital video signal. The output signal of the rate converting circuit 7 is supplied to a frame segmentation circuit 8. The 4-sample delay circuit 9 delays an input video signal until an average value y is developed. The output of this delay circuit 9 is supplied to a subtracter 10. Average data from the latch 11 is supplied to the subtracter 10. As a result, a difference between picture element data and average value data is detected with respect to each subblock at the subtracter 10. To an additional information generating circuit 12, this difference data is given. A detection signal from a distribution detecting circuit 13 and the clock from the input terminal 5 are supplied to the additional information generating circuit 12. The distribution detecting circuit 13 generates a detection signal corresponding to level distribution of each subblock. Additional information is developed from the detection signal, the output signal of the subtracter 10 and allowance information when necessary. The additional information contains a difference signal Δ and a 2-bit signal corresponding to each picture element data. Fig. 4 shows an outline of the development of the additional information. Picture element data of subblocks is represented by a 2-bit additional code. When the additional code is (2 bits of 01 : value of 1), y + Δ , which is equal to the sum of the average value y of its associated block and a difference; when the additional code is (00 : 0), the average value y of the block is decoded; when the additional code is (10 : -1), y - Δ , which is equal to the subtraction of the difference Δ from the average value y of the block; and when the additional code is (11 : -2), the decoding is done for the other cases. The distribution detection circuit 13 is constructed by a serial-to-parallel converter 20 and a pattern detector 21 as indicated by a broken line in Fig. 5. The output signal of the block segmentation circuit 2 is supplied to the serial-to-parallel converter 20 from an input terminal 22. The serial-to-parallel converter 20 supplies picture element data of a subblock, for example, x11, x13, x21, and x22 to the pattern detector 21 in a parallel fashion. The pattern detector 21 detects a pattern of distribution of the four picture element data to generate a detection signal Pd. The detection signal Pd is given to the additional information generating circuit 12. Allowance information is fed to the pattern detector 21 and the additional information generating circuit 12 from an input terminal 23 to set a range for allowance. The additional information generating circuit 12 forms additional data for every subblock using a difference signal, the detection signal Pd and the allowance information given from an input terminal 24. This additional data is taken out at an output terminal 25. A pattern detection made by the pattern detector 21 will be explained referring to Figs. 6, 7, 8 and 9. In these drawings, the axis of abscissas indicates a level I of picture element data within a subblock, while the axis of ordinates indicates a generation frequency F. Distribution of frequencies expressed by this graph is classified into m (m ≦ 4) representative levels. Fig. 6 shows (m = 1), i.e., the case where the expression can be done by one representative level. For four picture element data in this case, the value of 0, i.e., 2 bits of (00) are alloted. A decoded value x" (0) of this code signal (00) is the average value y. Fig. 7 shows the case of (m = 2). In this case, additional data is formed using values ± 1 and value -2. Distribution expressed by graphs on the left-handed side of Fig. 7 indicates that the frequency of the level of y + Δ is larger than the frequency 1 of other level. In this case, for picture element data of levels with larger frequencies, the value of 1, i.e., 2 bits of (01) are allotted, while the value of -2, i.e., 2 bits of (11) are allotted for other levels. A decoded value x" (1) of (01) is y + Δ, and a decoded value of (11) is represented by the following equation: x"(-2) = 4 × y - (4 - 1) × x"(1)) ÷ 1 = y + ((4 - 1) ÷ 1) × Δ In distribution expressed by central graphs of Fig. 7, there exist two frequencies of the level of y + Δ and the level of y - Δ. In this case, for picture element data of the level of one frequency, the value of 1, i.e., 2 bits of (01) are allotted, while for other, the value of -1, i.e., 2 bits of (01) are allotted. The decoded value x" (1) is y + Δ and the decoded value x" (-1) of (10) is y - Δ. Distribution by graphs on the right-handed side indicates that the frequency of level of the difference -Δ is larger than that of levels which are not equal to the difference -Δ. In this case, for picture element data of levels with larger frequencies, the value of -1, i.e., 2 bits of (10) are allotted, while for others, the value of -2, i.e., 2 bits of (11) are assigned. The decoded value x" (-1) of (01) is y - Δ, and the decoded value x" (-2) is calculated in a manner similar to that mentioned above. Fig. 8 shows the case of (m = 3). Distribution expressed by graphs on the left-handed side of Fig. 8 indicates that the frequency of the average value y is the largest, that the frequency of level of +Δ, which is the difference from the average value y is the second largest and that the frequencies of levels other than these levels are the smallest. In this case, 2 bits of (00) are allotted to picture element data of the average value y, 2 bits of (01) are allotted to picture element data of y + Δ, and 2 bits of (11) are allotted to picture element data of other levels. In place of y + Δ, similar treatment is made even when the frequency of level of y - Δ is the second largest. Namely, the first case of (m = 3) is the case where one of three can be expressed by (00). The decoded value x" (-2) can be calculated in a manner similar to the case of Fig. 7. Distribution expressed by graphs on the right-handed side of Fig. 8 is the case where two of three can be represented by (1 : 01) and (-1 : 10). In other words, that is the case in which the frequency of y + Δ or y - Δ is greater than the frequencies of levels other than these levels. In this case, 2 bits of (01) are allotted to picture element data of y + Δ, 2 bits of (10) are allotted to picture element data of y - Δ, and 2 bits of (11) are allotted to picture element data of other levels. The decoded value x" (-2) is calculated by the following equation as shown in Fig. 8 when each of the frequencies is 11, 12 and 13: x" = (4 × y - 12 × (y - Δ) - 13 × (y + Δ) ÷ 11 = y + (12/11) × Δ - (13/11) × Δ In cases other than the case of (m = 3) shown in Fig. 8, quantization is performed by disregarding actual distribution similarly to the conventional coding so as to develop two bits of (0 : 00), (1 : 01), and (-1 : 00). Here, the code (00) means the central value rather than the average value. In this example in which a subblock consists of four picture element, the frequency of each level is 1. Fig. 9 shows the case of (m = 4). Fig. 9 indicates when three out of four levels can be represented by 0 and ± 1. In distribution represented by a graph of Fig. 9, the frequency of the average value y is the most, the frequency of the level of y + Δ and that of the level of y - Δ are the second most, and the frequency of the levels other than these levels are the least. In this case, 2 bits (00) are allotted to picture element data of the average value y, 2 bits (01) are allotted to picture element data of y + Δ, and 2 bits (11) are allotted to picture element data of other levels. A decoded value x" (-2) is calculated by the following equation when each frequency is 11, 12, 13 and 14: x"(-2) = ((4 × y - 12 × (y - Δ) - 13 × (y) - 14 × (y + Δ)) ÷ 11 = y + (12/11) × Δ - (14/11) × Δ In cases of other than the case of (m = 4) shown in Fig. 9, quantization is done by disregarding the actual distribution as in the prior art coding, so that 2 bits of (0 : 00), (1 : 01), and (-1 : 10) are developed. It is to be noted that the code of (00) means the center value rather than the average value. In this example in which the subblock is composed of four picture elements, the frequencies of respective levels of Fig. 9 are 1, respectively. In the case of a small subblock such as (2 × 2) as in this embodiment, the case almost corresponds to either (m = 1) or (m = 2) and rarely corresponds to (m = 3) or (m = 4). Also, on the reproduction side, a calculation equation for decoding picture element data which are allotted 2 bits of (11) from other two-bit information within the subblock is decided. As described before, a detection signal Pd is generated from the distribution detecting circuit 13 to distinguish the case of (m = 1), the case of three (m = 2), the case of three (m = 3), and the case of two (m = 4). By the use of the detection signal Pd and a difference signal from the subtracter 10, the additional information generating circuit 12 generates difference information Δ and 2-bit data corresponding to each picture element. For instance, when the output of the distribution detecting circuit 13 indicates m = 2 and the second case (the distribution at the center of Fig. 7), 2 bits of (01) are generated in response to the positive sign of the output Δ of the subtracter 10, and 2-bits of (11) are provided in response to its negative sign. These additional data is supplied to the frame segmentation circuit 8. The frame segmentation circuit 8 combines a coded output from the rate converting circuit 7 and additional data from the additional data generating circuit 12 and further performs the addition of a synchronization signal and an ID signal as well as the processing of an error correction code, etc. Recording data corresponding to picture element data in the areas shown in Figs. 2 and 3 is shown in Fig. 10A. An output obtained when average value data is coded by ADRC is arranged at a position in the vicinity of the head of the recording data. Additional data relating to each picture element data of 16 subblocks are then arranged. It is to be noted that since the synchronization signal, a redundancy code of the error correction code, the ID signal, etc., are not essential to be present invention, their illustration is omitted. When the ADRC block of (4 × 4) consisting of the average values y11, ..., y44 is coded, the minimum value MIN (8 bits) and dynamic range DR (8 bits) and code signals (4 bits) y11′, ..., y44′ corresponding to each average value are arranged in that order. Next additional data on the subblock consisting of x12, x12, x21, and x22, that is, difference data (7 bits are needed to express the difference between picture element data of 8 bits) and code signals x11′, ..., x22′, each of which has 2 bits, are arranged. As a result, additional data of 15 bits (= 7 + 2 × 4) in total is generated with respect to one subblock. The addition of these bits to additional data of 16 subblocks makes 240 bits. Hereunder, additional data of each subblock is arranged sequentially, and additional data of the subblock of x77, x78, x87, and x88 is arranged finally. The above-mentioned output signal of the frame segmentation circuit 8 is supplied to a distributing circuit 14 and divided into recording signals of 4 channels. A first-channel (called channel A) recording signal is supplied to a recording circuit 15A whose output signal is supplied to a rotary head HA. Recording signals of the second, third and fourth channels (channels B, C, and D) are given to rotary heads HB, HC, and HD through recording circuits 15B, 15C, and 15D in a manner similar to the first channel. The recording circuits 15A to 15D are composed of a digital modulator and a recording amplifier. The recording signal of the channel A is consists of only coded signals (MIN and DR and code signals y11′, ..., y44') related to average values of recording data of Fig. 10A. The additional data is divided into the channels B, C and D. An example of a part of a rotary head mechanism section is shown in Fig. 11. Rotary heads HA1, HB1, HC1, and HD1 are provided in close contact with a drum 31 rotating with a predetermined frequency, and rotary heads HA2, HB2, HC2, and HD2 are provided in close contact with these heads at an angle of 180°. A magnetic tape TP is obliquely wound around the circumference of the drum 31 at a winding angle slightly larger than 180°. The magnetic tape TP is fed at a constant speed. As a result, as shown in Fig. 12, a track pattern where four tracks TA1, TB1, TC1, and TD1 formed by the rotary heads HA1, HB1, HC1, and HD1 and four tracks TA2, TB2, TC2, and TD2 formed by the rotary heads HA2, HB2, HC2, and HD2 are positioned alternately on a magnetic tape TP. The recording signal of the channel A consisting only of the coded output of average values is recorded onto the tracks TA1 and TA2 as mentioned above. Although this one embodiment is an HD VTR for recording a high resolution video signal, the magnetic tape TP recorded as mentioned above by the SD VTR for recording a standard resolution video signal can be reproduced. The SD VTR has a pair of rotary heads HA11 and HA12 provided at an interval of 180° on a rotary drum as shown in Fig. 13. Each head scans the magnetic tape TP alternately. The magnetic tape TP in which the track pattern of Fig. 12 is formed is fed at four-fold speed by the HD VTR and reproduced by the SD VTR. As a result, scanning tracks TA11 and TA12 extending over the four tracks are formed alternately as shown by a broken line in Fig. 12. By displacing scanning positions of the rotary heads HA11 and HA12 by a piezoelectric element, control is made so that the scanning positions TA11 and TA12 coincide with the tracks TA1 and TA2, respectively. Therefore, the SD VTR can provide a reproduced picture (one-fourth of the resolution of the high resolution video signal) by ADRC decoding of a coded signal related to an average value. Also, conversely with the above-mentioned manner, a tape recorded by the SD VTR can be reproduced by the HD VTR. In this sense, the bidirectional compatibility can be achieved. A recording circuit of the SD VTR compresses picture data by ADRC without differential coding. As shown by a broken line of Figs. 2 and 3, coding of four-bit fixed length is made for an ADRC block (4 × 4 = 16 picture elements) in the SD VTR. Since four ADRC blocks are formed from the area of Fig. 2, recording data shown in Fig. 10B is provided. For example, recording data corresponding to the ADRC block containing x11, x12, ..., x43, x44 is composed of the minimum value MIN, dynamic range DR and code signals x11′, x12′, ..., x43′, x44′. This recording data is recorded on the magnetic tape TP by the rotary head HA1 or the rotary head HA2. When the magnetic tape where the recording data indicated in Fig. 10B has been recorded is reproduced by the HD VTR, the running speed of the magnetic tape is lowered to one-fourth of the normal one. Tracking deviation due to this difference in the tape running speed is corrected by a piezoelectric element. The outputs of the rotary heads HA1 and HA2 among the rotary heads of the HD VTR, i.e., only a reproduced signal of the channel A are handled as effective reproduction data, while reproduction data of other channels are brought to 0. The processing of this reproduced data can be carried out by a decoder of ADRC provided at a reproduction circuit of the HD VTR. In this way, the HD VTR can provide a reproduced picture with the same resolution at the time of reproduction by the SD VTR and with the same picture elements as those of a high resolution video signal. In the above-mentioned one embodiment, four-picture element additional data is transmitted by every two bits for decoding picture elements allotted -2. However, since average value data is sent by ADRC coding, there is the case where additional data of three picture elements except for the one at a predetermined position out of four picture elements may be transmitted. For example, assuming that the difference from the average value is extremely small, there is a possibility that such transmission is sufficient by allotting two bits and giving (3 × 2) bits. In this way, the compression of data amount can be increased. This invention treats a block of the size provided by considering the ratio of resolution of two systems for video signals and enables the post-coding data amounts in both systems to be almost equal. Further, since average value information and additional data are coded by another method, a reproduced picture can be constructed by decoding the average value information. Therefore, there is an advantage of compatibility between the two methods. In addition, according to the invention the average value is obtained at the reception side, since 2 bits of (00) are allotted to the average value. Furthermore, since there is no offset in a range being represented by two bits, high efficiency of the coding can be accomplished by the invention. Having described a specific preferred embodiment of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims: A highly efficient coding apparatus for coding digital video signals according to a first standard having a resolution substantially N times higher than that of a second standard, the apparatus comprising: averaging means (3) for averaging the digital video data of N picture elements to generate averaged data, subtracting means (10) for generating subtracted data representing the difference between a plurality of video data of said N picture elements and said averaged data, encoding means (12) for encoding said subtracted data to generate additional data, and transmitting means (8,14) for transmitting the averaged data and said additional data in a predetermined order. A highly efficient coding apparatus according to claim 1, further comprising detecting means (13) for detecting a level distribution of said digital video data of N picture elements in the block, encoding means (12) for encoding each of the digital video data of N picture elements in response to the output of said detecting means such that each of said digital video data corresponds to one of a first value equal to said averaged data, second and third value which have the difference of ±Δ from said averaged data and a fourth value which can be selected freely, and wherein the transmitting means (8,14) transmits said averaged data, difference data Δ and encoded data in a predetermined order. A highly efficient coding apparatus according to claim 1 or 2, further comprising block encoding means (2) for encoding said averaged data in a block format allowing data compression. A highly efficient coding apparatus according to claim 3, wherein said block encoding means (4) includes block segmentation means for generating blocks of averaged data, first and second detecting means for detecting maximum and minimum values, respectively, of said digital video data representing the plural picture elements in each of said blocks, means for generating dynamic range information for each said block from said maximum and minimum values for the respective block, and encoding means for encoding said digital video data based on said dynamic range information. A highly efficient coding apparatus according to claim 3, wherein said block encoding means (4) includes block segmentation means supplied with said digital video data and for generating block data, and orthogonal transformation means supplied with said block data and for generating coefficient data including a DC component and a plurality of AC components for each block. A highly efficient coding apparatus according to any one of the preceding claims, wherein said subtracting means (10) generates subtracted data corresponding to N - 1 picture elements.

Inventors: KONDO TETSUJIRO, KONDO, TETSUJIRO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H04N7
IPC codes: H04N11, G11B20, H03M7, H04N5, H04N7, H03H7