Hybrid encoder for video signals.

p0001The invention relates to a hybrid encoder for video pictures, are summarized in the adjacent pixels of a video image to sub-blocks with a motion estimator and an inter-intraframe encoding.

p0002Such hybrid encoder is for example from UPDATED SPECIFICATION FOR THE FLEXIBLE PROTOTYPE nx 384 kbit / s VIDEO CODEC, CCITT SGXV, Working Party XV / 1, Specialists Group on Coding for Visual Telephony, Document # 249, July 1987 known. A hybrid encoder makes it possible to transcode the next by a video data source video data with a low loss of information into a signal with a lower bit rate. In this process two encoding principles - hence the name hybrid encoder - applied: The interframe principle and the intraframe principle.

p0003When interframe principle the correlation between consecutive video frames is (this term is used here for full and partial images) exploited. For this purpose, the video to be encoded data are compared with estimated values, and encodes only the signal differences between these two signals and transmitted. The better the estimated values ​​correspond to the to be coded video data so as to lower the bit rate of the signal to be transmitted. When intra-frame principle, the original content of a video image is transmitted, wherein a bit rate reduction is achieved, for example, by an adaptive quantizer.

p0004From the above-mentioned publication it is also known to form estimates a motion estimator. In video images with moving scenes successive video images have a similar image content. Some parts of the image contents of two successive video images change at all the subjects (eg immobile background), other parts of the image content change only in the current image from the previous image its position (eg, mouth movement of a person speaking) and other parts are completely new compared to the previous Image. Change with movement neither brightness nor color content of a shifted image section, then the place where that image section occurs in the following video image, labeled appropriately by a vector. Since the coding of such a vector far less data coding claimed as the encoding of the entire image area can be reduced in this manner the bit rate.

p0005In an image memory for this purpose in each case the previous to the current video image video image is stored. A video image is constructed like a matrix of a series of pixels. Each pixel is represented by three numbers. The first value is a measure of the brightness of the pixel (hereinafter referred to as luminance). The second and third numerical value of a pixel represents the color of the pixel (hereinafter referred to as chrominance). The current video image is divided into sub-blocks. For this purpose, adjacent pixels of a video picture are combined into a sub-block. This sub-block has, for example, the size of eight x eight pixels and represents a planar segment of the video image. By means of a search range circuit are selected from the video image stored in the image memory a plurality of partial blocks, which are located close to the actual sub-block. These sub-blocks are compared with the current sub-block. The part block which at least different from the current sub-block or which is identical to the current sub-block, ideally, is selected as an estimate.

p0006The transmission of the motion vector and the differences between the current sub-block and selected as an estimate of partial block only offers advantages when the differences between the current sub-block and the selected sub-block are low. With some content is to be transferred may desirably is equal to the entire sub-block. For this reason, checks an inter-intra decision which method each of the current sub-block to be transmitted at best and operated corresponding Signalwegumschalter.

p0007Because of the required high processing speed motion estimator and inter-intraframe encoding with respect to the components currently available must have a parallel-processing Stuktur, resulting in a significant expense for components.

p0008The present invention has for its object, a hybrid encoder of the type mentioned in such a way that simplifies the structure.

p0009This object is achieved in a generic hybrid encoder in that motion estimator and inter-intraframe encoding have a common calculation module.

p0010Further advantageous embodiments of the invention are subject of the dependent claims.

p0011A Ausführugnsbeispiel of the invention is illustrated by the drawings and described in greater detail and explained.<ul><li>Figure 1 shows a motion estimator.</li><li>Figure 2 shows an inter-intraframe encoding.</li><li>Figure 3 shows a combination of a motion estimator and an inter-intraframe encoding selector.</li></ul>

p0012Motion estimator and inter-intraframe encoding are part of a non-illustrated hybrid encoder for transmitting video images. The motion estimator determined from sub-blocks of a previous video image part block which best proves estimate of the transmission of the actual sub-block under the selection pending partial blocks. The Inter-intraframe encoding selector decides whether the amount of data required for transmission of the current sub-block with the aid of serving as an estimate of the selected sub-block is less than the amount of data required for transmission of the current sub-bracket as a whole.

p0013The motion estimator shown in Figure 1 comprises a first and a second image memory 1, 2, a calculation module 3 and a minimum value register 4. The calculation module 3 is composed of a subtractor 31, an absolute value 32 and a summer 33rd

p0014In the first image memory 1 the current video image and the second image memory 2 respectively which the current video image previous video image is stored. The pixels of the video images are stored in a known manner in the form of their representative luminance and chrominance values ​​as binary values. A sub-block to be transmitted, T of the current video image is supplied via a selection circuit not shown, a first input of the calculation module 3rd Via a likewise not illustrated search range circuit in each case a partial block T 'of the data stored in the second image memory preceding video image is selected and fed to a second input of the calculation module 3rd The inputs of the calculation module are respectively connected to a first and second input of the subtractor 31st The subtractor 31 subtracts the values ​​of each of the position of the respective sub-blocks corresponding each luminance and chrominance. The difference values ​​are the Absolutbetragbildner 32 supplied, in which all the negative difference values ​​are multiplied by the value -1. In this way be obtained from the difference values ​​difference amounts to be supplied to the input of summer 33rd In the summer 33, the difference amounts of the individual pixels are added. Before the start of each summation of the individual amounts of the content of the summer will be cleared by a control pulse.

p0015The output values ​​of the adder 33 are the minimum value register 4 is supplied. With the selection of a new actual sub-block of the contents of the minimum value register is set to the maximum storable value simultaneously. By means of a logic circuit, the respective minimum value for registry run value chen vergli with the value stored in the minimum value register. 4 If the new value is smaller than the one stored value as the new value is saved, the new value is greater then the stored value is not changed. Every time a new value is stored, a control pulse is generated by the logic circuit, which is led to the search range circuit. With this control pulse is the addressing formed for the currently selected sub-block of the previous video picture which corresponds to the motion vector stored in a vector register, not shown. In this way, among the selection taken from the second image memory 2 subblocks one picked out, which is the current sub-block most similar in terms of the summed difference amounts. This is, after passing through all the selected sub-blocks of optimum motion vector in the vector registers. At the same time the sum of the differential amounts, which is in the minimum value register, a measure of the length of the required for transmission of the current sub-block with the help of this serving as an estimated value selected portion goat transmission code. The calculation of this value is also already part of the Inter-Intra-picture decision.

p0016Figure 2 shows an inter-intraframe encoding, which is constructed with a second calculation module 3 '. The construction of the second calculation module 3 'is not different from the structure of the first calculation module 3, which is used in the motion estimator. Therefore, the second calculation module also consists of a subtractor 31 ', an absolute value generator 32' and an adder 33 '. There is also the inter-intraframe encoding from the frame memory 1, the minimum value register 4, an average register 5, a characteristic decider 6 and a register 7. A field T of the current Videobil of is as well as the motion estimator 'supplied to the first input of the calculation module. 3 The output of the calculation module 3 'is connected to the average register fifth The minimum value register 4 is the minimum value register of the already described the motion estimator.

p0017The outputs of the minimum value register 4 and the average value register 5 are conducted to inputs of a characteristic decider. 6 The characteristic discriminator 6 is executed in the embodiment as a PROM. Depending on the output values ​​of the minimum value register 4 and the mean value register 5, which are guided on its address inputs, a single bit is outputted to a signal output S1. This bit of the Signalwegumschalter hybrid encoder for intra-frame coding or inter-frame coding are switched accordingly in a known manner.

p0018The output of the calculation module 3 'is also fed to the input of a register 7th The register 7 is connected to the second input of the calculation module 3 that the second input of the subtracter is divided over the tab 7 cached value to a sixty-fourth 31 pending value. The register 7 has a further input of Cl, which can be by a control signal S2 of the contents of the register 7 is set to zero. This control signal is generated by a control circuit, not shown.

p0019In the calculation of the expenses for the transfer of all current part Bocks the average value of the actual sub-block is calculated and then the difference values ​​between the current sub-block and a sub-block whose pixels have all the calculated average determined and summed. Advantageously, the from the subtractor 31 for these calculations ', the absolute-32' will and the summer 33 'formed calculation module 3' is used. For this, the average value of the current portion of goat are with this calculation module 3 'in a first calculation step determined and formed in a second calculation step, the difference values ​​between the current sub-block and the mean.

p0020To calculate the average value of a sub-block first all luminance or chrominance values ​​all of the pixels of a sub-block must be added. Since the current sub-block is, however, first the subtracter 31 'is supplied, the content of register 7 is initially set to zero by the control signal S2. Hereby is at the second input of the subtracter 31 'of the value zero. In this way, the values ​​of the pixels pass the subtracter 31 'without changing their values ​​as of each pixel of the actual sub-block only the value is subtracted zero. Since all values ​​of the pixels are positive, they also happen to Abtastwertbildner 32 'without modification. In this way, at the output of the adder 33 'of the accumulated value of all the individual pixels of the actual sub-block to. This value is stored in the register 7 and there divided by sixty-four. The number sixty-four corresponds to the number of pixels of a sub block, so that the arithmetic mean of the pixels of a sub-block is formed in this way. The division by sixty-four is realized in the embodiment by the wiring of the outputs of the register 7, in which the eight lowest outputs of the register 7 were left open. The output of the ninth bit was applied to the input of the first bit of the subtracter 31 ', the output of the tenth bit of the input to the second bit of the subtracter 31' and so on.

p0021In this way is in the second calculation step on the second input of the subtractor of the mean value of the actual sub-block on. The subtractor 31 'now calculates the differences between the current sub-block and the arithmetic mean of the actual sub-block. From these values, the absolute values ​​are formed again and in the summer 33 'summed. The result of this calculation is stored in the average value memory. 5 On the basis of the minimum value memory 4 and stored in the average value memory 5 data decided by the characteristic decision maker 6 in a known manner, in which case the transmission of a motion vector or the transfer of the entire sub-block is more advantageous.

p0022By this calculation of the intra-picture value in two runs, the use of an additional adder for calculating the average of a sub-block is unnecessary. This leads to not inconsiderable savings because of this summers must be constructed also as a parallel processing unit because of the high processing speed. This is particularly advantageous because of the intra-picture value calculation also the same calculation module can be used as the calculation module used for the motion estimator. This saves on development costs for the calculation module in itself, on the other hand this is an economic advantage when the calculation module is manufactured as an integrated circuit. Instead of two different integrated circuits is only one to design, test and produce. It is definitely more cost effective from an integrated circuit to produce twice as much to produce than two different inte grated circuits.

p0023Figure 3 shows a particularly advantageous embodiment of the invention. 3 shows schematically the structure of a combination of a motion estimator and an inter-intraframe encoding selector with a single calculation module. The relation to the figures 1 and 2 which remained unchanged in their functional assemblies are designated by like reference numerals. The embodiment consists of a first and a second image memory 1, 2, a calculation module 3, a minimum value register 4, an average register 5, a characteristic of discriminator 6, a register 7, and a multiplexer 8. The first input of the calculation module is connected via a drive circuit, not shown, with the first image memory 1 connected. The output of the calculation module 3 is guided to the inputs of the minimum value memory 4 and the mean value register fifth By control commands to a control circuit not shown, the output values ​​of the calculation module 3 are selectively stored in the minimum value register 4 or in the average register fifth The output values ​​of the minimum value register 4 and the average value register 5 are carried to the inputs of the characteristic decider. 6 The output of the calculation module 3 is also fed to the input of the register 7 whose output is fed to a second input B of multiplexer eighth A first input A of the multiplexer is connected via a search range circuit not shown with the second image memory 2nd The output of the multiplexer is connected to the second input of the calculation module 3rd By a control pulse S3 to a control circuit not shown, the input A or the input B is selectively connected to the output of the multiplexer.

p0024Depending on the control pulses generated by the control circuit, not shown, the circuit arrangement shown can operate as motion estimator or as inter-intraframe encoding. If by the control pulse S2 of the input A of the multiplexer is connected to the output of the multiplexer 8, this circuit corresponds completely to the motion estimator shown in FIG. 1 If by the control signal S2, however, the input B of the multiplexer is connected to the output of the multiplexer 8, corresponds the circuit shown in Figure 3 completely the inter-intraframe encoding shown and explained in FIG. 2 In this way it is possible to allow the illustrated embodiment quasi time multiplexed selectively as a motion estimator or as inter-intraframe encoding, wherein only a single calculation module 3 is required. This is particularly advantageous because it is precisely the calculation module 3 has a large share of the development costs and the total price of a hybrid encoder for its complicated structure.