An image encoding and transmitting system

Abstract: An image encoding and transmitting system is an image transmission system for transmitting digital data such as TV telephones. The system for dividing input frame data into a plurality of blocks before transmitting them comprises on its sending side an intra-frame/inter-frame determiner (22) for receiving intra-frame data and inter-frame data and selecting either of them for output, and a difference collator (23) for having the intra-frame/inter-frame determiner (22) compulsorily output intra-frame data at the time of data input for the next frame when one or more data in each block forming inter-frame data are larger than a predetermined threshold. The system also comprises on its receiving side an picture element domain frame data storage (24) for storing received data in the picture element domain, and a motion vector detector (25) for detecting according to the contents in the storage a motion vector using the data in the block surrounding the discarded block in order to guess the data in the discarded block.

Description: Background of the Invention The present invention relates to an efficient image data encoding system used in a digital transmission of TV telephone and TV conference data by an NTSC method, or in a digital transmission of high-definition TV (HDTV) data, and more specifically to an image encoding and transmitting system used in an image transmission system for dividing input frame image data into a plurality of blocks comprising a plurality of picture elements, encoding them in block units, and transmitting the encoded data in cell units. The present invention further relates to an image processing method for encoding and transmitting data representing a succession of image frames, the frame image data being divided into a plurality of block units of picture elements, selectively encoded using an inter-frame encoding technique or an intra-frame encoding technique, and transmitted in packet units. An asynchronous transfer mode (ATM) has been widely accepted and is being standardized to realize a broadband ISDN, a new generation network. In the ATM, data are put into a single format "cell" (a fixed length packet) and transmitted by a label multiplexing technology. In an image communication field, it is regarded as an efficient improvement in the utilization of lines and regenerated image quality through a variable bit rate transmission. However, in an efficient encoding system based on an inter-frame encoding process, the quality of images are badly deteriorated if a cell-discarding operation makes an error in image data during transmission. Therefore, an efficient encoding system having a cell-discard compensation function is earnestly required. Recently, various image data processors have been digital oriented, and new systems for transmitting digital image data signals have been extensively developed in many application fields such as TV telephones, etc. Generally, image data involve a large volume of information when transmitted. For example, when TV data are digitalized, they require 100Mb/s transmission capacity and involve 1,500 times as much as voice data. In the TV broadcast, a screen is switched 30 times in a second, and a frame is switched every 1/30 second. Normally, picture elements are arranged in a two-dimensional array in one screen corresponding to one frame. Therefore, there have to be a large volume of information for image data of one frame even though the density of one picture element can be represented by 8 bits. However, the contents of an image in each frame may not vary greatly even when a frame is switched every 1/30 second. That is, a large part of an image is static including the sky and a scene in the background. Only a small part of it varies in each frame. Therefore, an inter-frame encoding system has been developed to compress and encode image data. In the inter-frame encoding system, for example, the difference in density data is obtained between corresponding image pictures in two time-series frames. The difference is encoded by a Huffman code, for example, and transmitted to the transmission line. If the density does not vary for most picture elements, the difference between picture elements results in "0" and can be represented by about 2 bits. A large difference between picture elements requires 8 or more bits. However, since only large differences must be encoded, total transmission data can be greatly compressed. By contrast, a system of encoding data in 1 frame "as is" is referred to as an "intra-frame encoding system." In the inter- and intra-frame encoding systems, two basic operations "sampling" and "quantization" are required for representing image signals digitally. There are two methods of sampling an image. First, an image is sampled by representing by density values for a discrete point array corresponding to picture elements. Second, a density value function (image function) defined on the XY plane corresponding to a frame plane is expanded orthogonally, and the expansion coefficient is determined to be a sampling value. Figure 1 is a block diagram for explaining the general configuration of the image transmission system using an orthogonal transform. In Figure 1, noises are removed through a filter from inputted image data by a preprocessor 1, and picture element data are divided in block units. The block-division does not mean an orthogonal transform collectively performed on data comprising KxN picture elements in a two-dimensional array in one frame, but is performed to shorten the transformation time by obtaining a transformation coefficient for each block comprising 4x4 to 16x16 picture elements. In a source encoder 2, data are quantized for the reduction of bits after the inter-frame encoding, the transformation-encoding, etc. as encoding processes for removing redundancy in space and time directions. The orthogonal transforms performed in this technology are, for example, Adamar transform, cosine transform, Karounen Roebe transform, etc. Among them, the discrete representation in cosine transforms is commonly used, and the discrete cosine transform (DCT) is applied most. In such orthogonal transformation-encoding systems, the inter-relation in a small area is regarded and an orthogonal transform is performed using picture elements of a small area as a numerical string. The resultant transformation coefficient corresponds to a frequency component indicating each level ranging from a low frequency to a high frequency. Since an image signal normally has a low frequency component rather than a high frequency component, a larger number of bits are assigned to a low frequency component and a smaller number of bits to a high frequency component prior to the quantization. Thus, the volume of transmission data can be reduced greatly. Figure 1 shows a variable length encoder 3 for encoding data by a Huffman code, run-length code, etc. to eliminate statistical redundancy, and a cell assembler 4 for assigning side information for detecting cell-discard and a header to a cell. Thus, an assembled cell is outputted through a network. On the receiving side, a cell disassembler 5 detects cell-discard in a cell inputted through the network, and the cell is disassembled to data. Then, the received bit string is decoded by a variable length decoder 6, and image data are decoded by a source decoder 7 by performing the source encoding process in reverse. Then, a post-processor 8 performs an unblock process, a noise removal process using a filter, etc., and the data are outputted. Figure 2 is a block diagram for explaining the configuration for the inter-frame DCT encoding system as the first example of a typical conventional encoding system. In Figure 2, a subtracter 11 on the sending side calculates the difference between inputted image data divided into blook data and the data obtained by multiplying the block data stored in a frame memory 9 at the same block position but in the preceding frame by the leak coefficient α provided by a leak coefficient unit 10. The difference and the inputted data are applied to an intra-frame/inter-frame determiner 12 for determining which is effective, to encode the data in the present frame, that is, to encode the intra-frame data as is, or to encode the difference between the data in the present frame and those at the corresponding position in one frame before the present data. The data determined to be more effective are applied to a discrete cosine transform (DCT) unit 13, and quantized by a quantizer 14. The output of the quantizer 14 and the intra-frame/inter-frame determination result indicated by the broken line shown in Figure 2 are outputted to the variable length encoder 3 shown in Figure 1. Simultaneously, the output of the quantizer 14 is inversely transformed again to the picture element domain by an inverse discrete cosine transform (IDCT) unit 15, added by an adder 16 to the product obtained by multiplying the data stored in the frame memory 9 by α from the leak coefficient unit 10, and then stored again in the frame memory 9. However, when an intra-frame data encoding is selected, the adder 16 does not add the data in the prior frame according to the input of a determination signal as shown by the broken line, but stores the output of the IDCT unit 15 as is in the frame memory 9. In Figure 2, on the receiving side, the input data are inversely transformed to the picture element domain by an IDCT unit 17. The result is added by an adder 20 to the data obtained by multiplying the data in the preceding frame stored in a frame memory 18 by # from a leak coefficient unit 19, and then outputted to the post-processor 8 shown in Figure 1 and stored again in the frame memory 18. When an intra-frame data encoding is selected, the data in the prior frame are not added. For a block which does not receive data due to cell- discard, the prior frame data is added to the input 0, and the result is stored in the frame memory 18. That is, at the cell-discard, the prior frame data are stored as is to the frame memory 18. In Figure 2, both on the sending and the receiving sides, the leak coefficient unit exists between the output of the frame memory and the adder. The product obtained by multiplying the output of the frame memory by the leak coefficient α is used as a value of the data in the preceding frame. If the leak coefficient α is set to a value between 0 and 1 and an error E arises between the contents stored in the frame memories on both the sending and the receiving sides, the error results in Ex α n after n frames. The error gradually gets smaller with time, and finally converges to zero. Therefore, the quality of a regenerated image can be restored when the error value has decreased down to near zero even though an error E has arisen on the sending and the receiving sides due to cell-discard and has incurred the deterioration in the quality of a regenerated image. Figure 3 is a block diagram for explaining the configuration for realizing the DCT inter-frame encoding system as the second embodiment of the conventional encoding system. The configuration of this system is similar to the system shown in Figure 2 except the following points: the discrete cosine transform (DCT) unit 13 is located in the source encoder 2, the input image data are transformed by the DCT unit 13 to a frequency domain coefficient, and the inter-frame or intra-frame data encoding system is selected for the transformed coefficient data. On the receiving side, data in the frequency domain are decoded using the frame memory 18 depending on the selection of the inter-frame or intra-frame encoding system. The result is transformed by the IDCT unit 17 to the picture element domain, and outputted to the post-processor 8. Figure 5 is a configurational block diagram for explaining the motion compensation inter-frame DCT encoding system of the prior art technology. It is similar in its configuration to Figure 2 showing the first example of the prior art technology. However, since the intra-frame encoding system is not used in the operation shown in Figure 5, the intra-frame/inter-frame determiner 12 is not provided on the sending side. Instead, a motion vector detector 100 for detecting a motion vector of each block according to inputted data and the data in the preceding frame stored in the frame memory 9 and a variable delay unit 101 for delaying the contents stored in the frame memory 9 and outputting them to the leak coefficient unit 10 are added to the sending side. Also on the receiving side, a variable delay unit 102 for delaying by the necessary time period the data in the preceding frame stored in the frame memory 18 according to a motion vector received from the sending side and outputting them to the leak coefficient unit 19 is added. In the conventional encoding system shown in Figures 2 and 3, the image quality can be automatically restored with time using a leak coefficient α even though the quality of an image has deteriorated due to cell-discard. For a block in which the time difference is comparatively small between the previous frame and the present frame, an error in the image data between the sender and the receiver is small, and can rapidly converge to zero using the leak coefficient. Therefore, the deterioration of the image quality can be limited to a visually admitted level. However, for a block in which the time difference is comparatively large, the error between these image data becomes large and the deterioration in the image quality is badly outstanding when the cell-discard rate is high because the error takes much time in converging using a leak coefficient. From IEEEE-Journal of Selected Communications, Vol. 7, No. 5, June 1989, pages 807-814 a selective recovery method of video packet loss in fast packet switching networks is known. According to this method the receiver detects a damaged picture area caused by packet loss, makes error concealments, notifies the transmitter and continues decoding. The transmitter continues encoding without using the effected area. From EP-A-O 422 575 an image data transmission system is known which comprises at the receiving side a unit for detecting a loss of a packet and a unit for compensating the lost block data by a loss compensating method designated by the transmission side. Summary of the Invention An object of the present invnetion is to shorten the time taken for restoring the deteriorated quality of an image, that is, for converging to zero the error in the image data between a sender and a receiver caused by cell-dischard. According to the present invention, this object is solved as defined in claims 1 and 5, respectively. Brief Description of the Drawings One of skill in the art can easily understand additional features and objects of this inventidn from the description of the preferred embodiments and some of the attached drawings. In the drawings: Figure 1 is a block diagram for explaining the general configuration of the image transmission system; Figure 2 is a block diagram for explaining the configuration of the first embodiment of the inter-frame DCT encoding system; Figure 3 is a block diagram for explaining the configuration of the second embodiment of the DCT inter-frame encoding system; Figure 4 is a block diagram for explaining the configuration of the motion compensation inter-frame DCT encoding system according to the third example of the prior art technology. Figure 5 is a block diagram for explaining the principle of the present invention; Figure 6 shows the concept of the compulsory intra-frame encoding system; Figure 7 shows an error in the compulsory inter-frame encoding system; Figure 8 shows how to convert picture element data to a frequency domain coefficient. Figure 9 is a block diagram for explaining the configuration of the first principle of the present invention; Figure 10 shows the detailed configuration of the intra-frame/inter-frame determiner, the difference collator, and the one-frame delay unit shown in Figure 9. Description of the Preferred Embodiment Figure 5 is a block diagram for explaining the principle of the present invention. It shows the principle of the image encoding and transmitting system used in an image transmission system in which image data in an inputted frame are divided into blocks each comprising a plurality of picture elements, the data are encoded in block units, and the encoded data are transmitted in cell units. For the detailed explanation of the present invention, a transmission method in which encoded data are transmitted in an ATM cell, for example. However, an encoded data transmission method is not limited to the method using the ATM cell, but can be realized using any kind of packet such as variable length packets, fixed length packets, etc. Figure 5 is a block diagram for explaining the first principle. It shows the principle of the image encoding and transmitting system for minimizing the influence of cell-discard by performing a compulsory intra-frame encoding on the frame data after the data having a comparatively large difference are transmitted through an inter-frame encoding so as to prevent the image quality from being greatly deteriorated when data having a large difference are cell-discarded. In Figure 5, an intra-frame/inter-frame determiner 22 receives inputted frame data and the first difference data which indicate the difference between the inputted frame data and the data in the preceding frame or between the inputted frame data and the data obtained by multiplying the data in the preceding frame by a constant, for example, a leak coefficient α, and selects and outputs either of the intra-frame data as the inputted frame data or the inter-frame data as the first difference data. The selection is determined by calculating a sum of squares of data in each block, collating the sums of squares for an intra-frame data and an inter-frame data, and selecting and outputting whichever has a smaller sum of squares. Thus, the length of the data code transmitted to the receiving side can be shortened. A difference collator 23 receives the second difference data between the inputted frame data and the data in one frame before the present frame, and causes the inter-frame/intra-frame determiner 22 to compulsorily output the intra-frame data when the data at the same block position in the next frame are inputted when more than one piece of data in each block forming the difference data is larger than a predetermined threshold. Although comparatively large difference data are inter-frame -encoded, transmitted, and then cell-discarded, the quality of the image can be prevented from being deteriorated by intra-frame-encoding the next frame data. The inter-frame/intra-frame determiner 22 and the difference collator 23 are provided on the sending side in an image transmission system. As shown in Figure 5 for explaining the first principle, an object of the present invention is to shorten the time taken for converging to zero an error caused by cell-discard in image data between a sender and a receiver, that is, to shorten the time taken for reconstructing discarded data in a block having a large inter-frame difference. If the inter-frame encoding system is performed in spite of a comparatively large inter-frame difference, the data at the same block position in the next frame are compulsorily intra-frame-encoded. Therefore, the next frame can be encoded without the influence of the preceding frame even though a large difference block data may be discarded, thereby greatly shortening the time taken for restoring acceptable image quality. As described above, when data having a comparatively large inter-frame difference are transmitted, an intra-frame encoding is compulsorily selected for the same block position in the next frame, and, on the receiving side, the data in the discarded block can be replaced using a motion vector for the blocks surrounding the discarded block. Figure 6 shows the concept of the first principle, that is, the compulsory intra-frame encoding system. Figure 7 indicates the prior art technology in which the difference between the present frame and the preceding frame are transmitted even though the difference is comparatively large unless an intra-frame encoding is selected from between the intra-frame encoding and the inter-frame encoding. Therefore, the time taken for reconstructing the deteriorated image quality caused by cell-discard is kept until, at the maximum, an error converges to zero using a leak coefficient. In the concept of the present invention shown in Figure 6, an inter-frame coding is selected, for example. If the difference is comparatively large, a compulsory intra-frame-encoding is selected for the next frame. Therefore, the error in the next frame is immediately converged to zero even though data having a large difference are discarded. Figure 7 is a view for explaining an error in the compulsory intra-frame encoding system. Figure 7A indicates the prior art technology in which an error converges based on an almost equal time constant regardless of an error level. Inter-frame data having a large difference are discarded. When an error is very large, it takes a long time for it to converge to zero. By contrast, in the present invention shown in Figure 7B, an error can converge in almost the same time as the conventional system if the difference is smaller than a predetermined threshold and a compulsory intra-frame encoding is not selected for the next frame. However, an error immediately converges to zero when the difference is larger than a predetermined threshold and a compulsory intra-frame encoding is selected for the next frame. Figure 8 shows a block diagram for explaining how to convert picture element data to a coefficient for a frequency domain by the discrete cosine transform. For example, a discrete cosine transform is performed on 8x8 picture element data to obtain 64 transformation coefficients for the frequency domain. The coefficients refer to the frequency component, and the coefficient Coo at the upper left corner generally indicates a direct current component. The coefficients toward right and downward therefrom show the higher frequency components. Figure 9 is a block diagram for explaining the configuration of the embodiment of the first principle. It shows the configuration on the sending side where a discrete cosine transform is performed on inputted data, and an intra-frame/inter-frame determination is made on the transformed data in the coefficient domain like in the second example of the encoding system of the prior art technology shown in Figure 3. The same parts as those in Figure 3 are assigned the same numbers. The configuration shown in Figure 9 comprises, in addition to the configuration on the sending side shown in Figure 3, a subtracter 30 for calculating the difference between the output of the DCT unit 13 and the output of the frame memory 9, that is, for calculating an inter-frame difference for all data in a block, a difference collator 31 for determining whether or not the difference is larger than a predetermined threshold, a one-frame delay unit 32 for delaying by one frame the output of the difference collator 31 and having the intra-frame/inter-frame determiner 12 select a compulsory intra-frame encoding for the next frame when the difference collator 31 determines that the difference is larger than the threshold. Figure 10 is a detailed block diagram of the intra-frame/inter-frame determiner 12, the difference collator 31, and the one-frame delay unit 32 shown in Figure 9. In Figure 10, the difference collator 31 corresponds to comparators 33a - 33n and an AND circuit 34, and the one-frame delay unit 32 corresponds to a first-in-first-out memory (FIFO) 35. The number of comparators 33a - 33n is equal to the number of the transformation coefficient data in a block. In each comparator, an inter-frame difference of block data is compared with a threshold. If the absolute value of the difference is larger than the threshold, "0" is outputted. If it is smaller than the threshold, "1" is outputted. If the inter-frame differences for all transformation coefficient data in a block are smaller than the threshold, the AND circuit 34 outputs "1". If any one absolute value of the difference in any data is larger than the threshold, it outputs "0", and the value is stored in the FIFO 35. The intra-frame/inter-frame determiner 12 shown in Figure 5 can be formed of a sum-of-squares calculator 36a for obtaining a sum of squares of data in transformation coefficient data in a block for the inter-frame difference data outputted by the subtracter shown in Figure 9, a sum-of-squares calculator 36b for obtaining a sum of squares of data in transformation coefficient data in a block for the intra-frame data outputted by the DCT unit 13, a comparator 37 for comparing the outputs of two sum-of-squares calculators, an AND circuit 38, a delay unit 39a for delaying the output of the subtracter 11 by the time taken for intra-frame/inter-frame determination, a delay unit 39b for delaying the output of the DCT unit 13 by the above described time, and a selector 40 for outputting the output from either of two delay units, each being shown in Figure 10. In Figure 10, the comparator 37 outputs "0" when a sum of squares of an inter-frame difference data is larger than a sum of squares of an intra-frame data, and outputs "1" when a sum of squares of an inter-frame difference data is smaller than a sum of squares of an intra-frame data. When the comparator 37 outputs "0", the AND circuit 38 outputs "0". At this time, the selector 40 outputs the output of the delay unit 39b, that is, intra-frame data, to the variable length encoder 3 shown in Figure 22. By contrast, an inter-frame encoding may be selected when the comparator 37 outputs "1". In this case, the FIFO 35 must also output "1". That is, the difference in all data in a block between the present and the previous frames must be smaller than a predetermined threshold. Then, the AND circuit 38 outputs "1", the selector 40 outputs the output from the delay unit 39a, that is, the inter-frame difference data outputted by the subtracter 11, to the variable length encoder 3. If the FIFO 35 outputs "0" while the comparator 37 outputs "1", that is, if the inter-frame difference at the same block position between the present and previous frames is larger than a predetermined threshold, the AND circuit 38 outputs "0", thereby selecting a compulsory intra-frame encoding. As described above, the present invention reduces the serious deterioration of image quality caused by cell-discard by, on a sending side, performing a compulsory intra-frame encoding on the next frame after sending data having a comparatively large difference and encoded by the inter-frame encoding system. Thus, the present invention can limit the deterioration of the image quality to a visually acceptable level, and greatly improve the quality of images processed by an image transmission system. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: An image encoding and transmitting system for dividing inputted frame data into a plurality of blocks comprising picture elements, encoding them in block units, and transmitting said encoded data in packet units, said system comprising on its sending side: intra-frame/inter-frame determining means (22) for receiving first difference data as the difference between inputted frame data and data in the preceding frame or the difference between inputted frame data and data obtained by multiplying said data in the preceding frame by a constant Δ, and selecting and outputting either of the intra-frame data as the inputted frame data or the inter-frame data as the first difference data, and difference collating means (23) for receiving inputted frame data and second difference data between said inputted frame data and the data in one frame before the present frame, and having said inter-frame/intra-frame determiner (22) compulsorily output intra-frame encoded data of the next frame for the same block position when more than one piece of data in each block forming the second difference data are larger than a predetermined threshold, wherein the deterioration of image quality of frame data having a large difference can be prevented. The image encoding and transmitting system according to Claim 1, wherein said intra-frame/inter-frame determining means (22) comprises: an intra-frame/inter-frame determiner (12), said difference collating means comprises: a difference collator (31) for determining whether or not the value of one or more data in blocks involved in said second difference data is larger than a predetermined threshold, and a one-frame delay unit (11) for delaying said determination result by 1 frame when said difference collator (31) determines that one or more data in said block is larger than said threshold to compulsorily output said data in said frame to said intra-frame/inter-frame determiner (12), said image transmitting system further comprises on its sending side: a discrete cosine transform unit (13) for performing a discrete cosine transform on inputted image data, a first subtracter for obtaining the difference between said input frame data as an output of said discrete cosine transform and data obtained by multiplying the data in the preceding frame by a leak coefficient α as said constant to output the result as said first difference data to said intra-frame/inter-frame determiner (12), a quantizer (14) for quantizing an output from said intra-frame/inter-frame determiner (12), an adder (16) for outputting the sum of an output from said quantizer (14) and data obtained by multiplying the data in the preceding frame by a leak coefficient α when said intra-frame/inter-frame determiner (12) outputs inter-frame data, and outputting an output from said quantizer (14) as is when it outputs intra-frame data, a frame memory (9) for storing an output from said adder (16), a leak coefficient unit (10) for multiplying an output from said frame memory (9) by a leak coefficient α to output the result to said first subtracter (11) and said adder (16), and a second subtracter (30) for obtaining the difference between an output of said discrete cosine transform (13) and an output from said frame memory (9) to output it as said second difference data to said difference collator (31). The image encoding and transmitting system according to claim 2, wherein said difference collator (31) comprises: comparators (33) as many as the number of transformation coefficients in one block, for comparing the absolute value of said first difference data for each piece of data with a predetermined threshold, and outputting "0" when said absolute value of said first difference data is greater than said threshold and "1" when it is smaller than said threshold, and an AND circuit (34) for receiving an output of each of said comparators (33), wherein said one-frame delay unit comprises a first-in-first-out memory (35) for delaying by one frame an output from said AND circuit (34). The image encoding and transmitting system according to Claim 3, wherein said intra-frame/inter-frame determiner (12) comprises: a first sum-of-squares unit (36a) for receiving an output from said first subtracter (11) and calculating a sum of squares of data in each block for said first difference data, a second sum-of-squares unit (36b) for receiving inputted frame data as an output from said discrete cosine transform unit (13), and calculating a sum of squares of data in each block for said input frame data, a comparator (37) for comparing an output from said first sum-of-squares (36a) with an output from said second sum-of-squares (36b), and outputting "0" when said output from said first sum-of-squares (36a) is larger than said output from said second sum-of-squares (36b), and "1" when it is smaller than said output from said second sum-of-squares, an AND circuit (38) for receiving an output from said comparator (37) and an output from said first-in-first-out memory (35), a first delay unit (39a) for delaying an output from said first subtracter (11) to the time point when a comparison result is outputted by said comparator (37), a second delay unit (39b) for delaying an output from said discrete cosine transform unit (13) by the delay time of said first delay unit (39a), and a selector (40) for selecting and outputting an output from said first delay unit (39a) when said AND circuit (38) outputs "1", and an output from said second delay unit (39b) when said AND circuit (38) outputs "0". An image processing method for encoding and transmitting data representing a succession of image frames, the frame image data being divided into a plurality of block units of picture elements, selectively encoded using an inter-frame encoding technique or an intra-frame encoding technique, and transmitted in packet units, said method comprising: receiving the frame image data for a current frame after the frame image data has been divided into block units and before encoding, calculating first difference data as the difference between inputted frame data in each block of said current frame and data in the corresponding blocks of a preceding frame multiplied by a constant, selecting and outputting either the encoded frame data as intra-frame data, or the first difference data as inter-frame data, calculating second difference data as the difference between the input data for the current frame and the data for the previous frame, and compulsorily outputting the intra-frame data as the data for the next frame for the same block position when more than one piece of data in each block forming the second difference data are larger than a predetermined threshold. The image processing method of claim 5 further comprising: performing a discrete cosine transform on inputted image data before said inputted frame image data is used in said first difference calculating step.

Inventors: HAMANO TAKASHI, MATSUDA KIICHI, SAKAI KIYOSHI, HAMANO, TAKASHI, MATSUDA, KIICHI, SAKAI, KIYOSHI, Hamano, Takashi, c/o Fujitsu Limited, MATSUDA, KIICHI, C/O FUJITSU LIMITED, SAKAI, KIYOSHI, C/O FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: H04N7
IPC codes: G06T9, H04N7, H04Q11, H04L12