Image processing apparatus and method

Abstract: An image processing system determines a characteristic of a moving picture, when moving-picture information is compressed, by comparing the contents of contiguous frames comprising the moving picture. The characteristic can be such that the background is not moving, but a part of the picture is moving. A compression method is selected in accordance with the characteristic and used to compress the image data. The compressed data includes the image data and information for designating the procedure to expand the image data. When the receiver receives the compressed image data, data expansion processing is performed based on the information indicating the compression procedure. Since the image processing system compresses the image by the compression procedure best suited to the characteristic of the image, information is not lost and efficient compression can be performed.

Description: BACKGROUND OF THE INVENTION The present invention relates to an image processing apparatus and method which records or transfers moving-picture information, and reproduces the recorded or transferred information. Conventionally, the above image processing apparatus compresses a frame or a plurality of frames comprising moving-picture information by a predetermined single type of compression method, and records or transfers the compressed information. Then, the recorded or transferred information is returned to as before in accordance with the method that the information has been compressed. However, in the conventional technique, when the compression method is not suitable to all or a part of the moving-picture information, a problem arises in that necessary information is lost during the compression or the compression rate is insufficient. For example, when the compression is performed by thinning frames of the moving picture, this method is suitable to an inactive moving picture, however, the reproducibility of an active moving picture is inferior. On the other hand, when the compression is performed by recording the difference between frames, this method is suitable to active moving picture, while the compression efficiency for inactive moving picture is insufficient. It is known from EP-A-0420627A to provide selection of compression procedure based on the operation of an apparatus which produces predicted frames using each procedure and compares the results with the actual new frame. It is also known from US-A-4,667,233 to provide apparatus in addition to compression encoding apparatus to determine the appropriate compression procedure prior to compression based on discrimination of image movement in each of a number of blocks in the image. Accordingly, in light of the above problems, it is an object of the present invention to provide an image processing apparatus and method having a mechanism such that image information is efficiently compressed, recorded, and transferred without losing necessary image information. According to the present invention, the foregoing object is attained by an image processing apparatus and method according to claims 1 and 9. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. Fig. 1 is a block diagram showing the construction of an image transfer system of an embodiment of the present invention; Fig. 2 is a diagram illustrating a data format when a compressed moving-picture information is recorded/transferred; Fig. 3 is a flowchart of the operation of an information compression; and Fig. 4 is a flowchart of the operation of an information expansion. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. <Construction of the System> Fig. 1 is a block diagram of an image transfer system of the present embodiment. In Fig. 1, a moving-picture information source 1 generates a moving-picture information which is subjected to the processing. A transmission-side image processing apparatus 2 compresses and transmits the moving-picture information. An information transfer apparatus 3 is an apparatus which transfers information, e.g. LAN (Local Area Network). A reception-side image processing apparatus 4 receives and expands the compressed information and reproduces a moving picture. Furthermore, the transmission-side and reception-side image processing apparatuses are respectively constructed as following. In the transmission-side image processing apparatus 2, the compressor 5 selects the most appropriate compression method for characteristic of each image scene inputted from the moving-picture information source 1 and executes the compression processing. A storage 6 stores a plurality of procedures of compression methods which are selected and executed by the compressor 5. A recorder 7 records the compressed image information (including the information concerning the selected compression method) on a magnetic disk. A transmitter 8 transmits the image information which is processed by the compressor 5. In the reception-side image processing apparatus 4, a receiver 9 receives the image information which is transmitted via the information transfer apparatus 3. An expander 10 selects the expansion method corresponding to the received moving-picture information and executes the processing. A storage 11 stores a plurality of expansion methods which are selected and executed by the expander 10. A reproducer 12 reproduces an original moving picture before the compression from the expanded image. Furthermore, the recorder 7 records the compressed information in the same way as the transmission side. <Explanation for Compression and Expansion Processings> In the image transfer system with the construction described above, the moving picture is transferred and reproduced as following. The moving-picture information inputted from the moving-picture information source 1 is inputted to the transmission-side image processing apparatus 2 and compressed by the compressor 5. At this time, the compressor 5 selects the most appropriate compression method from the compression methods stored in the storage 6 in accordance with the characteristic of the moving-picture information. For example, the storage 6 prepares two types of procedures. One is a compression procedure 1 to compress the information by thinning frames. The other is a compression procedure 2 to compress the information by determining the information of the frame which is contiguous to/different from the frame of a first picture as difference information. The operation of the moving-picture processing by the compressor 5 is explained by the flowchart of Fig. 3. At step S301, when the moving-picture information is received from the moving-picture information source 1, the movement of the moving picture is examined at step S302. When the image is inactive, since there is less problem in thinning the frames comprising the moving picture, the process proceeds to step S308 where the compressor 5 selects the compression procedure 1 from the storage 6. When the procedure is determined, a parameter indicative of the ratio for thinning the frames is determined at step S309. This compression method is well known and the parameter is determined by a well-known method. When the image is active, the process proceeds to step S303 where characteristic of the movement is determined. Furthermore, when the moving picture is such that an object is moving over the background which is inactive, only the information of the moving object is needed. Therefore, the compression procedure 2 is selected at step S304. In this case also, the parameter indicating the number of frames compressed is determined at step S305. When it is determined that the moving picture is not appropriate for both procedures, the information is not compressed. Accordingly, when the compression procedure is determined, the information is compressed at step S306 in accordance with the selected procedure. The storage 6 can be a memory storing the program which executes the determined procedure or electric circuit. In the former case, the compressor 5 reads out the program which executes the selected procedure from the storage 6 and the processor processes the image information as data. In the later case, the selected circuit is activated, the image data is inputted to the circuit, and the compression processing is executed. Selection of the compression method of steps S302 to S303 can be performed by a user by monitoring the moving picture. However, in this embodiment, the transmission-side image processing apparatus 2 automatically performs the selection as following. For selection of a compression procedure, at the start of the compression of the moving picture, a difference between the frames for a predetermined number of frames of the moving picture which is subject to the compression is respectively obtained for each pixel by the compression procedure 2. For example, on the obtained differences, the number of the pixels for which the sum of differences is not zero is examined. When the sum of the differences of each pixel concerning to the predetermined number of frames (or over the predetermined number of frames) is less than a first threshold, the difference between the frames is small. That is, the movement is inactive and the image is compressed by the compression procedure 1 that is thinning a frame. On the other hand, when the number of pixels whose the difference is not zero is less than a second threshold, the difference between the frames is limited to a partial area of the frame. That is, only partial area is regarded as active and the image is compressed by the compression procedure 2. Furthermore, in other cases, the image is regarded as considerably active and recorded without compression. Furthermore, the parameter indicative of thinning intervals in the compression procedure 1 can be determined in accordance with the difference value. Still further, the first and second thresholds can be set by the user. An example for selecting a compression procedure at the start of the compression is described above. Then, an example of dynamically changing the compression procedure in accordance with the change of the state of moving picture is described below. It is assumed that the compressor 5 performs compression by the compression procedures 1 and 2 in parallel. When the compression is performed by using a program, a processor executes a plurality of programs simultaneously. When the compression is performed by each dedicated circuit, the moving-picture information is inputted into the circuits and compressed in parallel. Accordingly, the result of compression corresponding to the selected compression procedure is selected and recorded. Selection of the compression procedure is performed as following. The difference between the frames obtained by the compression procedure 2 is determined. If the difference is smaller than a predetermined threshold for a predetermined number of frames continuously, the result of the compression procedure 1, that is thinning a frame, is selected. If the difference is larger than the predetermined threshold, the result of the compression procedure 2 is selected. If the difference is continuously larger than the threshold, compression is not performed. The difference and threshold can be compared whenever the difference is obtained, or once in a predetermined number of operations, or in a predetermined duration. At step S307, the compressed image information is outputted from the compressor 5 and inputted to the transmitter 8. Fig. 2 is a diagram illustrating a data format of the data of the compressed moving-picture information at recording or transferring. Concerning the data whose compression method and parameter are the same, a method field 21, parameter field 22, and data field 23 are grouped into one, and this arrangement is repeated until the image information is all formatted. The data format ends-with an end code 24. In this data, the information indicating the procedure to expand the data stored in the data field 23 is stored in the method field 21. For example, when frames are thinning out as a compression method, a processing which compensates the thinned-out frames is designated in the method field 21 as an expansion method. When only the difference information between frames is taken out from the image, the common portion with the previous frame is taken out and the processing to compensate by the difference information is designated. Information indicating that an expansion processing is not necessary on the image which is not compressed is stored in the method field 21. These designations can be performed by coding each compression method and designating the code. The parameter field 22 stores the information indicative of a parameter value required for the expansion processing. When a compression method is to thin out frames, the parameter value is a value which designates if a frame is thinned out every other frame or every two frames. The most appropriate parameter value which is suitable to the characteristic of the moving picture is selected in the same way as the selection of the compression method and stored in the parameter field 22. The data field 23 stores the compressed moving-picture data which is expanded by the expansion method indicated by the method field 21. The moving-picture information compressed by the compressor 5 can be directly transmitted by the transmitter 8, or once stored in a recording medium such as memory, disk, or tape by the recorder 7 and read out and transmitted from the recording medium. The compressed moving-picture information which is transmitted from the transmitter 8 is received by the receiver 9 of the reception-side image processing apparatus 4 via the information transfer apparatus 3. After the reception, the expansion processing can be immediately performed by the expander 10, or the information can be once stored in the recording medium by the recorder 7, and then the expansion processing can be performed. The reception-side image processing apparatus 4 receives the compressed image information, the expansion processing is performed on it, and a moving picture is reproduced. The procedure is described along with the flowchart of Fig. 4. At step S401, the expander 10 receives the compressed moving-picture information in the format of Fig. 2. At step S402, the method field 21 is read out of the information and the expansion method corresponding to the content of the method field 21 is selected from the storage 11. The expansion method stored in the storage 11 at least includes an expansion method corresponding to the compression method stored in the storage 6. Means for executing this expansion method can be such that the expander 10 selectively reads and executes the program stored in the memory. An expansion processing which is executed by appropriately connecting the expansion procedure prepared in a hardware such as an electric circuit can be considered. Note that the compression procedures 1 and 2 correspond to expansion procedures 1 and 2 respectively. The content of the method field is tested at step S403. If the information written in the method field is the procedure 1, the process proceeds to step S409 where the expansion procedure 1 is selected so as to execute the procedure 1. If the written information is the procedure 2, the process proceeds to step S405 where the expansion procedure 2 is selected. If it is determined that the received data is not compressed in either case, then the expansion processing is not performed. When the expansion method is determined, the parameter field 22 is read at step S410 or S406 and a parameter value is obtained in accordance with each expansion method when the processing by the selected expansion method is executed. At step S407, the data field 23 is read and the expansion processing is performed by using the expansion method selected by the previous step and the parameter value with respect to the data. As a result of the expansion processing, the moving-picture information is returned to an original form (an original moving-picture) before the compression and the information is transferred to the reproducer 12 at step S408. The reproducer 12 reproduces the moving-picture information transferred from the expander 10 and the reproduced picture is displayed on a CRT display or the like. Accordingly, the moving picture inputted from the moving-picture information source 1 is reproduced through the compression and expansion processings. The above processings are repeated until the end code 24 is read out. Furthermore, a single moving picture can be compressed by a single type of compression method or the compression processing can be performed by changing an arbitrary frame such as a scene whose characteristic of the moving picture has been changed. Information can be transferred from the transmission-side image processing apparatus 2 to the reception-side image processing apparatus 4 via a detachable medium (such as a flexible disk) recorded by the recorder 7 of the transmission-side image processing apparatus 2 and data can be read out of the media and reproduced in the reception side. As described above, a plurality of compression/expansion methods are prepared in the transmission-side and reception-side apparatuses beforehand, an information compression procedure and parameter which are suitable to the characteristic is selected to compress an moving picture, whenever the characteristic of the inputted moving picture has been changed. Furthermore, for the reproduction, information loss caused by compression is prevented and a moving picture which is faithful to the master picture can be reproduced by the expansion procedure in accordance with the compression procedure of the received data. The present invention can be applied to a system constituted by a plurality of devices, or to an apparatus comprising a single device.

Claims: An image processing apparatus comprising: input means (1) operable to input moving-picture information of a plurality of frames; first compression means (5) operable to compress the moving-picture information; second compression means (5) operable to compress the moving-picture information by a compression procedure which is different from a compression procedure performed by said first compression means; selection means (5;S303) operable to select said first or second compression means; and output means (8) operable to output the moving-picture information compressed by the compression means selected by said selection means, characterized by: determination means (5;S302,S303) operable to determine movement of the moving-picture by obtaining differences between frames, wherein said first compression means utilises said differences between frames as compressed information, and said selection means is operable to select (S304,S308) either the first or second compression means in accordance with the movement of the moving-picture determined by said determination means. Image processing apparatus as claimed in claim 1, wherein said second compression means comprises thinning means for thinning out frames of the moving-picture information. An image processing apparatus as claimed in claim 1, wherein said determination means comprises summation means operable to obtain a sum of the differences between corresponding pixel values of contiguous frames as a measure of the movement of the moving-picture and said selection means comprises first judging means operable to judge whether the sum of the differences is less than a first predetermined threshold. An image processing apparatus as claimed claim 3, wherein said selection means is operable to select said second compression means when said first judging means judges that the sum of the differences is less than the first predetermined threshold. An image processing apparatus as claimed in claim 1, wherein said determination means comprises counting means operable to count the number of pixels having no differences in pixel values from corresponding pixels in a contiguous frame, as an index of the movement of the moving-picture, and said selection means comprises second judging means operable to judge whether the number of pixels having no differences in pixel values from corresponding pixels in a contiguous frame is less than a second predetermined threshold. An image processing apparatus as claimed in claim 5, wherein said selection means is operable to select said first compression means when said second judging means judges that the number of pixels having no differences in pixel values from corresponding pixels in a contiguous frame is less than the second threshold. An image processing apparatus as claimed in any preceding claim further comprising first control means operable to control said first and second compression means so as to compress the same moving-picture information simultaneously. An image processing apparatus as claimed in any preceding claim further comprising second control means operable to control said determination means to execute determination of movement periodically during the input of moving-picture information from said input means and to control said selection means to execute the selection dynamically in accordance with the result of the determination by said determination means. An image processing method comprising: an input step (S301) of inputting moving-picture information including a plurality of frames; a first compression step (S308;S309;S306) of compressing the moving-picture information; a second compression step (S304;S305;S306) of compressing the moving-picture information by a compression procedure which is different from a compression procedure performed in said first compression step; a selection step (S302;S303) of selecting said first or second compression step; and an output step (S307) of outputting the moving-picture information compressed in the compression step selected in said selection step, characterized by: a determination step (S302;S303) of determining movement of the moving-picture by obtaining differences between frames, wherein said differences between frames are utilised as compressed information in said first compression step, and either the first or second compression step is selected in said selection step in accordance with the movement of the moving-picture determined in said determination step. An image processing method as claimed in claim 9, wherein, in said second compression step, the moving-picture information is compressed by thinning out frames of the moving-picture information. An image processing method as claimed in claim 9, wherein sum of the differences between corresponding pixel values in contiguous frames is obtained as the movement of the moving-picture in said determination step and it is judged whether or not the sum of the differences is less than a first predetermined threshold in said selection step. An image processing method as claimed in claim 11, wherein, in said selection step, said second compression step is selected when it is judged that the sum of the differences is less than the first predetermined threshold. An image processing method as claimed in claim 9, wherein the number of pixels having no differences in pixel value from corresponding pixels in an adjacent frame in a frame are counted, as an index of the movement of the moving-picture in said determination step, and it is judged whether the number of pixels having no differences in pixel value from corresponding pixels in an adjacent frame is less than a second predetermined threshold. An image processing method as claimed in claim 13, wherein, in said selection step, said first compression step is selected when it is judged that the number of pixels having no differences in pixel values from corresponding pixels in an adjacent frame is less than the second threshold. An image processing method as claimed in any of claims 9 to 14, wherein, in said first and second compression steps, the same moving-picture information is compressed simultaneously and the moving-picture information compressed in said first or second compression step is selectively output in accordance with selection in said selection step. An image processing method as claimed in any of claims 9 to 15, wherein the determination in said determination step is carried out periodically during the input of moving-picture information input in said input step and the selection in said selection step is carried out dynamically, in accordance with the result of the determination in said determination step.

Inventors: SUZUKI SHIGEO, SUZUKI, SHIGEO, Suzuki, Shigeo, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1993
Main classification: H04N7
IPC codes: H04N7, H04N5, G06T9