JP4109879B2 - Image distribution system, communication apparatus, distribution apparatus, control method thereof, and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image distribution system, a communication apparatus, a distribution apparatus, and a control method and storage medium in which an image distribution apparatus and one or more client terminals are connected by a data transmission medium, and more particularly to control based on an image change detection function. .
[0002]
[Prior art]
Image distribution systems or monitoring systems that distribute images continuously via data transmission media such as the Internet and Intranet are already in widespread use in society, and include various functions such as live video transmission, indoor / outdoor monitoring, and observation of animals and plants. Used in the field. Furthermore, some of these systems have a function of detecting temporal changes in images (image change detection function). In response to detecting the change, it sent an image or notified that the change was detected.
FIG. 10 shows a transmission procedure of encoded data and an image change detection result in an image distribution device with an image change detection function or a monitoring device according to a conventional general technique.
[0003]
As shown in the figure, first, an image data transmission request is sent from the client terminal, and the latest image data (encoded data) held by the image distribution apparatus is transmitted in response thereto. The client terminal transmits the next image data transmission request after receiving the image data (encoded data). Therefore, since the transmission frame rate of the image data (encoded data) depends on the transmission speed of the data transmission medium, it is usually smaller than the frame rate of the encoded data output from the JPEG encoding unit. That is, a part of the image data (encoded data) is discarded without being transmitted. On the other hand, since the image change detection notification shown in FIG. 10 is unilaterally transmitted from the image distribution apparatus to the client terminal for each changed frame, if there is an image change in all frames, the image change detection is performed. Is detected at a rate larger than the transmission frame rate of image data (encoded data).
[0004]
[Problems to be solved by the invention]
However, in the above-described conventional technology, only a simple image change detection result such as binary information informing the presence or absence of a change for each frame is transmitted from the image distribution apparatus to the client terminal.
[0005]
Further, as described above, since image data (encoded data) and an image change detection result cannot be transmitted in synchronization, detailed image change detection information such as which region of which image frame has changed at which timing, etc. Could not be known at the client terminal.
[0006]
Therefore, when the user tries to set up the image change detection device because the detection result is not displayed accurately while the received image is synchronized with the detection result, the detection is performed by trial and error several times. I had to check the situation.
[0007]
For example, consider a case in which an image change detection unit of an image distribution apparatus tries to determine parameters for setting under what conditions a change is detected. If the frame rate of the received image is low and all change information output at a higher rate cannot be recognized, the detection status cannot be completely grasped, and parameters must be determined by trial and error several times.
[0008]
Further, change information could not be recognized at a frame rate higher than the frame rate of the image.
[0009]
The present invention has been made in view of the above problems, and provides an image change detection system that can always provide detailed image change information to a user in synchronization with image data regardless of the transmission timing of the image data. It is an object.
[0010]
In particular, it is an object of the present invention to make it possible to recognize a detection result more accurately even if the frame rate of a received image is not so high due to a limitation of a communication line.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, an image change detection system according to the present invention is provided in an image distribution device,Input means for inputting image data for N frames, first holding means for sequentially holding the image data for N frames for one frame, and image data for the one frame held in the first holding means Encoding means for generating encoded data, and second holding means for acquiring and holding image data of one frame in N frames sequentially held for one frame in the first holding means, and Of the N frames input from the first holding means, the image data of (N-1) frames excluding the image data held in the second holding means are held in the second holding means. Image change information generating means for comparing image data of frames before each of the image data to generate image change information, encoded data generated by the encoding means, and ( -1) Data distribution means for distributing image change information for a frame to the communication device, wherein the communication device receives data distributed by the data distribution means, and decodes the encoded data Decoding means for generating decoded data, and display means for displaying the received image change information for (N-1) frames while switching in time series so as to overlap the display of the decoded data.It is characterized by providing.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
【Example】
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0013]
FIG. 1 is a block diagram showing a schematic configuration of an image distribution system or a monitoring system having an image change detection function according to the present invention. In this configuration, the user can set the image change detection parameter of the image distribution apparatus from the client terminal.
[0014]
This image change detection parameter is a condition for determining under which conditions the change is recognized.
[0015]
In this figure, there are a camera 100 and an image distribution device 200 on the image transmission side, and a client terminal 300 on the image reception side. The image distribution apparatus 200 and the client terminal 300 are connected via a data transmission medium such as the Internet or an intranet. Although a plurality of client terminals can be connected, only one client terminal is shown in the figure for the sake of simplicity. Further, one or both of the image distribution apparatus 200 and the client terminal 300 do not have to be dedicated devices, and can be realized by a form in which predetermined software is installed in a computing device such as a PC (personal computer).
[0016]
The analog video signal output from the camera 100 is input to the image distribution apparatus 200, converted into a digital signal (image data) by the A / D conversion unit 210, and then stored in the frame memory 220. The JPEG encoding unit 240 reads the image data stored in the frame memory 220, performs JPEG encoding, and then passes the encoded data to the data synthesis unit 260. The image data stored in the frame memory 220 is transferred to the frame memory 230 at regular intervals (frame memory update cycle). The image change detection unit 250 compares the current image data read from the frame memory 220 with the past image data read from the frame memory 230 to detect the image change, and the detailed image change information as shown in FIG. Is passed to the data composition unit 260. In addition, this image change detection is discriminate | determined for every block of the predetermined unit which divides | segments an image.
[0017]
The image change information is composed of a signal of 0 or 1 depending on the presence or absence of change detection for each block of a predetermined size that divides the image. In the embodiment, 1 is given to the block whose change is detected.
[0018]
The data synthesis unit 260 stores the latest encoded data for one frame passed from the JPEG encoding unit 240 and the image change information for one or more frames passed from the image change detection unit 250. The encoded data for the minute is discarded without being stored. When the data composition unit 260 receives the composite data transmission request from the communication unit 270, the data composition unit 260 composes the stored encoded data for one frame and image change information for one or more predetermined frames to create composite data. , The data is transferred to the communication unit 270 and all the stored encoded data and image change information are deleted. Here, there are the following two methods for creating the composite data, and either method may be adopted.
(I) Using an application marker of JPEG data, image change information is inserted into the header portion of the encoded data.
(II) A unique data format is defined in advance and synthesized according to this definition.
[0019]
The communication unit 270 transmits the composite data to the client terminal 300 according to a predetermined procedure as shown in FIG. The communication unit 270 receives the encoding parameter and the image change detection parameter from the client terminal 300 according to a predetermined procedure, sets the encoding parameter in the JPEG encoding unit 240, and sets the image change detection parameter in the image change detection unit 250. Set. The JPEG encoding unit 240 operates according to the set encoding parameter, and the image change detection unit 250 operates according to the set image change detection parameter.
[0020]
In the client terminal 300, the communication unit 310 receives the composite data according to a predetermined procedure. The synthesized data is passed to the data separation unit 320 and separated into encoded data for one frame and image change information for one or a plurality of frames. The encoded data for one frame is transferred to the JPEG decoding unit 330, decoded into image data, and displayed on the display unit 350. On the other hand, image change information for one or a plurality of frames is processed by a central processing unit (not shown) and displayed as a graphic on the display unit 350 according to the procedure illustrated in FIGS. The parameter setting unit 340 displays a GUI (graphical user interface) for inputting the encoding parameter and the image change detection parameter on the display unit 350, and receives the encoding parameter and the image change detection parameter input from the input unit 360 by the user. . These parameters are transferred to the communication unit 310 and transmitted to the image distribution apparatus 200 according to a predetermined procedure.
[0021]
In FIG. 1, a thin solid line A indicates a flow of image data or encoded data, a thick solid line B indicates a flow of synthesized data, a dotted line C indicates a flow of image change information, and a broken line E indicates an encoding parameter and The flow of image change detection parameters is shown, and the alternate long and short dash line D shows the flow of GUI data.
[0022]
FIG. 2 shows a synthetic data transmission procedure in the image distribution apparatus with image change detection function or the monitoring apparatus according to the present invention.
[0023]
As shown in the figure, since a composite data transmission request is first sent from the client terminal 300, the image distribution apparatus 200 transmits the latest composite data in response thereto. The client terminal 300 transmits the next composite data transmission request after receiving the composite data.
[0024]
FIG. 3 is a diagram for explaining image change information for one frame.
[0025]
In the same figure, the entire group of left squares shows a frame, and each square shows a block of a predetermined size obtained by dividing the frame. This block corresponds to a block for JPEG encoding. Thereby, the trouble of making a block for the detection result can be saved. Each block has a block number. In this example, 10 blocks are included in the X-axis direction and 8 blocks are included in the Y-axis direction. The image change detection unit 250 calculates the presence / absence of an image change for each block, gives bit 1 to a block having an image change, gives bit 0 to a block having no image change, and blocks all bits. Image change information is created by arranging in numerical order. The image change information created in this way can be combined with the encoded data without changing the fixed-length data, but is stored after being compressed using entropy encoding such as run-length encoding in the data combining unit 260, It may be combined with encoded data as variable length data. Then, when the image data is large, the change information becomes large, or even if the capacity allocated to the header portion of the image is small, it is easy to record sufficiently. This is particularly effective when the number of frames of image change information to be synthesized at a time is large. In the case where the image change information is entropy-encoded in the data synthesis unit 260, the image change information obtained as variable length data in the data separation unit 320 must be restored to a fixed-length bit string by entropy decoding.
[0026]
FIG. 4 is a display example of image data and image change information displayed on the display unit 350.
[0027]
In the drawing, a rectangular frame line 1001 indicating a plurality of change detection blocks (blocks having image changes) is drawn on the image 1000 as image change information.
[0028]
FIG. 5 is a flowchart showing a display procedure of image change information for a plurality of frames. Here, the number of frames of the image change information included in the composite data is set to fn, and the frame counter of the image change information indicating which frame the image change information is set to fc. However, the effective range of fc is from 0 to fn-1.
[0029]
In the figure, fc is initialized to 0 in step S01. In step S02, one frame of image data is drawn on the display unit 350. As a result, all previously drawn image data and image change information are erased. In step S03, image change information for the fc-th frame is drawn on the display unit 350. Details of step S03 will be described with reference to FIG. In step S04, 1 is added to fc, and in step S05, it is determined whether or not fc has reached fn. If fc is greater than or equal to fn, the image change information for all frames has already been drawn, and the process ends. Conversely, if fc is less than fn, the process proceeds to step S06, where a timer is set and the process is interrupted. At this time, the time (seconds) set in the timer is slightly shorter than the value obtained by dividing the average data amount (bits) of encoded data for one frame by the average transmission rate (bits per second) of the data transmission medium. Good. However, since the average amount of encoded data for one frame and the average transmission speed of the data transmission medium cannot be obtained unless they are measured for a certain period of time, a predetermined time is required until these values are obtained. You only have to set it. If a time-out notification is received from the timer in step S07, the process returns to step S02. With the above processing, image change information for fn frames is displayed while switching in time series with respect to image data for one frame.
[0030]
For example, while displaying a single frame image, only the change information is updated to display multiple frames as a moving image.
[0031]
FIG. 6 is a flowchart showing a display procedure of image change information for one frame. Here, the number of blocks in the X axis direction included in one frame is nx, the number of blocks in the Y axis direction is ny, the block counter in the X axis direction indicating the number of blocks in the X axis direction is bx, Y axis The block counter in the Y-axis direction indicating the number of the block in the direction is by, the image change information at the block position (bx, by) is d (bx, by), the block width is bw, and the block height is bh, a predetermined drawing color is cr. However, bx is an effective range from 0 to nx-1, and by is an effective range from 0 to ny-1.
[0032]
In the figure, in step S11, both bx and by are initialized with 0. In step S12, it is determined whether d (bx, by) is greater than 0 (0 or 1). If it is greater than 0 (1), the block has changed, and the process proceeds to step S13. Since (0) is a block that has not changed, the process proceeds to step S14. In step S13, a rectangular frame indicating a change detection block is drawn at the block position (bx, by) using a predetermined drawing color cr, and the process proceeds to step S14. At this time, the X coordinate of the upper left corner of the quadrangle is obtained by calculating bx multiplied by bw, and the Y coordinate calculated by by multiplied by bh. The width of the quadrangle is bw and the height is bh. Note that the rectangular drawing color cr is determined in advance by the caller of the processing procedure of FIG.
[0033]
In step S14, 1 is added to bx, and in step S15, it is determined whether bx has reached nx. If bx is greater than or equal to nx, all the blocks (one block line) corresponding to the current by have been processed, and the process proceeds to step S16. If bx is less than nx, the process returns to step S12. In step S16, 0 is substituted for bx, 1 is added to by, and then the process proceeds to step S17. In step S17, it is determined whether or not by has reached ny. If by is greater than or equal to ny, all blocks have been processed, and the process ends. Conversely, if by is less than ny, the process returns to step S12. Through the above processing, image change information for one frame is displayed.
[0034]
FIG. 7 is a flowchart showing a display procedure of image change information for a plurality of frames. Here, the number of frames of the image change information included in the composite data is set to fn, and the frame counter of the image change information indicating the number of frames of the image change information is set to fc. However, the effective range of fc is from 0 to fn-1.
[0035]
In the figure, fc is initialized to 0 in step S21. In step S22, one frame of image data is drawn on the display unit 350. In step S23, the image change information for the fc-th frame is drawn on the display unit 350 using the fc-th drawing color determined in advance. The detailed processing procedure of step S03 is the same as that shown in FIG. In step S24, 1 is added to fc, and in step S25, it is determined whether or not fc has reached fn. If fc is greater than or equal to fn, the image change information for all frames has already been drawn, and the process ends. Conversely, if fc is less than fn, the process returns to step S23. With the above processing, image change information for fn frames is displayed in different display colors with respect to image data for one frame. At this time, since the image change information for the old frame is drawn in order, the image change information for the newer frame is overdrawn for a block that has changed in a plurality of frames.
[0036]
(Second Embodiment)
The present embodiment is different from the first embodiment only in how image change information is displayed, and the apparatus configuration is almost the same, and detailed description thereof is omitted.
[0037]
FIG. 8 is a flowchart showing pre-processing of a display procedure of image change information for a plurality of frames in the second embodiment. Here, the number of frames of the image change information included in the composite data is fn, the frame counter of the image change information indicating which frame the image change information is fc, and the number of blocks in the X-axis direction included in one frame. nx, the number of blocks in the Y axis direction is ny, the block counter in the X axis direction indicating the number of blocks in the X axis direction is bx, the block number in the Y axis direction indicating the number of blocks in the Y axis direction Assume that the block counter is by and the image change information at the block position (bx, by) for the fc-th frame is d (fc, bx, by). However, fc is an effective range from 0 to fn-1, bx is an effective range from 0 to nx-1, and by is an effective range from 0 to ny-1.
[0038]
In the figure, in step S31, fc, bx and by are all initialized to 0. In step S32, d (fc, bx, by) is initialized with zero. In step S33, it is determined whether or not d (fc, bx, by) is greater than 0 (0 or 1). If it is greater than 0 (in the case of 1), the block has changed, and the process proceeds to step S34. In the case of (0), since the block has not changed, the process proceeds to step S35. In step S34, 1 is substituted into d (fc, bx, by), and the process proceeds to step S37. In step S35, 1 is added to fc, and in step S36, it is determined whether or not fc has reached fn. If fc is equal to or greater than fn, the image change information for all frames at the block position (bx, by) has been examined, and the process proceeds to step S37. Conversely, if fc is less than fn, the process returns to step S33. In step S37, 0 is substituted for fc, 1 is added to bx, and the process proceeds to step S38. In step S38, it is determined whether bx has reached nx. If bx is greater than or equal to nx, all the blocks (one block line) corresponding to the current by have been preprocessed, so the process proceeds to step S39. Conversely, if bx is less than nx, the process returns to step S32. In step S39, 0 is substituted for bx, 1 is added to by, and then the process proceeds to step S40. In step S40, it is determined whether or not by has reached ny. If by is greater than or equal to ny, all blocks have been preprocessed, so the preprocessing is terminated. Conversely, if by is less than ny, the process returns to step S32. Through the preprocessing described above, image change information for one frame is added, and image change information for fn + 1 frames is obtained. Thereafter, when 1 is added to fn and the processing shown in FIG. 7 is executed, image change information for a plurality of frames is displayed in different display colors for one frame of image data, and a plurality of frames are displayed. When there is an image change at the same position, another display color is used at that position (displayed as the display color of the image change information added last).
[0039]
(Third embodiment)
In this embodiment, compared with the first and second embodiments, only the display method of image change information is different, and the apparatus configuration and the like are almost the same, and detailed description thereof is omitted.
[0040]
FIG. 9 is a flowchart showing preprocessing of a display procedure of image change information for a plurality of frames according to the third embodiment. Here, the number of frames of the image change information included in the composite data is fn, the frame counter of the image change information indicating which frame the image change information is fc, and the number of blocks in the X-axis direction included in one frame. nx, the number of blocks in the Y axis direction is ny, the block counter in the X axis direction indicating the number of blocks in the X axis direction is bx, the block number in the Y axis direction indicating the number of blocks in the Y axis direction The block counter is by, the image change information at the block position (bx, by) for the fc-th frame is d (fc, bx, by), and the multi-value image change at the block position (bx, by) obtained from a plurality of frames The information is dm (bx, by). However, fc is an effective range from 0 to fn-1, bx is an effective range from 0 to nx-1, and by is an effective range from 0 to ny-1.
[0041]
In the figure, in step S51, fc, bx and by are all initialized to 0. In step S52, dm (bx, by) is initialized with zero. In step S53, d (fc, bx, by) is added to dm (bx, by), and 1 is added to fc. In step S54, it is determined whether or not fc has reached fn. If fc is equal to or greater than fn, the image change information for all frames at the block position (bx, by) is added, and the process proceeds to step S55. Conversely, if fc is less than fn, the process returns to step S53. In step S55, 0 is substituted into fc, 1 is added to bx, and then the process proceeds to step S56. In step S56, it is determined whether bx has reached nx. If bx is greater than or equal to nx, all the blocks (one block line) corresponding to the current by have been preprocessed, so the process proceeds to step S57. Conversely, if bx is less than nx, the process returns to step S52. In step S57, 0 is substituted for bx, 1 is added to by, and then the process proceeds to step S58. In step S58, it is determined whether or not by has reached ny. If by is greater than or equal to ny, all blocks have been preprocessed, so the preprocessing is terminated. Conversely, if by is less than ny, the process returns to step S52. Through the above preprocessing, multivalued image change information obtained by adding a plurality of pieces of image change information for each block position is obtained. When a different display color is given for each value or value range of the multi-value image change information and the same processing as the processing shown in FIG. 6 is executed, the image change for a plurality of frames is performed on the image data for one frame. The display is performed using different display colors depending on the information addition result.
[0042]
As described above, the image change information for a plurality of frames can be displayed for the image data for one frame while synchronizing the received image and the detection result.
[0043]
Further, when image data for one frame and image change information for a plurality of frames are obtained by the data separation means, the image change information for a plurality of frames is displayed in time series while the image data for one frame is displayed. Since the display is performed while switching (for example, only the image change information is updated and displayed like a moving image), the change information corresponding to the time change can be recognized.
[0044]
Further, when image data for one frame and image change information for a plurality of frames are obtained by the data separation means, the image change information for a plurality of frames is simultaneously superimposed and displayed on the image data for one frame. Therefore, even if the frame rate of the image is low, only the change detection information can be recognized at a high frame rate. This is effective when importance is attached to the change detection information.
[0045]
In addition, when displaying the image change information for multiple frames at the same time, the display color is changed for each image change information for each frame, and the image changes only at the position where the image changes in order from the oldest frame. Since the information is drawn, the change information corresponding to the time change can be recognized.
[0046]
Also, when displaying the image change information for multiple frames at the same time, the display color is changed for each image change information for each frame, and if there is an image change at the same position in multiple frames, Since another display color is used for the position, it becomes possible to recognize the change information corresponding to the time change, and it is easy to recognize the position where the change is detected.
[0047]
In addition, when image change information for multiple frames is superimposed and displayed at the same time, image change information for each frame is added at the same position, and the display color is changed according to the addition result. It is possible to recognize change information according to the position, and it is easy to recognize at which position the change is detected.
[0048]
【The invention's effect】
  As described above, according to the present invention,While displaying the representative image data, the image change information for a plurality of frames is displayed while being switched in time series so as to overlap the display of the representative image data, so that the change information corresponding to the time change can be recognized. .
[0049]
In particular, the present invention is very effective when the frame rate of an image cannot be increased due to communication line limitations.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image distribution system or a monitoring system having an image change detection function in an embodiment.
FIG. 2 is a synthetic data transmission procedure in an image distribution device with an image change detection function or a monitoring device in the embodiment.
FIG. 3 is a diagram for explaining image change information for one frame in the embodiment.
4 is a display example of image data and image change information displayed on a display unit 350. FIG.
FIG. 5 is a flowchart illustrating a display procedure of image change information for a plurality of frames in the embodiment.
FIG. 6 is a flowchart illustrating a display procedure of image change information for one frame in the embodiment.
FIG. 7 is a flowchart illustrating a display procedure of image change information for a plurality of frames in the embodiment.
FIG. 8 is a flowchart showing preprocessing of a display procedure of image change information for a plurality of frames in the second embodiment.
FIG. 9 is a flowchart showing pre-processing of a display procedure of image change information for a plurality of frames in the third embodiment.
FIG. 10 is a transmission procedure of encoded data and an image change detection result in an image distribution apparatus with an image change detection function or a monitoring apparatus according to a conventional general technique.
[Explanation of symbols]
100 cameras
200 Image Distribution Device
210 A / D converter
220 (first) frame memory
230 (second) frame memory
240 JPEG encoding unit
250 Image change detection unit
260 Data composition unit
270 communication unit
300 client terminals
310 Communication unit
320 Data separator
330 JPEG decoding unit
340 Parameter setting section
350 display
360 input section
1000 images
1001 Display example of image change information (rectangular frame indicating a plurality of change detection blocks)

Claims (17)

An image distribution system in which an image distribution device and a communication device are connected by a data transmission medium,
In the image distribution device,
Input means for inputting image data for N frames;
First holding means for sequentially holding the image data for N frames for one frame ;
Encoding means for encoding the image data of the one frame held in the first holding means and generating encoded data;
Second holding means acquires the image data of one frame in the N frame that will be sequentially one frame held in said first holding means, for holding,
Of the N frames input from the first holding means, each of the image data of (N-1) frames excluding the image data held in the second holding means is held in the second holding means. Image change information generating means for comparing image data of frames before each of the image data and generating image change information;
Data distribution means for distributing the encoded data generated by the encoding means and the image change information for the (N-1) frames to the communication device ,
In the communication device,
Data receiving means for receiving data distributed by the data distribution means;
Decoding means for decoding the encoded data and generating decoded data;
An image distribution system comprising: display means for displaying the received image change information for (N-1) frames while switching in time series so as to overlap the display of the decoded data.   2. The image distribution system according to claim 1, wherein when the image change information for the (N−1) frames is displayed in the communication device, a display color is changed for each image change information of each frame. The image distribution device further includes data combining means for combining the encoded data and image change information for (N-1) frames, and distributes the combined data obtained by the data combining means to the communication device. ,
3. The communication apparatus according to claim 1, further comprising a separating unit that separates the received composite data into image change information for (N-1) frames with respect to the encoded data. The image delivery system as described in any one of Claims.   In the communication apparatus, when displaying the image change information for the (N-1) frames, the display color of the position is different depending on whether or not there is an image change at the same position in a plurality of frames. The image distribution system according to any one of claims 1 to 3, wherein   In the communication device, when displaying the image change information for the (N-1) frames, the image change information for each frame is added for each same position, and the display color is changed according to the addition result. The image delivery system according to any one of claims 1 to 4.   In the image distribution apparatus, the image data held in the first holding unit is encoded by being divided into blocks of a predetermined size, and the image change information is change information for each block. The image delivery system according to any one of claims 1 to 5.   The image distribution system according to claim 6, wherein in the image distribution apparatus, in displaying the image change information for the (N−1) frames, a color for each block is set and displayed. Encoded data obtained by encoding one frame of image data, receiving means for receiving image change information of the one frame of image data and N frames displayed after the one frame of image data, and the code decodes the data, and decoding means for generating decoded data, said N frames image change information received by the receiving means, so as to overlap the display of the image data decoded by said decoding hands stage And a display means for displaying while switching in time series.   9. The communication apparatus according to claim 8, wherein when the image change information for the N frames is displayed in the communication apparatus, a display color is changed for each image change information of each frame. In the communication device, when displaying the image change information for the N frames, the display color of the position is different depending on whether or not there is an image change at the same position in a plurality of frames. The communication device according to any one of claims 8 to 9.   2. The display apparatus according to claim 1, wherein when the image change information for the N frames is displayed in the communication apparatus, the image change information for each frame is added at the same position, and the display color is changed according to the addition result. The communication device according to any one of 8 to 9.   12. The communication device according to claim 8, wherein the image data of one frame is divided into blocks of a predetermined size and encoded, and the image change information is change information for each block. The communication apparatus as described in any one. The communication apparatus according to claim 12, wherein, in the display of the image change information for the N frames, a color for each block is set and displayed in the communication apparatus. A control method of an image distribution system in which an image distribution device and a communication device are connected by a data transmission medium,
In the image distribution device,
An input process for inputting image data for N frames;
A first holding step of sequentially holding the image data for N frames for one frame in a first holding unit;
An encoding step of encoding the image data of the one frame held in the first holding means and generating encoded data;
Acquiring image data of one frame in the N frame that will be sequentially one frame held in said first holding means, a second holding step of holding the second holding means,
Of the N frames input from the first holding means, each of the image data of (N-1) frames excluding the image data held in the second holding means is held in the second holding means. An image change information generation step of comparing image data of a frame before each of the image data and generating image change information;
A data distribution step of distributing the encoded data generated by the encoding means and the image change information for the (N-1) frames to the communication device;
In the communication device,
A data receiving step for receiving data distributed by the data distribution step;
A decoding step of decoding the encoded data and generating decoded data;
A display step of displaying the received image change information for (N-1) frames while switching in time series so as to overlap the display of the decoded data. A receiving step of receiving encoded data obtained by encoding one frame of image data, and image change information of the one frame of image data and N frames displayed after the one frame of image data;
A decoding step of decoding the encoded data and generating decoded data;
A display step of displaying the image change information for the N frames received in the reception step while switching in time series so as to overlap the display of the image data decoded in the decoding step. A method for controlling a communication device.   16. The method according to claim 15, wherein when the image change information for the N frames is displayed in the communication device, a display color is changed for each image change information of each frame.   A storage medium storing a program for causing a computer to execute the steps constituting the control method according to any one of claims 14 to 16.

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