JPWO2014122708A1 - Screen encoding device, screen decoding device, screen encoding transmission system - Google Patents

Abstract

The video encoding device detects a frame sequence having a moving image region based on the history of the update region, and extracts an image of a region corresponding to the moving image region in the frame immediately before the first frame in the detected frame sequence as a reference image Then, using the extracted reference image, the image of the moving image area of the first frame in the detected frame sequence is subjected to inter-frame prediction encoding.

Description

  The present invention relates to a system for compressing and transmitting computer screen data via a network, and more particularly to a screen encoding device, screen decoding device, and screen encoding transmission system for improving the compression transmission efficiency of screen data including a moving image area. The present invention relates to a screen encoding method, a screen decoding method, and a program.

  There is a thin client system that enables a remote computer to be operated from a terminal connected to a network. In this case, screen data transmission and response with high visibility can be achieved even under conditions using a low-speed communication network by compressing screen data output by a computer into a small amount of encoded data using a compression encoding technology for screens. Remote control with excellent performance is possible.

  With the diversification of computer applications and the advancement of information display technology, the opportunity to transmit screen data with a composite configuration that includes moving image display in addition to graphic images centered on characters and line drawings has increased. In general, a compression technique suitable for the characteristics of an image to be transmitted differs. For example, if a compression method for graphic images is used for encoding a moving image that requires high-efficiency compression due to an enormous amount of information, not only the compression efficiency is bad, but also undesirable deterioration in terms of subjective quality occurs.

  Therefore, by analyzing the characteristics and update frequency of the image included in the screen data to be transmitted, the newly appearing moving image area is automatically discriminated, and the encoding method for the detected moving image region is changed to an image encoding method other than moving image. Has been proposed as a first related technique related to the present invention (see, for example, Patent Document 1). In this way, by adaptively switching between video encoding methods and non-video image encoding methods, computer screen data including video regions can be encoded and transmitted with high compression and high visibility. It is.

  By using standard video encoding methods such as MPEG-4 and H.264 for video area encoding, electronic parts and software for video encoding / decoding with high availability and high processing performance can be used. It is. This is advantageous in realizing a high-performance screen encoding device and screen decoding device at low cost.

  On the other hand, when converting from a JPEG stream encoded by the JPEG system to an H.264 stream, a JPEG decoded image signal is used as it is as a reference image for inter-coding. (For example, refer to Patent Document 2). More specifically, the second related technique includes a JPEG decoding unit, an H.264 encoding unit, and a JPEG / H.264 multiplexing unit. When the JPEG decoding unit receives an encoded stream (JPEG stream) of an image signal that has been intra-encoded in JPEG, it decodes it to generate a decoded image signal, and the H.264 encoding unit performs intra encoding. When the notification of selection is received, the JPEG stream is output. When selecting the H.264 intra coding, the H.264 encoding unit accumulates the decoded image signal generated by the JPEG decoding unit in the memory and notifies the JPEG decoding unit that the intra encoding is selected. When selecting H.264 inter-coding, the past decoded image signal stored in the memory is used as a reference image, and the decoded image signal generated by the JPEG decoding unit is Encode and output an H.264 stream. The JPEG / H.264 multiplexing unit multiplexes the JPEG stream output from the JPEG decoding unit and the H.264 stream output from the H.264 encoding unit, and outputs a multiplexed stream.

JP 2011-238014 A JP 2011-41178 A

  However, the first related technique related to the present invention has room for improvement in the compression efficiency at the time of switching the encoding method immediately after the moving image area is detected. MPEG-4, H.264, and other video coding methods reduce the amount of information based on predictive coding (inter-coding) that refers to previously coded images, but inter-coding can be used. Is limited to frames other than the first frame of a series of frame sequences constituting a moving image. Therefore, since the reference image does not exist at that point in time for the first image immediately after the coding method is switched for moving images, predictive coding (inter coding) cannot be performed. As a result, intra-frame coding (intra coding) is applied to the head image, and the compression efficiency is lower than that of inter coding.

  This problem is particularly significant in real-time screen coded transmission applications where there is a delay in the automatic determination of moving image areas. For example, when a moving image display window is opened in a screen to be transmitted and playback of a moving image is started, the moving image region discriminating unit in the screen encoding device continuously displays images in the region where the moving image display window is placed. It is detected from the time change of the input image, and the moving image display window is detected as a moving image area. At this time, in order to prevent a window other than the moving image display window from being erroneously detected as a moving image region, a delay of one frame or more occurs in the detection of the moving image region. As a result, after the moving image is displayed in the moving image window, an image of one frame or more is encoded by a compression method other than that for moving images, and an image in the moving image area immediately after being detected with a delay is also intra-encoded. Such an encoding process is poor in compression efficiency because the number of frames to be inter-coded is small as compared with the case where the encoding method is switched to that for moving images immediately after the moving image is displayed in the moving image window. As a result, the amount of transmission data increases, causing problems such as an increase in transmission delay time and a decrease in screen quality.

  In the second related technique related to the present invention, a JPEG decoded image signal is used as it is as a reference image when performing H.264 inter-coding. Therefore, it is suitable for switching the encoding method of the entire screen from JPEG to H.264. However, when a video area newly appears on a part of the screen from the state where the entire screen is a still image, only that video area is converted to an encoding method such as H.264 suitable for video. The second related technique cannot be applied.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a moving image region when screen data encoding is performed while adaptively switching between a moving image encoding method and another image encoding method. It is an object of the present invention to provide a screen encoding device that solves the problem that the compression efficiency immediately after the detection of the image is detected.

A screen encoding apparatus according to the first aspect of the present invention provides:
A screen input unit for inputting a frame of screen data;
A screen storage unit for storing the input frame;
An update area detection unit that detects an area in which the pixel value has changed as compared to the frame input immediately before among the input frames, as an update area;
A moving image region detecting unit that detects a frame sequence having a moving image region based on the history of the update region;
A moving image encoding unit that performs inter-frame predictive encoding of the image of the moving image region in the frame sequence having the moving image region;
An image encoding unit that encodes an image of the update region other than the moving image region in the input frame;
A reference image supply unit that extracts, as a reference image, an image of a region corresponding to the moving image region in the frame immediately preceding the first frame in the frame sequence having the moving image region detected by the moving image region detection unit;
The moving image encoding unit performs inter-frame prediction encoding on the image of the moving image area in the first frame of the frame sequence having the moving image area, using the reference image.

A screen decoding apparatus according to the second aspect of the present invention provides:
A moving picture decoding unit that decodes an image of the moving picture area in a frame sequence having the moving picture area based on inter-frame prediction;
An image decoding unit that decodes an image in an update area other than the moving image area in the frame;
A frame synthesis output unit that synthesizes the decoded image and outputs it as an output frame;
A screen storage unit for storing the output frame;
A reference image supply unit that extracts, as a reference image, an image of an area corresponding to the moving image area in the frame immediately preceding the first frame in the frame sequence having the moving image area;
The moving image decoding unit decodes the image of the moving image area of the first frame in the frame sequence having the moving image area by inter-frame prediction using the reference image.

  The screen encoding transmission system according to the third aspect of the present invention is a system in which the screen encoding device according to the first aspect and the screen decoding device according to the second aspect are connected by communication means.

The screen encoding method according to the fourth aspect of the present invention is:
Enter the frame of screen data,
Memorize the input frame above,
Among the input frames, the area where the pixel value has changed compared to the frame input immediately before is detected as an update area,
Based on the history of the update area, detect a frame sequence having a video area,
Inter-frame predictive encoding the image of the moving image area in the frame sequence having the moving image area,
Encode the image of the update area other than the video area in the input frame,
Extracting an image of a region corresponding to the moving image region in the frame immediately preceding the first frame in the frame sequence having the moving image region as a reference image;
In the inter-frame predictive coding, the image of the moving image area in the first frame of the frame sequence having the moving image area is subjected to inter-frame predictive coding using the reference image.

The screen decoding method according to the fifth aspect of the present invention is:
Decoding the image of the moving image region in the frame sequence having the moving image region based on inter-frame prediction;
Decode the image in the update area other than the video area in the frame,
The decoded image is combined and output as an output frame and stored,
Extracting an image of a region corresponding to the moving image region in the frame immediately preceding the first frame in the frame sequence having the moving image region as a reference image;
In decoding the image of the moving image area, the image of the moving image area of the first frame in the frame sequence having the moving image area is decoded by inter-frame prediction using the reference image.

A program according to the sixth aspect of the present invention is:
Computer
A screen input unit for inputting a frame of screen data;
A screen storage unit for storing the input frame;
An update area detection unit that detects an area in which the pixel value has changed as compared to the frame input immediately before among the input frames, as an update area;
A moving image region detecting unit that detects a frame sequence having a moving image region based on the history of the update region;
A moving image encoding unit that performs inter-frame predictive encoding of the image of the moving image region in the frame sequence having the moving image region;
An image encoding unit that encodes an image of the update region other than the moving image region in the input frame;
Function as a reference image supply unit that extracts, as a reference image, an image of a region corresponding to the moving image region in the frame immediately preceding the first frame in the frame sequence having the moving image region detected by the moving image region detection unit;
The moving image encoding unit performs inter-frame prediction encoding on the image of the moving image area in the first frame of the frame sequence having the moving image area, using the reference image.

A program according to the seventh aspect of the present invention is:
Computer
A moving picture decoding unit that decodes an image of the moving picture area in a frame sequence having the moving picture area based on inter-frame prediction;
An image decoding unit that decodes an image in an update area other than the moving image area in the frame;
A frame synthesis output unit that synthesizes the decoded image and outputs it as an output frame;
A screen storage unit for storing the output frame;
Function as a reference image supply unit that extracts, as a reference image, an image of an area corresponding to the moving image area in the frame immediately preceding the first frame in the frame sequence having the moving image area;
The moving image decoding unit decodes the image of the moving image area of the first frame in the frame sequence having the moving image area by inter-frame prediction using the reference image.

  Since the present invention has the above-described configuration, compression immediately after a moving image area is detected when compressing and transmitting a screen image while adaptively switching between the moving image encoding unit and another image encoding unit. Efficiency can be increased.

It is a block diagram of the screen coding transmission system concerning a 1st embodiment of the present invention. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 1st Embodiment of this invention. It is a block diagram of the moving image encoding part of the screen coding apparatus in the 1st Embodiment of this invention, and the moving image decoding part of a screen decoding apparatus. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 2nd Embodiment of this invention. It is a flowchart showing operation | movement of the reference image supply part of the screen coding apparatus in the 2nd Embodiment of this invention. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 3rd Embodiment of this invention. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 4th Embodiment of this invention. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 5th Embodiment of this invention. It is a block diagram of the screen coding apparatus and screen decoding apparatus in the 6th Embodiment of this invention. It is a block diagram of the moving image encoding part of the screen encoding apparatus in the 7th Embodiment of this invention. It is a block diagram of the moving image decoding part of the screen decoding apparatus in the 7th Embodiment of this invention. It is a block diagram of the 1st related art relevant to this invention.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
[First embodiment]

  FIG. 1 shows the configuration of a screen encoding transmission system according to the first embodiment of the present invention. This screen transmission system includes a screen encoding device 110 and a screen decoding device 120. The screen encoding device 110 acquires a frame of screen data to be transmitted supplied from the information processing device 130 as pixel map format image data, converts this into encoded data, and transmits the screen data via the digital communication network 140. The data is transmitted to the decryption device 120. The screen decoding device 120 decodes the screen encoded data received via the digital communication network 140 and outputs the screen data to the screen display device 150.

  FIG. 2 shows configurations of the screen encoding device 110 and the screen decoding device 120. The screen encoding device 110 includes a screen input unit 111, a screen storage unit 112, an update region segment detection unit 113, a moving image region detection unit 114, a moving image encoding unit 116, an image encoding unit 115, and a reference image supply unit 117. . The screen decoding device 120 includes a moving image decoding unit 121, an image decoding unit 122, a screen synthesis output unit 124, a screen storage unit 125, and a reference image supply unit 123.

  The operation of each part constituting screen encoding apparatus 110 will be described. The screen input unit 111 inputs screen (input screen) data output from the information processing apparatus 130 that is a transmission target in units of frames. The screen storage unit 112 stores a frame of input screen data. The update area classification detection unit 113 extracts the difference between the frame of the previous input screen stored in the screen storage unit 112 and the frame of the current input screen in units of pixels, and detects an area where the pixel value has changed as an update area. To do. The update area is extracted by approximating an image area (update area) having an appropriate size and shape for encoding. The moving image area detection unit 114 selects an area (moving image area) of an appropriate size to be compression-encoded by the moving image encoding means from the past update frequency of the update area, image characteristics, and past moving image area determination history information. To detect. That is, the moving image area detection unit 114 detects a frame sequence having a moving image area based on the history of the update area. At that time, the moving image area once detected is subjected to a determination process including a continuation condition determination that continues to remain at the same position over a plurality of consecutive frames until the update pattern changes. In accordance with the moving image region determination result, the moving image encoding unit 116 compresses and encodes the moving image region, and the image encoding unit 115 compresses and encodes other non-moving image update regions that are not detected as the moving image region. The obtained encoded data is transmitted to the screen decoding apparatus 120 according to an appropriate communication means and communication protocol. The reference image supply unit 117 extracts a reference image from the immediately preceding input screen stored in the screen storage unit 112 when the moving image encoding unit 116 starts encoding of the moving image region, and sends the reference image to the moving image encoding unit 116. Supply. Details of the operations of the reference image supply unit 117 and the moving image encoding unit 116 will be described later.

  The operation of each part constituting the screen decoding device 120 will be described. The video decoding unit 122 decodes the data encoded by the video encoding unit 116 of the screen encoding device 110, and the image decoding unit 121 is the data encoded by the image encoding unit 115 of the screen encoding device 110. Is decrypted. The screen synthesis output unit 124 synthesizes the images obtained as the decoding results and outputs the synthesis results to the external screen display device 150 as screen data. The screen storage unit 125 stores the output screen data, and supplies the previous output screen for the screen synthesis output unit 124 to synthesize the next output screen. The reference image supply unit 123 extracts a reference image from the immediately preceding output screen stored in the screen storage unit 125 and supplies the reference image to the video decoding unit 122 when the video decoding unit 122 starts decoding the video region. Details of the operations of the reference image supply unit 123 and the video decoding unit 122 will be described later.

  The compression coding of the non-moving image update area by the image coding unit 115 and the image decoding unit 121 is performed according to a general graphic image or natural image image coding technique. For example, compression coding using a technique that combines color reduction / palletizing processing with run-length coding and entropy coding, a predictive coding technique that uses correlation with neighboring pixels, and a coding technique based on discrete cosine transform or wavelet transform . A plurality of encoding means using different compression techniques may be provided inside, and the compression method may be switched according to the analysis result of the characteristics of the image to be encoded.

  The configuration of the moving image encoding unit 116 and the moving image decoding unit 122 is shown in FIG. These perform compression encoding and decoding of moving image data by using a general moving image encoding technique that combines inter-frame prediction encoding by motion compensation and entropy encoding. In addition, as necessary, the color space / sample ratio conversion of the moving image region image is performed before encoding and after decoding. For example, when MPEG-4 or H.264 standard method is used as the moving image encoding technique, the pixel format of the screen data is RGB, and the pixel formats of the moving image encoding unit 116 and the moving image decoding unit 122 are YUV420 or YUV422, Conversion is performed before encoding and after decoding.

  The moving image encoding unit 116 includes a reference image storage unit 1162 that stores a locally decoded image of a moving image region encoded in the past as a reference image, and the moving image decoding unit 122 decodes a decoded image of the moving image region decoded in the past. Is stored therein as a reference image. When a moving image area having the same position and size is continuously detected for two or more frames, the moving image encoding unit 116 uses the past encoded image stored in the reference image storage unit 1162 as a reference image, Similarly, the video decoding unit 122 performs the inter-frame prediction encoding decoding process while using the image stored in the reference image storage unit 1222.

  On the other hand, when encoding the head image after detecting the moving image area, the moving image encoding unit 116 uses the image supplied from the reference image supply unit 117 (in the screen encoding device 110) as a reference image before starting the encoding. It inputs into the memory | storage part 1162, and performs inter-frame prediction encoding using it as a reference image. The video decoding unit 122 inputs the image supplied from the reference image supply unit 123 in the screen decoding device 120 before starting decoding to the reference image storage unit 1222, and uses it as a reference image to decode inter-frame prediction encoding. Process. With the above operation, the moving image encoding unit 116 and the moving image decoding unit 122 of the screen encoding transmission system according to the present embodiment use inter-frame predictive encoding for all images including the image immediately after the moving image region detection. Compress and encode. However, this does not preclude intra-coding every certain number of frames.

  When the moving image area detection unit 114 newly detects a moving image area, the reference image supply unit 117 in the screen encoding device 110 extracts partial image data at the same position in the frame of the previous input screen stored in the screen storage unit 112. After reading out and performing an appropriate color space / sample ratio conversion as necessary, the result is supplied to the moving image encoding unit 116 as the first reference image. When the encoded data of the moving image area at the new position is input to the moving image decoding unit 122, the reference image supply unit 123 in the screen decoding device 120 outputs immediately before being stored in the screen storage unit 125 in the screen decoding device 120. The partial image data at the same position in the frame of the screen is read out, and an appropriate color space / sample ratio conversion is performed as necessary, and the result is supplied to the moving picture decoding unit 122 as the first reference image.

  FIG. 12 shows the configuration of a screen encoding device 1010 and a screen decoding device 1020 based on the first related technique related to the present invention. The screen encoding apparatus 1010 includes a screen input unit 1011, a screen storage unit 1012, a changed region segment detection unit 1013, a moving image region detection unit 1014, a moving image encoding unit 1016, and an image encoding unit 1015, and a reference image supply unit No function corresponding to 117 is provided. The screen decoding apparatus 1020 includes a moving image decoding unit 1021, an image decoding unit 1022, a screen synthesis output unit 1023, and a screen storage unit 1024, and does not have a function corresponding to the reference image supply unit 123. When the screen encoding device 1010 and the screen decoding device 1020 based on the first related technology shown in FIG. 12 are compared with the screen encoding device 110 and the screen decoding device 120 according to the present embodiment shown in FIG. The presence / absence of a reference image supply unit that supplies the encoding unit and the moving image decoding unit to the first reference image of the moving image region differs from whether or not the first image of the moving image region is encoded using inter-frame prediction. The feature of the screen coding and transmission system according to the present embodiment is that the screen information including the moving image region can be compression-encoded from the first image immediately after the moving image region is detected by using inter-frame predictive coding with high compression efficiency. Advantage.

  In the screen encoding transmission system of the present embodiment, the image data of the input screen stored in the screen storage unit 112 of the screen encoding device 110 and the image of the output screen stored in the screen storage unit 125 of the screen decoding device 120 are used. It does not match the data due to compression distortion at the time of encoding and irreversibility of color conversion / sample ratio conversion. Therefore, as a result, image quality degradation occurs in which the compression distortion generated in the previous screen output propagates to the decoded image in the moving image area generated by the moving image decoding unit 122. However, since this deterioration is comparable to the deterioration in image quality caused by normal screen compression transmission, it is not noticeable. It is also known that the amount of error propagation attenuates due to the image change in the moving image area and the filter effect of decimal pixel precision motion compensation. Furthermore, in a screen transmission system with a limited communication path speed, the gain of code amount reduction and compression distortion reduction by applying inter-frame predictive coding to the first moving image region image is large, and the propagation of the above-mentioned inter-frame error propagation. The image quality degradation due to is relatively negligible.

<Effect of this embodiment>

  As described above, the screen encoding device 110 of the screen encoding transmission system according to the first embodiment of the present invention is used by the video encoding unit 116 immediately after the video region detection unit 114 detects the video region. By including the means 117 for supplying the reference image, the inter-frame predictive coding can be used even when the leading image after the moving image area is detected is coded. As a result, the compression encoding efficiency of the output screen of the information processing apparatus 130 including the moving image area is improved, and the effects of reducing the amount of encoded data required for screen transmission, reducing the transmission delay, and improving the image quality are obtained.

[Second Embodiment]

  A screen coded transmission system according to the second embodiment of the present invention will be described. Since this screen coded transmission system shares many of the configurations and operations with the screen coded transmission system according to the first embodiment, only the differences from the screen coded transmission system according to the first embodiment will be described.

  The configuration of the screen encoding device 210 and the screen decoding device 220 according to the second embodiment of the present invention is shown in FIG. Compared to the screen coding transmission system according to the first embodiment, the screen coding apparatus 210 includes the coding history storage unit 218, and the reference image supplied from the reference image supply unit 217 to the moving image coding unit 216. The generation procedure is different. The operation of each part of the other screen encoding device 210, the timing at which the reference image supply unit 217 supplies the reference image to the moving image encoding unit 216, and the configuration and operation of the screen decoding device 220 are the same as those in the first embodiment. .

  The encoding history storage unit 218 in the screen encoding device 210 includes the position information of the update areas (the moving image area and the non-moving image update area) encoded by the image encoding unit 215 and the moving image encoding unit 216, the input time, A compression condition parameter indicating the type and condition of the encoding method is stored as encoding history information. The reference image supply unit 217 is obtained by decoding the encoded data on the screen decoding device 220 side based on the encoding history information and the image data of the previous input screen stored in the screen storage unit 212. A reference image to be supplied to the moving image encoding unit 216 is generated while performing processing for reproducing the compression distortion added to the output screen within a possible range.

  FIG. 5 shows an example of the procedure of compression distortion reproduction processing in the reference image supply unit 217. This process is executed immediately after the moving image area is detected. First, the position information of the detected moving image area is acquired (S1), a work buffer of the same size is secured (S2), and the pixel data of the previous screen at the same position as the moving image area extracted from the screen storage unit 212 is obtained. The reference image is copied to the work buffer as an initial value (S3). Next, an after-mentioned iterative process is performed while taking out the coding history of the past update area from the coding history storage unit 218 in the chronological order from the oldest (S4 to S11). An image on the work buffer obtained by performing this iterative process for all the update areas is a reference image generated by the reference image supply unit 217 according to the present embodiment. After performing appropriate pixel format conversion (color space, sample ratio) as necessary, the reference image is supplied to the moving image encoding unit 216 (S12).

  In the iterative process in the procedure of FIG. 5, the compression condition parameter of the past i-th update area is acquired (S5), and the following process is performed. (1) Skip if the past update area has no shared pixel with the currently detected moving image area (S6). (2) When the past i-th update area has a shared pixel and is non-moving picture update, a process of reproducing and generating a compression-added image after compression according to the compression condition parameter of the past i-th update area Execute (S6 to S8). However, the application target image of the process is not the input screen at the time of the past i-th update area but the input screen image immediately before the current time. This is stored in the screen storage unit 212. The distortion image obtained as a result is overwritten while aligning the position of the shared pixel in the work buffer (S8). (3) If the past i-th update area is a moving picture area having a shared pixel, the data of the previous input screen held in the screen storage unit 212 is overwritten on the shared pixel of the work buffer (S6, S7, S9). .

  In the above iterative process, as an example of the process for reproducing the compression distortion, the image compression encoding process of the same procedure is executed on the application target image, and the encoded data obtained as a result is converted into the image encoding unit of the screen decoding device 220. There is a method of decoding with a common procedure. In addition, any other method may be used as long as the same compression distortion reproduction result can be obtained. Alternatively, another method may be used as long as the compression distortion can be reproduced approximately even if accurate reproduction is not possible.

<Effect of this embodiment>

  As described above, the screen coding apparatus 210 of the screen coded transmission system according to the second embodiment of the present invention is the same as the screen coded transmission system according to the first embodiment of the present invention after detecting the moving image area. Inter-frame predictive coding can be used for coding the head image. Furthermore, since the reference image supply unit 217 of the screen encoding device 210 generates a reference image while reproducing the compression distortion generated on the decoding screen of the screen decoding device 220, the reference image of the screen encoding device 210 and the screen decoding device 220 It is possible to match the reference image, propagation of compression distortion due to inter-frame prediction is reduced compared to the screen coding transmission system according to the first embodiment of the present invention, and the image quality is improved. Therefore, the screen coding system of the present embodiment is more effective in reducing the amount of data required for coding transmission of a screen including a moving image area, shortening transmission delay, and improving image quality.

  Furthermore, the compression distortion reproduction process is executed in the reference image supply unit 217 only in the past update area that affects the moving image area, and is performed only at the first time point when the moving image area is newly detected. Therefore, the load of the compression distortion reproduction process for generating the reference image can be minimized. This can save performance and power consumption required for the screen encoding device 210 as compared with the case where compression distortion reproduction processing is performed on all encoded update regions.

[Third embodiment]
A screen coded transmission system according to the third embodiment of the present invention will be described. Since this screen coded transmission system has much of the same configuration and operation as the screen coded transmission system according to the first embodiment, only the differences from the screen transmission system according to the first embodiment will be described.

  The configuration of the screen coding apparatus 310 and the screen decoding apparatus 320 in the screen coding and transmission system according to the third embodiment of the present invention is shown in FIG. The screen encoding device 310 and the screen decoding device 320 according to the present embodiment are different from the screen encoding device 110 and the screen decoding device 120 according to the first embodiment shown in FIG. The reference screen generation procedure of the reference screen supply unit 323 is different, and the others are the same as those in the first embodiment shown in FIG.

  When a moving image area is newly detected, the reference image supply unit 317 in the screen encoding device 310 of the present embodiment reads partial image data at the same position in the frame of the previous input screen stored in the screen storage unit 312. Then, after the smoothing filter 318 is operated, the result is supplied to the moving image encoding unit 316 as the first reference image. In addition, the reference image supply unit 317 performs color space / sample ratio conversion before or after the filter processing as necessary.

  Similarly, the reference image supply unit 323 in the screen decoding device 320 stores the encoded data of the moving image region at the new position into the video decoding unit 322 and stores the encoded data in the screen storage unit 325 in the screen decoding device 320. The partial image data at the same position on the immediately preceding output screen is read out, the smoothing filter 326 is applied, and the result is supplied to the moving picture decoding unit 322 as the first reference image. In addition, the reference image supply unit 317 performs color space / sample ratio conversion before or after the filter processing as necessary.

  Examples of the smoothing filters 318 and 326 to be operated include an average value filter, a low-pass filter, and a median filter. By applying these to the reference images on the encoding side and the decoding side, it is possible to reduce the propagation of compression distortion that tends to appear as high-frequency noise components, linear and point noise. Note that smoothing filters 318 and 326 having characteristics common to the screen encoding device 310 and the screen decoding device 320 are preferably used so that the difference between the reference images on the encoding side and the decoding side does not increase.

<Effect of this embodiment>

  As in the first and second embodiments, the screen coding and transmission system according to the third embodiment of the present invention improves the compression coding efficiency of a screen including a moving image area. Further, according to the present embodiment, the inter-frame propagation of compression distortion is reduced by the smoothing filters 318 and 326, and the image quality of the moving image area is improved. The reason is that the high-frequency image signal component contained in the reference image on the transmission side and the reference image on the reception side is eliminated by smoothing, so that the difference between the reference image on the transmission side and the reference image on the reception side becomes small. This is because the linear noise components that are visible to the human eye are less noticeable by smoothing.

[Fourth Embodiment]
A screen coded transmission system according to the fourth embodiment of the present invention will be described. Since this screen coded transmission system has many configurations and operations in common with the screen coded transmission system according to the third embodiment, only the differences will be described.

  The configuration of the screen encoding device 410 and the screen decoding device 420 of this embodiment is shown in FIG. Compared to the apparatus configuration of the third embodiment shown in FIG. 6, the screen encoding apparatus 410 and the screen decoding apparatus 420 are different from each other in that they include compression distortion characteristic estimation units 419 and 427. When the image encoding unit 415 and the moving image encoding unit 416 encode the update region, the compression distortion characteristic estimation unit 419 of the screen encoding device 410 encodes the time, the position of the update region, the type of encoding method, and the compression condition. The parameter information is received, information necessary for estimating the characteristics of the compression distortion generated in the decoded image of the encoded screen is extracted and stored in the internal storage means. Then, when the reference image supply unit 417 generates a reference image from the previous input screen after detecting the moving image area, the compression distortion characteristic estimation unit 419 estimates the characteristic of the compression distortion generated in the decoded image of the previous input screen. The estimation result is output to the reference image supply unit 417. The reference image supply unit 417 determines the type and intensity of the smoothing filter 418 to be applied to the reference image from the estimation result, the intensity, or the image area and direction in which the smoothing filter 417 is applied, and the smoothing filter 418 is determined according to the determination result. To generate a reference image to be supplied to the moving image encoding unit 416.

  Similarly to the compression distortion characteristic estimation unit 419 of the screen encoding device 410, the compression distortion characteristic estimation unit 427 of the image decoding device 420 also updates an update area decoded from the encoded data input by the image decoding unit 421 and the moving image decoding unit 422. The information of the encoding time and position, the type of encoding method, and compression condition parameter information are received, information necessary for estimating the characteristics of compression distortion occurring in the decoded image is extracted and stored in the internal storage means. Then, when the reference image supply unit 423 generates a reference image from the previous output screen, the compression distortion characteristic estimation unit 427 estimates the characteristic of the compression distortion generated on the previous output screen, and supplies the estimation result as the reference image supply. Output to the unit 423. The reference image supply unit 423 determines the type and intensity of the smoothing filter 426 to be applied to the reference image from the estimation result, the intensity, or the image region and direction in which the smoothing filter 426 is to be applied, and the smoothing filter 426 according to the determination result. To generate a reference image to be supplied to the moving picture decoding unit 422.

  Examples of the compression distortion characteristic estimation method and the specific control method of the smoothing filter are shown in (1)-(4) below.

(1) For each pixel extracted as a reference image, the amount of compression distortion in the vicinity of the pixel is estimated from the type of compression method and the compression parameter of the image area in which the pixel was last encoded. The strength of the smoothing filter is controlled so that the smoothing filter is strengthened in the vicinity of a pixel having a large amount of compression distortion and the smoothing filter is weakened in the vicinity of a pixel having a small amount of compression distortion. The estimation of the amount of compression distortion and the control of the filter strength may be performed not on a pixel basis but on a pixel set or block unit of a predetermined size.
(2) When it is estimated that there is a high possibility of occurrence of linear noise on the outer periphery of the update area encoded in the past due to the difference in the compression method and compression conditions, the directionality of the area on the boundary line The linear noise is reduced by operating a smoothing filter having a certain level.
(3) A deblock filter (a non-uniform smoothing filter suitable for removing line noise in a lattice shape) is applied to a place where block noise is likely to occur due to block-by-block encoding processing.
(4) Change the characteristics of the smoothing filter to be applied by the compression method when the image area has been encoded in the past. For example, an average value filter with a large number of taps is applied to an image region that has been coded by subtractive color, and an image region that has been subjected to compression coding using discrete cosine transform has a low characteristic of removing local random noise. A pass-pass filter is activated.

These smoothing filters are operated so that the screen encoding device and the screen decoding device are equal in operation.
<Effect of this embodiment>

  Since the characteristics and amount of compression distortion are estimated from the past coding history and an appropriate smoothing filter is adaptively applied to reduce the estimated compression distortion, propagation of the compression distortion of the reference image can be suppressed. As a result, the compression efficiency and image quality of the moving image area are improved.

[Fifth Embodiment]

  A screen encoded transmission system according to the fifth embodiment of the present invention will be described. Since this screen coded transmission system shares many of the configurations and operations with the screen coded transmission system according to the fourth embodiment, only the differences will be described.

  The configuration of this screen encoded transmission system is shown in FIG. The configuration of the screen encoding device 510 is the same as that of the fourth embodiment except for the reference image supply unit 517. The reference image supply unit 517 determines the type, strength, or smoothing of the smoothing filter 518 that acts on the reference image based on the compression distortion characteristic generated in the decoded image of the previous screen estimated by the compression distortion characteristic estimation unit. Control the image area and direction to be filtered. Then, the reference image supply unit 517 describes the information about the type and strength of the smoothing filter 518 that has been actuated, or information on the image area and direction that has been subjected to the smoothing filter as coded image data as reference image generation parameters. To the screen decoding device 520.

The screen decoding device 520 smoothes the reference image in the same procedure as the screen coding device 510 in accordance with the type and strength of the smoothing filter described in the encoded data, or the information of the image area and direction applied with the smoothing filter. The activating filter 526 is activated. In the screen decoding apparatus 520, since the compression distortion characteristic estimation is not performed, the compression distortion characteristic estimation unit is omitted.
<Effect of this embodiment>

  According to the present embodiment, similarly to the screen coding transmission system according to the fourth embodiment, propagation of compression distortion can be suppressed by controlling an appropriate smoothing filter, and the compression efficiency and image quality of the moving image area are improved. Furthermore, since the configuration of the screen decoding device is simple, it can be easily realized at low cost.

[Sixth Embodiment]
A screen coded transmission system according to the sixth embodiment of the present invention will be described. Since this screen coded transmission system shares many of the configurations and operations with the screen coded transmission system according to the fifth embodiment, only the differences will be described.

  FIG. 9 shows the configuration of the screen encoded transmission system. The configuration of the screen encoding device 610 is the same as that of the fifth embodiment except for the reference image supply unit 617 and the compression distortion characteristic estimation unit 619. The compression distortion characteristic estimation unit 619 of the screen encoding apparatus 610 of this system estimates the tendency of the compression distortion from the past encoding history, and is finally encoded by a compression method that is not suitable for removing the compression distortion by the smoothing filter 618. The estimated image area is estimated, and the estimation result is output to the reference image supply unit 617. Then, the reference image supply unit 617 controls the smoothing filter 618 so as not to act on the image region where the compression distortion removal by the smoothing filter 618 is not suitable, and includes information on the image region where compression distortion removal is not suitable. The reference image generation parameter is included in the encoded data and output to the screen decoding device 620. Alternatively, the reference image supply unit 617 may perform past encoding history for an image region where compression distortion removal by the smoothing filter 618 is not suitable, as in the screen encoding device 210 according to the second embodiment of the present invention. From the (updated image position, compression parameter) and the image of the previous input screen, a process for reproducing the compression distortion generated in the decoded image is performed. The reference image supply unit 623 of the screen decoding device 620 removes the compression distortion by the smoothing filter 626 if the reference image generation parameter in the encoded data includes information on an image region that is not suitable for the removal of the compression distortion. Control is performed so that the smoothing filter 626 does not act on an unsuitable image region. The operation other than the above is the same as that of the fifth embodiment.

  As a compression method that is not suitable for removing compression distortion by a smoothing filter, for example, there is an image compression method by color reduction or palette formation.

<Effect of this embodiment>

  According to the fifth embodiment, an image region in which compression distortion removal by the smoothing filter is not suitable is identified, and the smoothing filter is not applied, or a method of reproducing the compression distortion in the decoded image on the encoding device side is used. Compared with the screen transmission system, the propagation of compression distortion in the moving image area is suppressed, and the image quality is improved.

[Seventh Embodiment]
A screen encoded transmission system according to the seventh embodiment of the present invention will be described. Since this screen coded transmission system has many configurations and operations in common with the screen coded transmission system according to the first embodiment, only the differences will be described.

  The screen coded transmission system of the present embodiment replaces the moving picture coding unit 116 included in the screen coding device 110 in the screen coded transmission system according to the first embodiment shown in FIG. The second embodiment is different from the second embodiment in that the conversion unit 716 is used and the moving image decoding unit 122 illustrated in FIG. 11 is used instead of the moving image decoding unit 122 included in the screen decoding device 120. The configuration and operation of other parts are the same as those in the second embodiment.

  Referring to FIG. 10, the moving image encoding unit 716 includes an (internal) moving image encoding unit 7161 and a head image encoded data truncation unit 7162. The (internal) moving image encoding unit 7161 includes a predictive encoding unit 7163, a reference image storage unit 7164, and an entropy encoding unit 7165. The moving image encoding unit 716 starts encoding the moving image region when the moving image region detecting unit 114 detects the moving image region. Inter-frame prediction encoding is performed on the first image in the moving image area using the image supplied from the reference image supply unit 117, and the reference image held in the internal reference image storage unit 7164 is used for the second and subsequent frames. To encode. This function is the same as that of the moving image encoding unit 116 of the first embodiment. However, the moving image encoding unit 716 according to the present embodiment does not directly store the image supplied from the reference image supply unit 117 in the internal reference image storage unit 7164 but performs intra-frame encoding and local decoding using the predictive encoding unit 7163. An image is generated and stored in the reference image storage unit 7164. At this time, the encoded data after entropy encoding output from the entropy encoding unit 7165 is discarded by the leading image encoded data truncation unit 7162 without being output to the outside of the screen encoding device 110.

  Next, referring to FIG. 11, the moving image decoding unit 722 includes a reference image encoding unit 7221, an (internal) moving image decoding unit 7222, and a head image truncation unit 7223. The reference image encoding unit 7221 includes an (intraframe) predictive encoding unit 7224 and an entropy encoding unit 7225. The (internal) video decoding unit 7222 includes an entropy decoding unit 7226, a prediction decoding unit 7227, and a reference image storage unit 7228. When the encoded data of the moving image area at the new position is input, the moving image decoding unit 722 uses the image supplied from the reference image supply unit 123 in the screen decoding device 120 to perform image decoding based on inter-frame prediction encoding. The second and subsequent frames are decoded using past decoded images stored in the internal reference image storage unit 7228. This function is the same as that of the moving image decoding unit 122 of the first embodiment. However, the moving picture decoding unit 722 of the present embodiment does not directly store the image supplied from the reference image supply unit 123 in the internal reference image storage unit 7228, but uses the prediction encoding unit 7224 of the reference image encoding unit 7221. Encoded data that has been encoded (intra-frame prediction) and further entropy-encoded by the entropy encoding unit 7225 is stored in the reference image storage unit 7228 by causing the entropy decoding unit 7226 and the prediction decoding unit 7227 of the moving image decoding unit 7222 to decode the encoded data. To do. At this time, the head image data output from the predictive decoding unit 7227 is discarded by the head image truncation unit 7223 without being supplied to the screen synthesis output unit 124.

  Here, the internal video encoding unit 7161 included in FIG. 10 encodes the input image sequence by a general video encoding procedure, and the internal video decoding unit 7222 included in FIG. Decode the data using a general video decoding procedure. Like the moving picture encoding unit 116 and the moving picture decoding unit 122 of the first embodiment shown in FIG. 2, it is not necessary to have a function of directly inputting a reference image from the outside. With this feature, when the screen encoding device 110 or the screen decoding device 120 is configured using a standard moving image encoding method such as MPEG-4 or H.264 as a moving image compression means, a function of inputting a reference image from the outside is provided. General video coding / decoding electronic parts and software that are not available can be used.

<Effect of this embodiment>
The screen coding transmission system according to the seventh embodiment of the present invention uses inter-frame predictive coding when coding the first image after detecting the moving image area, similarly to the screen coding transmission system according to the first embodiment. It is possible to improve the compression encoding efficiency of the screen including the moving image area. As a result, there are effects of reducing the amount of encoded data required for screen transmission, reducing transmission delay, and improving image quality. Furthermore, since the present screen encoding transmission system, encoding apparatus, and decoding apparatus can use general moving picture encoding / decoding electronic parts and software that do not have a function of inputting a reference image from the outside, a high-performance apparatus There is an advantage that can be easily realized at low cost.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above-described embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  In addition, this invention enjoys the benefit of the priority claim based on the patent application of Japanese Patent Application No. 2013-020403 for which it applied for a patent in Japan on February 5, 2013, and was described in the said patent application. The contents are all included in this specification.

DESCRIPTION OF SYMBOLS 110 ... Screen encoding apparatus 111 ... Screen input part 112 ... Screen memory | storage part 113 ... Update area division | segmentation detection part 114 ... Moving image area | region detection part 115 ... Image encoding part 116 ... Moving picture encoding part 117 ... Reference image supply part 120 ... Moving picture Decoding device 121 ... Image decoding unit 122 ... Video decoding unit 123 ... Reference image supply unit 124 ... Screen composition output unit 125 ... Screen storage

Claims (27)

A screen input unit for inputting a frame of screen data;
A screen storage unit for storing the input frame;
An update area detection unit that detects an area in which the pixel value has changed as compared to the frame input immediately before, among the input frames, as an update area;
Based on the history of the update region, a moving image region detection unit that detects a frame sequence having a moving image region,
A moving image encoding unit that performs inter-frame predictive encoding of the image of the moving image region in the frame sequence having the moving image region;
An image encoding unit that encodes an image of the update region other than the moving image region in the input frame;
A reference image supply unit that extracts, as a reference image, an image of a region corresponding to the moving image region in a frame immediately preceding the first frame in the frame sequence having the moving image region detected by the moving image region detection unit;
The video encoding unit is a screen encoding device that performs inter-frame predictive encoding of an image of the video area in a first frame of a frame sequence having the video area using the reference image. An encoding history storage unit that stores the time and position of the update region encoded in the past by the moving image encoding unit and the image encoding unit, and a compression condition parameter as an encoding history;
The reference image supply unit, in the frame sequence having the moving image area, from the encoding history and the image of the area corresponding to the moving image area in the frame immediately before the first frame in the frame sequence having the moving image area. The screen encoding apparatus according to claim 1, wherein the reference image is generated by reproducing a compression distortion generated in a decoded image in a region corresponding to the moving image region in a frame immediately preceding the first frame. The reference image supply unit includes a smoothing filter, and causes the smoothing filter to act on an image in a region corresponding to the moving image region in a frame immediately preceding the first frame in the frame sequence including the moving image region. The screen encoding device according to claim 1, wherein the screen encoding device generates a reference image. A compression distortion characteristic estimation unit that estimates a compression distortion characteristic generated in a decoded image in an area corresponding to the moving image area in the frame immediately preceding the first frame in the frame sequence having the moving image area;
4. The screen encoding according to claim 3, wherein the reference image supply unit controls a type or intensity of the smoothing filter or an image region or a smoothing direction on which the smoothing filter is applied according to the estimated compression distortion characteristic. apparatus. The reference image supply unit includes the filter parameter describing the type or strength of the smoothing filter applied to the reference image or the image region or the smoothing direction to apply the smoothing filter, and outputs the encoded data. Item 5. The screen encoding device according to Item 4. The moving image encoding unit encodes an image of an area corresponding to the moving image area in a first frame in a frame sequence having the moving image area after intra-frame encoding the reference image supplied by the reference image supply unit. The screen encoding apparatus according to claim 1, wherein a code generated by intra-frame encoding of the reference image is not included in encoded data output by the apparatus. The compression distortion characteristic estimation unit estimates the amount of compression distortion generated in the decoded image,
The screen encoding apparatus according to claim 4, wherein the reference image supply unit controls the strength of the smoothing filter in accordance with the estimated amount of compression distortion. The compression distortion characteristic estimation unit estimates an image region and a direction in which block noise or linear noise occurs in the decoded image,
The screen encoding device according to claim 4, wherein the reference image supply unit controls an image region on which the smoothing filter is applied and a smoothing direction according to the estimation result. The compression distortion characteristic estimation unit estimates an image region suitable for compression distortion removal by the smoothing filter,
The screen encoding device according to claim 4, wherein the reference image supply unit causes the smoothing filter to act on an image of the estimated image region. A compression distortion characteristic estimation unit that estimates a compression distortion characteristic generated in a decoded image by encoding an image of the frame of the input video and estimates an image area that is suitable for removal of compression distortion by a smoothing filter and an image area that is not suitable; Prepared,
The reference image supply unit includes the smoothing filter, and based on the result of the estimation, causes the smoothing filter to act on an image in an image region suitable for removing compression distortion by the smoothing filter. 3. The screen encoding according to claim 2, wherein the reference image is generated by performing a compression distortion reproduction process based on the encoding history for an image in an image region where compression distortion removal by the smoothing filter is not suitable. apparatus. The screen encoding apparatus according to claim 4, wherein the estimation of the compression distortion characteristic and the control by the smoothing filter are performed in a pixel unit or a pixel set unit of a predetermined size. A video decoding unit that decodes an image of the video region in a frame sequence having a video region based on inter-frame prediction;
An image decoding unit that decodes an image in an update area other than the moving image area in the frame;
A frame synthesis output unit that synthesizes the decoded image and outputs it as an output frame;
A screen storage unit for storing the output frame;
A reference image supply unit that extracts, as a reference image, an image of an area corresponding to the moving image area in the frame immediately preceding the first frame in the frame sequence having the moving image area;
The video decoding unit is a screen decoding device that decodes an image in the video area of the first frame in a frame sequence having the video area by inter-frame prediction using the reference image. The reference image supply unit includes a smoothing filter, and causes the smoothing filter to act on an image in a region corresponding to the moving image region in a frame immediately preceding the first frame in the frame sequence including the moving image region. The screen decoding apparatus according to claim 12, which generates a reference image. A compression distortion characteristic estimation unit that estimates characteristics of compression distortion generated in a decoded image in an area corresponding to the moving image area in the frame immediately preceding the first frame in the frame sequence having the moving image area;
The screen according to claim 13, wherein the reference image supply unit controls a type or intensity of the smoothing filter or an image region or a smoothing direction on which the smoothing filter is applied according to the estimated compression distortion characteristic. Decoding device. The screen decoding device according to claim 13, wherein the reference image supply unit controls the type or strength of the smoothing filter or an image region or a smoothing direction on which the smoothing filter is applied according to a filter parameter input from the outside. A reference image encoding unit that performs intra-frame encoding of the reference image generated by the reference image supply unit;
The moving image decoding unit uses the image obtained by decoding the encoded data generated by the reference image encoding unit as the reference image, and the image of the moving image region in the first frame in the frame sequence having the moving image region. The screen decoding device according to claim 12 for decoding. The compression distortion characteristic estimation unit estimates the amount of compression distortion generated in the decoded image,
The screen decoding device according to claim 14, wherein the reference image supply unit controls the strength of the smoothing filter in accordance with the amount of the compression distortion. The compression distortion characteristic estimation unit estimates an image region and a direction in which block noise or linear noise occurs in the decoded image,
The screen decoding device according to claim 14, wherein the reference image supply unit controls an image region on which the smoothing filter operates and a smoothing direction according to the estimation result. The compression distortion characteristic estimation unit estimates an image region suitable for compression distortion removal by the smoothing filter,
The screen decoding device according to claim 14, wherein the reference image supply unit causes the smoothing filter to act on the estimated image region. The screen decoding device according to claim 14, wherein the compression distortion characteristic estimation and the smoothing filter control are performed in units of pixels or a set of pixels having a predetermined size.   A screen encoding transmission system in which the screen encoding device according to claim 1 and the screen decoding device according to claim 12 are connected by a communication means. A screen encoding transmission system in which the screen encoding device according to claim 4 and the screen decoding device according to claim 14 are connected by communication means, wherein the screen encoding device and the screen decoding device have equal characteristics. A screen encoding transmission system using the smoothing filter.   A screen encoding transmission system in which the screen encoding device according to claim 5 and the screen decoding device according to claim 15 are connected by a communication means. Enter the frame of screen data,
Storing the input frame;
Among the input frames, an area in which the pixel value has changed compared to the frame input immediately before is detected as an update area,
Based on the history of the update area, detect a frame sequence having a moving image area,
Inter-frame predictive encoding the image of the moving image area in the frame sequence having the moving image area,
Encode the image of the update area other than the moving image area in the input frame,
Extracting an image of a region corresponding to the moving image region in the frame immediately before the first frame in the frame sequence having the moving image region as a reference image;
In the inter-frame predictive coding, a screen coding method for performing inter-frame predictive coding of an image in the moving image area in a first frame of a frame sequence having the moving image area using the reference image. Decoding the image of the moving image area in the frame sequence having the moving image area based on inter-frame prediction;
Decode the image of the update area other than the video area in the frame,
Combining and decoding the decoded image and outputting it as an output frame;
Extracting an image of a region corresponding to the moving image region in the frame immediately before the first frame in the frame sequence having the moving image region as a reference image;
In the decoding of the image of the moving image area, a screen decoding method for decoding the image of the moving image area of the first frame in a frame sequence having the moving image area by inter-frame prediction using the reference image. Computer
A screen input unit for inputting a frame of screen data;
A screen storage unit for storing the input frame;
An update area detection unit that detects an area in which the pixel value has changed as compared to the frame input immediately before, among the input frames, as an update area;
Based on the history of the update region, a moving image region detection unit that detects a frame sequence having a moving image region,
A moving image encoding unit that performs inter-frame predictive encoding of the image of the moving image region in the frame sequence having the moving image region;
An image encoding unit that encodes an image of the update region other than the moving image region in the input frame;
Function as a reference image supply unit that extracts, as a reference image, an image of a region corresponding to the moving image region in the frame immediately preceding the first frame in the frame sequence having the moving image region detected by the moving image region detection unit;
The moving image encoding unit is a program that performs inter-frame predictive encoding of an image of the moving image area in the first frame of a frame sequence having the moving image area using the reference image. Computer
A video decoding unit that decodes an image of the video region in a frame sequence having a video region based on inter-frame prediction;
An image decoding unit that decodes an image in an update area other than the moving image area in the frame;
A frame synthesis output unit that synthesizes the decoded image and outputs it as an output frame;
A screen storage unit for storing the output frame;
Function as a reference image supply unit that extracts, as a reference image, an image of a region corresponding to the moving image region in a frame immediately preceding the first frame in the frame sequence having the moving image region;
The moving image decoding unit is a program for decoding an image in the moving image area of the first frame in a frame sequence having the moving image area by inter-frame prediction using the reference image.

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