JP2006229661A - Image display method, image encoder, image decoder, and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To protect the copyright of an image content, and to promote the sales of the image content by allowing a user to view an image with high quality. <P>SOLUTION: In an image encoder 100, encoding parts 10, 12, 14, 16 and 18 encode animation data. A quality information adding part 18 adds a prescribed setting value to the encoded animation data in order to perform display while changing the quality with the passage of time. The setting value can be the one for reducing at least one of the resolution, image quality, and frame rate of the animation step by step. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image display method, an image encoding device, an image decoding device, and an image display device that can be used to reproduce a moving image acquired by content distribution or the like.

  In recent years, with the spread of infrastructure such as DVD media, digital broadcasting, and on-demand communication via a network, the use of digital contents has been expanded. Since digital content does not deteriorate in quality due to copying, copyright management is important. The demand for legitimate protection of copyrighted works such as digital contents is expected to increase further in the future.

  In order to protect the copyright of an image, Patent Document 1 discloses a technique for setting and reproducing information reproduction permission level (hereinafter referred to as a protection level) step by step according to the content user. That is, a high-quality moving image is distributed to a person with a high protection level, and a low-quality moving image is distributed to a low-level person.

In addition, with the spread of infrastructure as described above, the number of image content providers has increased and competition has intensified. These merchants recognize the importance of copyright protection, but are struggling to expand sales of image content. Also, image content providers whose main revenue source is advertising revenue are aiming to increase the number of users of the content they provide.
JP-A-9-163306

  In Patent Document 1, a person with a low protection level views a low-quality moving image, and cannot view an original high-quality image. With low-quality moving images, it is difficult to impress the content of people with low protection levels. Therefore, the advertising effect of the content is not expected so much, and it is not sufficient to promote the purchase of the content and the subscription to the content distribution service.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image display method, an image encoding device, an image decoding device, and an image display that can achieve both copyright protection and use promotion of image content. To provide an apparatus.

  In order to solve the above-described problem, an image display method according to an aspect of the present invention displays a moving image while changing quality over time according to a predetermined set value. “Quality” may be degraded. According to this aspect, since the image providing side can show the high-quality and low-quality images to the user, it is possible to impress the high-quality images while protecting the copyright of the image content.

  The set value may be one that gradually reduces at least one of resolution, image quality, and frame rate of the moving image. Further, at least one of the luminance and the color difference of the moving image may be reduced stepwise. Further, the moving image display area may be narrowed in stages. Narrowing the “display area” may reduce the size of the image itself to be displayed, and “stepwise” may include changing the quality state of the moving image by 3 or more. The visible area may be made smaller without changing the size of the image itself. According to this aspect, the quality of the image shown to the user can be adjusted, and when the quality is lowered, the copyright can be protected.

  A predetermined advertisement may be displayed outside the moving image display area. According to this aspect, the image providing side can obtain advertisement opportunities and income sources.

  The set value may be fixed according to the user's predetermined action. The “predetermined action” may be data transmission for showing a legal intention to pay a fee to the image providing side. The “set value” may be fixed to a value during normal playback. According to this aspect, cancellation of copyright management can be associated with acquisition of consideration, and sales of image content can be promoted.

  Another aspect of the present invention is an image encoding device. This apparatus includes an encoding unit that encodes moving image data, and an adding unit that adds a predetermined set value to the encoded moving image data so that the quality is displayed as time passes. According to this aspect, since the image providing side can show the high-quality and low-quality images to the user, it is possible to impress the high-quality images while protecting the copyright of the image content.

  Yet another embodiment of the present invention is also an image encoding device. This apparatus includes an encoding unit that encodes moving image data and a quality setting unit that gives a setting value for changing the quality to the encoding unit so that the quality is displayed as the quality changes over time. According to this aspect, since the image providing side can show the high-quality and low-quality images to the user, it is possible to impress the high-quality images while protecting the copyright of the image content. Further, when a section for degrading quality is provided, the capacity of encoded image data to be distributed can be reduced.

  Yet another embodiment of the present invention is an image decoding device. The apparatus includes a decoding unit that decodes the encoded moving image data, and a quality setting unit that gives the decoding unit a setting value set so that the quality changes with time. The decoding unit performs decoding while changing the quality according to the set value. According to this aspect, even if the image content is copyright-managed, a high-quality image can be seen in a part of the section, and the user can easily evaluate the image content.

  Yet another embodiment of the present invention is an image display device. This apparatus displays a moving image while changing the quality over time according to a predetermined set value. According to this aspect, even if the image content is copyright-managed, a high-quality image can be seen in a part of the section, and the user can easily evaluate the image content.

  It should be noted that any combination of the above-described constituent elements and a conversion of the expression of the present invention between a method, an apparatus, a system, a computer program, a recording medium, and the like are also effective as an aspect of the present invention.

  According to the present invention, it is possible to achieve both copyright protection and use promotion of image content.

  The outline of the present invention will be described. A content creator or a copyright holder changes parameters such as an image quality and a frame rate in an arbitrary period of a moving image so that the quality is deteriorated when the content is reproduced. The viewer can view the video with the original quality by making some contract such as paying the content provider. The parameters to be changed include resolution, image quality, frame rate, and color. Further, the display area may be narrowed. In that case, a message or an advertisement for prompting charging can be inserted outside the area.

  In order to realize this, first, an example will be described in which encoded image data generated without adjusting the quality on the code side is distributed to the decoding side, and a moving image is displayed while adjusting the quality on the decoding side.

(Embodiment 1)
FIG. 1 is a configuration diagram of an image encoding device 100 according to the first embodiment. The configuration of the image encoding apparatus 100 can be realized in hardware by a CPU, memory, or other LSI of an arbitrary computer, and is realized by a program having an encoding function loaded in a memory in software. However, here, functional blocks that are realized by their cooperation are depicted. Accordingly, those skilled in the art will understand that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof.

  The orthogonal transform unit 10 performs wavelet transform, discrete cosine transform, and the like on the input original image. For example, when performing wavelet transform, the orthogonal transform unit 10 divides the input original image into subbands, calculates wavelet transform coefficients of each subband image, and generates layered wavelet transform coefficients. Specifically, the orthogonal transform unit 10 applies a low-pass filter and a high-pass filter in the x and y directions of the original image, and divides into four frequency subbands to perform wavelet transform. These subbands are LL subbands having low frequency components in both x and y directions, and HL subbands having low frequency components in either one of x and y directions and high frequency components in the other direction. And an HH subband having a high frequency component in both the x and y directions. The number of vertical and horizontal pixels in each subband is ½ that of the image before processing, and a subband image having a resolution, that is, a quarter of the image size, can be obtained by one filtering.

  Of the subbands thus obtained, the orthogonal transform unit 10 performs filtering again on the LL subband, further divides it into four subbands LL, HL, LH, and HH, and performs wavelet transform. . The orthogonal transform unit 10 performs this filtering a predetermined number of times, hierarchizes the original image into subband images, and outputs the wavelet transform coefficients of each subband. The quantization unit 12 quantizes a predetermined coefficient such as a wavelet transform coefficient output from the orthogonal transform unit 10 with a predetermined quantization width.

  The entropy encoding unit 14 entropy encodes the quantization value quantized by the quantization unit 12. For example, encoding is performed while scanning sequentially from the upper bit brain. Thus, the encoding target of the entropy encoding unit 14 is an original image and functions as an image encoding unit.

  The quality information adding unit 18 decodes the encoded stream encoded by the image encoding apparatus 100 and displays information for controlling the quality when displayed (hereinafter referred to as quality information) as the encoded stream. Append. This quality information defines at least one of various parameters such as resolution, image quality, frame rate, display range, color difference, brightness and the like at the time of decoding in association with the passage of time at the time of decoding. For example, in the case of resolution, decoding is performed at full resolution for 5 minutes after decoding is started, decoding is performed by removing high frequency components for the next 5 minutes, and decoding is performed by removing medium frequency components and high frequency components for the next 5 minutes. As described above, it is possible to set to decode and display while reducing the resolution with time. Finally, only the DC component may be decoded and displayed. This decoding method is suitable for decoding an encoded stream having an SVC (Scalable Video Codec) function such as the wavelet transform described above.

  When controlling the image quality, the number of bits to be decoded is reduced as the time elapses, among the coefficients such as the wavelet transform coefficient and the discrete cosine transform coefficient composed of a plurality of bits. When the image quality is degraded, the lower bits are gradually not decoded.

  The display area can be controlled by setting a region of interest (ROI) in the image. Information for specifying the region of interest (hereinafter referred to as ROI information) includes information such as position, shape, size, and image quality. This ROI information can also be set to reduce its size as time passes. Details of the contents of the quality information including other parameter data will be described later.

  The quality information adding unit 18 can be described in the header of the encoded stream. There are various levels in the header, but they can be described at any level. For example, quality information can be described in a stream header, a sequence header, a GOP (Group of Picture) header, a frame header, a picture header, and the like.

  The quality information adding unit 18 can generate information that invalidates the quality management performed on the decryption side in accordance with the user's fee payment from the decryption side. This information is added to the encoded data of the image by the encoded stream generation unit 16 to be described later, or independently sent to an image decoding device to be described later on the user side, and quality control of the moving image by the image decoding device. Is disabled.

  The encoded stream generation unit 16 generates an encoded stream based on the encoded data of the image input from the entropy encoding unit 14 and the encoded data of quality information from the quality information adding unit 18. Then, the generated encoded stream is output to a network or a recording medium.

  As described above, according to the present embodiment, it is possible to realize an image encoding device that achieves both copyright protection and promotion of use of moving images. The image provider can protect the copyright by degrading the quality of the moving image over time. In addition, it is possible to make a user impress with high-quality images in a certain section and make an impression, and to promote the sale of content and the subscription to a content distribution service. For example, by distributing the start of the program for free and with high image quality, it attracts viewers, and gradually lowers the quality from the middle of the program, thereby increasing the viewer's willingness to purchase content to the end of the program be able to.

  Further, since the image providing side does not need to prepare the moving image data for viewing and reproduction separately, the content creation is simple and the storage area can be reduced. Furthermore, when the display area is narrowed, the surplus area can be used as an advertising space for the company or other companies, and it is also possible to obtain advertising fee income.

(Embodiment 2)
FIG. 2 is a configuration diagram of the image decoding apparatus 200 according to the second embodiment. The image decoding apparatus 200 decodes an encoded stream to which quality information is added, such as an encoded stream encoded by the image encoding apparatus 100 described above.

  The stream acquisition unit 20 acquires an encoded stream from the outside and primarily stores it in the stream memory 22. An encoded stream transmitted by stream distribution may be acquired, or an encoded stream recorded on a recording medium such as a DVD-ROM may be acquired.

  When the stream level to be decoded is specified from the quality setting unit 36 described later, the stream acquisition unit 20 discards a part of the acquired encoded stream and passes it to the variable length decoding unit 24 according to the stream level. . For example, high frequency components can be discarded to reduce resolution.

  The stream memory 22 temporarily holds the encoded stream input from the stream acquisition unit 20. The variable length decoding unit 24 decodes the encoded stream delivered from the stream acquisition unit 20 for each bit plane, decodes quantized pixel data and various parameters, and outputs the decoded pixel data to the inverse quantization unit 26. In the case of a stream in which interframe predictive coding is used, a motion vector is also decoded. In the case of a stream that is entropy-encoded, entropy decoding is performed.

  The inverse quantization unit 26 inversely quantizes the input pixel data and outputs it to the orthogonal inverse transform unit 28. When a quantization scale is designated from a quantization scale setting unit 38 to be described later, inverse quantization is performed based on the quantization scale. The orthogonal inverse transform unit 28 restores the pixel value transformed by discrete cosine transform or wavelet transform. In the case of a stream in which interframe predictive coding is used, the difference value of the corresponding pixel between frames is restored. The orthogonal inverse transform unit 28 outputs the pixel value and the like to the pixel value calculation unit 30. The pixel value calculation unit 30 writes the restored pixel value in the image memory 42.

  The image memory 42 temporarily holds the pixel value restored by the pixel value calculation unit 30. The image memory 42 may use the same memory as the stream memory 22 as long as the address space is different.

  The reference data designating unit 40 is necessary in the case of a stream using interframe predictive coding such as MPEG. The reference data designating unit 40 designates the pixel value of the reference image held in the image memory 42 indicated by the motion vector passed from the variable length decoding unit 24 as a reference value. In that case, the pixel value calculation unit 30 adds the reference value designated by the reference data designating unit 40 and the difference value acquired from the corresponding orthogonal inverse transformation unit 28 to obtain the pixel value on the image memory 42. Restore. Further, when the luminance setting or the color difference correction is designated by the quality setting unit 36, the pixel value calculation unit 30 corrects the luminance value or the color difference.

  The frame reconstruction unit 32 reconstructs moving image data by combining the pixel values restored by the pixel value calculation unit 30 in units of frames. When the frame rate is designated from the quality setting unit 36, reconstruction is performed at the frame rate. When the display size is designated from the quality setting unit 36, the pixels are thinned out or increased. The display unit 50 displays the moving image data constructed by the frame reconstruction unit 32. Note that the display unit 50 may be externally attached. In this case, the image decoding apparatus 200 decodes the encoded stream and outputs decoded data to a display apparatus (not shown) connected by a cable or wirelessly. It will be.

  The quality management unit 34 acquires quality information added to the encoded stream input from the outside. Further, when information for invalidating the above-described quality control is separately transmitted, it is acquired. Based on the acquired quality information, the quality management unit 34 manages the elapsed time of moving image playback, the charging status, and the like, and designates the quality designated by the quality information to the quality setting unit 36.

  The quality setting unit 36 sets parameters for adjusting the quality in each unit based on the quality designated by the quality management unit 34. First, when changing the resolution, the stream level is specified in the stream acquisition unit 20. FIG. 3 is a diagram illustrating an example in which the resolution is lowered with time. Time elapses from left to right in the figure. The screen 60 on the left shows a screen decoded using all frequency components in the encoded stream. The center screen 62 shows a screen obtained by discarding high-frequency components in the encoded stream and decoding them. The screen 64 on the right shows a screen decoded using only the DC component and the low frequency component in the encoded stream. As described above, the resolution is low when the high frequency component is not used, and the resolution is high when the high frequency component is used. For an encoded stream having the SVC function, the resolution can be easily changed by specifying which frequency component is used as a stream level.

  Next, when changing the image quality, the quality setting unit 36 sets the quantization scale in the quantization scale setting unit 38. FIG. 4 is a diagram illustrating an example in which the image quality is lowered with time. The image quality is lowered from the left screen 70 to the right screen 74. The quality setting unit 36 sets the quantization scale in the quantization scale setting unit 38 so that the quantization scale gradually decreases. When the ROI function is installed, such as JPEG2000, the entire screen may be designated as the ROI area and the ROI information may be changed.

  Next, when changing the display area, the quality setting unit 36 sets ROI information in the quantization scale setting unit 38. FIG. 5 is a diagram illustrating an example of narrowing the display area with time. As the left screen 80 changes to the right screen 84, the display area becomes narrower. The quality setting unit 36 narrows the ROI region with respect to the center. The area other than the ROI area may be black or may be a CM area as shown in FIG. An advertisement such as a logo mark or a message displayed in the CM area may be encoded in advance with the image, or may be superimposed by the pixel value calculation unit 30 of the image decoding apparatus 200.

  If the processing of FIG. 5 and the processing of FIG. 3 or FIG. 4 are combined, the resolution or image quality of the area other than that area is lowered while maintaining the resolution or image quality of the area narrowing with respect to the center. You can also.

  Next, when changing the image size to be displayed, the quality setting unit 36 sets the display size in the frame reconstruction unit 32. FIG. 6 is a diagram illustrating an example in which an image is reduced as time elapses. As the left screen 90 changes to the right screen 94, the image is reduced. The quality setting unit 36 does not need to do anything when the display size designated by the quality management unit 34 is the same as the restored moving image size. When the display size is smaller than the restored moving image size, the frame reconstruction unit 32 is set so that pixels are thinned out at a constant rate. When the designated display size is larger than the restored moving image size, the number of pixels is increased by calculating from adjacent pixel values. This enlargement / reduction processing may be performed by providing a dedicated enlargement / reduction circuit in hardware when the burden on the system becomes large.

  Next, when changing the frame rate, the quality setting unit 36 designates the frame rate to the frame reconstruction unit 32. FIG. 7 is a diagram illustrating an example in which the frame rate is lowered with time. The frame rate indicates the frame update frequency. In FIG. 7, the frame rate is decreased with the passage of time. For the same period, the frame rate is reduced to 8, 4, or 2. If the frame is not updated, a still image is obtained, and the quality setting unit 36 can also make a still image.

  Next, when changing the brightness of the display image, the quality setting unit 36 sets a luminance correction value in the pixel value calculation unit 30. The pixel value calculation unit 30 adds or subtracts the original luminance value according to the correction value. Add to brighten and subtract to darken.

  Next, when changing the color of the display image, the quality setting unit 36 sets a color difference correction value in the pixel value calculation unit 30. The pixel value calculation unit 30 corrects the color difference according to the correction value. By correcting the original color difference value so that the corrected color difference value approaches zero, it is possible to approximate a black and white image. When the color difference value becomes zero, a black and white image is obtained.

  The quality setting unit 36 may perform a combination of two or more of the parameter changes described above. Further, when the quality setting unit 36 receives information for invalidating quality management, the quality setting unit 36 sets the parameters described above to normal values. Note that the quality at the start of moving image playback can also be set arbitrarily. In addition, the quality can be increased with the passage of time depending on the application, such as when it is desired to clearly display the image of the rear part, such as in an end roll of a movie.

  As described above, according to the present embodiment, it is possible to realize an image decoding device that achieves both copyright protection and promotion of use of moving images. The image provider can protect the copyright by degrading the quality of the moving image over time. In addition, it is possible to make a user impress with high-quality images in a certain section and make an impression, and to promote the sale of content and the subscription to a content distribution service. Further, when the display area is narrowed, the surplus area can be used as an advertising space of the company or other companies, and it is possible to obtain advertising fee income.

  The user can appreciate a high-quality image for a part of the section, and can obtain a material that appropriately determines whether or not to purchase the content. By signing a contract with the content provider, the user side can play back moving images with normal quality. Further, when an advertisement is displayed outside the display area, the possibility that the user side can use the content at a low fee or free of charge increases, and such a mechanism has a great advantage for the user side.

  Next, an example in which encoded image data generated by adjusting quality on the code side is distributed to the decoding side will be described.

(Embodiment 3)
FIG. 8 is a configuration diagram of an image encoding device 300 according to the third embodiment. The image coding apparatus 300 can perform coding using inter-frame coding, but since this is a general process, that portion is omitted in FIG.

  When the luminance value or the color difference value is changed by the quality setting unit 318 described later, the pixel value correcting unit 302 corrects those values according to the setting value from the quality setting unit 318. When performing the correction, the image memory 304 is used. When the luminance value or the like is not changed, it is not necessary to provide the pixel value correction unit 302 and the image memory 304.

  The orthogonal transform unit 306 performs wavelet transform, discrete cosine transform, and the like. When the resolution is specified by a quality setting unit 318 described later, for example, the number of wavelet transforms is adjusted accordingly. The quantization unit 308 quantizes a predetermined coefficient such as a wavelet transform coefficient output from the orthogonal transform unit 306 with a predetermined quantization width. When a quantization scale is designated from a quantization scale setting unit 320 described later, the quantization is performed based on the quantization scale. The variable length encoding unit 310 encodes the bit string passed from the quantization unit 308 for each bit plane. In addition, various parameters necessary for decoding are encoded. Note that the bit string may be entropy encoded.

  The stream generation unit 312 assembles encoded data of an image input from the variable length encoding unit 310 and generates an encoded stream. Then, the generated encoded stream is output to a network or a recording medium. When a frame rate and a display size are designated by a quality setting unit 318 described later, the frame rate and the display size are changed accordingly. Note that the stream generation unit 312 can use the stream memory 314. The decoding apparatus that has received the encoded stream can decode it as usual.

  The quality management unit 316 manages various types of quality set by the image provider so that the quality of the moving image changes with time, and sets it in the quality setting unit 318. In addition, when the quality management is canceled due to the viewer's content purchase, the quality setting unit 318 sets it.

  The quality setting unit 318 sets parameters for adjusting the quality in each unit based on the quality designated by the quality management unit 316. First, when changing the resolution, the orthogonal transform unit 306 is designated the number of wavelet transforms. When changing the image quality, the quantization scale is set in the quantization scale setting unit 320.

  When changing the display area, the quality setting unit 318 sets ROI information in the quantization scale setting unit 320. When changing the image size to be displayed, the display size is set in the stream generation unit 312. Even when the frame rate is changed, the frame rate is designated to the stream generation unit 312.

  When the brightness of the display image is changed, the quality setting unit 318 sets a luminance correction value in the pixel value correction unit 302. When changing the color of the display image, a color difference correction value is set in the pixel value correction unit 302. Similarly to the quality setting unit 36 described in the second embodiment, the quality setting unit 318 sets parameters in each unit, and each unit can similarly change the quality of the moving image.

  As described above, according to the present embodiment, it is possible to realize an image decoding apparatus that achieves both copyright protection and promotion of use of moving images. In addition, when generating moving image data with degraded quality on the encoding side, the capacity of the encoded data can be reduced. Therefore, the amount of traffic on the network can be reduced, and the recording capacity of the user terminal that has received the traffic can be saved. Furthermore, it can be decoded by an existing decoding device, and encoded data with high versatility can be generated.

  The present invention has been described based on the embodiments. The embodiments are exemplifications, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. .

  In the above embodiment, the user's charging status is managed by a server separate from the image encoding devices 100 and 300, and when the user pays a fee, the image encoding devices 100 and 300 are notified, Quality control may be canceled. In this case, an existing billing system can be used.

  In the first and second embodiments, the example in which the quality information is added to the encoded stream and transmitted to the decoding side has been described. In this regard, quality information may be separately downloaded on the decoding side. Without this information, it is expected that the user will download voluntarily if it is set so that playback cannot be started. In this case, it is not necessary to add quality information to the encoded stream on the encoding side, and the configuration of the encoding apparatus can be simplified.

1 is a configuration diagram of an image encoding device according to Embodiment 1. FIG. It is a block diagram of the image decoding apparatus which concerns on Embodiment 2. It is a figure which shows the example which reduces the resolution with progress of time. It is a figure which shows the example which reduces image quality with progress of time. It is a figure which shows the example which narrows a display area with progress of time. It is a figure which shows the example which reduces an image with progress of time. It is a figure which shows the example which reduces a frame rate with progress of time. It is a block diagram of the image coding apparatus which concerns on Embodiment 3.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Orthogonal transformation part, 12 Quantization part, 14 Entropy encoding part, 16 Encoded stream production | generation part, 18 Quality information addition part, 20 Stream acquisition part, 22 Stream memory, 24 Variable length decoding part, 26 Inverse quantization part , 28 orthogonal inverse transform unit, 30 pixel value calculation unit, 32 frame reconstruction unit, 34 quality management unit, 36 quality setting unit, 38 quantization scale setting unit, 40 reference data designation unit, 42 image memory, 100 image code 200 image decoding device.

Claims (13)

  An image display method, wherein a moving image is displayed while changing quality over time according to a predetermined set value.   The image display method according to claim 1, wherein the setting value is a stepwise decrease in at least one of resolution, image quality, and frame rate of the moving image.   The image display method according to claim 1, wherein the set value is a value that gradually decreases at least one of luminance and color difference of the moving image.   The image display method according to claim 1, wherein the set value narrows the display area of the moving image in a stepwise manner.   The image display method according to claim 4, wherein a predetermined advertisement is displayed outside the moving image display area.   6. The image display method according to claim 1, wherein the set value is fixed according to a predetermined action of the user. An encoding unit for encoding moving image data;
An adding unit for adding a predetermined set value to the encoded moving image data so that the quality is displayed as the quality changes with time;
An image encoding device comprising: An encoding unit that encodes moving image data so that the quality is displayed while changing over time;
A quality setting unit that gives a setting value for changing the quality to the encoding unit;
An image encoding device comprising:   9. The image encoding apparatus according to claim 7, wherein the set value is a value that gradually decreases at least one of resolution, image quality, and frame rate of the moving image.   The image encoding device according to claim 7, wherein the set value is a value that gradually decreases at least one of luminance and color difference of the moving image.   The image encoding apparatus according to claim 7, wherein the set value narrows a display area of the moving image in a stepwise manner. A decoding unit for decoding the encoded moving image data;
A quality setting unit that provides the decoding unit with a setting value set so that the quality changes with time, and
The image decoding apparatus, wherein the decoding unit performs decoding while changing the quality according to the set value.   An image display device that displays a moving image while changing quality over time according to a predetermined set value.

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