KR20090071873A - System and method for controlling coding rate using quality of image - Google Patents

Abstract

A system and a method for controlling coding rate using quality of image are provided to control compression ratio of image by measuring the image quality without decreasing bandwidth of subscriber device. An image is compressed or encoded and stored and transmitted to a subscriber device(601). The subscriber image is made up based on the error packet information from the subscriber device(602). The quality of subscribe image is measured by comparing the subscriber image with the original image(603). According to the image quality measurement result, the compression ratio of image is controlled(604).

Description

System and method for controlling coding rate using quality of image}

The present invention relates to a compression rate control system and method through measuring the quality of an image, and more particularly, to measure the quality of a transmission image based on error packet information from a subscriber end, and to encode using the measured image quality. The present invention relates to a compression rate control system and a method for measuring the quality of an image for preventing an error in the image by adjusting the size of the image information by adjusting the compression rate of a visual image.

Recently, VDSL (Very High-data Rate Digital Subscriber Line) and Fiber-To-The Home (FTTH) have been implemented to increase the subscriber network bandwidth, which has led many Internet subscribers to video on demand (VOD) and Internet Protocol TeleVision (IPTV). Interested in video services, etc. As a result, telecom operators are concentrating their efforts to provide various video services.

In the Internet-based video service, video is often lost due to Internet-based characteristics such as packet drop and delay, compared to video service using airwaves.

After all, since the loss of the image affects the quality of the image, a method of measuring the quality of the image is required to solve this problem.

FIG. 1 is a diagram illustrating a conventional method for measuring image quality, showing a full reference (FR) method.

First, the image service device 11 transmits the original image (the image obtained through the camera or the image stored in advance) to the image quality measuring device 13 and the subscriber device 12, respectively.

Then, the subscriber device 12 transmits the image received from the image service device 11 to the image quality measurement device 13. At this time, the received image is an image passing through the network.

Thereafter, the image quality measuring device 13 compares the original image with the image received from the subscriber device 12 and measures the quality of the image.

The conventional image quality measuring method is a method of measuring the quality of the image most accurately, but the subscriber device 12 once again receives the image received from the image service device 11 to the image quality measuring device 13. Since there is a need to transmit, there is a problem of reducing the limited bandwidth of the subscriber.

FIG. 2 is an explanatory diagram of another embodiment of a conventional method for measuring image quality, and illustrates a reduced reference (RR) method.

First, the image service device 21 transmits the original image (the image acquired through the camera or the image stored in advance) to the subscriber device 22.

At this time, the image service device 21 extracts the characteristic information of the image (for example, edge information such as an outline, an average value of pixels of each region of the image, etc.) from the original image and transmits it to the image quality measuring apparatus 23.

Thereafter, the subscriber device 22 extracts the feature information from the image received through the network and transmits the feature information to the image quality measurement device 23.

Then, the image quality measuring device 23 compares the feature information transmitted from the image service device 21 with the feature information transmitted from the subscriber device 22 and measures the quality of the image.

The conventional image quality measuring method has an advantage of not limiting the limited bandwidth of the subscriber device 22 because the quality of the image is measured using feature information having a smaller capacity than that of the original image, but compared with the FR method. There is a drawback of poor accuracy.

Meanwhile, in the conventional compression rate adjusting method, the quality of the image is measured by comparing the original image and the image reproduced through the codec, and then, the compression rate of the codec is set by using the same.

The conventional compression rate adjustment method is a compression rate adjustment method by self-evaluation in a codec excluding a network state, and it is difficult to use in actual video service. That is, since the compression rate is adjusted based on the evaluation result according to the performance of the codec without considering the state of the network, the subscriber device cannot normally play the video.

Therefore, there is a need for a method for measuring the quality of an image with high accuracy without reducing the bandwidth of the subscriber device and a method for adjusting the compression rate of the image using the same, and to solve such a demand, it is an object of the present invention. to be.

The present invention measures the quality of the transmitted video based on the error packet information from the subscriber end, and adjusts the size of the video information by adjusting the compression rate of the video at the time of encoding using the measured video quality, thereby preventing the occurrence of the error of the video. The purpose of the present invention is to provide a compression rate control system and method through measuring the quality of an image.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned above can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In accordance with an aspect of the present invention, there is provided an apparatus for adjusting a compression rate by measuring an image quality, the apparatus comprising: encoding means for compressing and encoding an image according to an image quality measurement result from the image quality measuring means; Packet construction means for constructing a video encoded by the encoding means into packets; Packet storing means for storing a packet constructed by said packet constructing means; And the image quality measuring means for measuring the quality of the subscriber image by comparing the original image after constructing the received image (hereinafter referred to as the subscriber image) in the subscriber device based on the error packet information from the subscriber device.

In addition, another apparatus of the present invention for achieving the above object, in the subscriber device for adjusting the compression rate of the image, an error packet when assembling the packet received from the compression rate control device for adjusting the compression rate of the image according to the quality of the image Packet assembly means for delivering information to the error packet collecting means; The error packet collecting means for collecting the error packet information from the packet assembling means and transmitting the collected error packet information to the compression rate adjusting apparatus; And decoding means for decoding the packet assembled by the packet assembling means.

On the other hand, the method of the present invention for achieving the above object, the compression rate control method in the apparatus for adjusting the compression rate, comprising the steps of compressing and encoding the image to form a packet and transmitting to the storage and subscriber device; Constructing a received image (hereinafter referred to as a subscriber image) at the subscriber device based on the error packet information from the subscriber device; An image quality measuring step of measuring the quality of the subscriber image by comparing the subscriber image with the original image; And a compression ratio adjusting step of adjusting the compression ratio of the image according to the image quality measurement result.

In addition, the method of the present invention for achieving the above object, in the method of adjusting the compression rate in the subscriber device, for the error packet generated when assembling the packet received from the compression rate control device for adjusting the compression rate of the image according to the quality of the image An error packet detecting step of detecting information (hereinafter, referred to as error packet information); And collecting the detected error packet information and transmitting it to the compression rate adjusting device.

In addition, in the present invention, in order to measure a full reference (FR) -based image quality having the best image quality measurement effect, the time stamp of the RTP packet is not transmitted to the image quality measurement system after reconstructing the image at the subscriber end. Information and sequence number information are stored in the packet during delay or lost, and transmitted to the video quality measurement system together with the information indicating the degree of influence affected by this error packet, and transmitted according to the degree of influence at the transmitting side. Choose bandwidth adjustment or error correction code and other codecs.

In addition, the present invention removes the information as much as the delay and loss packet information from the original image information on the basis of the error packet information, and after reconstructing the image to measure the quality of the image compared to the original image, based on the Adjust the compression rate.

In addition, the present invention estimates the quality deterioration information of the image generated during the reconstruction of the image when decoding at the receiving end, and transmits the estimated image deterioration information to the transmitting side along with the error packet to adjust the transmission bandwidth and the compression ratio during encoding do.

In addition, the present invention measures the quality of the image based on the 'Full Reference' according to the degree of reconstruction of the image after reconstructing the error image based on the RTP error packet.

In addition, the present invention analyzes how the packet affects the reconstruction of the image when an error occurs at the subscriber end when transmitting the image information, and reconstructs the image only for a certain period of the image at the transmitting side according to the degree of the effect. It is possible to measure image quality based on 'Full Reference'.

The present invention as described above has the effect of measuring the quality of an image using a FR (Full Reference) method that is most effective for measuring image quality if only a small amount of data is received from the subscriber device rather than the entire image. .

In addition, the present invention estimates the quality of the image based on the image information processed by the actual error in the receiving device, and controls the transmission bandwidth based on the received information, so that a little software can be installed without any large hardware added to the subscriber device. It is possible to measure the quality of video for a large number of subscribers without the economic burden on the device, thereby increasing the quality of the video service.

The above objects, features, and advantages will become more apparent from the detailed description given hereinafter with reference to the accompanying drawings, and accordingly, those skilled in the art to which the present invention pertains may share the technical idea of the present invention. It will be easy to implement. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is an example of an RTP packet used in the present invention.

In general, as a protocol for providing a video service such as IPTV or VoD, a real-time transport protocol (RTP) or MPEG2-Transport Stream (MPEG2-TS) is used between a set-top box of a subscriber end and a video service device.

As shown in FIG. 3, an image is stored in the payload 301.

The time stamp 302 stores reproduction time information of an image loaded on the payload 301. That is, the video service server initializes and transmits the time stamp when the first video is transmitted. The next packet to be transmitted is filled with information indicating a time interval that should be displayed when the video is actually played.

The sequence number 303 stores sequence information of packets transmitted from an actual video service server.

Meanwhile, in the case of H.264 or MPEG4, the encoded video is composed of an I-frame transmitted every time the screen is changed and a B-frame indicating a change in the screen when the screen is not greatly changed. have. In this case, if the I-frame is included by the error packet, the image has a great influence. However, when the content of the error packet is composed of the B-frame, the effect is relatively small or the error correction technique is applied to the image. The impact may be minimal.

Therefore, it is possible to estimate the effect of the decoding on the receiving side to some extent without significantly degrading the performance.

Figure 4 is a configuration diagram of an embodiment of a compression ratio control system by measuring the quality of the image according to the present invention.

As shown in FIG. 4, the compression rate control system through measuring the quality of an image according to the present invention configures a received image at the subscriber device 420 based on error packet information from the subscriber device 420. Compression ratio adjustment for adjusting the compression ratio of the image transmitted to the subscriber device 420 after measuring the quality of the received image by comparing the mutual image to the original image transmitted to the subscriber device 420 Apparatus 410, and the subscriber device 420 for collecting the error packet information generated according to the network conditions when the image is received from the compression rate control device 410 to transmit to the compression rate control device 410. .

In this case, the compression rate adjusting device 410 encodes the corresponding video according to the subscriber's desired video to receive the video service, and transmits the encoded video to the subscriber device 420 by loading the encoded video on a protocol such as RTP or MPEG2-TS. .

In addition, the subscriber device 420 may additionally collect image quality degradation information and transmit the image quality degradation information to the compression rate adjusting device 410 along with the error packet information.

Then, the compression rate adjusting device 410 adjusts the transmission bandwidth and the transmission speed by using the image quality degradation information from the subscriber device 420.

Hereinafter, the compression rate adjusting device 410 and the subscriber device 420 will be described in more detail.

First, the compression rate adjusting device 410 is a packet encoding unit 411 for compressing and encoding the image according to the image quality measurement result from the image quality measuring unit 414, the packet encoded by the encoder 411 A packet constructing unit 412 for transmitting to the subscriber unit 420, a database 413 for storing the packet constructed by the packet forming unit 412, and error packet information from the subscriber unit 420. And an image quality measuring unit 414 configured to measure the quality of the received image by comparing the original image with the received image (subscriber image) of the subscriber device 420 based on the received image.

Here, the encoder 411 adjusts the compression rate as shown in Table 1 below.

In general, even when the subscriber device 420 normally receives image information, the encoder 411 has a basic compression ratio.

When an error occurs in the subscriber device 420, the quality of the image reflecting the influence of the error is measured and the index is divided into 1 to 5. In this case, 5 indicates that the image is normally received, and 1 indicates that the quality of the received image is the worst.

Therefore, in the normal case, the compression rate is transmitted as it is, and in 4, 20% is further compressed. Proceed like this to allow for up to 80% additional compression in case of 1.

The image quality measuring unit 414 may include an error information receiver 415 for receiving error packet information from the error packet collecting unit 422, error packet information received by the error information receiver 415, and The image composer 416 for composing the received image and the original image in the subscriber device 420 using the packet stored in the database 413, and the received image and the original image configured in the image composer 416. A decoder 417 for decoding, and an image quality measurer 418 for measuring the quality of the received image by comparing the received image and the original image decoded by the decoder 417.

At this time, the image quality measuring instrument 418 compares the original image and the image reflecting the error to measure the quality of the image. In this case, it is generally desirable to use the PSNR (Peak Signal to Noise Ratio), which is generally the fastest and easiest to measure.

In addition, the error information receiver 415 determines whether to increase the transmission bandwidth or use an error correction code for smooth transmission of the packet based on the image quality degradation information received from the subscriber device 410. 412 may be controlled.

Next, the subscriber device 420, the packet assembly unit 421 for delivering the error packet information to the error packet collection unit 422 when assembling the packet received from the compression rate adjusting device 410, the packet assembly unit ( An error packet collecting unit 422 for collecting error packet information from the 421 and a decoding unit 423 for decoding the packets assembled by the packet assembling unit 421.

Here, the packet assembly unit 421 checks the error packet by analyzing the sequence number and time stamp of the packet received from the compression rate adjusting device 410. That is, the packet information skipping the sequence number and the timestamp field due to an incorrect or lost sequence number from the received RTP packet are analyzed, and the packet information that does not reach the normal time is transmitted to the error packet collection unit 422.

In addition, the error packet collecting unit 422 transmits the collected error packet information to the image quality measuring unit 414 together with its IP information.

Additionally, the subscriber device 410 further includes an image quality degradation information collecting unit 424 for collecting image quality degradation information.

Hereinafter, the image quality degradation information collecting unit 424 will be described in detail.

The decoder 423 decodes the packet assembled by the packet assembly unit 421 to form an image. In this case, if an image is composed based on an error packet or a delayed packet, a perfect image may not be formed.

The degree of composition of the image varies depending on the type of the image data at the time of image composition. That is, an image encoded in H.264 or MPEG4 is composed of an I-frame image and transmitted when the entire contents of the screen are changed. Only the changed part is composed of B-frames and transmitted.

In this case, when the packet received by the packet assembly unit 421 of the subscriber device 420 is not processed due to an error or delay, if the information of the image contained in the lost packet is an I-frame, the quality of the image is greatly affected. However, if the lost packet is a B-frame, the error compensation of the image may cause the user not to notice it or cause a relatively small decrease in image quality.

Accordingly, the image quality deterioration information collecting unit 424 specifies, for example, an image quality deterioration level of about 5 when an I-frame is lost when constructing an image, and an image of about 1 degree when a B-frame is lost. Specifies the level of deterioration.

However, although the I-frames do not appear in succession, the B-frames continue to some extent, so there may be more B-frames affected by packet loss.

Therefore, the image quality deterioration information collecting unit 424 designates the image quality deterioration level of 1 when the first B-frame is lost, and continuously adds 1 to the deterioration level of the image when the B-frames lost continuously occur. Specify.

By specifying the level of deterioration of the image in this way, it is possible to obtain rough information on the quality of the image without significantly affecting the processing of the image.

In addition, instead of controlling the bandwidth after measuring the quality of the image on the transmitter side, controlling the bandwidth based on the image quality degradation information calculated by the receiver is' Full Reference ',' Reduced Reference ',' No This is because it is very difficult to measure the quality of an image at a level that processes 15 to 30 frames per second using either method.

Accordingly, in the present invention, the control such as bandwidth for smooth transmission of the image is controlled based on the image quality deterioration information, and the error packet information is used to reconstruct the image received by the subscriber device 420.

5 is an exemplary view showing the structure of a database according to the present invention.

Information about the target subscriber for measuring the image quality is stored in the subscriber information storage 501. The subscriber information stores information such as subscriber name, subscriber IP information, bandwidth, address and location, quality measurement time, and quality measurement result.

The RTP packet storage 502 stores the RTP packet for the designated subscriber received from the image quality measuring unit 414. The RTP packet is stored as it is transmitted to the subscriber for video service.

The RTP error packet information store 503 stores the RTP error packet information received from the subscriber device 420. The RTP error packet information does not store the RTP packet itself in which an error occurs, but stores position information about an RTP packet in which an error occurs. That is, the sequence number and timestamp of the RTP packet are stored so that it can be known later in which packet among the RTP packets in the RTP packet storage.

6 is a flowchart illustrating an embodiment of a compression rate adjusting method in a compression rate adjusting apparatus according to the present invention.

First, the image is compressed and encoded into a packet, and then stored and transmitted to the subscriber device (601).

Thereafter, a received image (hereinafter referred to as a subscriber image) at the subscriber device is configured based on the error packet information from the subscriber device (602).

Thereafter, the quality of the subscriber image is measured by comparing the subscriber image with the original image (603).

Thereafter, the compression rate of the image is adjusted according to the result of measuring the image quality (604).

7 is a flowchart illustrating a method of adjusting a compression ratio in a subscriber device according to the present invention.

First, in operation 701, information about an error packet generated when assembling a packet received from a compression rate adjusting device for adjusting a compression rate of an image according to the quality of an image is detected (hereinafter, referred to as error packet information).

Thereafter, the detected error packet information is collected and transmitted to the compression rate controller (702).

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention can be used to improve the quality of end-to-end video service.

1 is a diagram illustrating an embodiment of a conventional image quality measuring method;

2 is a diagram illustrating another embodiment of a conventional method for measuring image quality;

3 is an example of an RTP packet used in the present invention;

4 is a configuration diagram of an embodiment of a compression ratio control system through measuring image quality according to the present invention;

5 is an exemplary view showing the structure of a database according to the present invention;

6 is a flow chart of an embodiment of a compression rate adjusting method in the compression rate adjusting apparatus according to the present invention;

7 is a flowchart illustrating a method of adjusting a compression ratio in a subscriber device according to the present invention.

* Explanation of symbols for the main parts of the drawings

410: extrusion rate control device 411: encoder

412: packet construction unit 413: database

414: Image quality measuring unit 420: Subscriber device

421: packet assembly unit 422: error packet collection unit

423: encoder 424: image quality degradation information collector

Claims (14)

In the compression rate control apparatus by measuring the quality of the image, Encoding means for compressing and encoding an image according to an image quality measurement result from the image quality measurement means; Packet construction means for constructing a video encoded by the encoding means into packets; Packet storing means for storing a packet constructed by said packet constructing means; And The image quality measuring means for measuring the quality of the subscriber image by configuring the received image (hereinafter referred to as the subscriber image) in the subscriber device based on the error packet information from the subscriber device and comparing with the original image Compression rate control device by measuring the quality of the image comprising a. The method of claim 1, The encoding means, Compression rate control apparatus for measuring the quality of the image, characterized in that the compression rate increases as the image quality measured by the image quality measuring means is lower than the reference value. The method according to claim 1 or 2, The image quality measuring means, Error information receiving means for receiving error packet information from the subscriber apparatus; Image constructing means for constructing the subscriber image and the original image by using the error packet information received by the error information receiving means and the packet stored in the packet storing means; Decoding means for decoding the subscriber video and the original video configured by the video constituting means; And Image quality measuring means for measuring the quality of the subscriber image by comparing the subscriber image and the original image decoded by the decoding means Compression rate control device by measuring the quality of the image comprising a. The method of claim 3, wherein The image quality measuring means, Compression rate control device for measuring the quality of the image, characterized in that for measuring the quality of the subscriber image using a Peak Signal to Noise Ratio (PSNR). The method of claim 4, wherein The error information receiving means, And receiving the image quality degradation information from the subscriber device so as to be used for transmission bandwidth and transmission rate adjustment. In the subscriber device for adjusting the compression rate of the image, Packet assembling means for delivering the error packet information to the error packet collecting means when assembling the packet received from the compression rate control device for adjusting the compression rate of the image according to the quality of the image; The error packet collecting means for collecting the error packet information from the packet assembling means and transmitting the collected error packet information to the compression rate adjusting apparatus; And Decoding means for decoding the packet assembled by the packet assembly means Subscriber device for adjusting the compression rate of the image comprising a. The method of claim 6, Image quality deterioration information collecting means for collecting image quality deterioration information according to the type of a frame when decoding the packet in the decoding means. Subscriber device for adjusting the compression rate of the image further comprising. The method according to claim 6 or 7, The packet assembly means, Subscriber device for adjusting the compression rate of the image, characterized in that the error packet is identified by analyzing the sequence number and time stamp of the packet received from the compression rate control device. In the compression rate adjusting method in the compression rate adjusting apparatus, Compressing and encoding an image into a packet, and then storing and transmitting the image to a subscriber device; Constructing a received image (hereinafter referred to as a subscriber image) at the subscriber device based on the error packet information from the subscriber device; An image quality measuring step of measuring the quality of the subscriber image by comparing the subscriber image with the original image; And Compression ratio adjusting step of adjusting the compression ratio of the image according to the image quality measurement result Compression rate control method in a compression rate adjusting apparatus comprising a. The method of claim 9, The compression rate adjusting step, The compression rate control method of the compression rate adjusting device, characterized in that the compression rate is increased as the measured image quality is lower than the reference value. The method according to claim 9 or 10, The image quality measuring step, A compression rate control method in a compression rate adjusting apparatus, characterized in that the quality of the subscriber image is measured using a peak signal to noise ratio (PSNR). In the compression rate adjusting method in the subscriber device, An error packet detecting step of detecting information (hereinafter, referred to as error packet information) about an error packet generated when assembling a packet received from a compression rate adjusting device for adjusting a compression rate of an image according to an image quality; And Collecting the detected error packet information and transmitting the detected error packet information to the compression rate adjusting apparatus; Compression rate control method in a subscriber device comprising a. The method of claim 12, Collecting image quality degradation information according to a type of frame when decoding the assembled packet; Method of adjusting the compression rate in the subscriber device further comprising. The method according to claim 12 or 13, The error packet detection step, And adjusting an error number by analyzing a sequence number and a timestamp of a packet received from the compression rate adjusting device.

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