JP2006191371A - Image coding device and the image coding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the deterioration of picture quality in a frame block boundary at the time of compositing and encoding an original picture and a frame block. <P>SOLUTION: This image coding device is provided with: an image inputting part 101 for managing an input image; an image frame preparing part 102 for preparing an image frame being the background of an original; an image composition part 103 composed of a composition deciding part 105 and an encoding parameter deciding part 106 and a low pass filter 109; and an image encoding part 104 for performing moving image encoding. Only when it is decided that the boundary is included in the encoding unit by the composition deciding part 105, and it is decided that the encoding parameter is within a reference value by the parameter deciding part 106, a composite image is generated by using the low pass filter 109. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image encoding device and an image encoding method used for a videophone terminal or the like.

  Conventionally, an image encoding apparatus that encodes an original image signal corresponding to an original image has a circuit configuration shown in FIG. That is, as shown in FIG. 5, an original signal input unit 502, a fixed signal transmission unit 503, and an image encoding unit 505 are configured. Further, a switch 504 that switches the output between the original signal input unit 502 and the fixed signal transmission unit 503. And a timing circuit 501 for controlling switching of the switch 504 (see, for example, Patent Document 1).

In such a configuration, an original image signal corresponding to an original image output from the original signal input unit 502 and a fixed signal corresponding to a fixed value output from the fixed signal transmission unit 503 are switched by a switch 504 according to the timing circuit 501. The encoding target image is combined and input to the image encoding unit 505, and the image encoding unit 505 encodes the combined encoding target image to generate a bitstream.
JP 2000-165866 A

  However, in the conventional image encoding device, when the bit rate at the time of encoding in the image encoding unit 505 is small, a sufficient amount of code cannot be allocated to the image to reproduce the original image. The band component is roughly quantized, and there is a problem that distortion of the high band component becomes conspicuous at the boundary between the original image of the decoded image and the flat portion of the background frame.

  The present invention has been made in view of the above points, and an image encoding device and an image encoding capable of reducing deterioration in image quality at a frame frame boundary when an original image and a frame frame are combined and encoded. It aims to provide a method.

  An image encoding apparatus according to the present invention includes an image input unit that manages original image data to be encoded, an image frame generation unit that generates background data other than the original image data, and an image composition unit that combines the original image and the background. And an image encoding device having an image encoding means for encoding a composite image generated by the image composition means, wherein the image composition means determines whether the area includes an encoding unit including an image boundary. In this case, a configuration is adopted in which a control through a low-pass filter is performed on the image boundary area in accordance with the encoding parameter of the image encoding means.

  The image encoding method of the present invention is an encoding method in which a composite image obtained by combining an original image and a background other than the original image is an encoding target, and the composite image to be encoded is an encoding unit. Whether or not the boundary between the original picture and the background is included is determined, and if the boundary is included, it is generated through a low-pass filter according to the encoding parameter.

  According to the present invention, the low-pass filter applied to the encoding unit including the image boundary is controlled according to the encoding parameter of the image encoding unit, thereby suppressing the increase in the maximum processing amount and reducing the original image at the low rate. The distortion at the boundary between the background and the background can be reduced, and the deterioration of the image quality at the frame frame boundary can be reduced.

  Further, by providing an image composition unit that controls a low-pass filter for each coding unit in accordance with the quantization coefficient calculated by the image coding unit, it is possible to further reduce distortion with optimized image quality. .

  In addition, with regard to the low-pass filter applied to the boundary part, by applying the low-pass filter only to the original image area and out of the filter application range for the background area, blurring near the boundary can be reduced, and image degradation is reduced. It can be prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of an image coding apparatus according to Embodiment 1 of the present invention. In FIG. 1, an image encoding apparatus 100 includes, on the input side, an image input unit 101 that manages input images and an image frame creation unit 102 that creates an image frame that is the background of an original image. In 103, a switch 107 that switches between an input image from the image input unit 101 and an image frame from the image frame creation unit 102, a combination determination unit 105 that switches the switch 107 based on image combination information, and encoding of encoding parameters A low-pass filter 109 according to an AND condition between an encoding parameter determination unit 106 for determining a rate and an image frame output by the synthesis determination unit 105, that is, the presence / absence of a boundary and the encoding rate output by the encoding parameter determination unit 106. The switch 108 for switching whether or not to interpose the image, and fills the boundary that is the image frame at a low encoding rate The and a low-pass filter 109 to apply, at the output side, a configuration having an image encoding unit 104 for performing image encoded by the encoding rate according to the coding parameter.

  The operation of the image coding apparatus configured as described above will be described. First, an original image input to the image input unit 101 is stored and managed in a memory in units of frames. In the image composition unit 103, based on image composition information including the size composition position of the original image, the composition determination unit 105 first controls the switch 107 to generate a composite image combining the original image and the background. At the same time, the synthesis determination unit 105 determines whether a boundary between the background and the original image exists in an image coding unit (for example, a macro block).

  When the combination determination unit 105 includes a boundary in the corresponding encoding unit, the encoding parameter determination unit 106 determines the encoding rate of the encoding parameter. As a result, the encoding rate is equal to or lower than a reference value (for example, 64 kbps). In this case, the switch 108 is controlled so that the low-pass filter 109 is interposed in the signal path.

  On the other hand, when the encoding rate is greater than the reference value, the switch 108 is controlled to be directly connected without the low-pass filter 109.

  Here, examples of the encoding parameter include a frame rate, an encoded image size, a quantization step, and the like in addition to the encoding rate (bit rate).

  In this manner, the image composition unit 103 generates a composite image, and the composite image is encoded into a bit stream by the image encoding unit 104.

  As described above, the low-pass filter 109 is used when the boundary between the background and the original image exists in image encoding units and the encoding rate is equal to or less than the reference value. When the encoding rate is low, the high frequency components are roughly quantized, which causes distortion of the high frequency components, but this distortion causes significant image quality degradation at the boundary between the background and the original image. Therefore, the low-pass filter 109 is disposed, and high-frequency components in the original image frequency region are reduced (high cut) to remove aliasing distortion.

  FIG. 2 is a diagram for specifically explaining a function example of the low-pass filter 109. FIG. 2 shows an example in which there is a boundary between the background and the original image in the image coding unit. For simplification, the image coding unit is 8 × 8 pixels, the horizontal pixel position is i, and the vertical pixel is An example in which the position is j and there is an image boundary between J = 3 and J = 4 will be described.

Here, P (i, j) represents a pixel value obtained by combining the original image and the background when the pixel position i in the horizontal direction is j and the pixel position in the vertical direction is j. The low-pass filter 109 performs a filter function only on the original image area and does not refer to the background area. Therefore, the background is output as it is, the boundary is left as it is, and the low pass filter 109 is applied only to the original image portion to perform high cut of the original image. That is, the line (i) and the next line (i + 1) are output in the original image area of the boundary part, and the previous line (i-1), the line (i), and the next line are output in the original image area in the boundary part. (I + 1) is output. The output F (i, j) of the low-pass filter in this case is, for example, as follows.
When j = 0-3 F (i, j) = P (i, j)
When j = 4 F (i, j) = P (i, j) * 3/4 + P (i, j + 1) * 1/4
When j = 5 to 7 F (i, j) = P (i, j-1) * 1/4 + P (i, j) * 1/2 + P (i, j + 1) * 1/4

  The above is an example in the case where there are upper and lower boundaries. However, when there are boundaries on the left and right, and when the corners of the original image are included, similar processing having appropriate coefficients can be applied. 3A shows the coefficients in the vertical and vertical output states of the low-pass filter 109 in the original image area, and FIG. 3B shows the coefficients in the horizontal and horizontal output states (b). 3 (c) shows each coefficient of the output state (c) in the vertical, horizontal, vertical and horizontal directions.

  As described above, according to the image encoding apparatus of the first embodiment, when the encoding rate is low, the low-pass filter 109 can be applied to the boundary between the original image and the frame frame, and distortion in the boundary region at the low rate is prevented. Will be reduced. In addition, since the low-pass filter 109 can be interposed in low-rate encoding with a relatively low processing load, it is possible to improve the image quality without greatly increasing the maximum processing load of the entire image encoding apparatus. Thus, by providing the image composition unit 103 that controls the low-pass filter 109 applied to the coding unit including the image boundary according to the image coding parameter, the increase in the maximum processing load is suppressed by the high cut, and the original image at a low rate can be obtained. Background distortion can be reduced.

  Further, by providing the low-pass filter function only in the original image area and providing the low-pass filter 109 outside the application range of the low-pass filter function in the background area, blurring near the boundary can be reduced.

(Embodiment 2)
FIG. 4 is a block diagram showing the configuration of the image coding apparatus according to Embodiment 2 of the present invention. In this figure, an image coding apparatus 300 includes an image input unit 101 that manages input images, an image frame creation unit 102 that creates an image frame as a background of an original image, a composition determination unit 105, and an encoding parameter determination unit 306. And a low-pass filter 109, and an image encoding unit 304 that performs moving image encoding. In the second embodiment, the quantization coefficient is input from the image encoding unit 304 to which the encoding parameter is input to the encoding parameter determining unit 306 and is handled as the encoding parameter.

  The operation of the image coding apparatus configured as described above is as follows. First, the input original image is stored and managed in the memory in units of frames by the image input unit 101. In the image composition unit 303, the composition determination unit 105 controls the switch 107 based on the image composition information including the size composition position of the original image. Generate a composite image that combines the original and background.

  On the other hand, the image encoding unit 304 calculates a quantization coefficient for each encoding unit, and notifies the encoding parameter determination unit 306 of the calculated quantization count. In addition, the synthesis determination unit 105 determines whether a boundary between the background and the original image exists in an image coding unit (for example, a macro block). If there is not, the switch 108 is directly controlled without going through the low-pass filter.

  The encoding parameter determination unit 306 determines the encoding rate of the encoding parameter when the synthesis determination unit 105 includes the corresponding encoding unit at the boundary. When the quantization coefficient is equal to or greater than the reference value, the encoding parameter determination unit 306 As in the case where the filter 109 is interposed, control is performed so that the low-pass filter 109 is not interposed when the value is smaller than the reference value. In this way, the image composition unit 303 generates a composite image. The composite image is encoded into a bit stream by the image encoding unit 304. Here, it becomes possible to control the low-pass filter 109 for each encoding unit, and to further improve the image quality. Note that the encoding parameter determination unit 306 may use one of the encoding rate (bit rate), the frame rate, the encoded image size, the quantization step, and the like as an encoding parameter, May be used in combination.

  As described above, according to the image coding apparatus of the second embodiment, the image synthesis unit 303 that controls the low-pass filter 109 applied to the coding unit including the image boundary by the quantization coefficient output from the image coding unit 304 is provided. By providing, it is possible to further reduce the distortion of the original image and the background at a low rate by suppressing the increase in the maximum processing load.

  In the above description, the image input unit 101 and the image encoding unit 104 have been described as means for handling moving images. However, the present invention can be similarly applied to still images. Further, although the image encoding parameter in the encoding parameter determination unit 106 is the encoding rate, the present invention can be similarly implemented by a combination of image size, frame rate, and the like. Further, although the encoding parameter determination units 106 and 306 are configured to switch the presence / absence of the low-pass filter 109, the encoding parameter determination units 106 and 306 can be similarly implemented by switching a plurality of low-pass filters having different characteristics. Further, although the image input unit 101 is configured to handle one original image, it can be similarly implemented as a configuration that handles a plurality of original images. Further, the image frame creation unit 102 can be implemented in the same manner as a configuration that generates a frame of a fixed color pattern or a configuration that handles graphic images. In the first embodiment, the composite image is directly output to the image encoding unit 104. However, in order to reduce the uncomfortable feeling at the image boundary, a configuration in which a filter having a characteristic different from that of the low-pass filter 109 is inserted may be used. It can be implemented. In addition, although the encoding unit is configured as a macroblock, the present invention can be similarly implemented as long as it includes a unit for performing frequency conversion even if the block constituting the macroblock is an encoding unit.

  The image encoding apparatus according to the present invention is suitable for use in an image encoding apparatus used for a videophone terminal or the like.

1 is a block diagram of an image coding apparatus according to Embodiment 1 of the present invention. The figure for demonstrating operation | movement of the low-pass filter of the image coding apparatus in Embodiment 1 of this invention. The figure for demonstrating the coefficient of the output state of the low pass filter of the image coding apparatus in Embodiment 1 of this invention The block diagram of the image coding apparatus in Embodiment 2 of this invention. Block diagram of a conventional image encoding device

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,300 Image coding apparatus 101 Image input part 102 Image frame creation part 103,303 Image composition part 104,304 Image coding part 105 Composition determination part 106,306 Coding parameter judgment part 107,108 Switch 109 Low pass filter

Claims (8)

Image input means for managing original image data to be encoded;
Image frame creation means for generating background data other than the original image data;
Image combining means for combining the original image and the background;
Image encoding means for encoding a composite image generated by the image composition means;
An image encoding device comprising:
The image synthesizing unit determines whether the region includes an encoding unit including an image boundary, and performs control of passing the image boundary region through a low-pass filter according to the encoding parameter of the image encoding unit. An image encoding device.   2. The image coding apparatus according to claim 1, wherein the image synthesizing unit controls the low-pass filter for each coding unit according to the quantization coefficient calculated by the image coding unit.   3. The image encoding device according to claim 1, wherein the low-pass filter performs a low-pass filter function only on an original image region and excludes a background region from an application range of the low-pass filter function. 4. An encoding method for encoding a composite image obtained by combining an original image and a background other than the original image,
It is determined whether the composite image to be encoded includes a boundary between an original picture and a background in an encoding unit, and if included, the image is generated through a low-pass filter according to an encoding parameter. Method.   5. The image encoding method according to claim 4, wherein the synthesized image to be encoded is generated through a low-pass filter according to a quantization coefficient.   6. The image encoding method according to claim 4, wherein the low-pass filter function is applied only to the original image area by the low-pass filter, and the background area is excluded from the applicable range of the low-pass filter function.   A computer-readable recording medium on which a program for executing the image encoding method according to any one of claims 4 to 6 is recorded.   A mobile communication system comprising the image encoding device according to any one of claims 1 to 3.

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