JPH08194824A - Picture encoding device and picture decoding device - Google Patents

Abstract

PURPOSE: To provide a picture encoding device capable of quickly extracting edge data by incorporating a specific quantizing means and a specific edge data determining means in an edge data extracting means. CONSTITUTION: The edge data extracting means is provided with a quantizing means 10 and an edge data determining means 12. Picture data to be encoded are supplied to respective means 10, 12. The means 10 classifies respective picture element values of the input picture data based upon a fixed threshold and reduces the sorts of picture element values to be obtained. The means 12 observes a picture element value quantized by the means 10 and judges a picture element having a picture element value different from its adjacent picture element value out of plural quantized picture element values as edge data. Since the number of gradation levels is reduced by the means 10 and a picture element having a picture element value different from its adjacent picture element value is simply selected, edge data are extremely easily detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding device and a decoding device for image data. In particular, the present invention relates to an image encoding device capable of performing high compression rate encoding based on image contour information.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed for encoding image data at a high compression rate. Most of such methods try to compress by using the statistical property of the image, but in recent years, a method of encoding by using visual characteristics when viewing the image data has been proposed. .

This is because most of the image data is a two-dimensional signal in which the real three-dimensional world is projected on a plane by a camera mechanism, and some of them are structures that are closely related to the real three-dimensional world. It is based on the idea that is reflected. In such a method, the structural characteristics of the image are positively used in encoding. From this point of view, as an image coding method, an edge,
A method that uses the two-dimensional structure of images such as contours and regions,
Methods and other methods that utilize three-dimensional motion of an object to be encoded have been studied.

In particular, the method of coding by extracting the two-dimensional structure is considered to be effective as coding for a still image.

The two-dimensional structure extraction coding method is classified into a method using contours and edge components and a method using collective region information. In particular, a method of extracting only edges and contours and encoding it as a binary line drawing is a method that has been studied for a long time for the purpose of recognizing the shape of an object. When using this method for image coding,
In many cases, the final purpose is not to represent the image as a simple line drawing but to reproduce it as a natural image having a brightness gradation.

Among the two-dimensional feature-based coding, some proposals have been made regarding a method using a contour line. For example, “Image Information Compression”, Hiroshi Harajima, 24 by Ohmsha
From page 3 to page 245, some coding methods based on a two-dimensional structure are introduced. For example, as a typical example introduced in this document, the coding algorithm of Sketch Based Coding by Carlsson is introduced. According to this encoding algorithm, the Laplacian-Gaussian operator is first used from the original image data to generate contour information from the zero crossings. Then, based on the contour information generated by using this Laplacian-Gaussian operator, the contour shape and the luminance component on the contour are encoded. In this way, only the contour is encoded, transmitted through the communication path, or stored in a predetermined storage means.

In order to decode the data encoded in this way, first, the contour shape and the luminance component on the contour are decoded based on the encoded data. That is, if the encoded image data is decoded as it is, the contour shape and its luminance component are obtained. Then, points other than the contour are interpolated by the criterion of variation minimum. In addition,
If desired, subsampled data of the coding residual may be added to improve the interpolation quality.

According to Carlsson's experiment on a still image, it has been confirmed that an image capable of sufficiently perceiving an object can be reproduced even if the compression rate is about several tenths to one hundredth.

This Sketch Based Codi
The state of encoding by the ng encoding algorithm is shown in FIG.
It is shown in (a)-(d). Here, FIG. 5A shows original image data to be encoded. The result of obtaining the contour information from the zero crossings of the original image data by using the Laplacian-Gaussian operator as described above is shown in FIG. The contour information as shown in FIG. 5B is called so-called sketch data.

Then, the contour information shown in FIG. 5 (b) is coded, and an example of decoding the coded data is shown in FIGS. 5 (c) and 5 (d). There is. The example shown in FIG. 5C is 0.11 bit /
This is an example of a decoded image when a point other than the contour is obtained by interpolation from the data on the contour in the case of pel, that is, the compression rate is 1/75. Pixel values are reproduced by interpolation in portions other than the contours, so that slight gradation is lost, but since the shape is reproduced almost accurately, it is easy to visually identify the target object. Further, in the example shown in FIG. 5D, data obtained by sub-sampling the coding residual with 16 × 16 pixels is added as coded data and sent to the decoding side, and this sub-sampling is performed on the decoding side. This is an example of the case where the decoding is performed based on the data. In this case, 0.13 bit /
The data amount is about pel, that is, the compression rate is 1/63.

[0011]

As described above, if the coding is performed based on the two-dimensional structure of the image data, for example, based on the contour, a high compression rate can be achieved without much deterioration of the visual image quality. It could be encoded.

However, the amount of image data to be handled has rapidly increased due to the development of communication and broadcasting in recent years.
Along with that, there is a demand for image coding with a higher compression rate, and the image compression rate can be changed according to the application based on the fact that the required image quality differs depending on the field of application, for example, the reproduction method. There is a strong desire to do so.

According to the above-mentioned method of encoding the information about the contour, the encoding can be performed at a very high compression rate, but on the other hand, the ratio of the extracted contour portion to the whole image data becomes. Whether it depends on the image. Therefore, when the amount of information that can be transmitted is limited, such as in a videophone, the inconvenience that the transmission time differs for each image occurs.

The present invention has been made in view of the above problems, and an object thereof is an encoding method based on contour information, and an image data encoding apparatus capable of easily changing a compression rate. Is to provide. Another object of the present invention is to construct coded data in a hierarchical manner and allow the receiving side or the decoding side to freely select image data of desired accuracy.

[0015]

In order to achieve the above-mentioned object, a first aspect of the present invention provides an edge data extracting means for extracting edge data of image data, and edge data extracted by the edge data extracting means. In the image encoding device including encoding means for encoding, the edge data extracting means quantizes the pixel value of each pixel of the image data to a predetermined N (N is an integer of 2 or more) level, Quantizing means for calculating a quantized pixel value, and a pixel in image data, in which the quantized pixel value of the pixel is different from the quantized pixel value of an adjacent pixel, is determined to be edge data. And an edge data deciding means for performing the same.

A second aspect of the present invention is the image encoding apparatus according to the first aspect of the present invention, wherein the number of quantization levels N in the quantization means is variable.

According to a third aspect of the present invention, image encoding is provided with edge data extracting means for extracting edge data of image data, and encoding means for encoding the edge data extracted by the edge data extracting means. In the apparatus, the edge data extraction means quantizes the pixel value of each pixel of the image data to a predetermined N (N is an integer of 2 or more) level, and calculates the quantized pixel value. The quantizing means is supplied with J (J is an integer of 2 or more) different numbers N1 to NJ as N, and the J kinds of quantized pixel values are quantized with respect to one image data. And a hierarchical quantization control means to be calculated by the quantization means, wherein the edge data extraction means extracts a plurality of edge data having different degrees of coarseness and fineness from one piece of the image data. An encoding device.

A fourth aspect of the present invention is the image encoding device of the third aspect, wherein the encoding means changes from the coarsest edge data for the N having the smallest value to the denser edge data. Hierarchical coding means for sequentially performing coding and outputting the sequentially coded edge data to the outside;
It is an image coding apparatus characterized by including.

A fifth aspect of the present invention is the image encoding device according to the fourth aspect of the present invention, wherein the hierarchical encoding means already includes the edge data to be output in the already output coarser edge data. If it exists, the image coding apparatus is characterized by coding and outputting only the remaining edge data excluding the already included edge data.

A sixth aspect of the present invention is an image decoding apparatus for decoding image data encoded by the image encoding apparatus according to the fourth or fifth aspect of the present invention, wherein the edge data input first is sequentially An image decoding apparatus comprising: a hierarchical decoding unit that decodes and sequentially decodes low-quality decoded image data to high-quality decoded image data.

A seventh aspect of the present invention is the image decoding apparatus according to the sixth aspect of the present invention, wherein when the layer decoding means limits the decoding time or the information amount of the image to be decoded,
The hierarchical decoding means suspends the decoding when the limit is exceeded during the sequential decoding of the image data, and the latest decoding obtained by the time of the suspension. The image decoding device is characterized by outputting the decoded image data as final decoded image data.

[0022]

The edge data detecting means in the first aspect of the present invention determines that pixels having different quantized pixel values are edge data. Therefore, it is possible to quickly and easily determine whether the data is edge data.

In the second aspect of the present invention, the number of quantization levels N is variable. Therefore, the compression rate can be adjusted according to the quality required for the image data.

The hierarchical quantization control means in the third aspect of the present invention supplies a plurality of quantization level numbers N to the quantization means and extracts a plurality of edge data. Therefore, a plurality of edge data having different degrees of coarseness and fineness can be obtained. Therefore, it is possible to arbitrarily select image data of desired quality according to the application of the image data. In the fourth aspect of the present invention, coarse edge data that is hierarchically encoded is sequentially encoded and output to dense edge data. Therefore, on the decoding side, it is possible to obtain plural kinds of image data in order from low-quality image data to high-quality image data by performing decoding in order from rough edge data.

In the fifth aspect of the present invention, when the edge data to be output is already included in the rough edge data preceding the edge data, the remaining edge data with that portion omitted is decoded. And output. Therefore, it is possible to prevent duplicate data from being encoded and output, and it is possible to reduce the encoding time and the transmission amount.

According to the hierarchical decoding means of the sixth aspect of the present invention, low-quality decoded image data to high-quality decoded image data are sequentially decoded. Therefore, it is possible to arbitrarily select the image data of the required image quality.

The hierarchical decoding means in the seventh invention is
If a certain limit occurs while decoding from low-quality decoded image data to high-quality decoded image data in order, decoding is stopped and the most obtained at that time is obtained. Outputs high quality decoded image data. Therefore, even when the amount of edge data differs for each image, it is possible to decode the image data at regular time intervals or obtain image data of constant quality (constant amount of information). Becomes

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an image coding apparatus and an image decoding apparatus which are preferred embodiments of the present invention. As shown in FIG. 1A, the image data to be encoded is first supplied to the quantizing means 10 and the edge data determining means 12. The quantizing means 10 classifies each pixel value of the input image data into classes based on a certain threshold value, and reduces the types of values that the pixel value can take. For example, the image data is 25
Image data of 6 gradations are often used.
6 gradations are reduced to 4 gradations. Such quantization is useful for detecting edge data in image data. The edge data determination means 12
Observe the pixel value quantized by the quantizing means 10,
A pixel having a pixel value different from the adjacent pixel value in the quantized pixel value is determined to be edge data. That is, in the image coding apparatus according to the present embodiment, it is determined that the portion in which the pixel value greatly changes is the pixel included in the edge data. In this way, the quantizing means 10 reduces the number of gradations and simply selects a pixel whose pixel value is different from the adjacent pixel value, whereby the edge data can be detected very easily. It is possible. In the conventional image coding apparatus, a Laplacian-Gaussian operator or the like has to be used in order to determine whether or not it is edge data as described above, and complicated calculation is required. On the other hand, according to the present embodiment, since it is only necessary to compare the values, it is possible to perform faster image coding.

Further, the quantizing means 10 is also suitable for quantizing to, for example, 2 levels or 8 levels in addition to quantizing to 4 levels. Quantization means 1 in this embodiment
For 0, quantization is performed based on the number of quantization levels N supplied from the hierarchical quantization control means as shown in FIG. Therefore, it is possible to meet each request by setting the quantization level number N to an appropriate value in accordance with the image quality required for the application, the amount of image data information, and the like.

The edge data thus determined is supplied from the edge data determining means 12 to the encoding means 16. The encoding unit 16 has the same configuration as that of the above-described conventional image encoding apparatus, encodes only edge data, and outputs encoded image data.

FIG. 1B is a block diagram showing the configuration of an image decoding apparatus which decodes the coded image data coded as described above and outputs the original image data. The configuration of the image decoding device shown here is almost the same as that of the conventional image decoding device. That is, the encoded image data is first decoded by the decoding means 18, and the original pixel value is obtained. Next, the pixel values within the edge data portion are interpolated and reproduced by the interpolating means 20. For this interpolation, various methods such as linear interpolation and spline interpolation can be used as in the above-described conventional decoding device.

As described above, according to the present embodiment, regarding the extraction of the edge data, each pixel value of the image data to be coded is quantized once, and the edge data is determined based on the quantized pixel value. . Therefore, the edge data can be easily extracted, and the number of quantization levels N is changed, so that the image coding can be performed with desired accuracy.

The hierarchical quantization control means 14 normally supplies one N to one image data, but it is also preferable to apply a plurality of quantization levels N to one image data. . That is, the quantizing means 10 performs quantization based on different quantization levels on one image data. Since edge data is determined based on different quantization in this way, image coding with various precisions is performed. In this case, the encoding means 16 outputs in order from data with coarse encoding precision to data with high encoding precision. As described above, the effect of sequentially outputting encoded data of a plurality of precisions appears when decoding an image. That is, the amount of edge data varies depending on each image data, but in general, it is often desired to keep the data amount for one image data to a constant value. In this way, in order to keep the information amount of the image data constant, it is possible to store the encoded data in order from the coarser precision and terminate the storage of the image data when the predetermined storage area becomes full. By doing so, although the accuracy is slightly different depending on each image data, the information amount for one image data can be set to a constant value, which can contribute to the management of the image data.

In other cases, for example, in a videophone, the number of frame images that can be sent per second is more important than the image quality. Further, in videophones and the like, the capacity of the communication line is generally very limited in many cases. Even in such a case, if the encoded data is output from the coarser precision and then the encoded image data with higher precision is output in order, it is possible to fully utilize the capacity of the communication line and It is possible to keep the number of the cells at a constant value.

Further, in the case where the encoded image data with high accuracy is sequentially transmitted from the encoded image data with high accuracy, the encoded image data with high accuracy, which is the encoded image data with high accuracy, is transmitted. It is preferable not to send the data already contained in. For example, a pixel extracted as edge data when quantized by the number of quantization levels 2 is always edge data when quantized by the number of quantization levels 4, so that it is obtained by the number of quantization levels 2, for example. Coded image data and quantization level number 4
It is preferable not to send the common part (pixels) with the coded image data obtained in step 1 when sending the coded image data obtained with the quantization level number 4. That is, when the encoded image data obtained with the quantization level number 4 is transmitted after the encoded image data obtained with the quantization level number 2 is newly transmitted with the quantization level number 4. Only the encoded image data that has been obtained is transmitted. By adopting such a configuration, it is possible to efficiently encode image data.

Various applications are conceivable for the coded image data hierarchically structured as described above. For example, when the number of pixels of image data is extremely large, the amount of encoded data obtained by encoding the image data may increase. In such a case, it can be considered that the decoding also takes a considerable amount of time. Therefore, it is impossible for the conventional image decoding apparatus to deal with the case where it is necessary to quickly know only the general state of the original image data. However, the image coding apparatus according to the present embodiment,
According to the image decoding apparatus, since the image data with coarse accuracy is first transmitted, it is possible to first inform the operator of the rough appearance of the image. Such applications may be used for inventory of image databases. For example,
It is considered that when searching for the target image data, it is often the case that only the image data representing a simple state is sufficient, not the accurate original image data. Especially when searching for image data, it is considered that the decoding speed is more important than the accuracy of the image data.

Next, how the edge data is extracted according to the present embodiment and how the original image is restored from the edge data will be described with reference to an explanatory photograph. FIG. 2 shows a claire that is often used as a standard image. This image cla
FIG. 3A shows a pixel obtained by quantizing ire with a quantization level number 4 and extracting a pixel whose quantized pixel value is different from the adjacent pixel value. For example, in the example shown in FIG. 3A, the number of pixels extracted as edge data is about 17% of the total number of pixels of image data. That is, the information amount of the image data is reduced to about ⅙ simply by the action of extracting the edge data. Only the pixels of the edge data obtained in this way are coded to generate coded image data. A diagram in which the original image is restored based on the encoded image data obtained in this way is shown in FIG.
It is shown in (b). The image shown in FIG. 3B is obtained by calculating the pixels belonging to the portion other than the edge data by interpolation from the pixel values of the pixels belonging to the edge data, as in the conventional image decoding apparatus described above. There is. As a result, although the gentle color tone and brightness changes are lost,
It can be seen that the shape of the person has been almost completely restored. FIG. 4 shows an example in which the number of quantization levels N is 2. FIG. 4A shows a state of the edge data extracted when the number N of quantization levels is 2. When the quantization level number N is 2, the number of pixels extracted as edge data is about 13% of the total number of pixels of the image data. FIG. 4B shows an example in which the values of pixels other than the edge data are reproduced by interpolation from the edge data extracted in this way to restore the original image. Image quality is shown in Figure 3.
Although deteriorated compared to the example shown in (b),
About the shape, it is reported almost accurately.

As described above, according to the present embodiment, the edge data of the image data can be easily obtained by quantizing each pixel value forming the image data. Therefore, it is possible to quickly extract edge data, and it is possible to obtain an image encoding device that can quickly process a large amount of image data.

Further, by changing the number N of quantization levels, it becomes possible to encode images with various precisions.

Then, hierarchical quantization was performed for various image level numbers N, edge data corresponding to each quantization was extracted, and a plurality of edge data having different degrees of coarseness and fineness were extracted. Then, since the coded image data of coarse precision to the coded image data of high precision are sequentially output, image data of desired precision can be obtained on the decoding side, and communication capacity and decoding time are limited. Even in such cases, it is possible to perform image coding / decoding by effectively utilizing the communication capacity and the decoding time.

Further, when a plurality of edge data having different degrees of coarseness and fineness are extracted and the coded image data thereof is transmitted, the data of high precision and the pixels included in the coarse precision data are also included. If you do not send data when sending highly accurate data, you can use the communication capacity efficiently,
Alternatively, the storage capacity can be efficiently used.

[0043]

As described above, according to the first aspect of the present invention, since the edge data can be easily extracted, there is provided an image coding apparatus capable of coding a large amount of image data quickly. The effect is obtained.

According to the second aspect of the present invention, the number of quantization levels N
Is variable, it is possible to perform image encoding with accuracy according to various uses.

According to the third aspect of the present invention, since one image data is encoded with various precisions, the decoding side can arbitrarily select the encoded image data with desired precision. Is possible.

According to the fourth aspect of the present invention, since the coded image data of coarse precision to the coded image data of high precision are sequentially output to the outside, the decoding side first obtains a rough picture of the image. Therefore, it is possible to sequentially generate image data with high accuracy.

According to the fifth aspect of the present invention, the pixels included in the coded image data with high accuracy and also included in the coded imaged data with coarse accuracy already transmitted previously. Does not send highly accurate image data again. As a result, it is possible to more efficiently generate and send the encoded image data.

According to the sixth aspect of the present invention, an image decoding apparatus for decoding the image data coded by the image coding apparatus described in the fourth or fifth aspect can be obtained. Alternatively, the same effect as the fifth aspect of the present invention can be obtained.

According to the seventh aspect of the present invention, when coded image data of a plurality of precisions are sent in sequence and the decoding time or the image information amount is limited, the limit is fully filled. Since the image can be decoded when it is used, the time or the amount of information can be effectively used.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an image encoding device and an image decoding device according to a preferred embodiment of the present invention.

FIG. 2 is an explanatory photograph showing an original image of the images used in FIGS. 3 and 4.

FIG. 3 is an explanatory photograph showing edge data and an image restored from the edge data when the number of quantization levels N is 4.

FIG. 4 is an explanatory photograph showing edge data obtained when the number of quantization levels N is 2 and an image restored from the edge data.

FIG. 5 is an explanatory photograph showing a state of encoding by a conventional encoding device.

[Explanation of symbols]

10 quantizing means, 12 edge data determining means, 14
Hierarchical quantization control means, 16 encoding means, 18 decoding means, 20 interpolation means.

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[Procedure amendment]

[Submission date] May 11, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an image encoding device and an image decoding device according to a preferred embodiment of the present invention.

FIG. 2 is an explanatory photograph of a halftone image in which an original image of the image used in FIGS. 3 and 4 is displayed on a display .

[Figure 3] Disupu edge data and reconstructed image from the edge data when the number of quantization levels N is 4
It is an explanatory photograph of a halftone image displayed on a ray .

FIG. 4 shows edge data obtained when the number of quantization levels N is 2 and an image restored from this edge data.
It is an explanatory photograph of a halftone image displayed on a display .

[5] The manner of encoding by the conventional encoding device Disconnect
It is an explanatory photograph of a halftone image displayed during play .

[Explanation of Codes] 10 Quantization Means, 12 Edge Data Determining Means, 14
Hierarchical quantization control means, 16 encoding means, 18 decoding means, 20 interpolation means.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H04N 1/411 7/24 H04N 7/13 Z

Claims (7)

[Claims] 1. An edge data extracting means for extracting edge data of image data, and an encoding means for encoding the edge data extracted by the edge data extracting means.
In the image coding apparatus including: the edge data extraction unit quantizes the pixel value of each pixel of the image data into a predetermined N (N is an integer of 2 or more) level, and calculates a quantized pixel value. And a pixel in the image data, in which the quantized pixel value of the pixel is different from the quantized pixel value of an adjacent pixel,
An image coding apparatus comprising: an edge data determining unit that determines that the data is edge data. 2. The image coding apparatus according to claim 1, wherein
An image coding apparatus, wherein the number of quantization levels N in the quantization means is variable. 3. Edge data extracting means for extracting edge data of image data, and encoding means for encoding the edge data extracted by the edge data extracting means.
In the image coding apparatus including the above, the edge data extraction unit sets the pixel value of each pixel of the image data to a predetermined N (N is 2).
Quantizing means for quantizing to an (integer above) level to calculate a quantized pixel value, and J (J is an integer of 2 or more) N different numbers N1 to NJ are supplied to the quantizing means. A hierarchical quantization control means for causing the quantization means to calculate the J kinds of quantized pixel values for one piece of the image data, wherein the edge data extraction means includes one piece of the image data. An image coding apparatus characterized by extracting a plurality of edge data having different degrees of coarseness and fineness. 4. The image coding apparatus according to claim 3,
The encoding means performs encoding in order from the coarsest edge data for the N having the smallest value to more dense edge data,
An image coding apparatus, further comprising: a hierarchical coding unit that outputs edge data coded in order to the outside. 5. The image coding apparatus according to claim 4,
When the edge data to be output is already included in the coarser edge data that has already been output, the hierarchical encoding means only extracts the remaining edge data excluding the already included edge data. An image encoding device characterized by encoding and outputting. 6. An image decoding apparatus for decoding image data coded by the image coding apparatus according to claim 4 or 5, wherein the edge data input first is sequentially decoded to obtain a low quality decoding. An image decoding apparatus, comprising: a hierarchical decoding unit that sequentially decodes encoded image data to high-quality decoded image data. 7. The image decoding apparatus according to claim 6, wherein when the decoding time or the amount of information of an image to be decoded is limited, the hierarchical decoding unit is , While decoding the image data in order, if the above limit is exceeded, the decoding is stopped, and the latest decoded image data obtained by the time An image decoding device characterized by outputting as general decoded image data.