JPH0722342B2 - Color image coding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an encoding method (hereinafter referred to as an encoding method) for efficiently transmitting a color image.

Here, the target color image is an image in which characters and figures are colored with two or more kinds of colors. Further, the transmission described here includes transmission between different places, that is, communication, and transmission at different times, that is, storage. In addition, the decoding circuit includes a function of decoding the transmitted code and converting it into data that can be displayed or recorded in the display device or the recording device, respectively. A run in the following description is a set of pixels having the same color continuously in the scanning line direction, and a run length (also referred to as a run length) is the number of pixels included in the run. The color run length coding method is a coding method in which a code indicating a run color is added as necessary to a run length code obtained by coding a run length using a modified Huffman code (MH code) or the like. Further, the character encoding method is an encoding method in which a character code uniquely corresponding to each character is assigned, and when a character has a color, a code indicating a color is added to the character code as needed.

FIG. 1 shows a configuration of a conventional color image encoding system in which all the constituent elements of an image are encoded by a single encoding system (for example, color run length encoding system) when encoding a color image. In the block diagram showing an example, (1
1) is a color run length encoding circuit, (12) is a color run length encoding / decoding circuit, and (13) is a memory for storing color image data. An encoding circuit (11) converts the input image data into a color run length code.
A decoding circuit (12) decodes the input color run length code, inversely converts it into the same image data as the image data input to the encoding circuit (11), and outputs it to the memory (13). The memory (13) stores the restored image data and can be displayed on a display device (generally pixel unit).
To read and output.

Further, FIG. 2 is a block diagram showing a conventional configuration example in a color image encoding system using a plurality of encoding systems. In the figure, (21) is a color image encoding circuit, and the circuit (2
In (1), (22) is a character encoding circuit for converting characters into character codes, and (23) is a color run length encoding circuit for converting figures and the like into color run length codes. Further, (24) is a color image decoding circuit, in the circuit (24), (25) is a code identification circuit for identifying whether the code is a character code or a run length code, and (26) is a character code. (27) is a color run length code decoding circuit for decoding a run length code, (28),
(29) is a memory that stores the decoded image data, (3
Reference numeral 0) is an image synthesizing circuit for synthesizing the image data stored in the memories (28) and (29).

Character and graphic data are independently input to the color image encoding circuit (21), the character data is converted into a character code by the character encoding circuit (22), and the graphic data is converted to a color run length encoding circuit (23). ) Is converted into a color run length code. In the color image decoding circuit (24), the input code in which the character code and the color run length code are mixed is
It is divided into a character code and a color run length code in a code identification circuit (25) and output to a character code decoding circuit (26) and a color run length code decoding circuit (27), respectively. The character code and the color run-length code are decoded in the character code decoding circuit (26) and the color run-length code decoding circuit (27), respectively, and stored in the memory (2
8) and the memory (29). The memory (28) and the memory (29) store image data similarly to the memory (13) described with reference to FIG. 1, and output the image data in a format that can be displayed on the display device. Memory (28) and memory (2
9), the priority order for displaying each is set, and the image data output from both memories (28) and (29) is displayed in the image synthesizing circuit (30) according to this priority order, for example, in the memory (28). When the data of the character portion overlaps the graphic data of the memory (29), the character portion is combined and output as image data of one image so that the character portion is preferentially displayed. Further, the connection between the memory (28) and the memory (29) and the character code decoding circuit (26) and the color run length code decoding circuit (27) may be switched. The apparatus configuration of the color image coding system shown in FIG. 2 is an example in which image data is coded by using two coding systems of a character coding system and a color run length coding system. In some cases, a graphics command encoding method that expresses a geometric figure or a texture encoding method that specifies a texture such as dither may be used. Further, not only two encoding methods but also three or more encoding methods are used. There is also. The graphic command encoding system will be briefly described below. Encoding is performed by dividing a figure into geometric figure elements and converting the figure into a code indicating the type, size and position of each geometric figure element. It is a method. For example, a straight line is described by a start point and an end point, and a curve is described by connecting arcs defined by three points of a start point, an end point, and an intermediate point.

The conventional color image coding method has the following drawbacks. That is, in the method of encoding an image using the single encoding method described in FIG. 1, as in the case of encoding an image with many characters using the color run length encoding method, Depending on the type, the transmission efficiency may be low, and if only the character encoding method is used, general graphics cannot be encoded. It cannot be transmitted depending on the encoding method used. An image is produced. Further, in the method using the plurality of encoding methods described in FIG. 2, a plurality of memories are required in the decoding circuit,
Equipment price becomes a problem. Further, in the case of changing a part of the image already transmitted in the figure encoding method used in FIGS. 1 and 2, for example, in the method of encoding in scan line units by the run length encoding method. All scanline information, including image components to be modified, must be encoded, including image components that are not modified. Further, in a coding method such as a graphic command coding method that divides into geometric figure elements and performs coding, even when a complicated figure is configured by superimposing simple figure elements, etc., the conventional method is complicated. Each part of such a figure must be encoded sequentially.

The present invention eliminates the above-mentioned drawbacks of the conventional encoding method, efficiently encodes a color image, reduces the memory capacity of the decoding circuit, and efficiently performs the synthesis of the color image in the decoding circuit. It is an object of the present invention to obtain a color image coding method capable of performing.

In order to achieve the above object, in the encoding method of the present invention, when the information is displayed in the decoding circuit in the information of the image constituent element at the time of encoding, the information indicating the priority order having the possibility of being changed for each image constituent element. Is added. Further, the code of the image constituent element includes the code of the lowest priority color (hereinafter referred to as an invalid color) which does not affect the color of the image data stored in the memory of the decoding circuit. The priority is
For each portion of the image where multiple image components overlap, the image component to be finally displayed is determined to have the highest priority. For example, when an image is composed of a character and a graphic in the background, if the character is given a higher priority than the graphic, the character is displayed without being obscured by the graphic regardless of the order of transmission. For images that change over time, such as simple animations,
The image components of the changing portion may be given high priority.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows that a color image is divided into two types of components, that is, a character and a graphic, the character encoding method and the color run length encoding method are used for the respective encoding methods, and the image data in the display in the decoding circuit is used. 2 is a block diagram showing the configuration of an embodiment in which the priority order is set to two levels and further invalid colors are used. In the figure, (21) is a color image encoding circuit, and in the circuit (21), 22) is a character encoding circuit,
(23) is a color run length encoding circuit. Further, (24) is a color image decoding circuit, in the circuit (24), (25) is a code identification circuit for identifying a character code and a color run length code, (26) is a character code decoding circuit,
(27) is a color run length code composite circuit, (31) is a priority determination circuit for determining priority and combining image data, and (32) is a memory for storing image data in the priority order. In FIG. 3, a color image encoding circuit (2
The character and graphic image data input to 1) are input to the character encoding circuit (22) and the color run length encoding circuit (23) together with priority data. The image data and the priority data input to the character encoding circuit (22) and the color run length encoding circuit (23) are converted into codes to which priority information is added. A character code and a code of mixed color run length codes input to the color image decoding circuit (24) are divided into a character code and a color run length code in the code identification circuit (25), and each of them is a character code decoding circuit (26). And a color run length decoding circuit (27). The character code decoding circuit (26) and the color run length code decoding circuit (27) convert the codes respectively inputted into image data including priority information. Priority decision circuit (3
1) compares the priority of the image data input from the decoding circuits (26) and (27) with the image data stored in the corresponding address in the memory (32), and the image with the higher priority is compared. Select data and store in memory (32). However, the outputs of the decoding circuits (26) and (27) and the memory (32)
When the priority order of the image data is the same, the image data output from the decoding circuits (26) and (27) are stored in the memory (32). Here, the image data stored in the memory (32) is converted into data values such as colors and gradations in pixel units for ease of comparison in the priority determination circuit (31) and ease of display on the display device. The format with priority added.

Next, an example of codes used in the color image encoding circuit (21) and the decoding circuit (24) in FIG. 3 will be described. FIG. 4 (a) is a diagram showing an example of a character code, and FIG. 4 (b) is a diagram showing an example of a color run length code. Character identification code CD and run identification code RD of FIGS. 4 (a) and (b)
Is a code that indicates that a character string and a run length code string follow, respectively.The character identification code CD is the color code of the run length code string.
It can be distinguished from CR, and the run identification code RD can be identified from the color code CS of the character code string. In addition, JIS kanji code etc. are used for the character code, and modified Huffman code (MH code) etc. are used for the run length code. Color code is next character code
It is a code indicating the color and priority of CC and run length code RC. An example of the bit configuration of the color code is shown in FIG. P, R, G, and B in the small rectangle in FIG. 5 (a) indicate priority, red, green, and blue, respectively, so the priority is two levels,
There are 8 colors. In addition, in the reference numeral of FIG.
The code having the bit configuration shown in FIG. 10B is always the lowest priority color, that is, the invalid color code. Here, the effect of the encoding according to the present invention will be described using the examples of images shown in FIGS. 6 and 7. The numbers shown by the leader lines of the components of the images in FIGS. 6 and 7 are the reference numerals of the colors shown in FIG. FIG. 6 (a) is a character image, and FIG. 6 (b) is a graphic image, which are encoded using a character code and a color run length code, respectively.
FIG. 6 (c) is an image in which the images of FIGS. 6 (a) and 6 (b) are decoded and combined in the color image decoding circuit (24) of FIG. The scanning lines m in FIGS. 6B and 6C are scanning lines at the same position, and the scanning line m overlapping the character has a higher priority of the character. Therefore, only the color of the pixel where there is no character is designated. This will result in a relatively long run.
This greatly improves the efficiency of color run length encoding compared to encoding many short runs separated by letters. Further, FIG. 7 is a diagram showing the effect of the invalid color in particular, and FIG. 7 (a) is an image already stored in the memory (32) of FIG. 3, and the image of FIG. 7 (a). The image of FIG. 7 (b) is superimposed on FIG. 7 (c).
This is the case when the image of is obtained. The scan lines n in FIGS. 7B and 7C are scan lines at the same position, and runs other than the triangles on the scan line n in FIG. 7B are invalid color runs. , When the image of FIG. 7 (a) and the image of FIG. 7 (b) are superposed, there is no difference in the colors of the constituent elements of FIG. 7 (a) other than the triangle of FIG. 7 (b). There is no effect.
As described above, the use of the invalid color has an effect that a plurality of images can be easily and efficiently superposed.

In the example described above, the types of image constituent elements of the color image are classified into characters and figures, and the character encoding method is used for the characters and the color run length encoding method is used for the figures. In this case, any encoding method that can be used for encoding a graphic such as a graphic command encoding method or a texture encoding method may be used. In addition, an encoding method used for figures or the like may be used for encoding characters. Further, in FIG. 3, two kinds of methods, that is, a character encoding method and a color run length encoding method are used for encoding the image data, but only one type or three or more types are applied depending on the type of the image constituent element. It is also possible to use the encoding method of. There is a possibility that more complicated images can be efficiently coded by using various kinds of coding methods. Further, by providing the decoding circuit with a plurality of image memories having priorities, more effective images such as simple animation can be efficiently encoded. FIG. 8 shows that the encoding method used for encoding is a graphic command encoding method in addition to the character encoding method and the color run length encoding method, and two image memories are used for the decoding circuit (24). FIG. 3 is a block diagram showing the configuration of an encoding and decoding circuit that is present. The code used here includes information for selecting one of the two memories (32) and (33) as information indicating the priority order, and the decoding circuits (26), (27) and ( The image data decoded in 35) is processed by the priority determination circuit (3
It is output to the memory (32) or the memory (33) according to 1). The image composition circuit (30) composes the image data in the memory (32) and the memory (33) into data that can be displayed by the display device in accordance with the priority order. In the above description, the color priority order and the memory priority order are fixed, but it is also possible to arbitrarily respecify these priority orders by transmitting a special control code,
Further, the priority may be automatically rotated (rotated), so that a more complicated image can be efficiently coded.

The input of the image data to the encoding circuit in FIGS. 3 and 8 is performed for each type of image constituent element.
As shown in FIG. 9, by providing a character / graphic recognition circuit (91) for automatically identifying image constituents of characters and graphics, image data in which character / graphics are mixed can be used as input image data. As a simple example of the character / figure recognition circuit (91) shown in FIG. 9, among input image data, only data having a fixed character shape (font) is recognized by pattern matching as character data, There is a method in which other data from which the character portion is removed is used as graphic data. The character / graphic recognition circuit (91) may be a circuit that executes a recognition method other than the above, such as automatic extraction of geometrical graphic elements. Also, even in the same figure, the code amounts of the color run length coding method and the graphic command coding method are often different. Therefore, as shown in FIG. 8, by adding a circuit for comparing the code amount by the color run length encoding system and the code amount by the graphic command encoding system and selecting a code with a smaller code amount, the code amount can be further increased. Can be reduced. The memories (32) and (33) and the image synthesizing circuit (30) included in the decoding circuit in FIGS. 3 and 8 may be omitted when these are provided in the display device. The memories (32) and (33) shown in FIGS. 3 and 8 are memories that normally store image data on a pixel-by-pixel basis. It may be a memory for storing.

The color code shown in FIG. 5 is 1 bit for priority and 3 for color.
Although it is composed of bits, the bit structure of the color code is
An appropriate bit configuration may be used depending on the type of image to be encoded. Further, the color code may be converted into a non-fixed-length color code according to the appearance frequency of the color. Further, in the above description, the information indicating the priority order is included in the color code, but it may be included in the code indicating the shape of the component, that is, the character code or the run length code, or may be an independent code. In the code string shown in FIG. 4, the character code and the run length code are identified by using the identification code, but the character code and the run length code are made distinguishable, and the identification code is not used. The code input in the code identification circuit (25) of FIG. 3 or 8 may be identified. The color code is added for each character code and run length code in the code string of FIG. 4, but only when the color of the character changes, as in the example of the character code string shown in FIG. A code is added to a character code, or, as in the example of the run length code string shown in FIG. 10 (b), a run without a color code is equal to the color of the previous run. Any code string can be used as long as it is a code string that can clarify the color of the image constituent element such as characters or runs.

As described above, according to the color image encoding method of the present invention, an encoding method suitable for the property of each component of the color image is used, and when the encoding is performed, the information of the image component is decoded. When converting into a signal suitable for display or recording in the circuit, since information indicating the priority order that can be changed for each image constituent element is added, the image constituent elements can be sequentially synthesized and displayed. Can be efficiently encoded.

[Brief description of drawings]

1 and 2 are block diagrams showing the configuration of a conventional color image encoding system, FIG. 3 is a block diagram showing an example of the configuration of a color image encoding system according to the present invention, and FIG. 4 is this invention. FIG. 5 is a diagram showing an example of the code format of the encoding system according to the present invention, FIG. 5 is a diagram showing an example of the configuration of the color code of the encoding system according to the present invention, and FIGS. FIG. 8 is a block diagram showing another example of the device configuration of the color image coding system according to the present invention, and FIG. 9 is a color image code of the color image coding system according to the present invention. FIG. 10 is a block diagram showing another example of the configuration of the encoding circuit, and FIG. 10 is a diagram showing an example of another format of the code string of the encoding method according to the present invention. (11), (21) ... Color image coding circuit, (12), (2
4) ... Color image decoding circuit, (13), (28), (2
9), (32), (33) ... memory, (22) ... character encoding circuit, (23) ... color run length encoding circuit,
(25) ... code identification circuit, (26) ... character code decoding circuit, (27) ... color run length code decoding circuit,
(30) …… Image synthesis circuit, (31) …… Priority level judgment circuit, (34) …… Graphic command coding circuit, (3
5) ... Graphic command code decoding circuit, (36)
...... Character / figure recognition circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-120553 (JP, A) JP-A-56-143486 (JP, A) JP-B-57-33753 (JP, B1)

Claims (2)

[Claims] 1. A color image coding method for coding a color image classified according to the type of image constituent element according to the kind of the image constituent element, wherein information indicating a priority order when displaying or recording by a decoding device is provided. A color image coding method, characterized in that the method is added to the code of the image constituent element. 2. The code of the image constituent element includes a code of the lowest priority color which does not affect the color of other request elements when being displayed or recorded in the decoding device. The color image encoding method according to claim 1.