JPH0744697B2 - Color image transmission device - Google Patents

Description

The present invention relates to a color image displayed on a display device having a frame memory and a color map that outputs RGB values using the contents of the frame memory as address values. In other words, each pixel relates to a color image transmission device that hierarchically transmits a color image having a color map address value, that is, a color number, instead of an RGB value as its pixel value.

[Prior Art] In recent years, image transmission devices have been used as remote monitoring and videophones. In such image transmission,
It is desirable to be able to determine the content of the image to be transmitted at an early stage of transmission, and various hierarchical transmission methods have been studied. The hierarchical transmission method includes (1) a method in which an image having a small number of gradations is first transmitted and then an image having a large number of gradations is gradually updated, and (2) an image having a low spatial resolution is first thinned out. And a pixel having a high spatial resolution by gradually increasing the number of pixels to be transmitted, and (3) a method combining the above two methods.

For example, in the case of a black-and-white image, assuming that 8 bits / pixel, the brightness of each pixel is such that the digital value 0 corresponds to black and 255 corresponds to white, and a linear relationship between the brightness and the digital value between them is established. , The digital value of each pixel is considered to be a binary number and is transmitted in order from the bit plane of the highest bit, so that the hierarchical image transmission device as described in (1) above can be easily configured. Further, the hierarchical image transmission apparatus as described in (2) above can be easily constructed by first thinning out pixels to transmit pixels having a low spatial resolution and gradually increasing the number of pixels to be transmitted to increase the spatial resolution.

On the other hand, in a color image displayed with a limited number of representative colors, since the pixel value of each pixel is the number of the representative color, the above linear relationship does not hold between the pixel value and the representative color. Therefore, even if the representative color is transmitted first and then the image data is transmitted in order from the bit plane of the highest bit as in the case of the monochrome image, a significant image cannot be reproduced stepwise on the receiving side. . Therefore, in a color image transmission apparatus that transmits such a color image, first, pixels are thinned out to transmit an image having a low spatial resolution, and the spatial resolution is gradually increased, thereby enabling hierarchical transmission. Then, when transmitting pixels, color run length coding is performed to reduce redundancy.

Figure 5 shows, for example, Journal of Television Society, Vo1.34, No.3,
Pages 186-193, 1980 "Trends in Image File Coding Systems"
FIG. 11 is a block diagram showing an outline of a conventional color image transmission device using the color run length encoding shown in FIG.

In FIG. 5, (11) is an image memory, and this image memory (11) stores a color image represented by a representative color number. (12) is a representative color storage unit, and this representative color storage unit (1
2) stores the representative colors necessary for displaying a color image. (Five
1) is a run length counting means, and this run length counting means (51) reads each pixel value from the image memory (11) and counts the number of consecutive pixels having the same number.
(52) is an encoding transmission means, and this encoding transmission means (52)
Transmits by reducing the redundancy of the run length data obtained by the run length counting means (51) by entropy coding or the like.

FIG. 6 shows a format of coded data transmitted by the color image transmission device. In the figure, (ID
1) and (ID2) are representative color numbers, and (RL1) and (RL2) are run length encoded data.

FIG. 2 is a specific system configuration diagram of the color image transmission device. In FIG. 2, (21) is a display device, which is a frame memory (22) and a color map (2).
3) and a display (24), and the frame memory (22) and the color map (23) correspond to the image memory (11) and the representative color storage section (12) of FIG. 5, respectively. The color map (23) is hardware that generates RGB values using the contents of the frame memory (22) as address values. Reference numeral (25) is a CPU, which executes run-length encoding according to a control program stored in a memory (26) and transmits encoded data from a communication port (27).

FIG. 7 is an explanatory diagram for the case of transmitting encoded data hierarchically. As shown in FIG. 7, the image is divided into square regions of NxN pixels, first the pixel at the position 1 is transmitted, then A few
By increasing the number of pixels to be transmitted in such a manner, an image with a higher spatial resolution can be obtained on the receiving side. This can be realized by controlling the address value of the pixel read by the run length counting means (51).

As described above, the conventional color image transmission device transmits the representative color and the run length encoded data. In addition, hierarchical transmission is performed by gradually increasing the spatial resolution.

[Problems to be Solved by the Invention] In the conventional color image transmission device as described above, it is possible to perform hierarchical transmission by gradually increasing the spatial resolution by thinning out the pixels and transmitting. However, since the value of each pixel is the number of the representative color and there is no linear relationship between the value and the representative color, the hierarchical transmission in which the number of gradations, that is, the types of colors gradually increases It is not possible to perform hierarchical transmission in which the spatial resolution and the number of gradations gradually increase.

The present invention was made to solve the above problems, and in the transmission of a color image represented by a limited number of representative colors, that is, a color image having a representative color number as a pixel value, An object of the present invention is to provide a color image transmission device capable of performing hierarchical transmission with respect to spatial resolution and number of gradations.

[Means for Solving the Problems] In the color image transmission device according to the present invention, the representative color is divided into a plurality of representative color groups according to the characteristic amount calculated by the characteristic amount calculating unit for calculating the characteristic amount of the representative color. Hierarchization means for giving a tree-like hierarchical structure between the representative color groups by repeatedly dividing, characteristic color creating means for creating characteristic colors representative of the representative groups of each layer, Hierarchical transmission means for transmitting hierarchical information created from the characteristic color of the representative color group to which it belongs and the number of the representative color group to which each pixel of the color image belongs in order from the highest hierarchy of the tree-like hierarchical structure is provided. It is characterized by

[Operation] According to the present invention, the characteristic amount calculating means calculates the characteristic amount of the representative color, and the hierarchizing means divides the representative color into a plurality of representative color groups according to the calculated characteristic amount, and this division is performed. By repeating the above, a hierarchical structure is given between these representative color groups. Then, the characteristic color creating means creates a characteristic color representative of each representative color group of each hierarchy, and the hierarchical transmission means comprises, for each hierarchy, the characteristic color of that hierarchy and the number of the representative color group to which each pixel belongs. Hierarchical information is created and this hierarchical information is transmitted in order from the highest hierarchy.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the outline of a color image transmission device according to an embodiment of the present invention, and FIG. 2 is a concrete system diagram thereof.

In FIG. 1, (11) is an image memory, and this image memory (11) stores a color image represented by a representative color number. (12) is a representative color storage unit, and this representative color storage unit (1
2) stores the representative colors necessary for displaying a color image. Here, the representative colors are numbered starting from 0,
This number corresponds to the number stored in the image memory (11). (13) is a characteristic amount calculation means, and the characteristic amount calculation means (13) calculates the characteristic amount for each representative color stored in the representative color storage section (12). As the feature amount, (a) luminance information L = 0.3R + 0.59G + 0.11B (b) color information (c) occurrence frequency of representative color, etc., and an amount obtained by combining these are considered.

Reference numeral (14) is a layering means, and the layering means (14) divides the representative color into a plurality of representative color groups according to the characteristic amount, and further repeats this division to form a hierarchical structure in the representative color group. give. For example, when the luminance information is used as the feature amount, the layering means (14) divides the representative color into a high-luminance group and a low-luminance group so that the number of representative colors in each representative color group is equal to each other, and each representative color is further divided. By repeating the division of the group into the high-luminance group and the low-luminance group, the division is continued until each representative color group finally becomes one representative color.

FIG. 3 shows the hierarchical structure between the representative color groups in a tree shape. In FIG. 3, each node has a number (0/1) representing the representative color group of each hierarchy and the characteristic color (C
10-C37) is given. The leaf at the bottom corresponds to the lowest layer, each representative color group consists of one representative color, and characteristic color = representative color (C30 to C37). For example, in the second layer, the representative colors are divided into four groups, and each representative color group is given a number (0/1). In this way, each representative color group is assigned a number based on the group division on the upper layer.

Next, the characteristic color of each representative color group
Calculated according to 5). For the characteristic color, (a) an arbitrary representative color belonging to each group is used as the characteristic color.

(B) When the occurrence frequency of each representative color can be used as the characteristic amount, the representative color having the highest occurrence frequency in each group or the average value of the representative colors is selected as the characteristic color.

Etc. And hierarchical transmission means (16)
Transmits the information of each pixel according to the hierarchical structure of the representative color group.

FIG. 4 shows the format of the encoded data transmitted by the hierarchical transmission means (16). That is, first, for the first layer, the characteristic color of each representative color group and the number of the representative color group to which each pixel belongs, that is, the number given to the node of the tree are transmitted, and subsequently, similar information is transmitted to the second layer.
The layers are transmitted in the order of the third layer.

The system configuration diagram in Fig. 2 is the same as that of the conventional example.
5) is the calculation of the characteristic amount of the representative color according to the control program stored in the memory (26), the hierarchization of the representative color group,
Each process of creating a characteristic color of each representative color group and hierarchical transmission is performed.

In the color image transmission device configured as described above,
Upon receiving the information of the i-th layer, the receiving side can reproduce the image using the characteristic color of the i-th layer, and when receiving the information of the lowest layer, the same image as the transmitting side can be reproduced. At this time, on the receiving side, it is possible to reproduce an image in which the number of colors gradually increases, which is impossible in the conventional color image transmission device. Further, in the transmission in which the spatial resolution is gradually increased, the pixels are first thinned out and transmitted according to the sampling pattern as shown in FIG. Good. However, the order of thinning and transmitting the pixels is not limited to the sampling pattern of FIG. 7, and any sampling pattern can be used. This can be easily realized by controlling the address of the pixel read from the image memory by the hierarchical transmission means. Furthermore, since the information transmitted by the hierarchical transmission means includes redundancy as in a normal image, the amount of data can be reduced by the encoding process for removing the redundancy.

[Effects of the Invention] As described above, according to the present invention, in a color image displayed with a limited number of representative colors, the representative colors are divided into representative color groups, and a tree-like pattern is formed between the representative color groups. Since the hierarchical structure is provided, there is an effect that it is possible to perform the hierarchical transmission of the color image according to this hierarchical structure, and in particular, the image reproduction in which the types of colors gradually increase on the receiving side.

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a color image transmission apparatus according to an embodiment of the present invention, FIG. 2 is a system configuration diagram thereof, FIG. 3 is a diagram explaining a hierarchical structure of a representative color group, and FIG. Is a format of encoded data, and FIG. 5 is a block diagram showing the outline of a conventional color image transmission device.
FIG. 6 is a coded data format for color run length coding, and FIG. 7 is a diagram for explaining a sampling pattern. (13) …… Feature amount calculation means, (14) …… Hierarchization means,
(15) …… Character color creation means, (16) …… Hierarchical transmission means. The same reference numerals in each drawing indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A device for transmitting a color image displayed with a limited number of representative colors, wherein a characteristic amount calculating means for calculating a characteristic amount of the representative color and a plurality of representative colors are provided according to the characteristic amount. Hierarchization means for giving a tree-like hierarchical structure between representative color groups by repeating division into representative color groups and dividing each of the divided representative color groups into a plurality of representative color groups; A hierarchy composed of a characteristic color creating means for creating a characteristic color representative of a representative color group, a characteristic color of a representative color group belonging to each hierarchy and a representative color group number to which each pixel of a color image belongs, for each hierarchy. A color image transmission apparatus comprising: a hierarchical transmission means for creating information and transmitting the hierarchical information in order from the uppermost layer of a tree-like hierarchical structure.