JP2552538B2 - Color image transmission method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a color image transmission method for transmitting a color still image using a communication line such as a subscriber line.

(B) Conventional technology Conventionally, research and development of a system for transmitting image information together with voice using a subscriber line (telephone line) has been actively conducted (for example, IEICE Technical Report IE80-43, pp. 9 to 9). See page 16, "Study on handwritten signal coding method" and IEICE technical report, IE86-14, pages 45 to 52, "Study on video communication using small screen".

Further, there is a video telephone that transmits an image taken by a television camera using a telephone line, as disclosed in, for example, Japanese Patent Laid-Open No. 62-17928. In a conventional videophone using an analog telephone line, the transmitted image is a still image due to the relationship between the transmission characteristic of the line and the amount of information to be transmitted.

Now, in the case of PCM-encoding an image including a halftone, if the halftone has 16 gradations, the density (gradation) is represented by 4 bits. For this reason, methods such as a method of transmitting one pixel with a fixed length of 4 bits, a DPCM coding for obtaining a density difference for coding, and a quasi-variable-length DPCM coding for mixing PCM and DPCM are adopted. It was

When transmitting a color image, the amount of information required is three times as large as when transmitting a halftone (black and white) image. That is, information on three colors of R (red), G (green), and B (blue) is required for each pixel. Therefore, a long communication time is required.

As a method of transmitting a color image, there is a method of transmitting a luminance signal and a color difference signal in a color television, but since it requires a very wide signal transmission band, it is applied to transmission using a telephone line. There wasn't.

(C) Problems to be Solved by the Invention The present invention has been made with the above points in mind, and provides a transmission method for transmitting a color still image in a short time using a communication line such as a telephone line. It is a thing.

(D) Means for Solving the Problems The present invention provides a color image transmission method for transmitting a color image in which one pixel is composed of three pieces of color information of R, G, and B using a communication line. The luminance information of each pixel is calculated from the three color information of R, G, and B, and the luminance information of all the pixels of the color image to be transmitted is transmitted, and then 1 / n (n is 2 or more) of the color image to be transmitted. Natural number) of the pixels, two types of color difference information obtained from the luminance information and the color information are calculated, the two types of color difference information are transmitted, and the receiving side reproduces a monochrome image from the received luminance information. A color image is reproduced by supplementing color information of a pixel in which a color difference signal is missing from the received two types of color difference information and the luminance information to obtain three color information for one pixel. Is.

Further, each of the two types of transmitted color difference information is an average value of n pixels.

(E) Action About half of the image to be transmitted or color difference information of pixels of (n-1) / n is not transmitted, but the color information or color difference of pixels for one screen is compensated for by the lack of pixels on the receiving side. Since the information is obtained, it is sufficient to transmit a smaller amount of information than transmitting three color information per pixel, and the transmission time can be shortened.

(F) Embodiment FIG. 2 is a schematic configuration diagram of a small color still image communication apparatus according to an embodiment of the present invention.

(1) is a color compatible CCD camera that captures a still image, and (3) is a video memory that has a memory corresponding to each color of R, G, B that composes a color image, and 4 bits per pixel for each color Allotted and expressed in 16 gradations for each color.
That is, 4096 colors can be expressed as a color image.

(2) shows a color image captured from the CCD camera (1) for each color information of R, G, B by 4 pixels for each color.
An interface for digitizing into bit values and outputting to the video memory (3), and (4) is a color CRT for synthesizing and displaying the contents of the video memory (3).

Reference numeral (5) is a CPU which controls the whole, and uses a buffer memory (6), and the brightness information and the color difference from the 4-bit data per pixel for each color of R, G, and B read from the video memory (3) are provided for each line. Calculate information.

(7) is a demom for modulating or demodulating transmission image information consisting of luminance information and color difference information calculated by the CPU (5), (8) is a telephone, and the telephone (8)
Input / output of a voice signal and transmission image information for a telephone call is controlled by a network control circuit (9) connected to a telephone line (10) (subscriber line). Reference numeral (11) is a plurality of key switches for issuing operation commands to the CPU (5) such as capturing a color still image by the CCD camera (1) and transmitting a color still image.

That is, the voice signal from the telephone (8) is sent to the telephone line (10) through the network control circuit (9), and the voice signal from the telephone line (10) is sent through the network control circuit (9) to the telephone (8). Is sent to and a call is made.

The information of the color still image captured by the CCD camera (1) is expanded in the video memory (3) and the CRT (4) is displayed.
The transmission image information consisting of luminance information and color difference information is calculated by the CPU (5), and this transmission image information is modulated by the modem (7) and is transmitted via the network control circuit (9) to the telephone line ( Sent to 10).

The transmission image information (luminance information and color difference information) sent from the telephone line (10) is input to the modem (7) via the network control circuit (9), demodulated by the modem (7), and then CPU.
At (5), three pieces of color information for each pixel for one screen are calculated from the transmitted image information, and each color information is developed on the video memory (3) and displayed on the CRT (4).

Next, the first embodiment of the transmission method according to the present invention will be described.
This will be described with reference to the flowcharts in FIGS. here
The color image captured by the CCD camera (1) is R,
PCM consisting of 3 color information of G and B, 4 bits for each color
16 gradations represented by the code are expressed, and 90x 1 screen
It shall consist of 90 pixels.

First, when the telephone line (10) is secured and connected to the receiving side, the image captured by the CCD camera (1) is fixed on the video memory (3) as an image to be transmitted. The image is fixed at a proper timing by pressing a specific key switch (11), and after the image is fixed, the image from the CCD camera (1) is not input to the video memory (3). Then, the CPU (5) is instructed to transmit an image by pressing another specific key switch (11).

The CPU (5) reads the first horizontal 1 line of the video memory (3) and writes it in the buffer memory (6). Each pixel is represented by the three color information of R, G, and B as described above, and the luminance y is represented by y = 0.3R + 0.59R + 0.11B. Therefore, the CPU (5) approximately calculates the luminance information by Y = (3R + 6G + B) / 10 (1). This brightness information Y is also a 4-bit PC
It is represented by the M code. The CPU (5) calculates the luminance information Y at each pixel, and the modem (7) and the network control circuit (9)
Then, the luminance information Y is transmitted to the telephone line (10). After repeating the calculation and transmission of the luminance information of the pixels (90 pixels) for one line, the CPU (5) samples every line of the pixels stored in the buffer memory (6) every other pixel (45 pixel sampling). Luminance information Y
The sampling frequency (band) is
It becomes 1/2), and color difference information is calculated every time sampling is performed.

The color difference information is calculated by ΔR = RY−R = (3R + 6G + B) / 10 (2) ΔB = BY−B = (3R + 6G + B) / 10 (3). The pigment information is also represented by a 4-bit PCM code. Then, the two calculated color difference information ΔR, Δ
B is the same as described above for the modem (7) and network control circuit (9)
Then, it is sent to the telephone line (10). Every other pixel (in this case, an odd number of pixels), calculation and transmission are repeated for one line (45 pixels), and when completed, the second horizontal one line is written from the video memory (3) to the read buffer memory (6). Then, similarly to the above, the calculation and transmission of the luminance information Y for one line (90 pixels) and the calculation and transmission of the color difference information ΔR, ΔB for half the pixels (45 pixels) of one line are performed. Further, the next horizontal 1 line is written in the buffer memory (6), the same process is performed, and when the transmission of the lines for one screen (90 lines) is completed, the transmission of the color image information is completed.

Now, on the receiving side that receives the transmission image information consisting of the luminance information Y and ΔR and ΔB, the luminance information Y of one horizontal line is first displayed.
And the color difference information ΔR and ΔB are received from the telephone line (10) via the network control circuit (9) and the modem (7) and stored in the buffer memory (6) by the CPU (5). And CPU
(5) calculates three color information of R, G, and B by the following formulas for a pixel having luminance information Y and color difference information ΔR and ΔB (that is, odd-numbered pixel), and stores it in the corresponding position of the video memory (3). Write each color information.

R = Y + ΔR (4) B = Y + ΔB (5) G = (10Y-3R-B) / 6 (6) A pixel having only luminance information Y in the buffer memory (6) (that is, an even pixel) is Three color information of R, G, and B are obtained from the color information of the pixels before and after by the formula.

Ri = (R _i-1 + R _{i + 1} ) / 2 (7) Bi = (B _i-1 + B _{i + 1} ) / 2 (8) Gi = (10Yi-3Ri-Bi) / 6 (9) ) However, R _i-1 , B _i-1 is the color information of the pixel immediately before Ri, Bi,
R _{i + 1} and B _{i + 1} are color information of the pixel immediately after Ri and Bi.
For the last pixel (90th pixel), Ri = R _i-1 , Bi
= B _i-1 .

Then, on the receiving side, the CPU (5) supplements the pixels lacking the color difference information with the preceding and following color information and stores three color information of R, G, B for one horizontal line (90 pixels) in the video memory ( Store in 3). Further, color information is similarly obtained for the next one line to be sent, and color information for one pixel (90 × 90 pixels) is established on the video memory (3) by repeating these. On the receiving side, color information is written in the video memory (3) line by line, so the CPU (4)
A color image sequentially received is displayed for each horizontal line from the top.

All values obtained by calculation in UPU (5) are rounded to 4 bits. In addition, Δ as the two color difference information
Although R and ΔB are selected, ΔR, ΔB and ΔG (= G-
Of course, it is possible to select any two of Y) and obtain three color information from the selected two color difference information and luminance information.

FIG. 3 is a flow chart for explaining another embodiment of the method of the present invention.

With the telephone line (10) secured and connected to the receiving side, the color information of the color image captured by the CCD camera (1) is transmitted by the specific key switch of the key switch (11) in the same manner as described above. Video memory as an image (3)
The CPU (5) is instructed to transmit the image. Then, the CPU (5) first displays one screen (90
One line of (90 pixels) is read to the buffer memory (6), the brightness information Y of each pixel is calculated, and the brightness information is sent to the telephone line (10) via the modem (7) and the network control circuit (9). Send Y. When the calculation and transmission of the luminance information Y of pixels for one line (90 pixels) are completed, the CPU (5) reads the next one line into the buffer memory (6) and similarly obtains the luminance information of pixels for one line. Calculate Y and send. Then, by repeating this, the luminance information Y for one screen (90 × 90 pixels) is calculated and transmitted.

Next, the CPU (5) again reads the first one line into the buffer memory (6) and samples every other pixel,
The color difference information ΔR and ΔB are calculated each time sampling is performed, and the telephone line (10) is passed through the modem (7) and the network control circuit (9).
Send to. After the calculation and transmission of the dye information ΔR and ΔB for one line (45 pixels) for every other pixel, the next one line is read to the buffer memory (6), and similarly, for every other pixel, half of the one line is read. The pixel color difference information ΔR and ΔB is calculated and transmitted. Then, by repeating this, the color difference information for one pixel (90 rows) is calculated and transmitted, and the transmission is terminated.

On the receiving side, first, the signal sent from the telephone line (10) is demodulated by the modem (7) and the CPU (5) and combined, and sequentially stored in the video memory (3) line by line as luminance information Y. By writing the luminance information Y into the video memory (3), luminance (black and white) pixels having a halftone are displayed on the CRT (4). By writing the transmitted (received) luminance information Y in the video memory (3) sequentially, CR
Black and white images are displayed in sequence on T (4), resulting in 1
A black and white image of the screen is displayed.

Next, the CPU (5) sends the color difference information ΔR and ΔB sent (received) next to the luminance information Y and the color difference information for each line from the luminance information Y previously received in the same manner as in the above embodiment. With respect to the pixels lacking in pixel number, the color information of the pixels (90 pixels) for one line is obtained while complementing the color information of the pixels before and after, and is written in the video memory (3). Further, the color information (90 pixels) of the line is obtained from the color difference information (45 pixels) of the next line sent and the luminance information of the line previously received, and stored in the video memory (3). Write. Then, by repeating this, color information for one screen (90 × 90 pixels) is obtained, and a color image is displayed on the CRT (4).

In another embodiment (FIG. 3), the CRT on the receiving side is used.
First, a monochrome image is sequentially displayed on one screen, and then the monochrome image is sequentially displayed instead of the color image. Therefore, the receiving side can grasp the entire image of the image to be received earlier than in the previous embodiment (FIG. 1).

In both embodiments, the three color information of R, G, and B is set to 1
To send the entire screen (90 x 90 pixels), 97200 (=
It is necessary to transmit 4 × 90 × 90 × 3) bits, but according to the present invention, 64800 (= 4 × 90 × 90 ÷ 4 × 45 × 90 × 2) bits are sufficient, and the amount of information to be transmitted is 2/3. Decrease to.

4 and 5 are a schematic configuration diagram and a flow chart of a small color still image communication apparatus for explaining an embodiment different from the other embodiments shown in FIG.

4 is different from FIG. 2 in that the color video signal output from the CCD camera (1 ') is converted into a luminance signal and two kinds of color difference signals by the interface (2a'), and these signals are A / D. The point is that the luminance information Y and two types of color difference information (for example, ΔR and ΔB) are digitized by the converter (2b ′) and stored in the video memory (3) for each pixel. Then, the luminance information and the two types of color difference information read from the video memory (3) are respectively D / A converter (12b).
Is converted into an analog value by, and input into the interface (12a) to output a color video signal, and a CRT (4) displays a color image based on the color video signal. In this embodiment, the size of one screen is 16 horizontal.
0 pixels, 100 rows vertically.

With such a configuration, the CPU (5) does not need to calculate the luminance information and the color difference information.

Now, an embodiment of the method of the present invention according to FIG. 5 will be described. Similarly to the above, with the telephone line (10) secured and connected to the receiving side, the brightness of the color image captured by the CCD camera (1 ') by operating a specific key switch of the key switches (11). Information Y and color difference information ΔR, Δ
Fix B to video memory (3).

Further, when the CPU (5) is instructed to transmit the image, the CPU (5) causes the luminance information Y and the color difference information Δ for two lines.
R and ΔB are read from the video memory (3) and written in the buffer memory (6). Then, first, the luminance information Y of the pixels for two lines in the buffer memory (6) is sent to the telephone line (10) via the modem (7) and the network control circuit (9).

Next, the CPU (5) calculates an average value of the color difference information ΔR and ΔB of the two lines stored in the buffer memory (6) at four pixels (two pixels vertically and horizontally) adjacent to each other from the end of the two lines. , Average color difference information (▲ ▼, ▲) for one pixel with respect to four pixels stored in the buffer memory (6).
▼) is sent to the telephone line (10) via the modem (7) and the network control circuit (9). Further, the average color difference information is similarly calculated and transmitted for the next four consecutive pixels. This process is performed for all the pixels of two lines stored in the buffer memory (6). Therefore, the color difference information for two lines is
Compressed to 1/4 and transmitted.

When the processing for the first two lines of the video memory (3) is completed, the two lines following the CPU (5) are stored in the buffer memory (6), and the same processing is performed for these two lines as well. This is repeated until the processing for the image data (160 pixels × 100 rows) for one screen is completed.

On the receiving side that receives the transmission image information consisting of the luminance information Y and the average color difference information ▲ ▼, ▲ ▼, the luminance information Y and the average color difference information ▲ ▼, ▲ ▼ of the horizontal two lines are first displayed.
Telephone line (10) to network control circuit (9) and modem (7)
Is received and stored in the buffer memory (6) by the CPU (5). Then, the CPU (5) sequentially writes the luminance information Y in the buffer memory (6) from a predetermined position of the video memory (3), and the average color difference information ▲ ▼, ▲
▼ Write each to the corresponding 4 pixel positions in the video memory (3). Therefore, in the sent average color difference information of (160 × 2) / 4 pixels, the information of one pixel is allocated to 4 pixels and written to 160 × 2 pixels.

When the writing of the information of the first two lines to the video memory (3) is completed, the same process is performed for the information of the next two lines sent subsequently, and finally one screen (160 pixels × 100 Line) luminance information Y and color difference information ΔR,
ΔB is stored in the video memory (3).

Then, the luminance information Y and the color difference information ΔR and ΔB in the video memory (3) are converted into analog values by the D / A converter (12b), input to the interface (12a), and the CRT (4).
A color image is displayed at.

In the embodiment shown in FIGS. 4 and 5, like the previous embodiment, all the luminance information Y for one screen is transmitted first, and then the color difference information compressed every two lines is transmitted. Is also good.

Further, although the color difference information is compressed to 1/4 in this embodiment, it is not particularly limited to this, and adjacent 2 pixels, 3 pixels, 6 pixels, etc. may be collected as one group,
The amount of color difference information to be compressed (1 / n) varies depending on the number of pixels n (n is an integer of 2 or more) that are grouped together. At this time, an average value is taken as the value of the representative color difference information of the pixels as a group, but it may be determined by so-called sampling which is used as the color difference information of any one pixel.

(G) Effect of the Invention As is apparent from the above description, the present invention sends luminance information and half or 1 / n pixel color difference information, and supplements the missing color information or color difference information on the receiving side for one screen. Information is obtained, color images can be transmitted with a small amount of information,
The transmission time can be shortened.

It is difficult for the human eye to distinguish the difference in color in the fine part of the color image, and if the monitor screen is small, such as about 3 to 5 inches, the color difference information is converted into the luminance information.
Even if the amount of information is 1/2, the image quality is hardly affected.

Further, even if the color information cannot be displayed on the receiving side, it is possible to display a monochrome image by incorporating only the luminance information.

In particular, if the luminance information is transmitted by one screen ahead, it becomes possible for the receiving side to quickly grasp the entire image of the transmitted image.

[Brief description of drawings]

1A and 1B are flowcharts according to an embodiment of the method of the present invention, FIGS. 2 and 4 are schematic configuration diagrams of respectively different small color still image communication devices according to the present invention, and FIGS. 3A and 3B. 5
Figures A and B are flow charts according to different embodiments of the method of the present invention. (1) (1 ') ... CCD camera, (2) (2a') ... interface, (2b ') ... A / D converter, (3) ...
Video memory, (4) ... CRT, (6) ... buffer memory, (7) ... modem, (8) ... telephone, (10) ...
... telephone line, (11) ... key switch, (12a) ... interface, (12b) ... D / A converter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Saito 2-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Hisashi Matsuyama 2-18-3 Keihanhondori, Moriguchi-shi, Osaka Within Yoko Electric Co., Ltd. (56) Reference JP-A-61-230586 (JP, A) JP-A-64-53680 (JP, A)

Claims (2)

(57) [Claims] 1. A color image transmission method for transmitting a color image in which one pixel includes three color information of R, G, B using a communication line, wherein three colors of R, G, B are provided on a transmission side. Calculates the luminance information of each pixel from the information, and after transmitting the luminance information of all pixels of the color image to be transmitted, 1 / n of the color image to be transmitted
Two types of color difference information obtained from the luminance information and the color information in pixels (n is a natural number of 2 or more) are calculated, and the two types of color difference information are transmitted, and the receiving side performs black and white from the received luminance information. After reproducing the image, the color information of the pixel in which the color difference signal is missing is supplemented from the received two types of color difference information and the luminance information to obtain three color information for one pixel, and the color image is reproduced. A color image transmission method characterized by. 2. Each of the two types of color difference information to be transmitted is n.
The color image transmission method according to claim 1, wherein the color image is an average value of pixels.