JP3205370B2 - Color image signal encoding device and decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image signal encoding apparatus and a decoding apparatus for encoding a color image in the form of a luminance signal and a color difference signal with high efficiency, and for decoding the encoded signal. About.

SUMMARY OF THE INVENTION The present invention relates to an apparatus for encoding a color image signal with high efficiency, a method for directly encoding a color difference signal, and a method for converting a color difference signal into a chromaticity corresponding to a color chromaticity on a one-to-one basis. By adaptively switching between a signal conversion method and a coding method according to an image, highly efficient and high-quality coding can be performed. Also, the signal encoded in this way is decoded with high efficiency.

[0003]

2. Description of the Related Art As one of band compression methods for a color television signal, a conventional RGB primary color signal is converted into a luminance signal and a RGB signal.
A method of converting the color signals into two color signals and transmitting the color signals while limiting the color signals to a narrow band is often used.

For example, in a studio standard, 4: 2:
Two systems are standardized.

At this time, the color signals include RY, B-
A color difference signal such as Y is used, and (R) is set so that the color signal directly corresponds to the chromaticity (hue, saturation) of the subject.
A method has also been proposed in which a chromaticity signal representing chromaticity such as -Y) / Y or (BY) / Y is used as a transmission color signal ("Color Television" edited by NHK, p. 199, Nippon Broadcasting Corporation). Association, 1961).

[0006]

By the way, the required band of the chromaticity information of the image is "1" compared to the luminance from the viewpoint of human vision.
/ 5 "or less.

However, in the chrominance signal which is widely used at present, the chromaticity of the object does not directly correspond to the signal value. Therefore, in order to maintain high image quality, "1/1" of the luminance signal band is required.
3 "or more is required.

In view of the above, the chromaticity signal described above has been proposed, but a divide signal is required to generate the chromaticity signal, and the analog circuit is unstable.

[0009] However, although such technical problems can be solved by digital technology developed in recent years, actual experiments have revealed that another problem is the chromaticity signal (RY) / Y, Since it is necessary to multiply the chrominance signal by the luminance signal in the process of restoring (BY) / Y to the three primary color signals on the image receiving side, the ringing of the filter for band-limiting the chromaticity signal is high in the luminance. It has been found that the image is amplified in the portion and the image quality greatly deteriorates in the received image.

[0010] For the same reason, quantization errors and noise in the transmission path are also amplified, and the image quality also deteriorates.

On the other hand, at present, in institutions such as JPEG and MPEG, regarding the coding of color images, a method using both motion compensation of a luminance signal and a color difference signal and discrete cosine transform (hereinafter, this method is referred to as “ An encoding scheme has been proposed in which each is encoded by a technique such as the "MC + DCT" scheme) and the signal obtained by these processes is adaptively quantized in accordance with the transmission capacity.

In this case, a high efficiency image coding apparatus employing such a method requires a high compression rate and high image quality. Therefore, in the coding of a color image, the coding efficiency of a color image is higher than that of a luminance signal due to the visual characteristics. A high information compression rate is applied to the color signal.

As a color signal, a color difference signal is usually used. However, in the case of an image having high saturation such as a fine vertical pattern and having many high-frequency components, compressing the information of the color difference signal deteriorates the image quality. Would.

Therefore, in such an image, there is a problem that either the compression ratio or the image quality is sacrificed.

In view of the above circumstances, the present invention encodes a color difference signal and a chromaticity signal of an image, and adaptively selects and outputs a signal having a smaller amount of information, thereby achieving higher image quality.
In addition, a high color information compression rate can be realized, and thereby a high-quality color image can be transmitted with a smaller amount of information, and when the transmission capacity is constant, a larger amount of information is converted into a luminance signal. It is an object of the present invention to provide a color image signal encoding device and a decoding device that can achieve high image quality of an image to be distributed and transmitted.

[0016]

According to the present invention, a color image is represented by a luminance signal and a chrominance signal, and the luminance signal and the chrominance signal are encoded respectively. What is claimed is: 1. A color image signal encoding apparatus for transmitting, comprising: a chrominance signal encoding circuit for directly encoding said chrominance signal; and a chrominance signal for converting said chrominance signal into a chromaticity signal corresponding to the chromaticity of color on a one-to-one basis. A chromaticity signal generating circuit, a chromaticity signal encoding circuit for encoding a chromaticity signal output from the chromaticity signal generating circuit, an information amount of the signal output from the chromaticity signal encoding circuit, and the chrominance signal. A switching control circuit that compares the information amount of the signal output from the encoding circuit and selects the signal with the smaller information amount, and captures the signal selected by the switching control circuit and the encoded luminance signal To generate a composite code signal It is characterized in that it comprises a multiplexing processing unit. According to a second aspect, in the color image signal encoding apparatus according to the first aspect, the chromaticity signal generation circuit generates an output signal proportional to the magnitude of the luminance signal when the luminance signal is small, and the luminance signal is A non-linear level conversion circuit that generates an output signal having a characteristic that the output signal is saturated when it is large, and a division circuit that generates the chromaticity signal by dividing the color difference signal by the output signal output from the non-linear level conversion circuit. It is characterized by having. According to a third aspect of the present invention, in the color image signal encoding apparatus according to the second aspect, the nonlinear level conversion circuit generates two output signals having independent characteristics with respect to the two color difference signals. According to a fourth aspect of the present invention, a color image is represented by a luminance signal and a color signal composed of either a color difference signal or a chromaticity signal, and a composite code signal in which the luminance signal and the chrominance signal are respectively encoded is received and decoded. A color image signal decoding device for separating a received composite code signal into a compressed luminance signal, a compressed color signal, and an identification signal for identifying whether the color signal is a color difference signal or a chromaticity signal. A separating circuit that generates a luminance signal from the separated compressed luminance signal; a color signal decoding circuit that decodes a color signal from the separated compressed color signal; and a color difference signal from the decoded color signal A color difference signal restoring circuit for restoring the color signal, and selecting a color difference signal output from the color signal decoding circuit when the color signal decoding circuit outputs the color difference signal based on the identification signal, It is characterized in that a changeover switch for selecting the color difference signal output from the color-difference signal recovery circuit when the chromaticity signal is outputted from. According to a fifth aspect of the present invention, in the color image signal decoding device according to the fourth aspect, when the luminance signal is small, the color difference signal restoration circuit generates an output signal proportional to the magnitude of the luminance signal, and the luminance signal is large. A nonlinear level conversion circuit for generating an output signal having a characteristic that the output signal is sometimes saturated; and a multiplication circuit for multiplying the output signal output from the non-linear level conversion circuit by the color signal to generate a color difference signal. It is characterized by: According to a sixth aspect of the present invention, in the color image signal decoding apparatus according to the fifth aspect, the nonlinear level conversion circuit generates two output signals having independent characteristics for two color difference signals.

[0017]

In the color image signal encoding apparatus according to any one of claims 1 to 3, the chrominance signal encoding circuit directly encodes the chrominance signal, and the chromaticity signal generation circuit includes:
The color difference signal is converted into a chromaticity signal corresponding to the chromaticity of a color on a one-to-one basis. In the chromaticity signal encoding circuit, after the chromaticity signal output from the chromaticity signal generation circuit is encoded, the information amount of the signal output from the chromaticity signal encoding circuit by the switching control circuit and the color difference The information amount of the signal output from the signal encoding circuit is compared, and a signal having a smaller information amount is selected based on the comparison result. The multiplexing processing section takes in the signal selected by the switching control circuit, generates a composite code signal, and transmits the composite code signal. Further, in the color image signal decoding apparatus according to any one of claims 4 to 6, the separating circuit separates the received composite code signal into a compressed luminance signal, a compressed chrominance signal, and a color difference signal or a chromaticity signal. And an identification signal for identifying whether the signal is a signal. The luminance signal decoding unit generates a luminance signal from the separated compressed luminance signal, the chrominance signal decoding circuit decodes the chrominance signal from the separated compressed chrominance signal, and the chrominance signal restoration circuit decodes the chrominance signal from the decoded chrominance signal. The color difference signal is restored. By switching the changeover switch based on the identification signal, the color difference signal output from the color signal decoding circuit is selected when the color difference signal is output from the color signal decoding circuit, while the color difference signal is output from the color signal decoding circuit. When the degree signal is being output, the color difference signal output from the color difference signal restoration circuit is selected.

[0018]

FIG. 1 is a block diagram showing an example of a television system to which an embodiment of a color image signal encoding apparatus and a decoding apparatus according to the present invention is applied.

The television system shown in FIG. 1 includes a color image encoding device 1 provided on the image transmitting side and a color image decoding device 2 provided on the image receiving side, and a luminance signal obtained by a television camera or the like. Y and the color difference signal R−
Y and BY are fetched to generate a composite code signal, which is supplied to the color image decoding device 2 and the luminance signal Y and
The color difference signals RY and BY are decoded.

As shown in FIG. 2, the color image encoding apparatus 1 includes a luminance signal compression processing unit 3, a color difference signal compression processing unit 4, a multiplex processing unit 5, and a quantization control circuit 6, The signal Y and the color difference signals RY and BY are fetched and individually compressed, multiplexed to generate a composite code signal, and transmitted to the transmission path 7.

When the luminance signal Y is inputted, the luminance signal compression processing section 3 applies M to the luminance signal Y in block units.
A luminance signal encoding circuit 10 for generating a signal Y _S by performing image compression processing of the C + DCT method;
The signal Y output from the luminance signal encoding circuit 10 at a quantization scale based on the quantization control signal output from
Variable quantization circuit 1 for generating a signal Y _S Q quantizes the _S
When the luminance signal Y is input, the luminance signal Y is subjected to image compression processing of the MC + DCT method in block units to compress the luminance signal Y, and the quantization control circuit 6 a signal Y _S obtained by the compression process in the quantization scale based on the quantization control signal output to produce a signal Y _S Q quantizes from, and supplies it to the multiplexing processing unit 5.

Further, the color difference signal compression processing section 4 outputs the color difference signal R
-Y and BY are input, the color difference signals RY,
A color difference signal encoding circuit 12 which generates a signal CM _S performs image compression processing MC + DCT scheme in block units for B-Y, has a non-linear level conversion circuit 13 and the two division circuits 14 and 15, A chromaticity signal generating circuit 16 for generating chromaticity signals p and q by dividing the chrominance signals RY and BY by a signal obtained by performing a nonlinear level conversion on the luminance signal Y as shown in the following equation: When a chroma signal encoding circuit 17 for generating an image compression process performs signal CC _S of MC + DCT scheme in blocks on the signal output from the chrominance signal generating circuit 16, the chroma signal coding select who information amount is compared with the signal CM _S output signal CC _S output from the circuit 17 from the color difference signal encoding circuit 12 is small, the switch control signal and the identification signal on the basis of the selection result And generate A switching control circuit 18, the signal CC _S output from the signal CM _S or the chromaticity signal coding circuit 17 is output from the color difference signal encoding circuit 12 in response to the switch control signal output from the switching circuit 18
Output from the selector switch 19 in either the select the selector switch 19 to output as signal C _S, quantization scale based on the quantization control signal output from the quantization control circuit 6 the signal C _S and a variable quantizer circuit 20 for generating a signal C _S Q quantizes.

P = (RY) / F (Y) (1) q = (BY) / F (Y) (2) Then, the color difference signals RY and BY are input. At this time, the color difference signals RY and BY
+ With DCT scheme performs image compression processing for generating a signal CM _S, the color difference signals R-Y, it converts the B-Y chrominance signal p, the q, blocks with respect to the chromaticity signal p, q Performs the image compression processing of the MC + DCT method to apply the signal C
_CS is generated, and one of the signals CM _S and CC _S having a smaller amount of information is selected. This selection is made, for example, for each block or for each field. Then, the signal C _S obtained by the selection processing is quantized on a quantization scale based on the quantization control signal output from the quantization control circuit 6 to generate a signal C _S Q, which is multiplexed. Supply to section 5. The above-described nonlinear level conversion circuit 13 will be described later in detail.

[0024] multiplexing processing unit 5 format of the transmission path and a signal C _S Q and identification signal output from the signal Y _S Q and the color difference signal compression processing unit 4 output from said luminance signal compression processor 3 A multiplexing circuit 21 for multiplexing in a matching format
And a buffer for temporarily storing the signal output from the multiplexing circuit 21 and transmitting the stored signal onto the transmission path 7 in accordance with the transmission control signal output from the quantization control circuit 6. And a multiplexing circuit for multiplexing the signal Y _S Q output from the luminance signal compression processing section 3, the signal C _S Q output from the color difference signal compression processing section 4, and the identification signal to provide a buffer circuit. After temporarily storing the stored signal in the transmission control circuit 22, the stored signal is transmitted to the transmission path 7 as a composite code signal based on the transmission signal output from the quantization control circuit 6.

The quantization control circuit 6 takes in the signal output from the multiplexing circuit 21 and calculates the information amount of the signal. When the information amount matches the transmission capacity of the transmission line 7, A transmission signal is generated, and the composite code signal is sequentially transmitted from the buffer circuit 22. When the information amount of the signal does not match the transmission capacity of the transmission path 7, the value of the quantization control signal is switched so that the quantization of the variable quantization circuit 11 provided in the luminance signal compression processing unit 3 is performed. The multiplexing circuit 2 controls the scale and the quantization scale of the variable quantization circuit 20 provided in the color difference signal compression processing unit 4.
The information amount of the signal output from 1 is matched with the transmission capacity of the transmission path 7.

Accordingly, if the information amount of the signal output from the multiplexing circuit 21 exceeds the transmission capacity of the transmission line 7, the quantization scale of each of the variable quantization circuits 11 and 20 is coarsened, If the amount of information of the signal output from the multiplexing circuit 21 is smaller than the transmission capacity of the transmission line 7, the quantization scale of each of the variable quantization circuits 11 and 20 is reduced, and the quantization The information amount is calculated again for the signal whose multiplexing scale has been changed, and the information amount of the signal output from the multiplexing circuit 21 matches the transmission capacity of the transmission path 7.

Next, the above-described nonlinear level conversion circuit 13
Will be described in detail.

First, the nonlinear level conversion circuit 13 has the characteristics shown in FIG. This figure shows two characteristics F
Examples of ₀ (Y) and F ₁ (Y) are shown.

The first characteristic F ₀ (Y) has a characteristic shown by the following equation.

F ₀ (Y) = Y + d (3) Therefore, when this characteristic F ₀ (Y) is used, the chromaticity signals p and q are expressed as follows: p = (R−Y) / (Y + d) (4) ) Q = (B−Y) / (Y + d) (5) In this case, “d” is an offset value for preventing the denominator from becoming zero and the chromaticity signals p and q from diverging.
Usually, it is set as shown in the following equation.

1 >> d (6) Therefore, the above equations (4) and (5) can be approximated as shown by the following equations. As is apparent from equations (7) and (8), Equations (4) and (5) represent the chromaticity of the color and 1
Corresponds to one.

P = (R−Y) / Y (7) q = (B−Y) / Y (8) Therefore, in the following description, it is treated as “d = 0”.

Here, assuming that an image is composed of fine stripes of any two colors and that the level of the three primary color signals for these stripes changes sinusoidally between the two colors, the three primary color signals are expressed by the following equation. Value.

[0034]

(Equation 1) Then, the luminance signal Y for the image signal represented by the equation (9) has a value represented by the following equation.

Y = Y ₀ + Y ₁ · cos (2πf ₁ t) (10) In this case, the variable “Y ₀ ” used in the equation (10),
“Y ₁ ” is a value represented by the following equation.

Y ₀ = m ₁₁ R ₀ + m ₁₂ G ₀ + m ₁₃ B ₀ (11) Y ₁ = m ₁₁ R ₁ + m ₁₂ G ₁ + m ₁₃ B ₁ (12) The constants “m ₁₁ ”, “m ₁₂ ”, and “m ₁₃ ” used in equation (12) are conversion coefficients from the three primary color signals RGB to the luminance signal Y, and are system parameters determined by the three primary colors unique to the image system. It is.

At this time, when the signal p is obtained with "d = 0", the following equation is obtained: p = R _C / (Y ₀ + Y ₁ · cos (2πf ₁ t)) + ζ _R (13) In this case, the variables “ _RC ” and “、 _R ” used in the equation (13) have the values shown in the following equation.

[0038] _{R C = R 0 - (R} 1 / Y 1) · Y 0 ... (14) ζ R = (R 1 -Y 1) / Y 1 ... (15) Then, as shown in (13) The following equation is obtained by Fourier series expansion of the signal p.

[0039]

(Equation 2) Here, since the signal p is an even function and b _k = 0 (17), the following equation is obtained by substituting the equation (17) into the equation (16) and rearranging the equation.

[0040]

(Equation 3) The coefficient used in the equation (18) "a _0/2",
“ _Ak ” takes a value represented by the following equation.

[0041]

(Equation 4) Then, in this equation (20), when the value shown in the following equation, | R _C | (21) or the value shown in the following equation is small,

(Equation 5) Since the value of the coefficient “| a _k |” also becomes small, the high-frequency component of the signal p can be reduced, and extremely efficient encoding can be performed without deteriorating the image quality.

Thus, in the case of a stripe in which only one color changes in luminance, for example, a single-color stripe such as a sweater stripe of a red thread, the following equation is established: R ₁ / R ₀ = G ₁ / G ₀ = B ₁ / B ₀ = (constant) (23) As a result, R _C = 0 (24), and a _k = 0 (25).

Therefore, as the signal p, the DC component “a”
It is sufficient to transmit only " ₀ ".

However, as is apparent from the above equation (20), if the value shown in the above equation (21) or (22) is large, the value of the coefficient “| _ak |” also becomes large. Although it is disadvantageous in terms of information compression, the switching control circuit 18 outputs the information amount of the signal CMS output from the chrominance signal encoding circuit 12 and the signal CC _S output from the chromaticity signal encoding circuit 17. _Since the information amount of _S is compared with the information amount of _S to select the smaller one, the optimal encoding method suitable for each image is adaptively selected.

The color image decoding apparatus includes a separating circuit 25, a luminance signal decoding unit 26, and a color difference signal decoding unit 27 as shown in FIG. After the signal is fetched and separated into a signal Y _S Q, a signal C _S Q and an identification signal, the signal Y _S Q is processed by the luminance signal decoding unit 26 and the luminance signal Y
And the color difference signal decoding unit 27 processes the signal C _S Q and the identification signal to process the color difference signals RY,
Decode BY.

[0046] When the composite code signal separating circuit 25 via the transmission path 7 is supplied, and the identification signal the composite code signal, and the signal Y _S Q, and separated into the signal C _S Q This separation The signal Y _S Q obtained by the processing is supplied to the luminance decoding unit 26, and the signal C _S Q and the identification signal are supplied to the color difference signal decoding unit 27.

The luminance signal decoding section 26 takes in the signal Y _SQ output from the separation circuit 25 and variably expands the signal Y _SQ , and blocks the signal Y _S obtained by the variable expansion processing. and a luminance signal decoding circuit 31 which decodes the luminance signal Y by performing image decoding processing of MC + DCT scheme in the unit, it takes in the signal Y _S Q output from the separation circuit 25 as well as a variable extension, The signal Y _S obtained by the variable decompression processing is subjected to image decoding processing of the MC + DCT method in block units to generate a luminance signal Y.

The chrominance signal decoding unit 27 takes in the signal C _SQ output from the separation circuit 25 and variably expands the signal C SQ, and includes the signal C SQ in the identification signal output from the separation circuit 25. It said variable extension chrominance signal by performing image decoding processing MC + DCT scheme in blocks the obtained signal C _S by treatment R-Y, B-Y or chrominance signals p, decodes the q based on the parameter Color signal decoding circuit 33 and one nonlinear level conversion circuit 3
And two multiplication circuits 35 and 36. The multiplication circuit 35 multiplies the luminance signal Y output from the luminance signal decoding unit 26 and the chromaticity signals p and q obtained by the chrominance signal decoding processing to obtain a chrominance signal R. -Y, BY restoration signal 37
And the color difference signals RY, BY from the color signal decoding circuit 33 based on the identification signal output from the separation circuit 25.
Is selected, the chrominance signals RY and BY output from the chrominance signal decoding circuit 33 are selected. When the chrominance signal is output from the chrominance signal restoration circuit 37, the chrominance signals are output. Two changeover switches 3 for selecting the color difference signals RY and BY output from the signal restoration circuit 37
8, 39.

After the signal C _SQ output from the separation circuit 25 is variably expanded, the signal C _S obtained by the variable expansion processing is MC + DC
The chrominance signals p and q and the chrominance signals RY and BY are decoded by performing a T-system color signal decoding process, and the luminance signal Y output from the luminance signal decoding unit 26 and the chrominance signal decoding process are performed. Are multiplied by the chromaticity signals p and q obtained by the above to restore the color difference signals RY and BY.

In parallel with this operation, the separation circuit 2
5 based on the identification signal output from
When the color difference signals RY and BY are output from the color signal decoding circuit 33 by switching between the color signal decoding circuits 33 and 39, the color difference signals RY and B- output from the color signal decoding circuit 33 are output.
When the chrominance signal is output from the chrominance signal restoring circuit 37, the chrominance signals RY and B- are output from the chrominance signal restoring circuit 37.
Select Y and output this.

[0051] In this way, this embodiment, color difference signals R-Y, the B-Y and the amount of information obtained signal CM _S "MC + DCT" and compressed in a manner, the luminance signal Y and the non-linear level conversion The obtained signals are used as the color difference signals RY and BY.
, The chromaticity signal pq obtained by dividing by “MC + DCT”
Compares the information amount of the signal obtained CC _S is compressed in a manner, to generate a signal C _S Q and variable quantizer by selecting it is small amount of information on the basis of the comparison result, the luminance signal Y Is compressed by the "MC + DCT" method, and the obtained signal Y _S is variably quantized and multiplexed with the signal C _SQ , thereby generating a composite code signal and transmitting it on the transmission line 7. Higher image quality and a higher color information compression ratio can be realized, thereby enabling transmission of a high quality color image with a smaller amount of information, and more information when the transmission capacity is constant. By assigning the amount to the luminance signal Y, it is possible to achieve higher image quality of the transmitted image.

In the embodiment described above, the characteristic "F ₀ (Y)" shown in FIG. 3 is used, but another characteristic "F ₁ (Y)" is used. May be.

The characteristic “F ₁ (Y)” is the characteristic “F
₀ (Y) "to prevent the image quality from being degraded due to ringing that occurs when a signal close to a pure chromaticity signal is used. As shown in 3-189833,
The characteristic “F ₁ (Y)” is, for example, when “Y <Y _th ” with respect to the threshold “Y _th ”, the characteristic becomes F ₁ (Y) = Y + d (26) and “Y> If Y _th ”, the characteristic approximates the polygonal line characteristic of F ₁ (Y) = Y _th + d = (constant) (27).

Even if this characteristic "F ₁ (Y)" is used, higher image quality and a higher color information compression rate can be realized as in the above-described embodiment, thereby reducing the amount of information. When the transmission capacity is constant, it is possible to distribute a larger amount of information to the luminance signal Y to achieve higher image quality of the transmitted image.

Further, the characteristic “F” used in the above-described embodiment is used.
_{When 1} (Y) ”is used, it is not always optimal to use one threshold“ Y _th ”for the color difference signals RY and BY.

Therefore, if a higher image quality is desired, FIG.
As shown in the figure, the chromaticity signal generation circuit 16 is provided with two nonlinear level conversion circuits 13a and 13b, and the characteristics "F _R (X)" and "F" of these nonlinear level conversion circuits 13a and 13b are provided.
_B (X) "may be mutually changed.

By doing so, the image quality can be improved as compared with the embodiment described above. FIG.
Similarly, in the non-linear level conversion circuit 34 of the color image decoding device 2 described in (1), two non-linear level conversion circuits 34 having different characteristics may be used.

In the above-described embodiment, the signal CM output from the chrominance signal encoding circuit 12 provided in the chrominance signal compression processing section 4 of the color image encoding device 1 is used.
_S and the signal CC output from the chromaticity signal encoding circuit 17
_{After S} is selected by the changeover switch 19, variable quantization is performed by the variable quantization circuit 20, but two variable quantization circuits 20a and 20b are provided in the color difference signal compression processing unit 4 as shown in FIG. The color difference signal encoding circuit 1
The signal CM _S output from the second variable quantizing circuit 2
0a, the signal output from the chromaticity signal encoding circuit 17 is variably quantized by the other variable quantization circuit 20b, and the signal CM output from each of these variable quantization circuits 20a and 20b. _S Q, CC
_The SQ may be selected by the changeover switch 19 and supplied to the multiplex processing unit 5.

Also in this case, similarly to the above-described embodiment, it is possible to realize a higher image quality and a higher color information compression ratio, thereby transmitting a high quality color image with a smaller amount of information. When the transmission capacity is constant, a larger amount of information can be allocated to the luminance signal Y to achieve higher image quality of the transmitted image.

In the above-described embodiment, the chrominance signal encoding circuit 12 and the chromaticity signal encoding circuit 17 are provided in the chrominance signal compression processing section 4 of the color image encoding device 1 so that the chrominance signal R- Although the Y and BY signals and the chromaticity signals p and q are individually compressed by the MC + DCT method, the sampling frequency of the color difference signals RY and BY is higher than the sampling frequency of the luminance signal Y. Utilizing the low level, the color difference signal compression processing unit 4
May be provided with one encoding circuit, and this encoding circuit may be used in a time-division manner to compress the color difference signals RY, BY and the chromaticity signals p, q by the MC + DCT method.

In the above description, the present invention has been described by taking the color difference signals RY, BY and the chromaticity signals p, q as examples, but other color difference signals RY, B −
The present invention may be applied to Y and chromaticity signals p and q.

[0062]

As described above, according to the present invention, it is possible to realize a higher image quality and a higher color information compression rate, thereby transmitting a high quality color image with a smaller amount of information. In addition, when the transmission capacity is constant, a larger amount of information can be allocated to the luminance signal to achieve higher image quality of the transmitted image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a color television signal transmission system to which an embodiment of a color image signal encoding device and a decoding device according to the present invention is applied.

FIG. 2 is a block diagram illustrating a detailed circuit example of the color image encoding device illustrated in FIG. 1;

FIG. 3 is a schematic diagram illustrating a characteristic example of the nonlinear level conversion circuit illustrated in FIG. 2;

FIG. 4 is a block diagram illustrating a detailed circuit example of the color image decoding device illustrated in FIG. 1;

FIG. 5 is a block diagram illustrating another example of a circuit configuration of the color image encoding device illustrated in FIG. 1;

FIG. 6 is a block diagram illustrating another example of the circuit configuration of the color image encoding device illustrated in FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 color image encoding device 2 color image decoding device 3 luminance signal compression processing unit 4 color difference signal compression processing unit 5 multiplex processing unit (transmission circuit) 6 quantization control circuit 12 color difference signal encoding circuit 13, 13a, 13b nonlinear level Conversion circuit 14, 15 Division circuit 16 Chromaticity signal generation circuit 17 Chromaticity signal encoding circuit 18 Switching control circuit

Continuation of front page (56) References JP-A-2-222394 (JP, A) JP-A-2-174489 (JP, A) JP-A-63-45990 (JP, A) JP-A-2-262765 (JP) JP-A-50-93724 (JP, A) JP-A-50-93725 (JP, A) JP-A-5-64235 (JP, A) JP-A-5-37963 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 11/00-11/22 H04N ^7/ 24-7/68

Claims (6)

(57) [Claims] 1. A color image signal encoding apparatus for representing a color image by a luminance signal and a color difference signal, and encoding and transmitting the luminance signal and the color difference signal, respectively, wherein the color difference signal is directly encoded. A chrominance signal encoding circuit, a chromaticity signal generating circuit for converting the chrominance signal into a chromaticity signal corresponding to the chromaticity of a color on a one-to-one basis, and encoding a chromaticity signal output from the chromaticity signal generating circuit A chrominance signal encoding circuit to be converted, and comparing the information amount of the signal output from the chromaticity signal encoding circuit with the information amount of the signal output from the chrominance signal encoding circuit, A switching control circuit for selecting the signal of the above, and a multiplexing processing unit for taking in the signal selected by the switching control circuit and the coded luminance signal to generate a composite code signal, Image signal coding apparatus. 2. The chromaticity signal generation circuit generates an output signal proportional to the magnitude of the luminance signal when the luminance signal is small, and generates an output signal having a characteristic that the output signal is saturated when the luminance signal is large. 2. The color image according to claim 1, further comprising: a non-linear level conversion circuit that generates the signal; and a division circuit that generates the chromaticity signal by dividing the color difference signal by an output signal output from the non-linear level conversion circuit. Signal encoding device. 3. The color image signal encoding apparatus according to claim 2, wherein said non-linear level conversion circuit generates two output signals having independent characteristics for two color difference signals. 4. A color image is represented by a luminance signal and a color signal composed of either a color difference signal or a chromaticity signal, and a composite code signal in which the luminance signal and the chrominance signal are respectively encoded is received and decoded. A color image signal decoding device for separating a received composite code signal into a compressed luminance signal, a compressed color signal, and an identification signal for identifying whether the color signal is a color difference signal or a chromaticity signal. A separation circuit for generating a luminance signal from the separated compressed luminance signal; a color signal decoding circuit for decoding a color signal from the separated compressed color signal; and a color difference signal from the decoded color signal A color difference signal restoring circuit for restoring the color signal decoding circuit, based on the identification signal, selecting a color difference signal output from the color signal decoding circuit when the color difference signal is output from the color signal decoding circuit; Color image signal decoding apparatus characterized by comprising a, a selector switch for selecting the color difference signal output from the color-difference signal recovery circuit when the chromaticity signal from the road is output. 5. The color difference signal restoration circuit generates an output signal proportional to the magnitude of the luminance signal when the luminance signal is small, and generates an output signal having a characteristic that the output signal is saturated when the luminance signal is large. 5. The color image according to claim 4, further comprising: a non-linear level conversion circuit for generating a color difference signal by multiplying an output signal output from the non-linear level conversion circuit by the color signal. Signal decoding device. 6. The color image signal decoding apparatus according to claim 5, wherein said nonlinear level conversion circuit generates two output signals having independent characteristics for two color difference signals.