JPH08336154A - Digital color encoder - Google Patents

Abstract

PURPOSE: To reduce cross color also when a one-dimensional Y/C separation is performed on a reception side by generating a composite color signal by the luminance signal preventing the transmission of the frequency components equivalent to color sub-carrier wave frequencies. CONSTITUTION: Inputted RGB signals are added in a matrix circuit 1 with a prescribed ratio, and a luminance signal Y and color difference signals R-Y and B-Y are generated. A prescribed band limit is performed for this color difference signal by a low-pass filter 3, the signal is inputted in a modulator 4, a color sub-carrier wave is modulated with the signal R-Y, and a quadrature two-phase balance modulation is performed for the color sub-carrier wave whose phase is shifted by a prescribed angle in a phase converter 12 by the signal B-Y. These output color carrier signals R-Y and B-Y are added in an adder 7, and further, these carrier color signals and the luminance signal Y for which a time adjustment is performed by a delay 8 via a trap filter 6 are added and a color composite signal is generated. As a result, a matter that the luminance signal frequency components in the vicinity of a color sub-carrier wave frequency is taken out as a color signal and is processed can be evaded and cross color can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color encoder for converting RGB primary color signals into a composite color signal (for example, NTSC signal) by a digital method.

[0002]

2. Description of the Related Art FIG. 7 is a circuit showing a conventional digital color encoder. By this circuit, as described below, an NTSC signal (composite signal) is generated from RGB primary color signals.

The matrix circuit 21 performs a matrix operation for synthesizing RGB primary color signals sampled at a predetermined sampling frequency at a predetermined ratio, and produces a luminance (Y) signal and a color difference (R-).
Y) signal and color difference (BY) signal are generated. Note that the relationship among the luminance signal, each color difference signal, and the composite signal (M) is expressed by the following Expression 1.

[0004]

## EQU1 ## Y = 0.30R + 0.59G + 0.11B V = (RY) /1.14 U = (B−Y) /2.03 M = Y + V · cosωt + U · sinωt

The LPFs 23, 23 apply predetermined band limitation to the color difference (RY) signal and the color difference (BY) signal, respectively. The modulator 24 is a color subcarrier (3.58 MHz)
And a phase shifter 2
The color subcarrier whose phase is shifted through 6 is color difference (BY)
Quadrature two-phase balanced modulation that is modulated by a signal is performed to generate a carrier color signal. The adder 25 adds the carrier color signal output from the modulator 24 and the luminance signal whose time has been adjusted through the delay 22 to generate a video signal (see Japanese Patent Publication No. 56-37755).

[0006]

By the way, on the side of the receiving device which receives the video signal generated by the digital color encoder, the process of decoding the video signal, that is, the Y / C for separating the luminance signal and the chrominance signal is performed. It is necessary to perform separation processing.

However, in the case of performing one-dimensional Y / C separation in which a video signal is simply passed through a band-pass filter to separate color signals, it is difficult to perform precise separation. Therefore, the color sub-carrier frequency within the luminance signal band is difficult. There is a problem that the frequency components in the vicinity are extracted as color signals and processed, resulting in so-called cross color.

On the other hand, as a Y / C separation method capable of reducing the cross color, a signal obtained by subtracting a signal between two lines by utilizing the fact that the phase of the color signal is opposite for each line The two-dimensional Y / C separation that extracts the color signal through a bandpass filter, and the fact that the phase of the color signal is opposite in each frame is used to subtract the signal between two frames into a band. A three-dimensional Y / C separation method for extracting a color signal through a pass filter has been used. However, these methods have a drawback that the cost is high because the circuit configuration is complicated.

In view of the above circumstances, the present invention has one
An object of the present invention is to provide a digital color encoder that reduces cross color even when performing dimension Y / C separation.

[0010]

In order to solve the above-mentioned problems, a digital color encoder according to the present invention has RGB color encoders.
In a digital color encoder for generating a composite color signal from primary color signals, input means for inputting RGB primary color signals sampled at a sampling frequency that is an integer multiple or integer ratio multiple of a color subcarrier, and output from this input means A signal combining means for combining RGB signals at a predetermined ratio to generate a luminance signal and a color difference signal; and a band-stop digital filter for blocking transmission of a frequency component of the luminance signal corresponding to the frequency of the color subcarrier. , A modulation means for generating a carrier color signal of an arbitrary phase according to the color difference signal, a luminance signal transmitted through the band stop digital filter and a carrier color signal generated by the modulating means are added to obtain a composite color. And an addition unit that generates a signal.

In the above arrangement, the band elimination digital filter may be a linear phase moving average filter or a linear phase notch type filter.

A signal terminal for outputting the luminance signal not processed by the digital filter and the carrier color signal output from the modulating means separately from the composite color signal may be provided.

A switching means for selectively inputting either the signal that has passed through the band-stop digital filter or the signal that has not passed through the band-stop digital filter to the addition means may be provided.

[0014]

According to the above arrangement, since the composite color signal is generated by the luminance signal in which the transmission of the frequency component corresponding to the frequency of the color subcarrier is blocked, the color subcarrier frequency is decoded in decoding the composite color signal. It is avoided that the luminance signal frequency component in the vicinity is taken out and processed as a color signal, and even if the receiving side is one-dimensional Y / C.
Even when separation is performed, cross color can be reduced.

If the luminance signal output from the signal synthesizing unit and the carrier color signal output from the modulating unit are output separately from the composite color signal, the luminance signal and the carrier color signal are separated. In addition to being compatible with the S-terminal standard transmitted through a channel, a luminance signal that does not pass through a band-stop digital filter is used, so that deterioration of contrast and resolution is prevented.

In addition, if either the signal that has passed through the band-stop digital filter or the signal that does not pass through the band-stop digital filter is selectively input to the adding means, either of cross color prevention and resolution or contrast reduction prevention is required. It is possible for the user to freely select the one with the highest necessity.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a block diagram showing a schematic configuration of a digital color encoder of the present invention. In the matrix circuit 1, RGB sampled at a sampling frequency that is an integer multiple or an integer ratio multiple of a color subcarrier is input from an input unit (not shown).
Primary color signals are input. The matrix circuit 1 performs a matrix operation for synthesizing the RGB primary color signals from the output means at a predetermined ratio to obtain a luminance (Y) signal, a color difference (RY) signal, and a color difference (BY) signal. To generate. The low-pass filters 3 and 3 are composed of digital filters and have a color difference (RY) signal and a color difference (B).
-Y) Each of the signals is subjected to a predetermined band limitation.

The modulator 4 has a color subcarrier (3.58 MH).
z) is modulated by a color difference (RY) signal, and quadrature two-phase balanced modulation is performed by modulating a color subcarrier whose phase is shifted by a predetermined angle through a phase shifter 12 by a color difference (BY) signal. The adder 7 adds the color carrier signals of the color difference (RY) signal and the color difference (BY) signal output from the modulator 4.

On the other hand, the luminance signal output from the matrix circuit 1 is input to the trap filter 6 which is a digital filter. The trap filter 6 blocks transmission of a frequency component of the luminance signal corresponding to the frequency of the color subcarrier.

The adder 5 adds the carrier color signal output from the adder 7 and the luminance signal time-adjusted by the delay 8 through the trap filter 6 to obtain a video signal (color composite signal). Is generated and is supplied to the video signal terminal 9. The delay 8 is the signal delay time of the low pass filter 3 and the trap filter 6
The delay time is set so as to cause a delay sufficient to eliminate the difference from the signal delay time due to.

Further, the digital color encoder is provided with a carrier color signal terminal 10 and a luminance signal terminal 11. A path for supplying the carrier color signal output from the adder 7 is connected to the carrier color signal terminal 10, and the brightness signal output from the matrix circuit 1 is supplied to the brightness signal terminal 11 through the delay 2. The route is connected. That is, the luminance signal output from the matrix circuit 1 and the carrier color signal output from the modulator 4 are output separately from the composite signal. The delay 2 is adapted to give a delay corresponding to the signal delay of the low pass filter 3 to the luminance signal.

FIG. 2 is a graph showing the relationship between the characteristics of the trap filter 6 (shown by the broken line in the figure) and the luminance signal (shown by the solid line in the figure). The horizontal axis represents frequency, but the sampling frequency is normalized to 2π. The vertical axis represents gain (amplitude).

Here, FIG. 2 shows a case in which the color subcarrier frequency component is included in the original band of the luminance signal. As can be seen from this figure, the trap filter 6 has the color subcarrier (3.58 MHz). ) By having a notch frequency in the vicinity, it is possible to sufficiently attenuate the luminance signal of the frequency component. Unlike the analog filter, the digital filter that constitutes the trap filter 6 can be easily configured to have a linear phase and a steep attenuation characteristic. Therefore, it is possible to minimize the deterioration of the resolution and the contrast due to the deterioration of the luminance signal characteristic due to the filter operation. Further, since the group delay distortion is "0", the deterioration of the image due to the time difference between the luminance signal and the color difference signal does not occur.

FIG. 3 is a circuit diagram showing a specific configuration of the trap filter 6 used when the sampling frequency is set to be 6 times as large as the color subcarrier. The trap filter 6 of FIG.
Inputs five signals in total including five delay elements 6a to 6e connected in series to the signal path to which the luminance signal is input, an undelayed luminance signal and a luminance signal that has passed through each of the delay elements 6a to 6e. Adder 6f for adding these,
And an arithmetic unit 6g that calculates the average value of the luminance signal by dividing the output of the adder 6f by 6. As described above, when the sampling frequency is an integral multiple of the color subcarrier, the notch frequency and the color subcarrier frequency can be matched by forming a moving average filter (comb filter) having a simple circuit configuration.

The delay elements 6a to 6e are each 1
A delay equal to the sampling period is given, and when the delay of the delay elements 6a to 6e is represented by an operator Z ^-1 , the transfer function H (Z) of the trap filter 6 is given by the following formula 2. expressed.

[0027]

## EQU2 ## H (Z) = (1 + Z ^-1 + Z ^-2 + Z ^-3 + Z ^-4 + Z ^-5 ) / 6

Further, the arithmetic unit 6g carries out processing for making the output of the adder 6f 1/6, and this 1/6 is 1/6.
Since this can be approximated as ≈2 ^-3 +2 ^-5 +2 ^-7 , this division processing can be realized by shift addition. Further, when the signal attenuation of the trap filter 6 alone having the above configuration is insufficient, the trap filter 6 having the above configuration is used.
It is possible to obtain a desired amount of attenuation by connecting 2 to 3 stages.

FIG. 4 is a graph showing the frequency-gain characteristics of the trap filter 6 having the configuration shown in FIG. The vertical axis represents gain, and the horizontal axis represents frequency. The phase characteristic is a linear phase, and the group delay distortion is "0". The frequency is expressed up to a range of 6/2 (π) of the sampling frequency. As can be seen from this graph, when the sampling frequency is an integral multiple of the color subcarrier, the frequency component of the luminance signal corresponding to the vicinity of the frequency of the color subcarrier is attenuated by the trap filter 6 having the moving average filter configuration. You can

FIG. 5 shows that the sampling frequency is 3.
FIG. 9 is a circuit diagram showing a specific configuration of the trap filter 6 used in the case of 4 (34/10) times. The trap filter 6 of FIG. 5 has four delay elements 6a to 6d connected in series to a signal path to which a luminance signal is input, an undelayed luminance signal, and a luminance signal that has passed through the delay elements 6a to 6d, respectively. Five calculators 6h to 6l for multiplying a predetermined multiplication coefficient, an adder 6m for inputting five signals from the respective calculators 6h to 6l and adding them, and this adder 6
The output of m is divided by 256 to calculate the average value of the luminance signal.

When the delays of the delay elements 6a to 6d are represented by an operator Z ^-1 , the transfer function H of the trap filter 6 is shown.
(Z) is expressed as the following Expression 3.

[0032]

## EQU3 ## H (Z) = (-16 + 128Z ^-1 + 32Z ^-2 +1
28Z ^-3 -16Z ^-4 ) / 256

The arithmetic units 6h to 6l can be easily realized by shifters. For example, "-16"
Is obtained by shifting the original value to the left by 4 bits to obtain the two's complement, "128" is performed by the 7-bit left shift, and "32" is performed by the 5-bit left shift. 1/256 "can be realized by performing 8-bit right shift.

The transfer function H (Z) is given by the following equation 4
Therefore, the circuit configuration according to the equation may be adopted.

[0035]

## EQU4 ## H (Z) = {-1 × (1 + Z ^-4 ) + 8 × (Z ^-1 +
Z ^-3 ) + 2Z ^-2 } / 16

FIG. 6 is a graph showing the frequency-gain characteristics of the trap filter 6 having the structure of FIG. The vertical axis represents gain, and the horizontal axis represents frequency.
The frequency is expressed up to a half of the sampling frequency (2π). As can be seen from this graph, when the sampling frequency is set to an integral multiple of the color subcarrier, the frequency component of the luminance signal corresponding to the vicinity of the frequency of the color subcarrier is obtained by using the linear phase notch type trap filter 6. Can be attenuated.

As described above, according to the present invention, since the video signal (composite color signal) is generated by the luminance signal in which the transmission of the frequency component corresponding to the frequency of the color subcarrier is blocked, this video signal is generated. It is avoided that the luminance signal frequency component in the vicinity of the color subcarrier frequency is taken out as a color signal and processed in the decoding of 1., and cross color is reduced even if the receiving side performs one-dimensional Y / C separation. be able to.

In this embodiment, the luminance signal output from the matrix circuit 1 and the carrier color signal output from the modulator 4 are output separately from the video signal. In addition to being compatible with the S terminal standard for transmitting a color signal on a separate channel, a luminance signal that does not pass through the trap filter 6 is used, so that deterioration of contrast and resolution is prevented.

Although not shown in FIG. 1, a path bypassing the trap filter 6, for example, a path from the delay 2 to the adder 5 is formed, and the path and the path from the trap filter 6 to the adder 5 are formed. Switch means (not shown) for selecting either
Either the signal that has passed through or the signal that has not passed may be selectively input to the adder 5. With such a structure, the user can freely select either the cross color prevention or the resolution or the contrast reduction prevention request, whichever is more necessary.

In the above embodiment, the case where the sampling frequency is 6 times the color subcarrier and the case where the sampling frequency is 3.4 have been described. By attenuating the gain near the carrier frequency,
It is possible to reduce cross color. Although the NTSC system is described in this embodiment, the present invention can be similarly applied to the PAL system.

[0041]

As described above, according to the present invention, in decoding a composite color signal, it is possible to prevent the frequency component near the color subcarrier frequency in the luminance signal band from being extracted and processed as a color signal. Therefore, even if the receiving side performs one-dimensional Y / C separation, cross color can be reduced.

When the luminance signal output from the signal synthesizing means and the carrier color signal output from the modulating means are to be output separately from the composite color signal, the luminance signal and the carrier color signal are output through different channels. In addition to being compatible with the S-terminal standard for transmission, a luminance signal that does not pass through a band-stop digital filter is used, so that deterioration of contrast and resolution is prevented.

Further, if either the signal that has passed through the band-stop digital filter or the signal that does not pass through the band-stop digital filter is selectively input to the adder, either cross color prevention or resolution or contrast reduction prevention is required. This has the effect that the user can freely select the one with the highest necessity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a digital color encoder of the present invention.

FIG. 2 is a graph showing the relationship between the characteristics of the trap filter of the present invention and a luminance signal, and is a diagram showing a case where a chrominance subcarrier frequency component is included in the original band of the luminance signal.

FIG. 3 is a circuit diagram showing a specific configuration of a trap filter used when the sampling frequency of the present invention is set to be 6 times the color subcarrier.

4 is a frequency of the trap filter having the configuration of FIG.
6 is a graph showing gain characteristics.

FIG. 5 is a circuit diagram showing a specific configuration of a trap filter used when the sampling frequency of the present invention is set to be 3.4 times the color subcarrier.

FIG. 6 shows the frequency of the trap filter having the configuration shown in FIG.
6 is a graph showing gain characteristics.

FIG. 7 is a block diagram showing a schematic configuration of a conventional digital color encoder.

[Explanation of symbols]

1 matrix circuit (signal combining means) 2 delay 3 low-pass filter 4 modulator 5 adder 6 trap filter (band stop digital filter) 7 adder 8 delay 9 video signal terminal 10 carrier color signal terminal 11 luminance signal terminal

Claims (5)

[Claims] 1. A digital color encoder for generating a composite color signal from RGB primary color signals, and input means for inputting RGB primary color signals sampled at a sampling frequency which is an integral multiple or an integral ratio multiple of a color subcarrier. A signal synthesizing unit for synthesizing the RGB signals output from the input unit at a predetermined ratio to generate a luminance signal and a color difference signal, and blocking transmission of a frequency component of the luminance signal corresponding to the frequency of the color subcarrier. A band-stop digital filter, modulating means for generating a carrier color signal of an arbitrary phase according to the color difference signal, a luminance signal transmitted through the band-stop digital filter, and a carrier color signal generated by the modulating means. And a summing means for generating a composite color signal. 2. The digital color encoder according to claim 1, wherein the band elimination digital filter is composed of a linear phase moving average filter. 3. The digital color encoder according to claim 1, wherein the band elimination digital filter is a linear phase notch type filter. 4. A signal terminal for outputting a luminance signal which has not been processed by the digital filter and a carrier color signal output from the modulating means separately from the composite color signal. 4. The digital color encoder according to any one of 3 to 3. 5. A switching means for selectively inputting a signal that has passed through the band-stop digital filter and a signal that has not passed through the band-stop digital filter to the adding means, according to any one of claims 1 to 4. Digital color encoder.