JPS5922436B2 - digital color encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color encoder implemented by digital means.

A color encoder is usually used to synthesize a composite color video signal defined by, for example, the NTSC system from three types of video signals corresponding to the three primary colors R, G, and B.

A conventional color encoder consists of analog means, and its basic configuration is shown in FIG. Input video signal R, G,
B is a matrix circuit 1 that outputs luminance signal Y) color difference signals I, Q (
R-Y and B-Y are often used instead of I and Q), and I and Q are limited by low-pass filters 2 and 3 to the band required for the color difference signal. Furthermore, the I, Q signals are composed of two orthogonal color subcarriers (2) (ω + 330), d
ll (ω +330) is balanced-modulated by balanced modulators 4 and 5, and an adder 6 calculates the color subcarrier component as the sum of the two, that is,
Carrier color signal (moderated chromo! 1 set)
signal)C. The carrier color signal component is added to the time-corrected luminance signal by the delay line 7 and the adder 8, and the NTS
This becomes a C signal. The problem with the color encoder using analog means as shown in FIG. 1 is that the balance of the balanced modulator cannot be kept stable.

Therefore, there is an achromatic subject, and even if the color difference signal becomes o, the color subcarrier component does not become zero, and the reproduced image is colored. In order to correct this, an automatic color subcarrier balancing circuit is required in addition to the tortoise configuration of FIG. 2
) High-precision resistors are required to obtain the correct matrix coefficients for the matrix circuit.

etc.

In order to solve such problems, it is conceivable to realize the basic configuration shown in FIG. 1 by digital means.

That is, instead of the analog input video signals R, G, B, the digital image signals R', G', B5 are encoded.
Matrix calculations, filtering, addition modulation, etc. are performed digitally using . The most difficult task is to realize a digital encoder! Ino is balanced modulation.

For analog balanced modulation, the modulator is, for example, a multiplier that multiplies the input signal 1 and the color subcarrier Cs(ωt+33). Attempting to implement this with digitized ν and color subcarriers and digital multipliers would be extremely complex, especially at ω/2π = 3.58MH
Considering that z, real-time calculation is impossible for the multiplier. A new digital color encoder that solves these problems uses a predetermined coefficient that is determined according to each phase of the color subcarrier at sampling points that are an integer (3 or more) times the color subcarrier in the digitized color difference signal. There is a digital color encoder that obtains a digital color sending signal by multiplying by (Digital Color Encoder, filed on February 15, 2013).An object of the present invention is to improve the above-mentioned digital color encoder.
It becomes an AM signal.

When converting this into an analog signal through a low-pass filter, etc., there is an aperture effect (a drop in high frequencies caused by the signal being held over a finite time width), so this can be exploited by using the special characteristics of the digital color encoder mentioned above. death,
This can be achieved using simple means. In order to achieve the above object, the present invention converts analog color signals such as red, green, and blue into digital signals, and uses the digitized color signals to convert a luminance signal into a digital signal and a color subcarrier into a digital signal. We create digital signals of multiple types of color difference signals that correspond to multiple phases that occur depending on the sampling point when sampling at an integer (3 or more) times, and compensate for amplitude changes due to the aperture effect. The digital signal of the color difference signal is periodically switched at the sampling period by a switch circuit to convert it into a time series signal, and the output of the switch circuit and the digital signal of the luminance signal are digitally added. It is designed to obtain a digital decoded color video signal.

According to the present invention, the device can be realized by simply setting the coefficient value to a predetermined value without providing a circuit for correcting the Abacha effect at the input or output section of the digital Gala encoder. I can do it.

The present invention will be explained in detail below using the drawings.

First, before explaining the present invention, a digital color encoder will be explained. NTSC system carrier color signal wave component C
It is determined that R-Y and B-Y are used as color difference signals, and if the carrier color signal is represented in a vector diagram, it becomes as shown in FIG.

Here, the relationship between the sampling time point and the value of the carrier color signal component is examined.

For example, at a sampling frequency 4 times the color subcarrier frequency, t
= If there is a sampling time point at o, then the sample π π 3
The phase (ωt) at the time of change becomes 0, 1, −, −π, and the second
Corresponding to the axes Xl and X2 corresponding to (b) ωTs image ωTvc on the vector diagram in the figure, and the axes X3 and It is given by Al9A2tA, , A4, which is obtained by projecting the vector of the fast wave component C onto each axis of the above-mentioned X, , X29X3 story series.

In addition, in the case of a sampling frequency that is three times the color subcarrier frequency, and when there is a sample π conversion point at t=o, the axis x and the axis X2
Projection A2, A,, A6 onto distant X,, X6
gives the value of the color subcarrier component C at the sampling time.

The projected components A1, . . ., A6 here are calculated from equation (4) and the vector diagram in FIG.

However, if the sampling time point deviates from t=o, the axes X1, . . . , X6 may be rotated by a phase corresponding to the deviation. On the other hand, to digitally represent a carrier color signal component is to approximate and give a value obtained by sampling the corresponding analog carrier color signal component with a digital signal, and in this case, the sampling frequency ωs is the color It is said that an integral multiple of 3 or more (for example, 3 times, 4 times, etc.) of the subcarrier frequency ω is appropriate.

If ωs=3ω, each sample value is X2,X,,X
Digital quantity A corresponding to 6-axis components A2, A, , A6
It is nothing but that , A≦ and AX appear sequentially as shown in Figure 3a. Also, if ω8 = 4ω, each sample value is
, A4 corresponds to the digital quantity A/, Aノ , AX, A
! This is the same as appearing sequentially as shown in FIG. 3b.
Using the above principle, the digitizer image signals R', G
To synthesize the DIGITANO I color sending signal component C' from ', B'', A≦, A4, A by 3 without using a multiplier.
At the frequency of ω, or A, 2, A no, Ai, A!
All you have to do is arrange them at a frequency of 4ω. FIG. 4 shows an example of the configuration of a digital encoder.

The analog resolution image signals R, G, B are sent to A/D converters 9, 10,
11 into digital video signals R', G7, and BI. }, the sampling frequency in this case does not necessarily have to be equal to ω, for example. The frequency may be an integer ratio of 8.

These are luminance signals Y', A! from the digital matrix circuit 12VC. , A: , converted to A6. Here Y
'=0.30R'+0.59G'+0.11B'. A! ,A! ,A! , is the digital low-pass filter 13,
Digital switch whose band is limited by 14 and 15 and opens and closes sequentially at the frequency of ω8=3ω; }d;=medium:゛19:
±Storage::? : The signals are added by a binary adder to become a digitally decomposed video signal, in this case an NTSC signal.

Next, the digital NTSC signal is converted into an analog NTSC signal by a D/A converter 19. If the encoder is digitized in this way, when A2=A5=A6=0, C'=0, and the balance of the modulator becomes perfect.

Furthermore, the matrix coefficients are not affected by component variations at all. In Figure 2, the axes X and ~X6 were considered based on the (R-Y) or (B-Y) axis, but each axis and each axis component were considered based on the 1 or Q axis. The same is true when considering. If there are at least two axes (but the axes cannot be in antiphase with each other), the color signal components to be conveyed can be expressed as a vector sum of the axes. For example, when ω8=4ω, Al, A2, O, O may be repeated as shown in FIG. 3c. That is, it may be considered that a color difference signal called VCO is used instead of A<<, N. However, in this case, switch 16A1
The output of +A2 is the DC component (in this example, ?-Li: !0.46
To correct this, for example, the matrix coefficient that determines the luminance signal is set to (0.30-0.46)R+(0.59+0.81).
It is necessary to correct it as follows: G+(0.11-0.34)B.

In the embodiment of FIG. 4, the analog NTSC signal obtained from the D/A converter 19 is, for example, 2π 2π
In this case, as shown in Fig. 5, PAMω with a width of one (=-)
The amplitude of the component which is a 3ωS signal and is effective as an NTSC signal is reduced due to the aperture effect (high-frequency reduction caused by the signal being held over a finite time width) determined by the above-mentioned width.

If the ω8 power level increases, the influence of the aperture effect on the luminance component can be ignored except for a slight decrease in resolution, but the influence on the carrier color signal component will decrease the degree of saturation and cannot be ignored. Due to the Abachaya effect, the color subcarrier component j is the third
In the case of figure a, 1.5 - 0.83 times, the field of b is π2/Yj
What about collation? 0.9 times π, in case of c, 0.45 times π
π
becomes smaller.

In the present invention, as a measure against this aperture effect, the coefficient of the matrix circuit 12 is selected in advance to be large enough to be a reciprocal multiple of the above value. For example, in the case of a, A! ,A′S,A
Is 2 the original value of π? In the case of double, b, Al, A6, A! ，
A! 1.5V] π? Double it.

In this way, the influence of the A.2Vi-chare effect can be substantially eliminated.

In the embodiment shown in FIG. 4, a configuration for obtaining an NTSC signal has been described, but obtaining a PAL signal can also be realized using a similar concept. For example, when switching at four times the color subcarrier frequency based on the Q axis, a certain scan line is
In the order of Q, -1, -Q, the next scan line is -1, Q, I,
It is only necessary to change the selection order of the switches so that the order becomes -Q. In the explanation so far, an example of ω8/ω=3 or 4 has been used, but an integer value higher than these may be used if necessary.

As described above, in the VC of the present invention, digital color subcarrier components can be easily obtained by periodically arranging the plurality of digital color difference signals at a frequency that is an integral multiple of the color subcarrier frequency. This greatly contributes to stabilization and higher precision.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional analog color encoder, FIGS. 2, 3, and 5 are diagrams showing the principle of the present invention, and FIG. 4 is a block diagram of a digital color encoder of the present invention. In Fig. 1, 1 is a matrix generator, 2, 3 are low-pass filters, 4, 5 are balanced modulators, 6, 8 are adders, 7 is a delay line, and in Fig. 4, 9, 10, 11 are A/D converter, 1
2 is a matrix circuit, 13, 14, 15 are low-pass filters, 16 is a switch, 17 is a delay line, 18 is an adder, 19
is a D/A converter.

Claims (1)

[Claims] 1 Analog video signal red (R), green (G), blue (B)
An analog-to-digital conversion circuit that converts a signal into a digital signal, and a plurality of sampling points that occur when sampling the digital signal from the digital signal at an integer (3 or more) multiple of the luminance signal and color subcarrier frequency. A digital matrix circuit that generates digital signals of a plurality of types of color difference signals that correspond to the phase and compensate for amplitude changes due to an aperture effect, and a digital matrix circuit that periodically switches the digital signals of the plurality of types of color difference signals at the sampling period. A digital color encoder comprising: a switch circuit for converting into a time-series signal; and an adder circuit for digitally adding the digital luminance signal and the output of the switch circuit to create a digital composite color video signal. .