JPH0362077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital color encoder that synthesizes a digital carrier color signal of a standard television system such as an NTSC system or a PAL system from an image pickup output signal obtained from a color video camera.

Traditionally, this type of digital color encoder is
The three primary color signals R, G, and B obtained as the imaging output signals of a color video camera form a point-sequential color difference signal sequence, and the analog carrier color signal is sampled by balanced modulation in which the scalar sum of the color difference signals is set to 0. A digital carrier color signal was synthesized that directly corresponds to the digital color signal. In the conventional digital color encoder as described above, the signal band is basically determined by the band of the color difference signal before point sequentialization, and there is no need for a special band filter for the carrier color signal. This has the disadvantage that the structure of the matrix circuit for forming the signal becomes complicated.

FIG. 1 is a block diagram showing the basic configuration of a four-phase modulation type digital color encoder. In FIG. 1, a matrix circuit 1 performs a predetermined matrix operation on three primary color signals R, G, and B obtained by a color video camera to form color difference signals u and v, as shown in FIG. 2A. , the color difference signals u and v are output point-sequentially. The color difference signals u and v synthesized in the matrix circuit 1 are band-limited via chroma filters 2 and 3, respectively, and then supplied to balanced modulators 4 and 5, respectively. In each of the balanced modulators 4 and 5, as shown in FIG. 2B, the sc
Balanced modulation is performed using the color difference signals u and v for the carrier wave signal C having a frequency of . The modulated outputs obtained from the balanced modulators 4 and 5 are alternately selected every 1/sc period via the signal selection circuit 6 and output as a carrier color signal CCi as shown in FIG. 2C. It is output from terminal 7.

Here, in the conventional example as described above, the order of the sampling carrier is i=0, 1..., and the signal spectra of each color difference signal ui, vi and carrier color signal CCi are as shown in FIGS. 3A and 3B. The balanced modulators 4 and 5 perform balanced modulation of the carrier signal C using the color difference signals ui and vi of the signal spectrum as shown in FIG. A carrier color signal CCi having a signal spectrum as shown is output. The carrier color signal CCi is used after its baseband component is band-limited in a post filter (not shown) having a cutoff frequency of 2sc.

FIG. 4 is a block diagram showing the basic structure of a three-phase modulation type digital color encoder. In FIG. 4, a matrix circuit 11 performs a predetermined matrix operation on the three primary color signals R, G, and B to form three types of color difference signals C ₁ , C ₂ , and C ₃ and output them point-sequentially. Each of the above color difference signals C ₁ , C ₂ ,
C ₃ are chroma filters 12, 13, and 1, respectively.
4, and is sequentially selected at a cycle of 1/sc through a 3-input signal selection circuit 15, and is outputted from a signal output terminal 16 as a carrier color signal _C0 as shown in FIG. . Each color difference signal above
By setting the scalar sum C ₁ +C ₂ +C ₃ =0 of C ₁ , C ₂ , and C ₃ to 0, the point-sequential color difference signal C ₁ ,
The baseband components of C ₂ and C ₃ are zero. Each of the color difference signals C ₁ , C ₂ and C ₃ has a signal spectrum as shown in FIG. 6A, and the carrier color signal C ₀ has a signal spectrum as shown in FIG. 6B. Carried color signal obtained at the signal output terminal 16
C ₀ is used after being band-limited via a poster filter (not shown) with a cutoff frequency of 1.5 sc.

By the way, in a color video camera that outputs a red R color signal, a cyan Cy color signal, and a green G color signal point-sequentially as imaging output signals, the point-sequential imaging output is C'=k{R・exp(jω _sc t+103゜) +G・exp(jω _sc t+103゜)+120゜) +(G+B)・exp(jω _sc t +103゜+240゜)｝...The carrier color signal of the NTSC system shown in the first equation, which is the first equation. Since a sampling carrier equal to 1 is generated, a carrier color signal can be obtained by band-limiting the point-sequential imaging output using a bandpass filter. However, in this case, the matrix function must be realized using the spectral characteristics of the optical filter, so it is extremely difficult to obtain a carrier color signal that is properly compatible with the NTSC system. It is difficult to carry out

SUMMARY OF THE INVENTION Therefore, the present invention provides a digital color encoder with a novel configuration in which a carrier color signal is synthesized from a point-sequential color signal sequence obtained by a color video camera, thereby simplifying the matrix circuit. It is.

In the digital color encoder according to the present invention, for the three primary color signals R, G, and B obtained by a color video camera, a filter characteristic of H ₀ (ω) having a bandwidth of less than 1/2 sc where the color carrier frequency is sc is used. After band-limiting with a low-pass filter, a point-sequential color signal train is formed, and the first sampling is performed from the point-sequential signal train through a band filter with a filter characteristic of H ₁ (ω) with sc as the center frequency. By taking out the carrier, e.g.
Obtain an NTSC carrier color signal.

In FIG. 7 showing an embodiment of a four-phase modulation type digital color encoder according to the present invention, a matrix circuit 21 is supplied with three primary color signals R, G, and B obtained by a color video camera. The matrix circuit 21 receives the three primary color signals R, G, B.
For, C ₁ C ₂ C ₃ C ₄ = r ₀ 0 0 0 0 b ₁ 0 g ₀ b ₀ 0 g ₁ 0 R G B...Perform the matrix operation of the second equation, which is the second equation, to obtain four types of color signals. C ₁ , C ₂ , C ₃ , and C ₄ are each output at a data rate of 4·sc. Matrix circuit 1 above
Four types of color signals C ₁ , C ₂ , C ₃ , C ₄ obtained in 1
are the first to fourth low-pass filters 22, 23, 24, each having a filter characteristic of H ₀ (ω).
25, the signal is band-limited to a bandwidth less than 1/2·sc and is supplied to a four-input signal selection circuit 26. The 4-input signal selection circuit 26 sequentially selects each of the color signals C ₁ , C ₂ , C ₃ , and C ₄ with 1/sc as one cycle, and obtains a data rate of sc as shown in FIG. A dot sequential color signal sequence C ₁ /C ₂ /C ₃ /C ₄ is formed.
A dot-sequential signal string formed by the signal selection circuit 26
C ₁ /C ₂ /C ₃ /C ₄ are φ ₀ and φ ₁ for the three primary color signals R, G, and B, as shown in the vector diagram of FIG.
This is equivalent to four-phase modulation with orthogonal modulation axes. Then, the point-sequential color signal sequence C ₁ /C ₂ /C ₃ /C ₄ obtained by the signal selection circuit 26 is passed through a band filter 27 having a filter characteristic of H ₁ (ω) with a center frequency of sc. , the first sampling carrier is outputted from the signal output terminal 28 as a carrier color signal C ₄ .

Carried color signal obtained at the signal output terminal 28
C ₄ 〓 is C ₄ 〓=r ₀・Rexp(jω _sc t+103°) +b ₁・Bexp(jω _sc t+13°) +(b ₀・B+g ₀・G)exp(jω _sc t−77°) +g ₁ · Gexp (jω _sc t−167°) ... It can be expressed by the third equation.

In the embodiment described above, the signal spectrum of the first color signal _C1 , that is, the _φ0 axis, formed by the matrix circuit 21, for example, can be shown as shown in FIG. That is, the first color signal C ₁ =r ₀ ·R is given a filter characteristic of H ₀ (ω) by the first low-pass filter 22 and is band-limited as shown in FIG. 10A. Then, the band-limited first color signal H ₀ (ω)·r ₀ R is downsampled to sc in the signal selection circuit 26 as shown in FIG. 10B. Furthermore, the downsampled first composite signal H ₀ (ω−ω _sc )・
r ₀・Rexp(jω _sc t+103°) is the band filter 27
The band is limited as shown in FIG. 10C.

Next, in FIG. 11 showing an embodiment of the three-phase modulation digital color encoder according to the present invention, the matrix circuit 31 inputs C ₁ C for the three primary color signals R, G, and B obtained by the color video camera. ₂ C ₃ = r ₀ 0 b ₁ r ₁ g ₀ 0 0 g ₁ b ₀ R G B ...Perform the matrix calculation of the fourth equation, and calculate the three types of color signals C ₁ , C ₂ , C ₃ and output at a data rate of 3.sc. Three types of color signals C ₁ , C ₂ ,
C ₃ is the first filter characteristic H ₀ (ω), respectively.
or third low-pass filter 32, 33, 34
The signal is band-limited to a bandwidth of less than 1/2·sc and supplied to the three-input signal selection circuit 35. The signal selection circuit 35 sequentially selects each of the color signals C ₁ , C ₂ , and C ₃ with 1/sc as one period, and creates a point-sequential color signal sequence C ₁ /C ₂ /C ₃ with a data rate of sc. form. The point-sequential signal sequence C ₁ /C ₂ /C ₃ formed by the signal selection circuit 35 has φ ₀ ,
This is equivalent to performing three-phase balanced modulation with modulation axes φ ₁ and φ ₃ . Then, the signal selection circuit 3
The point sequential color signal sequence C ₁ /C ₂ /C ₃ obtained in step 5 is
The first sampling carrier is output from a signal output terminal 37 as a carrier color signal C ₃ 〓 via a band filter 36 having a filter characteristic of H ₁ (ω) with a center frequency of sc.

Here, the carrier color signal C ₃ 〓 obtained at the signal output terminal 37 is: C ₃ 〓 = (r ₀ · R + b ₁ · B) exp (jω _sc t + φ ₀ ) + (g ₀ · G + r ₁ · R) exp (jω _sc t+φ ₁ ) + (b ₀・B+g ₁・G) exp(jω _sc t+φ ₃ )
...is shown in the fifth equation, and _each matrix _{constant r 0 ,} r _{1 ,} g _{0 , g 1 ,}
White balance can be maintained by setting b ₀ and b ₁ .

Note that the modulation axes _{φ 0} , φ _{1 ,} and φ ₃ are as shown in the vector diagram in FIG _.
-15°, phase difference between φ ₀ axis and R → signal (2°)
By ignoring the phase difference (-2 degrees) between the φ ₂ axis and the B→signal, the matrix circuit 31 can be simplified. In this case, each matrix constant r ₀ , r ₁ , g ₀ , g ₁ , b ₀ ,
b ₁ is, for example, r ₀ = g ₀ = 0.63, b ₀ = 0.45, g ₁ =
By setting 0.18, r ₁ = b ₁ = 0, C ₃ 〓=0.63R・exp(jω _sc t+105°) +0.63G・exp(jω _sc t+225°) +(0.45B+0.18G)・exp (jω _sc t−15°) ...The carrier color signal C ₃ 〓 expressed by the sixth equation can be output from the signal output terminal 37.

As is clear from the description of each embodiment above, according to the present invention, if the color carrier frequency is sc, then 1/2
Each of the three primary color signals is band-limited by a low-pass filter with a filter characteristic of H ₀ (ω) having a bandwidth less than sc, and the band-limited three primary color signals are converted into a point-sequential color signal with a period of 1/sc. The first sampling carrier of the point-sequential color signal train is taken out through a band pass filter having a filter characteristic of H ₁ (ω) with sc as the center frequency, and H ₀ (ω−ω _sc ) By combining and outputting carrier color signals in the ×H ₁ (ω) band, it is possible to directly generate digital carrier color signals compatible with the NTSC and PAL systems from the three primary color signals obtained by a color video camera. Since they can be synthesized, the configuration of the matrix circuit can be simplified and the intended purpose can be fully achieved.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing a general four-phase modulation type digital color encoder.
2 is a block diagram showing the basic configuration, FIG. 2 is a time chart for explaining the operation, and FIG. 3 is a signal spectrum distribution diagram of each signal. Figures 4 to 6 are diagrams showing a general three-phase modulation type digital color encoder. Figure 4 is a block diagram showing the basic configuration, and Figure 5 is a schematic diagram showing a dot-sequential color difference signal sequence. FIG. 6 is a signal spectrum distribution diagram of each signal. 7 to 10 are diagrams showing an embodiment of a four-phase modulation digital color encoder according to the present invention, and FIG.
Figure 8 is a block diagram showing the basic configuration, Figure 8 is a schematic diagram showing a dot-sequential color signal sequence, Figure 9 is a vector diagram showing the operating principle of four-phase modulation, and Figure 10 is the spectral distribution of each signal. It is a diagram. 11 to 13 are diagrams showing an embodiment of a three-phase modulation type digital color encoder according to the present invention. FIG. 11 is a block diagram showing the basic configuration, and FIG.
The figure is a vector diagram showing the operating principle of three-phase modulation, and FIG. 13 is a vector diagram showing the operating principle of three-phase modulation when simplifying the matrix circuit in this embodiment. 21, 31...matrix circuit, 22, 23,
24, 25, 32, 33, 34...Low pass filter, 26, 35...Signal selection circuit, 27, 36
... Bandwidth filter, 28, 37 ... Signal output terminal.

Claims (1)

[Claims] 1. Each of the three primary color signals is band-limited by a low-pass filter with a filter characteristic of H ₀ (ω) having a bandwidth less than 1/2·sc, where the color carrier frequency is sc, and the band-limited signal is The three primary color signals are dot-sequentialized to form a dot-sequential color signal train with a period of 1/sc, and the above-mentioned dot-sequential color signal train is passed through a bandpass filter with a filter characteristic of H ₁ (ω) with sc as the center frequency. Take out the primary sampling carrier of H ₀ (ω
A digital color encoder characterized in that it synthesizes and outputs carrier color signals in a band of −ω _sc )×H ₁ (ω).