JPH05316532A - Digital color difference signal demodulation circuit - Google Patents

Abstract

PURPOSE:To demodulate a color signal without color slurring even with respect to an input picture signal comprising a color difference signal subcarrier of a different phase. CONSTITUTION:Synthesis signals A, B from two cameras are inputted as input signals, and a fetch pulse 16b is always inputted to a register 11 when the signal A is received, a pulse 16c to a register 12 is inhibited, a selection circuit 13 selects a theta1, and a fetch pulse 16c is always inputted to the register 12 when the signal B is received, the pulse 16b to the register 11 is inhibited, a selection circuit 13 selects a theta2, then a phase deviation theta from the same camera is latched to prevent production of a phase jump. As a result, no color slurring is caused even when any pattern is selected between the signals A, B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color difference signal demodulation circuit for demodulating a color difference signal from an NTSC television signal by digital processing.

[0002]

2. Description of the Related Art Conventionally, when a color difference signal is demodulated by this type of digital processing, one method is to use a digital sine wave that is frequency-synchronized with the color difference signal subcarrier but not phase-synchronized. And a digital cosine wave is generated, and this is multiplied by the color difference signal subcarrier to demodulate the color difference signal. In this case, the demodulation axis of the color difference signal is not fixed, and the signal representing the demodulation axis (color burst color difference signals C ₁ and C ₂ )
When transmitting and modulating, it is necessary to modulate on the same axis as the demodulation axis.

As a second method, there is a method of demodulating a color difference signal by generating a digital sine wave and a digital cosine wave which are phase-synchronized with a color difference signal subcarrier and multiplying them. In this case, since the demodulation axis is fixed, it is not necessary to transmit a signal representing the demodulation axis, and modulation may be performed on a predetermined axis (for example, U axis or V axis) at the time of modulation. In the second method, conventionally, in order to perform phase synchronization, as shown in FIG. 2, the color burst signal is 180 ° with respect to the U axis of the modulation axis and 90 ° with respect to the V axis.
If it is advanced and demodulated correctly on the U and V axes, V
The axial component (E _R -E _Y ) has the property of becoming zero. Further, the property that the phase deviation θ from the normal demodulation axis can be obtained from the components on the U axis and the V axis is used. That is, the color burst signal is demodulated, the phase deviation θ between the demodulation on the normal U-axis and the V-axis is calculated from the amplitude value of the demodulated color difference signal, and the result is fed back to the color difference signal subcarrier generation circuit for demodulation. By correcting the demodulation axis, control is performed so that the demodulation axis is pulled into the regular demodulation axis. In the correction of the demodulation axis, in order to reduce the influence of noise and waveform distortion, the correction is performed gradually and the plural lines are averaged.

[0004]

In the conventional digital color difference signal demodulation circuit, the first method has a problem that the demodulation axis is not fixed, and the second method has a problem that the demodulation axis is not fixed. There is a problem that line time is required. For example, as shown in FIG. 3, when a signal obtained by multiplexing signals from two cameras is input, a phase jump of a color difference signal subcarrier occurs between A and B. However, there is a problem in that the demodulation axis does not pull into the normal axis for several lines after the screen is switched to each screen, causing color misregistration.

An object of the present invention is to make it possible to demodulate a color signal without color shift even with respect to an input image signal composed of color difference signal subcarriers having different phases.

[0006]

In order to achieve the above object, the present invention provides a color burst signal of an NTSC television signal with a phase angle at each sample point of a color difference signal subcarrier from a color difference signal subcarrier generation circuit. The color difference signal of the color burst is demodulated by multiplying by the sine wave and the cosine wave, and the phase deviation from the U axis and the V axis is detected from the two demodulated color difference signals and fed back to the color difference signal subcarrier generation circuit. A digital color difference signal demodulation circuit that corrects the phase angle of the demodulated color difference signal subcarrier, generates the sine wave and cosine wave that are phase-locked to the color burst of the color difference signal subcarrier, and demodulates the color difference signal by the U axis and the V axis. In, there are two or more registers that capture and store the phase deviation at a predetermined time, and at least two registers are provided at each predetermined time. Register stored phase difference of the time division select, in which so as to fed back to the chrominance signal subcarrier generating circuit.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a digital color difference signal demodulation circuit showing an embodiment of the present invention. In FIG.
The color difference signal sub-carrier generation circuit 100 includes an adder 14, a phase angle generation circuit 15, a pulse generation circuit 16, a sine wave generation circuit 18, and a cosine wave generation circuit 17. Digitized NTSC television signal (PCM)
Is input to the comb filter 1 and the subtractor 3, and in the comb filter 1, the difference [[-Z ^-1 + 2-
Z) / 4] is calculated to separate the color difference signal subcarrier components. The color difference signal subcarrier components separated are inputted to the band pass filter 2 is separated passes only the chrominance signal subcarrier component centered at 3.58MH _Z. The output of the bandpass filter 2 is input to the subtractor 3, the multiplier 4, and the multiplier 5. The subtractor 3 subtracts the color-difference signal subcarrier component from the NTSC signal to extract the luminance signal. The separated luminance signal is band-controlled by the low pass filter 6 to generate a luminance signal Y. In the multiplier 4 and the multiplier 5, sin (ωT) and cos (ω
T) is multiplied and demodulated to a baseband color difference signal.

Since the color difference signals demodulated by the multipliers 4 and 5 contain harmonic components, the low pass filter 7 and the low pass filter 8 are band-limited and then the base signal is added. Band color difference signal U (E _B −
It is output as E _Y) and V (E _R -E _Y).

The color difference signals U and V are input to the phase detection circuit 9 and the phase deviation is obtained. Since the obtained phase deviation is obtained in a short color burst section, it is affected by noise and waveform distortion, and it is necessary to obtain an accurate phase deviation by averaging a plurality of lines, which is input to the average value calculation circuit 10. Averaged. The averaged phase deviation θ is input to the register 11 and the register 12. _{One of} the phase deviations θ ₁ and θ ₂ output from the register 11 and the register 12 is selected by the selection circuit 13 and input to the adder 14. Adder 1
In 4, the phase angle from the phase angle generation circuit 15 (0 to 2π)
And the phase deviation θ _i are added and input to the sine wave generation circuit 18 and the cosine wave generation circuit 17, which generate a sine wave sin (ωT) and a cosine wave cos (ωT) from the reception phase angle, respectively, and the multiplier 4 And 5 to demodulate the baseband color difference signal. The frame pulse F synchronized with the input NTSC signal (PCM) is input to the pulse generation circuit 16 and acts as a reference signal for generating various pulses. Pulse generation circuit 1
6 inputs the address information 16d of the PCM signal to the phase angle generation circuit 15, and inputs the phase deviation θ to the registers 11 and 12 by the pulses 16b and 16c.
Is sent to the selection circuit 13 and the phase deviation θ ₁ or the phase deviation θ
_{The second} selection signal 16a is transmitted.

For example, when the composite signals from the two cameras shown in FIG. 3 are input as input signals and the color difference signal subcarriers f are frequency-synchronized but not phase-synchronized, the average value is calculated. If the output of the circuit 10 is input to the adder 14 as it is, a phase jump of f occurs at the boundary between A and B. For example, when the phase shifts to B, re-pulling of the phase occurs and color shift occurs. become.

However, according to the method of the present embodiment, for example, when receiving A in FIG. 3, the fetch pulse 16b is always input to the register 11 and the pulse 16c to the register 12 is prohibited, The selection circuit 13 selects θ ₁ ,
When receiving B of FIG. 3, the fetch pulse 16c is inputted to the register 12 and the pulse 16c to the register 11 is inputted.
By prohibiting b and selecting θ ₂ by the selection circuit 13, the phase deviation θ from the same camera is held and phase jump does not occur.

An operation time chart at this time is shown in FIG. Clocks 1 and 2 in FIG. 4 generate a pulse of 1 pulse for each line in each line by A and B in each screen of FIG.

The phase angle generation circuit 15 is a pulse generation circuit 1
The address information 16d is received from 6 and the phase angle at each sample point is periodically transmitted. For example, if the sampling frequency is four times f, four phases generate a phase angle of one cycle. This phase angle locks the frequency, but since the phase is free with respect to f, it is necessary to correct the phase difference with respect to f.
The fed back phase deviation θ is corrected. The sine wave generation circuit 18 and the cosine wave generation circuit 17 generate a sine wave and a cosine wave according to the phase angle from the adder 14.

The phase deviation θ is obtained by demodulating the color burst signal, as shown in FIG. 2, θ = tan ^-1 (V _i /
V _j ). Further, whether or not demodulation is performed in phase synchronization with the U axis and the V axis can be confirmed by setting the demodulation component V _i of the V axis of the color burst signal to zero.

In FIG. 1, there are two kinds of phase deviations θ _i , but they can be expanded to any number.

[0017]

As described above, according to the present invention, the phase deviation is stored for each phase of the color difference signal subcarrier f of the input image (PCM), and the color difference signal demodulation circuit is operated in a time division manner. There is an effect that the color signal can be demodulated without color shift even with respect to the input image signal composed of the color difference signal subcarrier f of the phase.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a modulation axis of a color difference signal according to an embodiment of the present invention.

FIG. 3 is a diagram showing a split multiple screen applied to an embodiment of the present invention.

FIG. 4 is a time chart explaining the operation of the embodiment of the present invention.

[Explanation of symbols]

 1 Comb Filter 2 Band Pass Filter 3 Subtractor 4,5 Multiplier 6,7,8 Low Pass Filter 9 Phase Detection Circuit 10 Average Value Calculation Circuit 11, 12 Register 13 Selection Circuit 14 Adder 15 Phase Angle Generation Circuit 16 Pulse generation circuit 17 Cosine wave generation circuit 18 Sine wave generation circuit 100 Color difference signal Sub-carrier generation circuit

Claims (3)

[Claims] 1. A color burst color difference signal is obtained by multiplying the color burst signal of an NTSC television signal by the phase angle at each sample point of the color difference signal subcarrier from the color difference signal subcarrier generation circuit multiplied by a sine wave and a cosine wave. The phase difference from the U axis and the V axis is detected from the demodulated and demodulated two color difference signals and is fed back to the color difference signal subcarrier generation circuit to correct the phase angle of the demodulated color difference signal subcarrier to obtain the color difference signal subcarrier. In the digital color difference signal demodulation circuit that generates the sine wave and the cosine wave that are phase-locked to the color burst of, and demodulates the color difference signal by the U axis and the V axis, the phase deviation is fetched at a predetermined time and stored. It has a register and selects the phase deviation stored in two registers at predetermined time intervals in a time division manner. Digital color difference signal demodulating circuit, characterized in that the feedback to the transmitting generator. 2. The digital color difference signal demodulation circuit according to claim 1, wherein the color difference signal sub-carrier generation circuit comprises an adder, a phase angle generation circuit, a pulse generation circuit, a sine wave generation circuit and a cosine wave generation circuit. 3. A digital color difference signal demodulation circuit according to claim 1, wherein more than two registers are provided for storing and storing the phase deviation at a predetermined time.