JPS6050111B2 - Color signal spatial frequency characteristic improvement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal spatial frequency improvement circuit suitable for application to a color television receiver.

The band of color difference signals in color video signals was originally 50.
Since it is about 0 kHz to 1.5 MHz, it has a narrow band compared to a wide band luminance signal which has a signal band of about 4.0 MHz. Therefore, the waveform of the color difference signal is duller than that of the luminance signal. That is, even if a part of the signal of the subject image output from the television camera is a luminance signal Yw), a color difference signal, for example, a red color difference signal Rw-Yw, and is a step signal as shown in FIGS. 1A and B, The spatial frequency of the video signal deteriorates due to band limitations and passage through the transmission system, and when demodulated by a receiver, the waveform becomes blunted as shown in C and D in the same figure.

Therefore, the R primary color signal formed from these signals Yw and Rw-Yw is also distorted (see E in the figure), making it impossible to faithfully reproduce the step signal. The waveform distortion is the color difference signal Rw-Yw
This is more noticeable, and therefore, when an image is reproduced, it has the disadvantage of color blurring, that is, deterioration of color resolution.

Here, in a color image, changes in brightness correspond to changes in chromaticity.

For example, when the luminance signal Yw changes in a stepwise manner as described above, the color difference signal Rw-Yw also changes in accordance with this change, so the present invention particularly focuses on the correlation between the luminance signal and the color difference signal. By superimposing the high frequency signal of the luminance signal on the color signal, the spatial frequency characteristics of the color signal are improved and color blurring is prevented. The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, in which the spatial frequency of the color difference signal is improved in stages. In the figure, 1a is an input terminal for a wideband luminance signal Yw separated from the video signal, and 1b is an input terminal for a demodulated R color difference signal (narrowband signal) RN-YN.

Similarly, 1C is an input terminal for the B color difference signal BN-YN. The luminance signal Yw and the color difference signals RN-YN and BN-YN are respectively supplied to the matrix circuit 2 to form the primary color signal RB. In the present invention, the color difference signal RN is calculated from the luminance signal Yw.
A correction signal Sp to be superimposed on -YN and BN-YN is formed.

This correction signal Sp is a low-frequency signal Y constituting the luminance signal Yw.
The high frequency signal YH of the luminance signal Yw has an amplitude that approximately corresponds to the ratio of the amount of change in the amplitude of N and the amount of change in the color difference signal at the time of this amplitude change. Since the amount of change in amplitude in each signal corresponds to the differential output of each signal, the correction signal Sp can be obtained from these differential outputs. To explain the red color difference signal, the low frequency component Y that makes up the luminance signal Y
When the differential output of N is YN'' (=DYN/Dt) and the differential output of the red color difference signal is (RN-YN)'', the correction signal S
PR is determined by the following formula.

Specific means for forming a correction signal will be explained using FIG. 2.

Broadband luminance signal Y supplied to terminal 1a (Fig. 3A)
) is separated into a high-frequency signal YH (B in the same figure) and a narrow-band low-frequency signal YN (C in the same figure) by a high-pass filter 3H and a low-pass filter 3L, and the low-frequency signal YN is further supplied to a differentiating circuit 4. After the differential output YN'' as shown in D in the figure is formed, it is supplied to the division circuit 5 together with the high-frequency signal YH, which is the basis of the correction signal SPR, and a division process of YH/YN'' is performed. As will be described later, the division circuit 5 generates a division output S when the differential output YN'' serving as the denominator approaches zero.

A special divider circuit is used such that the value also becomes zero. On the other hand, the color difference signal RN-YN (FIG. 3F) is differentiated by the differentiating circuit 7R (FIG. 3G), and then supplied to the multiplication circuit 8R together with the above-mentioned division output SD. '' multiplication processing is performed.

This multiplication output is the correction signal SPR (H in the same figure) to be obtained, and the correction amount, that is, the amplitude of the correction signal SPR is the ratio of the amount of change in the amplitude of the luminance signal and the color difference signal.The correction signals S and R are sent to the adder circuit 9R. Since the chrominance signal RN-YN is added to the narrowband color difference signal RN-YN, the amplitude change portion of the color difference signal RN-YN is corrected by the correction signal SPR as shown in FIG. 31. That is,
Since the color difference signal RY has its high frequency component supplemented by the high frequency signal YH of the luminance signal Yw, the spatial frequency of the color difference signal RY can be improved, and the primary color signal R after matrixing is As shown by the broken line in FIG. 1E, the signal is corrected to a normal step-like signal. By supplying this primary color signal to the picture tube, color blur can be completely removed and color resolution can be improved. The spatial frequency of the blue color difference signal BN-YN is also improved by the correction signal SPB formed based on the division output SD, and the reproduced image becomes of high quality.

By the way, when the color difference signal RN-YN changes as shown in FIG. 3F, the frequency characteristics of the color difference signal RN-YN cannot be improved with the polarity of the divided output SD shown in FIG. 3E. However, the differential output (RN
-YN)'' is negative in the falling part, so the multiplication output corresponding to the falling part of the signal has the opposite polarity,
As a result of being able to correct the dullness of the falling portion of the signal, the frequency characteristics are improved. Further, since the amount of correction of the correction signal SPR is the ratio of the amount of change in the amplitude of the luminance signal and the color difference signal, the amount of correction is neither too large nor too small.

FIG. 4 shows an example of the above-mentioned division circuit 5. In the figure, 5A is the first divider used when the divisor is positive;
B is a second divider used when the divisor is a negative divisor, and since they have the same configuration, only the first divider 5A will be described. However, the input polarity of the signal is reversed.
The first divider 5A has a first differential amplifier circuit 10A, Ql and Q2 are differential transistors, and both emitters are commonly connected via an emitter resistor R1 having the same resistance value. A transistor 9 and an emitter resistor R3 constituting the current source 11A are connected to this common connection point.

The base terminal 13a of the transistor O is supplied with a signal voltage serving as a divisor, in this example a positive differential output YJ, and the differential amplifier circuit 10A is supplied with a high frequency signal YH, which is a dividend in this example.
is supplied. A second differential amplifier circuit 12A is connected between the collectors of transistors Ql and Q2.

This circuit 12A is also composed of a pair of transistors Q4 and Q5 whose emitters are commonly connected, and a resistor R for a constant current source is provided on the emitter side. is connected. Transistor Q4
, each collector and power supply of Q5■. . There is a resistor 15 between
a and 15b are connected, and an output terminal is derived from this, and this differential output is supplied to the third differential amplifier circuit 17, and the configuration is such that the desired division output can be obtained from the terminal 17a. Ru. Note that transistors Q6 and Q7 connected to transistors Q4 and Q5 are collector loads of transistors Ql and Q2.

The relationship between the resistors R1 to R4 is selected as R1/R3=R2/R4. The operation of the division circuit 5 constructed in this way will be described. For convenience of explanation, it is assumed that the high-frequency signal Y6, which is the dividend, is constant and its voltage is 8.

Then, the base-emitter voltage and emitter current of each transistor Q1 to Q7 are determined as shown in the figure. It is well known that the voltage-current characteristic between the base and emitter of a transistor is given by equation (2), where the emitter current is IEl, and the base-emitter voltage is VBE.

Now, when the relationship between current and voltage is determined as shown in FIG. 4, the relationship between emitter currents 14, i5 and 16, 17 can be expressed as follows by using equation (2). From equations (3) and (4), we can transform equation (5) to obtain the emitter voltage.

, 17 are as if the voltage applied to the transistor Q3 is VA. Since the voltage of the signal differentially applied to the transistors Ql and Q2 is B, the collector currents 16 and 17 of the transistors Ql and Q2 are given by the following equations. However, in the example explained below, the circuit shown in FIG. 4 is formed on the same chip, so each transistor Q1 to
The base-emitter voltages VBE1 to VBE7 of Q7 are all equal. Therefore, it is simply indicated by VBE. The emitter current 14 of the transistor α is calculated from equation (6), and the base voltage of the transistors Q and Q7 is expressed as ■. This is the resistor R
. Current 1 flowing through. If the emitter current 14, j5 obtained in this way is supplied to the differential amplifier 17 shown in FIG. A proportional output current will be obtained. That is, the division power S. is obtained. Here, VA
= 0, currents 16 and 17 do not flow, so the output SD
is zero. Therefore, if VB is constant (however, ■8〉0
) and (1)9, the output changes as shown by curve 11 in FIG. ■Since the variable current source 11B operates at 9×0, in this case, the second divider 5B operates instead of the first divider 5A, and the divided output SD is as shown in FIG. This results in negative output. Note that in the case of ■8<0, the output characteristics are opposite to those described above. That is, the division output S at this time. becomes like curve 12. In this way, in the above-described division circuit 5, even if the divisor approaches zero, it becomes zero without being saturated, and VA,
(2) Even if both B change, the division output SD corresponding to the input can be obtained.

By the way, in order to distribute the positive and negative differential outputs YN'' to the above-mentioned current sources 11A and 11B, for example, a control circuit 40 as shown in FIG. 6 may be used.

In the figure, 42 and 43 are differential amplifier circuits, and a pair of transistors QlO and Q constitute one differential amplifier circuit 42.
Each emitter of transistor Qll is connected with one resistor R5, and only the emitter of one transistor Qll is connected with one resistor R5.
It is connected to a constant current source 45A composed of a resistor R6 and a resistor R6. The collector of the other transistor QlO is connected to the common terminal 41 of the first differential amplifier circuit 10A shown in FIG.
connected to a. The other differential amplifier circuit 43 similarly has differential transistors Ql3 and Ql4, and a resistor R7 is connected between the emitters.

Constant current circuit 45B is connected to the emitter of transistor Ql3, and the collector of the other transistor Ql4 is connected to common terminal 41b. The bases of the transistors QlO, Ql3 and Qll, Ql4 are connected in common, and a signal source 47 is connected to this common connection point.

In this example, the resistors R5 and R7 have the same resistance value, but there is no difference even if they are different. The operation of the control circuit 40 is as follows.

Resistors R, R7 are connected to transistors QlO and Ql4, respectively.
are interposed, so each transistor QlO, Qll
, Ql3 and Ql4 become unbalanced, and when there is no signal, emitter currents of transistors QlO and Ql4 hardly flow, and emitter current flows only in transistors Qll and Ql3. Therefore, if a signal YN'' is supplied that makes the base of transistor Ql3 positive, the emitter current flows only in transistor Ql3, and the base current of transistor QlO increases, so transistor QlO Since a collector current corresponding to the increase flows, the circuit 40 operates as a variable current source 11A at this time.When the signal YN'' is negative, a collector current corresponding to the signal YN'' flows through the transistor Qll, In the end, the operation is completely opposite to that described above, and in this case, the circuit 40 operates as the other variable current source 11B,
This allows the signal supply state to be controlled without using a mechanical switch or the like.

According to the configuration of the present invention described above, since the high-frequency correction signal Sp formed based on the luminance signal Yw is superimposed on the color difference signal, the spatial frequency characteristics of the color difference signal can be improved.
There is no color bleeding, and color resolution can be improved.

Furthermore, by superimposing the correction signal Sp in this way, it is possible to widen the band of the color difference signal, so when the circuit of the present invention is applied to the reproduction system of a video tape recorder (VTR), it is possible to Even if the band of the low-frequency converted carrier color signal to be recorded is made narrower than before, an image with better color resolution than before can be obtained.

Therefore, in this case, the luminance signal band can be expanded by the bandwidth obtained by narrowing the carrier color signal band, so that resolution can be improved. In the embodiment shown in FIG. 2, the high-pass filter 3H was used to form the high-frequency signal YH of the luminance signals Y, v, but as shown in FIG. The subtracted output of the area signal YN may also be used.
23 is a delay circuit for compensating for the delay caused by the intervention of the filter 3L.

Further, in the above-described embodiment, the correction signal is superimposed on the demodulated color difference signal, but the same effect as described above can be achieved even if the correction signal is added to the primary color signal. FIG. 8 shows an example of this.

The same reference numerals are given to the parts corresponding to those in FIG. 2, and the explanation thereof is omitted.
Adding circuits 20R to 20B are provided on each of the N transmission paths, and narrowband primary color signals RN-BN are formed using the low-frequency signals YN supplied thereto. After the primary color signals RN-BN are formed, each primary color signal RN is generated in the same manner as in FIG.
By forming a correction signal SPR-SPB corresponding to -BN and supplying it to the primary color signal RN-BN, the spatial frequency of the primary color signal RN-BN can be improved.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram for explaining the present invention, Fig. 2 is a system diagram showing an embodiment of the present invention, Fig. 3 is a waveform diagram for explaining its operation, and Fig. 4 is an example of a division circuit. Connection diagram shown, No. 5
6 is a connection diagram of other main parts of the division circuit, FIG. 7 is a system diagram showing a partial modification of FIG. 2, and FIG. It is a system diagram showing an example of. Yw is a wideband luminance signal, YH is a highband signal, YN is a lowband signal, RN-YN-BN-YN is a narrowband color difference signal, S
PR-SPB is a correction signal.

Claims (1)

[Claims] 1 A differential output of a low-frequency signal obtained by passing the luminance signal through a low-pass filter and a high-frequency signal obtained by band-limiting the luminance signal with a high-pass filter are supplied to a divider circuit, and the high-frequency signal is output from the differential output. In addition to forming a division output divided by A correction signal having an amplitude approximately corresponding to the ratio of the amount of change in the amplitude of the color signal is obtained, and this correction signal is added to the color difference signal to improve the spatial frequency characteristics of the demodulated color difference signal. A circuit for improving the spatial frequency characteristics of a color signal in a color television receiver, which obtains a primary color signal by combining the luminance signals in a matrix circuit.