JPS6129594B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a color television receiver.
The present invention relates to a color signal correction circuit that has the effect of improving both color transients and color reproducibility in minute areas in images. In an NTSC color television system, as a method to substantially expand the received color signal bandwidth, the brightness high frequency range proportional to the ratio of the low frequency range of the color signal and the luminance signal is used as the high frequency range of the color signal that is not originally transmitted. The method of applying it has been considered for a long time. This method will be briefly explained. In the NTSC color television system,
Broadband output from a color television camera (approximately
The luminance signal Y (=0.30R+0.59G+
0.11B) and the color difference signals RY and BY are combined and transmitted. However, for color difference signals, the band is limited to about 1.5 to 0.5 M〓. Here, if the low frequency component of the signal is indicated by the subscript L, and the high frequency component is indicated by the subscript H, the luminance signal Y demodulated in the color television receiver becomes Y _L + Y _H , and the color difference signal after color demodulation. CY becomes C _L -Y _L. If these signals are combined between the cathode and the grid of a color cathode ray tube as conventionally done (C
_L - Y _L ) + (Y _L + Y _H ) = C _L + Y _H , so the luminance signal is reproduced up to the high frequency component, but the color signal is only the low frequency component, and transient changes cannot be reproduced.
This is one of the limitations of the NTSC system. Therefore, on the assumption that the signal magnitude ratio C _L /Y _L of the low frequency part of the color signal and the luminance signal holds true also in the high frequency part, the color from C _L , Y _L , Y _H is calculated. A high frequency component CH (=C _L /Y _L Y _H ) is created and added to each primary color. In other words, the outline of the conventional method is to change the signal applied between the cathode and the grid of the cathode ray tube from the conventional C _L +Y _H to C _L +C _H in order to exceed the color resolution limit of the current NTSC system. This conventional method mainly has the following two drawbacks, and improvements have been made to address these drawbacks. These will be explained using FIGS. 1 and 2. One example of this improvement concerns color transients. For example, Figure 1
Let's consider the boundary between the colors when images of red and green adjacent to each other are received as shown in the figure below. At this time, the luminance signal low frequency component Y _L is as shown in 3 and includes a transient component Y _LT shown as 2. Further, the high frequency component Y _H is indicated by 4 (the cutoff frequency for this frequency separation is selected to be approximately 0.5M, which is the band of the color difference signal). On the other hand, R, G, B color signals are
_These are indicated by broken lines 7, 9, and 11, respectively, and the cathode of the cathode ray tube receives signals 8 (=R _L +Y _{H )} , 10 (=G _L +Y _H ), and 12
(=B _L +Y _H ) are applied, and the resolution at the color boundary deteriorates. If the signal processing described above is applied here, the result will be as follows. The high frequency component of the color signal is created from the transient 2 (=Y _LT ) of the low frequency component of the luminance signal and the transient of the color signal. For example, in the case of R, Y _LT 2
The quotient R _LT /Y _LT of R and the transient R _LT (polarity negative) shown in 5 is taken, and the luminance signal high frequency component Y is added to this.
Multiply by _H to obtain the high frequency component R _H shown in 13. Similarly, in the case of G, multiply the quotient G _LT /Y LT of Y _LT and _the transient G _LT (positive polarity) of G shown in 6 by Y _H to get 1.
Let it be the high frequency component _GH shown in 4. The same is true for B, but
In this example, since there is no _BLT , _BH is also zero as shown in 15. By adding the above color signal high frequency components R _H , G _H , B _H to the low frequency components, 16, 17, 18
As shown in , the transient response at the color boundary is improved (in B, unnecessary components like 12 are not included), and the color resolution is improved. Another example of improvement is the improvement of color reproducibility in small to small areas. This will be explained with reference to FIG. For example, a thin red line 20 on a black background 19
A luminance signal Y when a certain image is received is indicated by 21. At this time, the color signals R _L , G _L , B _L are 2
The broken lines are 2, 24, 26 (24, 26 are zero). In the conventional method, the luminance signal high frequency component Y _H is added to these, R _L + Y _H (23), G _L + Y _H
(25), B _L +Y _H (27) are applied to the cathode ray tube, making the color look whiter than it actually is. Therefore, similar to the improvement example described above, a high-frequency component C _H of the color signal is created to prevent colors in small areas from becoming white. In this case, there are no transients in the luminance and color signals, so the high-frequency component of the color signal C _H
The amount CL /Y which is the ratio of the high frequency component Y _H of the luminance signal to the ratio _CL /Y _L of the luminance signal and the low frequency component of the chrominance signal is _CL /
Guess Y _L × Y _H. 27, 28, 2 made in this way
C _L obtained by adding R _H , G _H , B _H (G _H , B _H are zero because G _L and B _L are zero) shown in 9 to R _L , G _L , B _L
+C _H signals 30, 31, 32 are applied to the cathode ray tube. As a result, the color reproducibility of minute parts can be improved without the part 20 becoming whitish. Next, a block diagram of a signal processing circuit that realizes the above will be explained with reference to FIG. 33 is a video signal input terminal; 37, 38 are arithmetic circuits for subtraction; 36, 41, 43 are addition; 42 are multiplication; and 39, 40 are arithmetic circuits for division. The division circuit 39 calculates a high frequency component of the color C _LT /Y _LT for improving the color transient.
・The divider circuit 40 that creates Y _H is a high frequency component of color C _L /Y _L Y to improve the color reproducibility of minute parts.
It is for making _H. Reference numeral 44 denotes a delay element, which is required at several locations other than those shown in the figure for time alignment of signals, but will be omitted here. 45 is an adjustment circuit for contrast adjustment, pedestal clamp, etc., 46 is an LPF, and 47 is an HPF, and these are luminance signal low frequency and high frequency components (Y _L , Y _H )
This is an extraction circuit. The cutoff frequencies of these filters are selected to be approximately 0.5M, which is the bandwidth of the color difference signal. Here, the output of the color difference signal demodulation circuit 35 is three channels of RY, G-Y, and BY.
The portion 56 surrounded by the broken line also requires two more channels of the same circuit, but is omitted here and is represented by CY. The operation of this block diagram will be explained step by step below. One of the video signals input from the 33 becomes the color difference signal (C-Y) _L through the chroma BPF 34 and the color difference signal demodulation circuit 35, and the other becomes the LP after passing through the adjustment circuit 45 such as a pedestal clamp.
Luminance signal low frequency component Y _L , HPF4 via F46
7 to produce a luminance signal high frequency component Y _H respectively. An adder circuit 36 adds (C-Y) _L and Y _L to obtain C _L as an output. And this C _L is the delay line 44
The difference of 50 between the passed value and the original C _L is obtained by 37 subtraction circuits. This is the color transient _CLT . Transient of luminance signal (Y _L shown as 49)
_T ) is similarly obtained as the output of the subtractor 38.
A division circuit 39 performs division of these signals C _LT and Y _LT
The signal C _LT /Y _LT shown at 51 is obtained. On the other hand,
A C _L /Y _L signal for improving the color reproducibility of fine parts is obtained as the output 54 of the division circuit 40 . The addition circuit 41 obtains the sum of these signals 51 and 54, and the multiplication circuit 42 multiplies the sum by the luminance signal high frequency component Y _H to obtain the color high frequency component C _H (=C _LT /Y _LT Y
_H + C _L /Y _L Y _H ) is obtained. Then, the addition circuit 43 adds C _L and applies the color signal C _L +C _H containing high frequency components to the cathode of the cathode ray tube from the terminal 48, thereby making it possible to obtain the above-mentioned improvement effect. In addition, in FIG. 3, each output of the division circuits 39 and 40 is added by the addition circuit 41, and this added output is multiplied by a high frequency luminance component, but instead of this, each output of the division circuits 39 and 40 is The same improvement effect can be obtained by multiplying by a high frequency luminance component and then adding the respective multiplication results. However, in the above conventional device,
As shown in FIG. 3, if a processing circuit for improving color transients and a processing circuit for improving color reproducibility of fine parts are operated in parallel, a serious problem will occur as described below. In FIG. 4, 57 is black, 58 is green, and there is a brighter green streak 60 inside. 59 is red and includes a red streak 60 with high brightness as in the case of green. Consider the waveforms of various parts when such an image is received and signal processed by the circuit shown in FIG. First, regarding the luminance signal, the video signal applied to the input terminal 33 in FIG. 3 is shown as 61 in FIG. 4, and its low frequency components and high frequency components are 62 and 64, respectively. Also,
The luminance transient _YLT is obtained by taking the difference between _YL and a signal obtained by delaying _YL , so it becomes a signal as shown in 63. On the other hand, for the color signal, C _L is first obtained at the output of the adder circuit shown in FIG. 36. If this is expressed in three primary colors, it becomes R _L shown in FIG. 4, 65, and G _L shown in 66 (hereinafter, B _L will be omitted). Color Transient C _LT
is obtained as the difference between C L and a signal obtained by delaying C _L , as in the case of luminance, as shown at 67 and 68. As a result, the outputs C _L /Y _L , C _LT /Y _LT of the division circuits 39 and 40 in FIG. 3 are 69, 70 and 71.
, 72, and the high frequency components of _the color _{signal obtained} by multiplying _these by Y _{H are} 73 _, 74.
,75,76. Here, 75 and 76 are 65 and 66, respectively.
, and corrects its rise and fall, and as mentioned above, color transients are improved. On the other hand, 73 and 74 improve the color reproducibility of minute parts (60 in Fig. 4).
Transient portions of color, such as portions a, b, c, and d surrounded by broken lines, also react and produce output. Therefore, these signals 73 and 74 are converted into R _LT /Y _LT Y _H (7
5), G _LT /Y _LT Y _H (76), the amount of correction for the color transient part may be insufficient (in case a) or too much (in cases b, c, d). ) will cause inconvenience. A signal such as a that reduces the effect of R _LT /Y _LT Y _H is produced when the polarity of the color transient and the luminance transient is opposite, that is, when the R signal moves from green to red, the chromaticity occurs when the brightness increases and the brightness decreases, b, c, d
A signal that emphasizes C _LT /R _LT Y _LT occurs when the color transient and the luminance transient have the same polarity. Therefore, as shown in Figure 3,
Conventional devices that simply operate a color transient improvement circuit and a circuit that improves color reproducibility in minute areas in parallel have the disadvantage that the amount of correction for color transient areas may be insufficient or excessive. It was hot. SUMMARY OF THE INVENTION An object of the present invention is to provide a color signal processing circuit that eliminates the above-mentioned drawbacks of the prior art and can simultaneously improve color transients and improve color reproducibility of fine parts. The gist of the present invention is that the color signal processing circuit described above is provided with a function of stopping the circuit operation for improving the color reproducibility of fine parts when improving the color transient part. In other words, the size of C _LT /Y _LT in Fig. 4 71 and 72 | C _LT /Y
A gate circuit is provided that stops the operation of the division circuit 40 in FIG. 3 when _LT | exceeds a certain value. Before entering into the description of the embodiments of the present invention, the division circuits shown in FIGS. 39 and 40 will be described. As for the division circuit, it is obvious that circuits related to other applications of the present applicant (Japanese Patent Application Nos. 53-72839-72841, etc.) can be used. The division circuit has a circuit configuration as shown in FIG. 5, and 77 is the signal A.
78 is an input terminal for signal B, 79 is an output terminal, 80 and 81 are constant current sources, and 82 and 83 are fixed voltage sources. Further, the symbol R with a subscript represents a resistance, and also represents the resistance value at the same time.
The symbol Q with a subscript represents a transistor,
The arrows in the figure indicate the current flowing through the branch and its direction. In this circuit, the division output is to create P such that P.A=C (constant) in the area surrounded by the broken line 84, and to multiply P and signal B (=C・B/A) to divide signals A and B. This operation will be explained below. Transistors Q ₅ and Q ₆ constitute a first differential amplifier, the base of Q ₅ is the input terminal of signal A, and the base of Q ₆ is connected to a fixed voltage source 82 to which voltage V ₃ is applied. There is. Reference numeral 80 denotes a constant current source that sinks a constant current of 2I _AO for this differential amplifier. _Q5 and
The current flowing to the collector of Q ₆ is the current value obtained by adding or subtracting I _A , which is the signal current based on input signal A, to the current I _AO obtained by dividing the above-mentioned sink current in half, and the current value is (I _AO + I _A ), respectively. ( _IAO - _IA )
It is. Q ₁ , Q ₂ , Q ₃ , and Q ₄ are first variable gain circuits and are connected as follows. Q ₁ and Q ₂ and
The emitters of Q ₃ and Q ₄ are coupled together and connected to the collectors of transistors Q ₅ and Q ₆ of the first differential amplifier, respectively. Also connect the bases of Q ₁ and Q ₃ and Q ₂ and Q ₄ respectively. Q ₁ and Q ₄ and Q ₂
and Q ₃ are coupled to each other, and connected to the power supply line via resistors R _C and R _D , respectively. Connect the collector of Q ₁ to the bases of Q ₁ and Q ₃ , and connect the collector of Q ₂ to the bases of Q ₂ and Q ₄ . In the above-described first differential amplifier and first variable gain circuit, the collector currents of Q ₁ , Q ₂ , Q ₃ , and Q ₄ are respectively expressed as I _C1 , I _D1 , I _D2 , and I _C2 , and
The sum of the collector currents of Q ₁ and Q ₄ is expressed as I _C , and Q ₂ and
The sum of the collector currents of _Q3 is represented by _ID . _Q5 and
The collector current of _Q6 is (I _A
O + I _A ) and (I _AO - I _A ). Here, if the base voltage of Q ₁ and Q ₃ is V ₁ and the base voltage of Q ₂ and Q ₄ is V ₂ , then the above I _C1 , I _C2 , I _D1 , I
As is well known, _D2 is expressed by the following formula. Here α: Current amplification factor of Q ₁ , Q ₂ , Q ₃ , Q ₄ is almost equal to 1 q: Electron charge is 1.60206×10 ^-19 coulombs k: Boltzmann constant is 1.38044×10 ^-23 Joule/K ° T: Absolute temperature (kT/q [V]; approximately 26 mV at room temperature) In the following description, it is assumed that the current amplification factor α is 1 (this assumption is actually applicable to many transistors). 1/1+ε ^x +1/1−ε ⁻¹ = 1
When I _{C and ID} are determined from equations (1) to (4) using the formula, the following equations are obtained. here Rewriting equations _{( 5 )} and ₍ 6 _{) as 1} -V ₂ ) on the horizontal axis and P on the vertical axis as shown in Figure 6.
What should be noted here is that P with respect to the change in (V ₁ − V ₂ )
The change in is extremely steep, and P changes from -1 to +1 when (V ₁ -V ₂ ) changes by only ±100 mV around 0. This means that
Considering that the first term (I _AO ) in equations (8) and (9) is a fixed quantity, even if I _A changes, by slightly controlling (V ₁ - V ₂ ), This means that I _C and I _D expressed by equations (8) and (9) can be maintained at constant values (of course, −1≦P≦1
There is naturally a limit to the range of variation in I _A in which I _C or I _D can be kept constant. Focusing on this point, as shown in Figure 5, the collectors of Q ₁ and Q ₄ are connected to the bases _of Q ₁ and Q ₃ , and _the
Connect the collector of to the base of Q ₂ and Q ₄ .
Now consider the case where I _A defined as above increases in the range I _A >0. If V ₁ - _{V 2} > 0 at first, then P > 0 _, and as I _A increases, I _C increases and I _D tends to decrease;
Since V ₁ decreases and I _D increases, V ₂ increases, the value of V ₁ −V ₂ decreases, and therefore the value of P decreases. Therefore, both the increase in I _C and the decrease in I _D are suppressed. Also, if V ₁ −V ₂ < 0 initially, then P < 0, and as I _A increases, I _C
decreases and I _D tends to increase, but a decrease in I _C causes V ₁ to rise, and an increase in I _D causes V ₂ to decrease, so the value of V ₁ - V ₂ increases, and therefore P As the value of becomes large (P<0, therefore |P| becomes small), the decrease in I _C and the increase in I _D are also suppressed. Furthermore, even when I _A decreases within the positive range, changes in I _C and I _D are similarly suppressed. However, this holds true only in the range of I _A >0, and changes in I _c and _ID are not suppressed in the range of I _A <0. The range of I _A <0 will be described later. To summarize the _above , in the range I _A > 0, (V ₁ - _{V 2 )} is ±
It changes automatically within a range of 100mV.
And V ₁ and V ₂ are Q ₁ (and Q ₄ ) and Q ₂ respectively
(and Q ₃ ) and the difference therebetween is within 100 mV at most, so the amount of voltage drop across R _C and the amount of voltage drop across R _D can be considered to be approximately equal.
That is, if (V ₁ −V ₂ ) is ignored, equation (10) holds true. R _C · I _C = R _D · I _D ... (10) On the other hand, since I _C + I _D = 2I _AO , the constant values of I _C and I _D can be found as follows.

[Table] 〓……………(11)
R _C

Claims (1)

[Claims] 1. A first circuit that separates a luminance signal included in a composite color television signal of the NTSC system or similar systems into a low-frequency brightness signal and a high-frequency brightness signal, and a color component after color demodulation. A first division circuit that divides the signal by the low frequency luminance signal, a circuit that detects a transient change in the luminance signal, a circuit that detects a transient change in the color component signal, and a circuit that detects the transient change in the color component signal. A second division circuit that divides by a transient change in the luminance signal, and a circuit that generates a high frequency component of the color component signal by multiplying the sum of the outputs of the first and second division circuits and the high frequency luminance signal. A chroma circuit characterized in that the operation of the first division circuit is stopped when the output of the second division circuit is equal to or higher than a predetermined level. 2 The product of the sum of the outputs of the first and second division circuits and the high-frequency luminance signal is the product of the output of the first division circuit multiplied by the high-frequency luminance signal, and the output of the first and second division circuits multiplied by the high-frequency luminance signal. Find the second product respectively,
Claim 1 is obtained by calculating the sum of the first and second products.
Chroma circuit described in section. 3. A circuit is provided which is supplied with the output signal of the second division circuit and uses its absolute value as an output signal, and the first division circuit stops operating when the output of this circuit is equal to or higher than a predetermined value. A chroma circuit according to any one of claims 1 and 2, characterized in that: