JPH0414987A - Digital color demodulation circuit - Google Patents

Abstract

PURPOSE:To demodulate a correct color difference signal and to prevent hue deviation even when an offset angle is any value other than 0 deg. by detecting a peak value of a color burst part, generating a color difference conversion table based on the peak value so as to demodulate a color difference signal. CONSTITUTION:A C data being an output of a Y/C separator circuit 205 enters latch circuits 207-210, in which the signal is latched in a prescribed timing, the C data enters a color burst detection circuit 211, where a peak value of a color burst signal is detected. Then the output of the circuit 211 is stored in conversion table circuits 212-215, in which the signal is calculated, and, e.g. outputs of both the conversion tables 212, 213 are added by an adder, from which color difference signals (R-Y), (R-B) are outputted. Since the correction function to demodulate the color difference signal based on the peak value is adopted, the reliability against a change with the passage of time or a temperature change is high and the color difference signal is always demodulated and hue deviation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital color demodulation circuit installed in color television receivers, video projectors, and video printers.

[Conventional Technique #I] Conventionally, a digital color demodulation circuit configured as shown in FIG. 6 can be considered. In other words, the NTSC signal supplied to the input terminal 601 enters an analog-to-digital converter (hereinafter referred to as an A/D converter) 602, is quantized, is demodulated into three primary color signals of RGB in a digital processing circuit 603, and is output. It is output to terminal 606.

On the other hand, the NTSC signal enters the burst synchronization PLL circuit 604 and generates a frequency four times as high (hereinafter referred to as 4*fsc) synchronized with the color burst signal, which is sampled clocked and supplied to the A/D converter 602. be done.

By the way, the adjustment circuit 605 is an adjustment circuit that adjusts the timing relationship of the phase angle between 4*fsc, which is the output of the burst synchronization PLL circuit, and the color burst signal.

The relationship between the phase angles of these two signals is shown in FIG. In other words, conventionally, the phase angle of the color burst (
An adjustment circuit 605 is provided so that the timing of 4*fsc with respect to the BY-axis reference O' is 0°, 90°, 180', 270'' (setting the offset angle to 0').

Then, it is demodulated into RGB based on the demodulation principle described below.

The NTSC signal is obtained by combining a luminance signal (hereinafter referred to as a Y signal) and a carrier color signal (hereinafter referred to as a chroma signal) to form the first equation.

N= Y + (RY)/1.14 cos θ+(B
-Y)/2.03" sin θN: NTSC signal Y: Luminance signal C is the second and third terms of the first equation and becomes the second equation.

C= (RY)/1.14 cosθ + (B-Y)
72.03" sin θ second equation 80°, 270°, chroma digital data C01C1, A/D converted and Y/C separated using this 4*fsc,
c2 and c3 become from the second equation to the third equation.

θ=O°: θ=9Q"; θ=180°: θ,=270": CO=■-Y)/1.14 + Ocl=
O+ (B-Y)/2.03c2 = -(R-Y)/
1.14 + 0c3= 0 −■−Y)
72.03 Third Equation From Equations (3-1) and (3-2), the color difference signal can be calculated using Equation 4.

-η of 1.14”cO (B-Y) = 2.03”d (4-2
) By adjusting the offset angle to 0° using the adjustment circuit 605, the color difference signal could be easily demodulated from the fourth equation.

[Problems to be Solved by the Invention] However, in the conventional demodulation circuit shown in FIG. 6, the reliability of the adjustment circuit 605 is poor, and the 4*
The phase angle of fsc fluctuates due to changes over time and temperature, and it is difficult to maintain the offset angle at Oo. As a result, there is a problem that the hue shifts.

An object of the present invention is to demodulate correct color difference signals and prevent hue shift even if the offset angle is any value other than O.

Measures for Solving Problem E] This is achieved by a correction function that detects the peak value of the color burst portion, creates a color difference conversion table based on the peak value, and demodulates the color difference signal using this color difference conversion table. Ru.

[Embodiment] FIG. 1 is a block diagram showing the configuration of an embodiment of a digital color demodulation circuit of the present invention.

The NTSC signal supplied to the input terminal 101 is
= O+x": θ=90+x'20=180+x':θ=270+X':cO=(RY)/1.14"cosx+(B-Y)7
2.03"5inx (5-1)cl = -(R-
Y)71.14”5inx + (B-Y)72.03
“cosx (5-2)c2 = −(RY)/1.
14”cosx + (B-Y)/2.03”5inx
(5-3)c3 = (RY)71.14”sin
x - (B-Y)/2.03"cosx (5-4)
From the fifth equation (5-1) and the equation (5-2), the color difference signal can be calculated using the sixth equation.

(RY) = 1.14”(co”cos x −c
l”sin x)(B-Y) = 2.03”(co”
sin x 10 cl ”cos x) 6th formula% formula%) By the way, as mentioned above, the color burst signal
The converted peak values are as shown in FIG. 5, and the seventh equation holds true.

hO=　a”sin　x h1 = a”cos x (a"a = ho umbrella ho + hl"hl) 7th formula Substituting the seventh equation into the sixth equation yields the eighth equation.

(RY) = 1.14”(cO”hI/a-cl
”ho/a) (8-1)(B-Y) =
2.03"(cO"hO/a - cl"hl/a)
(8-2) Equation 8 Furthermore, in order to have an ACC (automatic saturation corrector) function, the amplitude of the color burst of the standard NTSC signal is set to A (constant), and instead of 1.14 in Equation 8, (1, 14 By substituting ``A/a) and adding correction, the ninth equation is obtained.

(RY) =ω* (1,14”A*hl/(ho bookhO+hl”hl))-cl” (1,14”A”
hO/(ho umbrellaho+hl”hl) ) (9-1
).

(B-η=cO umbrella (2,03 umbrella A*hO/(ho umbrella ho
+h l umbrella h1)) 101” (2,03”A rate hl/
(ho”ho+hl”hl) ) (9-2) 9th
In the ninth equation, the term of the offset angle X° is eliminated.

The color difference signal (G-Y) is determined by Equation 10.

(G-η=-0,51 umbrella (R-Y) -0,19"(B
-Y) Equation 10 Finally, add the luminance signal Y and use Equation 11 to find the final high forces R, G, and B.

R=(R-η+Ya=((3-η+YB=medium-force+Y) Equation 11 Above, the principle of correcting the offset angle X° has been described.

Considering the above-mentioned points, the operation of FIG. 2 will be explained.

FIG. 2 is an internal block diagram of the digital processing circuit 104 of FIG. 1. A/D converted digital data is input to the input terminal 201, and Y data and C data separated by the line memories 203 and 204 and the Y/C separation circuit 205 are output. The C data referred to here is data in which the four types of cO, cl, C2, and C3 shown in Equation 5 are alternately repeated. The Y/C separation method utilizes the property of vertical correlation.

On the other hand, the input terminal 202 has a burst synchronized clock 4.
*fsc is input and the timing control circuit 206
clock pulses φ01 φ90 at 90” intervals,
φ180 and φ270 are output.

The C data output from the Y/C separation circuit 205 enters latch circuits 207, 208, 209, and 210, and is latched at a predetermined timing. That is, the latch circuits 207 and 209 latch CO, and the latch circuits 208 and 210 latch cl.

The C data enters a color burst detection circuit 211, which detects the peak value of the color burst signal portion. This corresponds to ho and hl in the seventh equation.

Then, in order to realize the calculation of Equation 9 based on these hO and hl, each term of Equation 9 is calculated and the result is sent to the conversion table circuit 2.
12.213.214.215. Sunahachi,
(9-1>The calculated value of the first term in the equation is sent to the conversion table 212,
The second term of equation (9-1) is stored in 213, the first term of equation (9-2) is stored in 214, and the second term is stored in 215. For example, the conversion table 212 contains data co20 to c (1-25
256 types of data, which are the calculation results of one term of equation (9-1) leading to 5, are stored in order.

In this embodiment, RAM is used for the above four conversion tables. FIG. 3 shows a conversion table circuit. The input data points to the address of the RAM, and the data bus becomes the output. Therefore, a calculation result corresponding to the value of C data, which is input data, is output.

In FIG. 2, the C data latched at a predetermined timing points to the address of the RAM, and the corresponding calculation result is output. The output of the conversion table 212 is (9-1
), the output of 213 shows the calculation result of the second term of equation (9-1), and the output of the re-conversion table is added by an adder 216 to the color difference signal (R-Y). Become. This is nothing but the calculation of equation (9-1)).

In exactly the same way, conversion tables 214 and 215 and adder 217
Equation (9-2) is executed by the action of , and a color difference signal (B-Y) is output.

The colorimetric difference signal enters the matrix circuit 218, and its output is output as a color difference signal (G-Y). This is the 10th
This is to realize the calculation of the expression, and it can be easily realized by using the above-mentioned conversion table.

Each color difference signal is further added with a Y signal by adders 219, 220, 221, which is calculated by executing Equation 11 and R
This means that the colors are demodulated into lG and B signals.

In this embodiment, the conversion table 212.213.214
．． The contents of 215 are updated once per field during the vertical blanking period.

[Effects of the Invention] As explained in detail above, the digital color demodulation circuit of the present invention has a configuration having a correction function of detecting the peak value of the color burst portion and demodulating the color difference signal based on the peak value. Therefore, it is highly reliable against changes over time and temperature, and has the effect of always demodulating the correct color difference signal and preventing hue shift.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment showing the configuration of a digital color demodulation circuit according to the present invention. FIG. 2 is an internal block diagram of the digital processing circuit of FIG. 1. FIG. 3 is a conversion table circuit diagram. FIG. 4 is a timing diagram showing the phase angle between the sampling clock and the color burst signal. FIG. 5 is a diagram showing peak values of a color burst signal portion. FIG. 6 is a diagram of a conventional digital color demodulation circuit. FIG. 7 is a timing diagram showing the phase angle between a conventional sampling clock and a color burst signal. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kisanbe Bensue 1 person Figure 3 Figure 4 Figure 5 Figure 6 Kuroduku Figure 7

Claims (1)

[Claims] Input the composite video signal (hereinafter referred to as NTSC signal),
A digital color demodulation circuit converts the NTSC signal from analog to digital using a quadruple sampling clock synchronized with the color burst, and demodulates the color based on the digital data. A digital color demodulation circuit characterized in that a color difference conversion table is created based on a high value, and a color difference signal is demodulated using the color difference conversion table.