JPS6050109B2 - digital color encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an improvement of a color encoder that directly digitizes the three primary color signals of an image pickup output signal of a color television camera to form an NTSC digital color television signal.

Conventionally, in order to digitize an NTSC color television signal, the composite color television signal as an output signal of an analog color encoder is converted into a composite signal form using a clock frequency set to, for example, four times the color subcarrier frequency. Since the system was digitized as it was, a high-performance analog-to-digital conversion circuit with a complex configuration was required.

We have also improved this by directly digitizing the three primary color signals, such as the shooting output signal of a color television camera, and then using those digital three primary color signals to perform signal processing similar to conventional analog color encoders. In the digital color encoder configured as follows,
The number of high-performance analog-to-digital conversion circuits required to construct such a digital color encoder increases, and the circuit configuration for color encoding is not always suitable for digital calculations. Furthermore, the circuit configuration of a digital color encoder that performs color encoding on digital three primary color signals is adapted to digital calculations, as described in Japanese Patent Application No. 1983-83513 filed by the applicant. In the ``color subcarrier frequency signal coding method'', digital green signal is encoded by a clock frequency equal to four times the color subcarrier frequency among the digital three primary color signals encoded by clock frequencies each having an integer ratio with the color subcarrier frequency. In addition to making the signal a luminance signal component,
Two types of digital color difference signals consisting of the difference between a digital red signal and a digital blue signal encoded with a clock frequency equal to the color subcarrier frequency and a clock frequency of the above-mentioned digital green signal lowered to 114, respectively. The clock frequency of
For example, the color signal components are represented by four-phase cyclic vectors each having a digital color difference signal consisting of a low frequency component equivalent to 0.6 MHz, which is equal to the color signal band, as components at a predetermined ratio,
The DC component of the circulation vector is used to correct the low range of the luminance signal component consisting only of the digital green signal,
Therefore, the clock frequency of the analog-to-digital conversion of the red signal and blue signal that forms the digital color difference signal as the low-frequency color signal component is reduced, and the cyclic vector is calculated at a low clock frequency corresponding to the color signal band. In this way, digital calculations in the digital color encoder are performed at a clock frequency as low as possible, but since the mid-high frequency components of the luminance signal are represented only by the digital green signal, the definition of the luminance signal is reduced, and Even if the digital calculation of the cyclic vector representing the color signal component is performed at a clock frequency as low as that of the color signal, the digital color signal component and luminance signal low-frequency correction component obtained by the digital calculation are not required for the final encoded output signal. Adding the digital green signal with the digital green signal using a high clock frequency has the drawback that it is not very advantageous overall in terms of digital calculation, and overall improvement in digital calculation has not been achieved.

The purpose of the present invention is to eliminate the various drawbacks mentioned above in the conventional art,
Reducing the number of analog-to-digital conversion circuits required for encoding color television signals, or simplifying the digital operations required for a digital color encoder by using a low-speed analog-to-digital conversion circuit with a low clock frequency, It is an object of the present invention to provide a digital color encoder that improves the mid-high frequency characteristics of a luminance signal expressed only by a digital green signal and improves the definition of the luminance signal.

That is, the digital color encoder of the present invention generates a first digital color difference consisting of a difference between a digital red signal and a digital green signal among digital three primary color signals encoded by clock frequencies each having an integer ratio with the color subcarrier frequency. a luminance signal component consisting of a chrominance signal component represented by a cyclic vector of a predetermined plurality of phases, each of which has a predetermined ratio of components, and a second digital color difference signal consisting of a difference between a digital blue signal and a digital green signal, and the digital green signal; a digital color encoder that configures a digital color television signal with the first and second components, and adds a luminance signal low-frequency correction component consisting of a DC component of the cyclic vector to the digital color television signal; The present invention is characterized in that a luminance signal mid-range correction component, which is formed by performing a digit shift on a binary code signal representing each of the digital color difference signals, is added to the digital color television signal. In the following, the invention will be described in detail by way of example embodiments with reference to the drawings.

First, an example of the basic configuration of the digital color encoder of the present invention is shown in FIG. 1, and then the cyclic vector configuration of the carrier color signal used for digital calculation in the digital color encoder of the present invention is sequentially shown in FIGS. 2 to 5. show.

In the circuit configuration shown in FIG. 1, the three primary color signals from each input terminal are guided to the respective converters and first subjected to direct analog-to-digital conversion. That is, a green (G) signal 1 having almost the same signal level as the luminance signal is guided to the analog-to-digital converter 3, and the color subcarrier frequency Fs is
The red (R) signal 2 and the blue (B) signal 3 are digitized and converted into binary code signals with a clock frequency equal to four times c, while the red (R) signal 2 and the blue (B) signal 3 are converted into analog signals via low-pass filters 1 and 2, respectively. - Commonly led to the digital converter 4, the color subcarrier frequency F,. The signal is alternately digitized and converted into a binary code signal using a clock frequency equal to twice that of the signal. Such digitization adds color subcarrier frequency F, to the green signal G. For example, the red signal R and blue signal B, which do not need to have such a wide band, are converted to a standard PCM signal with a frequency band twice as wide as the color subcarrier frequency F.
Convert to a standard PCM signal with a frequency band equal to l3C. The digital red signal 4 and the digital blue signal 5 with a clock frequency of 2fsc taken from the converter 4 are then guided to interpolators 5 and 6, respectively, 2f,.

Those signals 4 and 5 sampled at the clock frequency of
Perform signal interpolation to interpolate between each sample value of 4fs
Convert to a digital signal equivalent to that sampled at a clock frequency of 0. The interpolation of the intermediate sample value is a simple linear interpolation, and the intermediate value X of two consecutive samplings A and B is set to the average value of the sample values on both sides, i.e.,
B)/2 (1).

Therefore, from each interpolator 5 and 6 there is a digital green signal of 4 as well as a digital green signal from analog-to-digital converter 3.
Since a digital red signal and a digital blue signal are obtained in encoded form with a clock frequency of f, 0, these digital primary color signals are applied to subtracters 7 and 8, respectively.
supply to. On the other hand, the data from the analog-to-digital converter 3. The digital green signal G is supplied as a luminance signal component to the adder 11 via the limbal compensator 20, as well as to the subtracters 7 and 8 described above, and the digital red signal R and digital They are each subtracted from the blue signal B to form digital color difference signals RG and BG encoded at a clock frequency of 4 fsc, respectively.

Therefore, when subtraction is performed on the digital red signal and digital blue signal encoded at a clock frequency of 4fsc by the interpolators 5 and 6 as described above, the digital color difference signals are 2f, . If subtraction is performed on the digital red signal and digital blue signal that have a frequency band of up to It has a frequency band up to Fsc. However, the above-mentioned patent application
In the conventional encoding method described in Patent No. 2-83513, a digital color difference signal having a frequency band up to the latter FsO is formed for subsequent signal processing. 4f to ensure that the digital color television signal to be formed has sufficient definition.
As long as it is encoded at a clock frequency of 13C and theoretically has a frequency band of up to 2fsc, the digital calculation for color encoding can be performed in a comprehensive manner without forcing the clock frequency used to be reduced. From a practical standpoint, it's not that much of a disadvantage. Therefore, in the digital color encoder of the present invention, in consideration of the subsequent signal processing, the digital color difference signal R-
G and B-G are formed as described above. However, in the digital color encoder of the present invention,
As in the encoding method described in the above-mentioned Japanese Patent Application No. 52-83513, the luminance signal component is composed of a digital green signal, and the digital color difference signal as described above is used as a component of a predetermined ratio. The carrier color signal component is represented by a circulating vector, and the luminance signal component consisting only of the digital green signal is corrected using the DC component of the circulating vector. In addition to correcting the components, the brightness signal level is corrected for at least the middle range of the brightness signal, preferably the L middle and high range, using a correction signal directly generated from the digital color difference signal.That is, first,
The above-mentioned digital color difference signals RG and BG are guided to digital filters 12 and 13, respectively, and the clock frequency is set to 4f according to their integral characteristics.

When encoding an N'ISC color television signal by adding a low-pass characteristic corresponding to the color signal band to the encoded signal as it is, for example, the low-pass characteristic can be changed to 0.
．． Set to 6M soil.

On the other hand, in the digital color encoder of the present invention, the digital green signal is included as a luminance signal component, but the luminance signal consisting only of the green signal is somewhat different from the luminance signal formed more faithfully than the three primary color signals. Therefore, at least for the low frequency component, a correction signal consisting of the DC component of the carrier color signal circulation vector described above is added to obtain a completely faithful luminance signal component Y1, that is, Y=G+0.30(R-
G)+0.11(B-G) (2). However,
The luminance signal low-frequency correction component formed as the DC component of the carrier color signal circulation vector has a band of the digital color difference signal that is a component of the circulation vector, for example, up to 0.6MHz, so it can correct the low-frequency luminance up to 0.6MFIz. Only signal level correction can be performed. In the digital color encoder of the present invention, at least the color subcarrier frequency F,.

In order to correct the signal level for the mid-range luminance signal up to
The luminance signal correction components up to f3c, or up to F and c if such linear interpolation is not performed, are formed by digit shifting of the binary code signals constituting the digital color difference signals RG and BG mentioned above. do. That is, the digital color difference signal R-
For G, lower the binary code signal by two digits to 0.2
5(R-G), and for the digital color difference signal B-G, the binary code signal is lowered by three digits to 0.125(B
-G), and add the digital color difference signals with their digits lowered to the digital green signal G to obtain at least Fs. . Luminance signal in the same frequency band. Y'' for Y
=G+0.25(R-G)+0.125(B-G)
The format is (3).

Therefore, the luminance signal low-frequency correction component formed as the DC component of the carrier color signal circulation vector described above is
0.050 (R-G
)-0.015(B-G) (4), and by correcting the signal level, in the high range up to the upper limit frequency of the luminance signal, only the G signal, at least up to the color subcarrier frequency Fsc. , preferably 2fsc
In the mid-high range up to, the above formula (3) or 0
．． When the pressure is reduced to 6M, a luminance signal component in the form of the above-mentioned equation (2) is obtained, which becomes an almost completely faithful digital luminance signal component, and an image quality that is no different from that of a standard image is obtained.

In the circuit configuration shown in FIG. 1, in order to correct the luminance signal level, the digital color difference signal RG from the subtracter 7 is supplied to a digit shift circuit 9, where it is shifted by two digits to 0. 25 (R-G) signal to guide the adder 11, and the digital color difference signal B-G from the subtracter 8.
is supplied to the digit shift circuit 10 to perform a 3-digit shift, and 0.
125 (B-G) signals are formed and also led to the adder 11 and added to the digital green signal G from the analog-to-digital converter 3, respectively.

Next, the luminance signal low-frequency correction component expressed by the above equation (4) can be obtained as an unbalanced component generated in the circuit that forms the digital carrier color signal, that is, a DC component of the carrier color signal circulation vector.

In the digital color encoder of the present invention, N'
The VSC color television signal is set to four times the color subcarrier frequency FsO, that is, 4f. is encoded at a clock frequency of 0 to form a digital carrier color signal.
To this end, the carrier color signal is represented by a cyclic vector with an interphase period corresponding to the clock frequency. That is, N
'The carrier color signal of the ISC color television signal is
As shown in Figure 2a, the color subcarrier vectors (R-Y)/1.14 and (B-Y)/2.03 are orthogonal to each other. The subcarrier orthogonal vectors can be transformed into orthogonal vectors as shown in FIG. 2b.

If each of the vertical and horizontal vectors in the color subcarrier orthogonal vectors shown in Figure 2b are decomposed into symmetrical vectors with opposite polarities, they can be converted into four-phase vectors as shown in Figure 2c. When the four-phase vector shown in FIG. 2c is rewritten, it becomes as shown in FIG. 3. When the four-phase vector shown in the third diagram is made to go around every four clocks of the above-mentioned clock frequency 4fsc, the clock frequency is 4f. This is the four-phase carrier color signal circulation vector. Therefore, in order to obtain the luminance signal correction component expressed by the above-mentioned equation (4) from the carrier color signal circulation vector, each of the color difference signal components R-G and B-G constituting the four-phase vector shown in FIG. Section (4)
In the equation, it is sufficient to add the corresponding 0.05 (RG) and -0.015 (BG), respectively, and the four-phase carrier color signal circulation vector of the form shown in Fig. 4 is approximately obtained. can get. In the circuit configuration shown in the first diagram,
In order to obtain a digital carrier color signal component and a luminance signal low-frequency correction component using such a cyclic vector, the digital color difference signals R-G and B-G from the subtracters 7 and 8 are respectively supplied to a low-pass digital filter. , clock frequency 4f,. Integrate the code signal in its form and calculate its frequency band, for example, 0.6M, which corresponds to the color signal band.
After limiting the frequency range to a low frequency of up to Hz, the digital low frequency color difference signals R-G and B-G are transmitted to a programmed read-only memory (PROM) circuit 14-, respectively.
1 to 3 and 15-1 to 3 in parallel, perform digital operations as shown in FIG.
The calculation output signals of the circuit are sequentially switched and added so that signal components corresponding to each term of the four-phase circulation vector shown in FIG. 4 are obtained. That is, 0.15 (R-G) from PROM circuit 1, and 0.61 (R-G) from 14-2.
-G) and 14-3, each digital color difference signal of 0.05 (R-G) is obtained, and as shown in the figure, these digital color difference signals are guided to the changeover switch SWl, 4f. The clock frequency of 0.0 from the PROM circuit 14-3 is switched in a cycle of 4 clocks.
5 (R-G) signal is directly supplied to the adder 16,
It is commonly added to the switching output signal from switch SWl. On the other hand, 0.44 (B-G
), 0.11 (B-G) from 15-2 and 0.015 (B-G) from 15-3 are obtained, and these digital color difference signals are transferred to the changeover switch as shown in the figure. At the same time, the PRO
Only the 0.015 (B-G) signal from the M circuit 15-3 is directly supplied to the adder 17 and commonly added to the switching output signal from the switch SW2. From these adders 16 and 17, digital carrier color signal components and luminance signal low-frequency correction components represented by four-phase carrier color signal circulation vectors as shown in the fourth figure are obtained, so these signal components are added. 11 and added to the digital green signal whose signal level has been corrected up to the mid-high range, a digital luminance signal consisting of high, medium and low band components as described above is obtained.The digital carrier color described above is obtained. A digital color television signal in the form of a PCM signal is obtained by encoding the NTSC color television signal at a clock frequency of 4fs0. Incidentally, digit shift circuits 9 and 10 are constructed in substantially the same manner as the configuration example of the digital color encoder of the present invention described above.
0.30 (R-G) and 0.11 (B-G
), and a circuit configuration in which the PROM circuits 14-3 and 15-3 in the calculation system of the cyclic vector shown in the first figure are removed is also conceivable; Compared to the illustrated circuit configuration, the luminance signal mid-high range correction component calculation circuit is more complex than simply performing digit shifting of the binary code signal, and cannot provide the same sophisticated effects as the configuration shown in the first figure.

In any case, in the digital color encoder described above, the three primary color signals are encoded using two television signal analog-to-digital converters, thereby simplifying the circuit configuration. In addition, as shown in the configuration example shown in the first figure, the red signal and the blue signal are commonly led to a single high-speed analog-to-digital converter,
For example, 4f.

are encoded alternately with the clock frequency of 2f.
When converting into a digital red signal and a digital blue signal having a clock frequency of sc, either one of these converted output signals is delayed by one clock period to align their timings before subsequent signal processing, or , the digital red signal and digital blue signal taken out at alternate clock periods are directly subjected to the linear interpolation described above. Note that even if such encoding is performed, since the encoded output signals are used as color difference signals of low frequency components, the quality of the desired digital color television signal will not be degraded; Modal encoding greatly simplifies the construction of digital color encoders. As is clear from the above description, in the digital color encoder of the present invention, among the three primary color signals G, R, and B such as the image pickup output signal of a color television camera, the luminance signal component of the composite color television signal is almost equal to the luminance signal component of the composite color television signal. With a green signal G having a signal level of Therefore, the red signal R and the blue signal B are encoded using a single high-speed analog-to-digital converter or two low-speed analog-to-digital converters, and the luminance signal component consisting of only the green signal G is encoded. The signal level correction signal is converted into the two types of color difference signals R-
Since it is formed by a simple digit shift signal for G and B-G and a DC component signal of the carrier color signal circulation vector forming system for the low frequency component of the luminance signal, it is a digital signal with a simple configuration that does not cause deterioration in image quality. It is possible to manufacture a digital color encoder at a low cost for use in a studio system for television broadcasting, which will need to be installed in large numbers in the future.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of the digital color encoder of the present invention, and FIGS. It is a vector diagram which shows each order. 1, 2...Low pass wave generator, 3, 4...
Analog-digital converter, 5, 6... interpolator, 7, 8... subtracter, 9, 10... digit shift circuit, 11... adder , 12, 13...
・・Low pass wave generator, 14-1~3, 15-1~3...
...PROM circuit, 16, 17... Adder, S
Wl, SW2...Switch switch.

Claims (1)

[Scope of Claims] A first digital color difference signal consisting of the difference between a digital red signal and a digital green signal among digital three primary color signals each encoded by a clock frequency having an integer ratio with each color subcarrier frequency; A color signal component represented by a cyclic vector of a plurality of predetermined phases, each having a second digital color difference signal consisting of a difference between a digital blue signal and a digital green signal as components at a predetermined ratio, and a luminance signal component consisting of the digital green signal. In a digital color encoder that configures a digital color television signal and adds a luminance signal low-frequency correction component consisting of a DC component of the cyclic vector to the digital color television signal, the first and second digital A digital color encoder characterized in that a luminance signal mid-range correction component formed by performing a digit shift on each binary code signal representing a color difference signal is added to the digital color television signal. 2. Encoding the green signal with a clock frequency equal to four times the color subcarrier frequency to form said digital green signal, and coding the red and blue signals, respectively, with a clock frequency equal to twice the color subcarrier frequency; Claim 1, wherein the digital red signal and the digital blue signal are formed by linear interpolation.
Digital color encoder as described in section. 3. The cyclic vector of the predetermined plurality of phases is constructed by using the first and second digital color difference signals, each of which has been band-limited through a low-pass digital filter, as components of a predetermined ratio. A digital color encoder according to claim 1. 4. An analog red signal and an analog blue signal are alternately sampled by a single analog-to-digital converter to form said digital red signal and said digital blue signal, respectively. Digital color encoder as described in section.