JPH1093988A - Digital color encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital color encoder which can create a composite signal based on a signal that is acquired by using a sampling frequency which is set in a desired frequency. SOLUTION: A phase converter 23 seeks the phase of a color subcarrier based on the ratio of the 1st value Nc which indexes a sampling frequency that is stored in an Nc register 21 and the 2nd value Nsc which indexes a color subcarrier frequency that is stored in an Nsc register 22 and the counting value of a sampling counter 20, a modulator 24 creates a carrier color signal C based on the phase, and a digital adder 18 superimposes the signal C on a luminance signal Y and creates a composite signal M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color encoder for generating a composite signal (composite signal) used for a television, a VTR, and the like.

[0002]

2. Description of the Related Art Hitherto, there has been known a digital color encoder which generates a composite signal specified in the NTSC standard, the PAL standard or the like based on a digitized luminance signal and color difference signal. FIG. 3 is a block diagram showing a configuration of a conventional digital color encoder according to the NTSC system.

[0003] A delay circuit 14 shown in FIG.
1, a digital luminance signal (Y) synchronized with a clock of a predetermined sampling frequency is input. The delay circuit 14 delays the input luminance signal (Y) for a predetermined time. Digital color difference signals Cr (RY) and Cb (B-B) having different phases synchronized with a clock of a predetermined sampling frequency via input terminals 12 and 13 are supplied to low-pass filters (LPFs) 15 and 16, respectively. Y) is input. The low-pass filters 15 and 16 limit the input color difference signals Cr and Cb to required frequency bands and output the signals to the balanced modulators 31 and 32.

[0004] Balanced modulators 31 and 32 are provided with a low-pass filter.
Color difference signals Cr, Cb band-limited by
Of the color subcarrier frequency of the color subcarrier (3.58 MHz)
Each sampling time with an integer multiple of sampling frequency
At the sampling frequency and the color subcarrier frequency
Coefficient (e.g., the color sub-carrier frequency
When sampling at three times the sampling frequency,
Signal M described later₁ , M _Two , M_Three With the values of COS and SIN
Some (1,0), (-1/2, √3 / 2), (-1 /
2, −√3 / 2)) by multiplying the color difference signals Cr and Cb by
By periodically arranging digital values corresponding to
Carrier signals Sr and Sb are output after balance modulation of the color subcarrier
You.

[0005] The digital adder 17 includes a carrier signal Sr,
The carrier color signal C is generated by adding Sb. The digital adder 18 superimposes the carrier signal C on the luminance signal Y delayed by the delay circuit 14 so that the composite signal M
Generate The generated composite signal M is output to the outside via the output terminal 19.

The composite signal M is expressed as: M = Y + Cr.COS (.omega.t) + Cb.SIN (.omega.t). Here, Y is a luminance signal, Cr and Cb are color difference signals, and ω is an angular frequency of a color subcarrier. Here, in the case where the sampling frequency has a frequency three times the color subcarrier frequency and the composite signal M is generated,
The composite signal M is composed of signals M ₁ and M shown below.
₂ and M ₃ are represented by repeating in time division.

M ₁ = Y + Cr · COS (ω · 0) −Cb · SIN (ω · 0) M ₂ = Y + Cr · COS (ω · １ ／ ω) −Cb · SIN (ω · 1 / 3ω) M ₃ = Y + Cr · COS (ω · 2 / 3ω) −Cb · SIN (ω · 2 / 3ω)

[0008]

However, in the digital color encoder described above, a composite signal is generated by setting a sampling frequency having an integer multiple of the color subcarrier frequency. However, it is difficult to implement this in a certain system and use a clock unique to the system as a sampling frequency.

Further, even if it is attempted to increase the resolution of image data captured by a camera or the like, it is difficult to use a sampling frequency other than an integral multiple of the color sub-carrier frequency, and the resolution of the image data cannot be increased. There is a problem that sometimes. In view of the above circumstances, the present invention
It is an object of the present invention to provide a digital color encoder capable of generating a composite signal based on a signal obtained by using a sampling frequency set to a desired frequency.

[0010]

According to the present invention, there is provided a digital color encoder comprising: an input terminal for receiving a digital luminance signal and a digital color difference signal synchronized with a clock having a predetermined sampling frequency; A carrier chrominance signal generation circuit for generating a digital carrier chrominance signal obtained by modulating a color subcarrier having a carrier frequency with the chrominance signal; and generating a digital composite signal by superimposing the carrier chrominance signal on the luminance signal A digital adder that outputs the composite signal, and an output terminal that outputs the composite signal. The carrier chrominance signal generation circuit includes: (1) a sampling counter that counts the clock of the sampling frequency; and (2) a first index that indicates the sampling frequency. (3) The above color sub-carrier frequency A second register for storing a second value to be indexed (4) a ratio between a first value stored in the first register and a second value stored in the second register, and the sampling; A phase converter for obtaining the phase of the color subcarrier based on the count value of the counter; and (5) a modulator for generating the carrier chrominance signal based on the phase obtained by the phase converter. I do.

[0011] The digital color encoder of the present invention comprises:
The phase of the color subcarrier is determined based on the ratio of the first value indicating the sampling frequency to the second value indicating the color subcarrier frequency and the count value of the sampling counter that counts the clock of the sampling frequency, and the composite is obtained. Since a signal is generated, it is not always necessary to use a sampling frequency that is an integral multiple of the color subcarrier frequency as in the related art.As the sampling frequency, for example, a clock unique to a system in which a digital color encoder is mounted is used. It can be used, and the circuit can be simplified. Further, a sampling frequency other than an integral multiple of the color sub-carrier frequency can be used, and the resolution of image data can be increased. Further, the color sub-carrier frequency can be set arbitrarily, and the NTSC system, PAL system, etc.
A general-purpose digital color encoder suitable for any of a plurality of standards having different color subcarrier frequencies is realized.

Here, in the digital color encoder of the present invention, a third index indicating a ratio between the sampling frequency and the color sub-carrier frequency is used instead of both the first register and the second register. Third to store the value
And the phase converter obtains the phase of the color subcarrier based on the third value stored in the third register and the count value of the sampling counter.

Thus, instead of both the first register and the second register, a third register for storing a third value indicating the ratio between the sampling frequency and the color subcarrier frequency is provided. , Only one register is required, and the circuit configuration is simplified.

[0014]

Embodiments of the present invention will be described below. FIG. 1 is a block diagram showing a configuration of a digital color encoder according to one embodiment of the present invention. The same elements as those of the digital color encoder shown in FIG. 3 are denoted by the same reference numerals, and different points will be described.

The sampling counter 20 counts a clock having a sampling frequency. Nc register 21
The (first register according to the present invention) stores a first value Nc indicating a sampling frequency. The Nsc register 22 (a second register according to the present invention) stores a second value Nsc indicating a color subcarrier frequency.

The phase converter 23 calculates the ratio (Nsc / Nc) between the first value Nc stored in the Nc register 21 and the second value Nsc stored in the Nsc register 22 and the count value of the sampling counter 20. , The phase of the color subcarrier with respect to the sampling frequency is obtained. The modulator 24 calculates the values of COS and SIN at the phase obtained by the phase converter 23, and converts these values to the color difference signals Cr and
Cb is multiplied by Cb to modulate the chrominance subcarrier in a balanced manner and the carrier signals Sr,
Sb is output. Further, the modulator 24 outputs the carrier signals Sr,
The carrier color signal C is generated by adding Sb.

The digital adder 18 outputs the carrier signal C
Is superimposed on the luminance signal Y delayed by the delay circuit 14.
In this way, the composite signal M is generated and output from the output terminal 19 to the outside. FIG. 2 is a diagram showing a phase relationship between a sine waveform (referred to as a sampling waveform) A of a sampling frequency and a sine waveform B (referred to as a color subcarrier waveform) of a color subcarrier frequency in the digital color encoder shown in FIG. It is.

The phase of the sampling waveform A and the phase of the color sub-carrier waveform B are changed each time the color difference signal is sampled (in FIG. 2,
(Indicating 6 samplings) Nsc / Nc.
Based on this, the ratio (Nsc / Nc, 2Nsc) corresponding to the ratio Nsc / Nc between the first value Nc and the second Nsc and the count value stored in the sampling counter 20 is calculated.
/ Nc,..., 6Nsc / Nc), the phase of the color sub-carrier waveform B with respect to the sampling waveform A can be obtained.

Here, the composite signal M is: M = Y + Cr.COS (2π / Nsc / Nct · t) + C
b · SIN (2π / Nsc / Nc · t) By substituting the obtained phase into the above equation, a composite signal M is obtained.

In the present embodiment, an Nc register 21 for storing a first value Nc indicating a sampling frequency and an Nc register for storing a second value Nsc indicating a color sub-carrier frequency.
Although the description has been made using the sc register 22, a register for storing a value indicating a ratio between the sampling frequency and the color sub-carrier frequency is provided instead of the Nc register 21 and the Nsc register 22, and the value stored in this register is provided. The composite signal may be generated by calculating the phase of the color subcarrier based on the count value of the sampling counter.

[0021]

As described above, according to the present invention,
A clock unique to the system can be used as the sampling frequency, and the circuit can be simplified. Further, the resolution of the image data can be freely increased by using a sampling frequency other than an integral multiple of the color sub-carrier frequency. Furthermore, since the color sub-carrier frequency can be set arbitrarily,
A general-purpose digital color encoder suitable for any of a plurality of standards having different color subcarrier frequencies, such as the NTSC system and the PAL system, is realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a digital color encoder according to an embodiment of the present invention.

FIG. 2 is a diagram showing a phase relationship between a sine waveform (referred to as a sampling waveform) A of a sampling frequency and a sine waveform (referred to as a color sub-carrier waveform) B of a color sub-carrier frequency in the digital color encoder shown in FIG. It is.

FIG. 3 is a block diagram showing a configuration of a conventional digital color encoder based on the NTSC system.

[Explanation of symbols]

 11, 12, 13 input terminal 14 delay circuit 15, 16 low-pass filter 18 digital adder 19 output terminal 20 sampling counter 21 Nc register 22 Nsc register 23 phase converter 24 modulator

Claims (2)

[Claims] An input terminal for receiving a digital luminance signal and a digital color difference signal synchronized with a clock having a predetermined sampling frequency, and a digital signal obtained by modulating a color subcarrier having a predetermined color subcarrier frequency with the color difference signal. A carrier chrominance signal generation circuit for generating a carrier chrominance signal, a digital adder for generating a digital composite signal by superimposing the carrier chrominance signal on the luminance signal, and an output terminal for outputting the composite signal. A carrier counter for counting the clock of the sampling frequency; a first register for storing a first value indicating the sampling frequency; and a second register for indicating the color sub-carrier frequency. The second that stores the value of
The color subcarrier based on a ratio of a first value stored in the first register to a second value stored in the second register, and a count value of the sampling counter. A digital color encoder, comprising: a phase converter for obtaining the phase of the above; and a modulator for generating the carrier color signal based on the phase obtained by the phase converter. A second register for storing a third value indicating a ratio between the sampling frequency and the color subcarrier frequency, in place of both the first register and the second register. 2. The method according to claim 1, wherein the phase converter determines the phase of the chrominance subcarrier based on a third value stored in the third register and a count value of the sampling counter. Digital color encoder as described.