JPS63175594A - Luminance signal forming circuit - Google Patents

Abstract

PURPOSE:To obtain a luminance signal subjected to noise control and luminance reproducibility by introducing a 1st luminance signal when the momentary level at a low frequency of the 1st and a 2nd luminance signals is in a 1st dynamic range and leading the 2nd luminance signal at the exceeded portion when the level exceeds the said range. CONSTITUTION:A limiter 28 for limiting the dynamic range of a broad band luminance signal YH to twice is provided and a mixing circuit 27 mixing the output signal of the limiter 28 and a signal obtained by correcting a low-frequency luminance signal YL having normal luminance reproducibility by a gamma correction circuit 20 is provided. Then the mixing ratio of the signals YL, YH in the mixing circuit 27 is controlled by a control signal AGC. The mixing circuit 27 mixes much signals YL when a large amount of incident light comes and mixes much signals YH when the incident luminous quantity is less. Since the signal YL having excellent luminance reproducibility or the signal YH with excellent S/N is selected, the optimum luminance signal is always generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a luminance signal forming circuit, and is particularly suitable for application to a luminance signal processing circuit in a color television camera using a complementary color filter.

[Summary of the invention]

The present invention performs a matrix operation on the output signals of a camera having a complementary color filter to generate a first luminance signal having a first dynamic range, and also simply synthesizes the output signals of the cameras to obtain a first luminance signal having a first dynamic range. A second luminance signal having a large second dynamic range is generated, and when the instantaneous low-frequency levels of the first and second luminance signals are within the first dynamic range, the first luminance signal When the low-frequency instantaneous levels of the first and second luminance signals exceed the first dynamic range, the second luminance signal is derived at least in the signal portion exceeding the first dynamic range. By deriving the brightness signal, a brightness signal with controlled brightness reproducibility and noise can be obtained.

[Conventional technology]

A color television camera using a complementary color filter uses a complementary color filter that does not allow one color component of red (R), green (G), and blue (B) primary color light to pass through. That is, a yellow (YB) filter passes R and G components, and a cyan (CY) filter passes G and B components.
The magenta (MG) filter passes R and B components.
The white filter (W) passes R, G,
Allows all of the B primary color components to pass through.

If these complementary color filters are used, one filter passes R and G, or G and B1, or R and B color components and two color components, so it is suitable for imaging devices such as image pickup tubes and solid-state image sensors. The amount of light of the incident primary color signal increases, and thereby a large video signal output can be obtained even when imaging a dark subject.

FIG. 3 shows an example of a signal processing section of a television camera that uses a complementary color filter. Light from a subject that is input to the image pickup section 1 passes through the complementary color filter 2 and is irradiated onto an image pickup device 3 consisting of a COD device or the like. Ru. For example, as shown in FIG. 4, the complementary color filter 2 has unit sections of MG and Y.
It is assumed that a filter is used that allows the color components of E, G, and CY to pass through.

The signals obtained line-sequentially from the image sensor 3 are sent to the signal processing circuit 4.
As shown by the arrows in FIG. 4, the fields are exchanged and extracted one by one, and predetermined processing such as waveform shaping and AGC correction is performed, whereby a 3G+2R+2B signal is extracted from the signal processing circuit 4. This signal is detected by the detection circuit 5, and the detection circuit 5 outputs the 2RG signal and the 28-G signal line sequentially. Also, a part of the detection output is sent to the AGC detection circuit 2.
6, and this detection signal AGC is applied to the signal processing circuit 4. The line sequential signal is applied to the adder 6, and also applied to the switch circuit 9 through the IH (horizontal scanning period) delay circuit 7, and further applied to the adder 6 through the IH delay circuit 8. The two input signals are each added by 1/2 and applied to the switch circuit 9. As a result, the switch circuit 9 outputs the 2B-G signal and the 2R-
G signals are obtained, and these signals are applied to the primary color separation circuit 10. This primary color separation circuit 10 generates R, G, and B primary color signals using the above signal and a signal from an IH delay circuit 23, which will be described later. These primary color signals are adjusted to a predetermined white balance eight times by a white balance circuit 11, and then subjected to gamma correction by a chroma-gamma correction circuit 12. This gamma-corrected primary color signal is sent to the matrix circuit 13.
By performing matrix synthesis, the matrix circuit 13 obtains RY, BY color difference signals and a low-frequency luminance signal YL. Among these signals, the color difference signal is applied to the encoder 14.

On the other hand, the 3G+2R+2B signal obtained from the signal processing circuit 4 is passed through a low-pass filter 15 to extract a wideband signal of about 4 MHz, for example. This wideband signal is subjected to gamma correction in a gamma correction circuit 1G, and then is applied to an arithmetic circuit 18 and an adder I9 through an IH delay circuit 17 as a wideband luminance signal Y11.

At the same time, the luminance signal YL is subjected to gamma correction in the gamma correction circuit 20 and then applied to the arithmetic circuit 1. A luminance signal having a magnitude obtained by subtracting the broadband luminance signal YH from the luminance signal YL is obtained from this arithmetic circuit 18, and this signal is passed through a low-pass filter 21, for example, I
The signal becomes a signal having a MHz band and is applied to the adder 19.

Furthermore, 3G+2R+2 obtained from the signal processing circuit 4
The B signal is averaged by a low-pass filter 22 into a signal having a band of, for example, I MHz. This signal is applied directly to the vertical aperture correction circuit 25, and also applied to the correction circuit 25 through the IH delay circuit 23, and further applied to the correction circuit 25 through the IH delay circuits 23 and 24.

The aperture correction signal obtained from this correction circuit 25 is applied to the adder 19. The aperture-corrected luminance signal YL+H obtained from the adder I9 is applied to the encoder 14. The encoder 14 receives the color difference signal R-
Based on Y, 1B-Y and the luminance signal Y violet ◆ 2, a television signal SV according to the standard television system is generated and output. The IH delay circuits 7.8.17.23.24 are used for time adjustment to match the arrangement of the complementary color filter 2 in FIG. 4 and signal processing. Incidentally, a circuit similar to the circuit shown in FIG. 3 is disclosed in Japanese Patent Application No. 61-229073 filed by the present applicant.

Since the luminance signal YL obtained in this circuit is adjusted by the white balance circuit 11 in the preceding stage, it is a signal with good luminance reproducibility. However, this signal YL is contaminated with noise due to signal processing at the subsequent stage of the detection circuit 5. That is, this signal YL has a normal luminance reproducibility but is characterized by a poor S/N ratio.

On the other hand, the above signal Y. is basically 3G+2R+2 obtained by simply combining the output signals of the image sensor 3 with the signal processing circuit 4.
Since it is a pseudo luminance signal of B, the luminance reproducibility is poor, but it has a feature of relatively good S/N.

Therefore, in the circuit shown in Fig. 3, the difference between the signal Y and the signal Y By this, S of signal YH
/N while maintaining the good luminance reproducibility of the signal YL.

[Problem that the invention seeks to solve]

In the circuit shown in FIG. 3 described above, it is decided at the time of design whether to focus mainly on good luminance reproducibility or mainly on good S/H, and depending on the signal condition, brightness reproducibility or S/N may be affected. Sometimes it wasn't always appropriate.

Further, when considering the dynamic range of the luminance signal and the IH delay circuit 7.8, the following problem occurred.

In FIG. 3, if all or most of the luminance signal YL□ supplied to the encoder 14 is to be the signal YH, the IH delay circuit 7.8 should be twice as large as the one required only for the chroma signal. It is sufficient to use one with a dynamic range of . However, if this is done, the luminance reproducibility deteriorates as described above.

Therefore, all or most of the luminance signals YL and H are converted into the signal Y.
If you set it to L, the brightness reproducibility will improve, but if you do this, the brightness signal generally requires a dynamic range of three times or more, so the IH delay circuit 7.8 also needs to have a dynamic range of three times or more. becomes. Therefore, if an IH delay circuit having twice the dynamic range is used to improve luminance reproducibility, the S/N of the chroma signal will deteriorate by 3 dB or more compared to the case where luminance reproducibility is ignored.

[Means for solving problems]

In the present invention, there is provided a means for performing matrix calculation on output signals of a camera having a complementary color filter to generate a first luminance signal having a first dynamic range; means for producing a second luminance signal having a second dynamic range larger than the first luminance signal range; means for deriving a luminance signal of the first and second luminance signals, and when the low-frequency instantaneous levels of the first and second luminance signals exceed the first dynamic range, the second luminance signal is derived at least in a signal portion exceeding the first dynamic range. means for deriving a luminance signal.

[Effect]

The signal YL with good luminance reproducibility or the signal Yll with good S/N can be selected depending on the amount of light incident on the camera, and there is no need to use an IH delay circuit with a particularly wide dynamic range.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and parts corresponding to those in FIG. 3 are given the same reference numerals and their explanation will be omitted.

In the present invention, a limiter 28 is provided that doubles the dynamic range of the signal Y, and the gamma correction circuit 20 corrects the output signal of the limiter 28 and the luminance signal YL having normal luminance reproducibility. A mixing circuit 27 is provided to mix the signals. And the signal Y L in this mixing circuit 27,! The mixing ratio with :YH is controlled by the control signal AGC. This mixing circuit 27 is constructed of gain control amplifiers 29, 30, an inverter 31, an adder 32, etc. as shown in the figure. The output signal of the gain control amplifier 30 and the output signal of the adder 32 are supplied to the arithmetic circuit 18.

The control signal AGC changes depending on the amount of light incident on the imaging section 1. The mixing circuit 27, whose mixing ratio is controlled by this signal AGC, is configured to mix a large amount of the signal Yl when the amount of incident light is large, and to mix a large amount of the signal Y when the amount of incident light is small. It should be noted that the IH delay circuits 7.8 have twice the dynamic range.

According to the above configuration, the gain control amplifier 30 outputs the low frequency component YL of the signal YH whose dynamic range is doubled.
A signal consisting of I and high-frequency components Y, , (YLI + Yl
(+) is obtained. Further, the adder 32 outputs the above signal (Y
t, t+Y□) and signal YL (YL + Y
LI +YHu) is obtained. This signal (YL +YL
I + Ylll) has twice the dynamic range, and among them (Y, , +YLI) is gain controlled by the signal AGC. Therefore, as the output of the low-pass filter 21, the mixing ratio of YL and YLl is controlled and the signal of the difference between the signal (Yt + YLI) having twice the dynamic range and the signal YL having twice the dynamic range <( YL YLI)-YL I) is obtained.

Further, in the adder 19, the above-mentioned difference signal and the signal YH (however, the dynamic range is not limited to 2 times but has a dynamic range of 3 times) are added, and as a result, YL, H= (YL +Yt+) YLI + (Y
t++Y+++) is obtained. Of this signal Yt+o, (Yt +Yt+)-YLl has twice the dynamic range, and (YLI + Ylll) has a dynamic range of 3.
It has twice the dynamic range.

Therefore, when the amount of incident light is large, a large amount of the signal YL is mixed, so the difference signal ((YL YLI) Y L I
1, (Y t Y t + ) is substantially YL
-YL+=YL. Therefore, YL at this time becomes range watercress. In this case, if the dynamic range of the input signal is twice or less, the above equation becomes Yt+YL+Y.

becomes. Further, when the dynamic range of the input signal is twice or more, (YL YLI) (double dynamic range) is the subsummation of both YL and YLI. Therefore, if these saturation levels are made equal, Y
Since L YLI=0, Yllll −YLI +
Y) 11 (3 times the dynamic range).

Figure 2 A shows the output luminance signal Y when the amount of incident light is large.
This shows the frequency characteristics of tal+, in which the signal YL is used in parts where the dynamic range is less than double in the low range, and the low-frequency component YLI of signal YH is used in parts where it exceeds twice the dynamic range.
is used.

Next, when the amount of incident light is small, the mixing amount of signal YL becomes small, so the above difference signal ((Yt + YLI)
(YL +Yt+) of Ylll is substantially Y,
10YL=YLI, and the difference signal becomes substantially zero. Therefore, Y L + H at this time is Ylll1
= YLI + Yl(+ (3 times the dynamic range).

FIG. 2B shows the frequency characteristics of the output luminance signal YL+o when the amount of incident light is small, and it can be seen that the signal YL is hardly used, and only the signal YH-YLI+Yll is used.

According to this embodiment, for example, when the subject of the camera is bright enough and the amount of incident light is large enough so that S/N is not a problem, the output luminance signals YL and l+ include many signals YL with good luminance reproducibility. mixed in. At the same time, if the dynamic range of the signal is doubled or more, the signal Y1. Therefore, an IH delay circuit 7.8 having twice the dynamic range can be used.

Furthermore, when the amount of incident light decreases and AGC starts to work, a large amount of the signal YII with a good S/N is mixed into the signal Yt+, so it is possible to prevent deterioration of the S/N and also 7.8 will also hardly be used.

In the embodiment, a pseudo signal Y is always used in the high frequency range of the signal YL+H;
．． This takes into consideration the frequency characteristics of No. 8. However, the present invention is not limited thereto, and it goes without saying that signal processing similar to that described above may be performed for high frequencies as well.

〔Effect of the invention〕

According to the present invention, the signal YL with good luminance reproducibility or the signal Y6 with good S/H depending on the amount of light incident on the camera. Since the brightness signal can be selected, it is possible to always form an optimal luminance signal. Furthermore, there is no need to use an IH delay circuit with a large dynamic range.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of an output luminance signal, FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is a diagram showing an arrangement of complementary color filters. . In addition, in the symbols used in the drawings, 2---------1--Complementary color filter 4--
−−−−−−−−−−−−−1 signal processing circuit 5−−−−−−−
−−−−−−−−−Detection circuit 10・−1−−−−−−−
---Primary color separation circuit 11-----White balance circuit 13-----1--Matrix circuit 18----------1 Arithmetic circuit 19-
----1------ Adder 26---------
--- A G C detection circuit 27-1111 --- It is a mixed circuit.

Claims (1)

[Claims] A first luminance signal having a first dynamic range is generated by performing a matrix operation on output signals of a camera having a complementary color filter, and a first luminance signal having a first dynamic range is generated by simply synthesizing the output signals of the camera. A second luminance signal having a second dynamic range larger than the range is produced, and when the instantaneous levels of the low range of the first and second luminance signals are within the first dynamic range, the first luminance signal is When the low-frequency instantaneous levels of the first and second luminance signals exceed the first dynamic range, the second luminance signal is derived at least in the signal portion exceeding the first dynamic range. A luminance signal forming circuit designed to derive a signal.