JPS5862990A - Frequency separation type single tube color camera - Google Patents

Abstract

PURPOSE:To prevent the generation of uneven luminance, by controlling signals with a voltage in response to a change after a prescribed time of an average level of a luminance signal, after the gain of a variable gain amplifier amplifying the luminance signal is changed for the amplification. CONSTITUTION:A limimance signal Y is applied to LPFs 10, 11 of an integration circuit constitution having a sufficiently longer time constant in comparison with 1H via analog switches 8 and 9. Outputs of both the LPFs are applied to input terminals of a differential amplifier 12 respectively, the outut of the amplifier 12 is applied to one input terminal of a changeover switch and a constant voltage E is applied to another terminal and a circuit 13 is controlled with an FF14. Every time a horizontal synchronizing signal comes, the Q and Q' of the FF14 are made opposite in phase and the switches 8 and 9 are turned on at each 1H. Thus, the signal Y is applied to the LPFs 10 and 11 alternately at each 1H and a voltage in response to the average level of the signal Y is outputted.

Description

[Detailed description of the invention] The present invention relates to a frequency-separated single-tube color camera.

Figure 1 shows a conventional frequency-separated single-tube color camera. In Fig. 1, an optical image of the subject is formed on a stripe filter (not shown), and then the image of the subject that has passed through the stripe filter is again formed on the target surface of an image pickup tube l made of a vidicon or the like. be done. An image formed on the target surface of the image pickup tube 1 is scanned by an electron beam, and an electric signal corresponding to the image is outputted from the image pickup tube 1.

A stripe filter is obtained by superimposing two filters, one of which has the transparent part colored cyan (
Reflects the red component. ) portion in the scanning direction, for example 61
They are arranged alternately at a pitch of μ (microns) to form a striped pattern. The other sheet has a striped pattern in which transparent portions and yellow (reflecting blue components) portions are arranged alternately at a pitch of, for example, 47 μm in the scanning direction. Therefore, the output of the image pickup tube 1 was modulated with a frequency component of 3.9 MHz amplitude-modulated with a red signal corresponding to the brightness of the red component light, and a blue signal corresponding to the brightness of the blue component light. 5. l,
M) (Contains the frequency component of z and a relatively low-frequency green signal component corresponding to the brightness of the green component light.

After the output of the image pickup tube 1 is amplified by the preamplifier 2, the center frequencies are 3.9 MHz and 5.1 MHz, respectively.
Hz to each of two bandpass filters (not shown) and an LPF (low pass filter) 3. LPF3
For example, ()~3 included in the output of preamplifier 2 by
．． A low frequency component of 2 MHz is separated and extracted and supplied to the amplifier 4. This low frequency component is amplified by an amplifier 4 and then clamped to a predetermined potential at a predetermined portion in a process section 5, and is used in a television transmitting/receiving system that includes various conversion processes in which the input-to-output relationship is not linear. , so-called γ correction is performed to make the overall characteristic from the camera to the picture tube linear.
An NTSC composite video signal is obtained by a color encoder (not shown) or the like from each of the red and blue signals output from each of the two bandpass filters (not shown) of h and 5.1 MH2.

In the above configuration, the optical image of the subject is formed on the stripe filter, so if there is density unevenness in the stripe filter, the amplitude of the brightness signal Y changes depending on the density of the stripe filter, causing brightness unevenness. Something happened.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a frequency separation type single tube color camera that can prevent the occurrence of uneven brightness.

The frequency separation type tube color camera according to the present invention has the advantage of adjusting the gain of the variable gain amplifier that amplifies the luminance signal, the luminance after being amplified by the variable gain amplifier, and the average level of the signal after a predetermined period of time. It is configured to control the voltage according to changes.

Hereinafter, the present invention will be explained in detail with reference to FIG. 2. In FIG.
are connected in the same way as in FIG. However, in this example, the output of the LPF 3 is supplied to the variable gain amplifier 6, and the output of the variable gain amplifier 6 is supplied to the process section 5. The luminance signal Y output from the process section 5 is supplied to the voltage generation circuit 7. In the voltage generation circuit 7, the luminance signal Y is transmitted through each of the analog switches 8 and 9 as luminance signal supply means (1) ((L horizontal scanning time)
An LPF with an integrating circuit configuration that has a sufficiently long time constant compared to
It is supplied to each of lO and l. L P F 10゜1
1 is supplied to each of the positive phase and negative phase input terminals of the differential amplifier 12. The output of the differential amplifier 12 is supplied to one input terminal of the changeover switch circuit 13 as the output of the voltage generation circuit 7 . A constant voltage source E is connected between the other input terminal of the changeover switch circuit 13 and ground.

Further, the Q output of the T-type flip-flop 14 is supplied to the control input terminal of the changeover switch circuit 13. This Q
The output is also provided to an analog switch 90 control input terminal.

The Q output of flip-flop 14 is supplied to the control input terminal of analog switch 8. flip flop 14
The horizontal synchronizing signal Q (, 5 sync,
) are supplied with five. Then, the output of the differential amplifier 12 and the constant voltage E are selectively output from the output terminal of the changeover switch circuit 13 according to the Q output of the clip-flop 13, and are supplied to the gain control input terminal of the variable gain amplifier 6. .

In the above configuration, the horizontal synchronization signal (H, 5sync,
) arrives, the state of the flip-flop 14 changes from the set state to the reset state or from the reset state to the set state, and the Q and (outputs of the flip-flop 14 each become a pulse signal with opposite phases to each other. Each of the analog switches 9 and 8 whose control input terminals are supplied with each of the Q and 14 outputs is turned on alternately for each LH, and the luminance signal Y is alternately output from the LPFIO for each LH.

11. LPFIO,ll are both L
The luminance signal Y is integrated with a time constant that is sufficiently longer than that of the luminance signal Y, and a substantially constant voltage corresponding to the average level of the luminance signal Y in each of 18 consecutive periods is outputted. The differential voltage between the respective outputs of LPF1O and LPF11 (C) is amplified by the differential amplifier 12 and supplied to one input terminal of the changeover switch circuit 13.

Here, when the Q output of the flip-flop 14 becomes high level, the switch 8 is turned off and the switch 9 is turned on, so that the changeover switch circuit 13 selectively outputs the output of the differential amplifier 12. Then, when the output voltage of LPFII is higher than the output voltage of LPFIO, the output voltage of the differential amplifier 12 becomes low, and when the Q output of the flip-flop 14 becomes high level, the differential amplifier 1
The output voltage of 2 can be supplied to the variable gain amplifier 6.
The gain of the gain amplifier 6 decreases. At this time, the signal Y amplified by the variable gain amplifier 6 is supplied to the LPFll via the switch 9, and the output voltage of the LPFll is lowered. Next, when the Q output of the flip-flop 14 becomes low level, the constant voltage E is outputted from the changeover switch circuit 13, and the gain of the variable gain amplifier 6 is set to a predetermined gain. At this time, the luminance signal Y amplified by the variable gain amplifier 6 is supplied to the LPFIO via the switch 8, and
PFll outputs a voltage corresponding to the average level of the luminance signal Y.

Through the above feedback loop, LPFI (1, 11
Since the output voltages of all the IHs are controlled to be the same, fluctuations in the average level of the luminance signal Y for each lBI caused by uneven density of the stripe filter are prevented, and uneven brightness for each IH is prevented. I go to cram school because it prevents this.

As detailed above, the frequency separation type single tube color camera according to the present invention outputs a composite video signal while preventing the occurrence of brightness unevenness for each LH, so that the low frequency (50 KHz or less) component of the composite video signal is Emphasis will be placed on those with a good S/N ratio. Furthermore, since the frequency-separated single-tube color camera according to the present invention has a feedback loop including a process section that performs γ correction, etc., it is not affected by changes in the characteristics of its component parts over time. be.

[Brief explanation of the drawing]

, FIG. 1 is a block diagram showing a conventional example of a frequency separation type single-tube color camera, and FIG. 2 is a block diagram showing an embodiment of the present invention. Explanation of symbols for main/essential parts l...Image tube 2...Preamplifier 3...
LPF 5...Process section 6...Variable gain amplifier 7...Voltage generating circuit 13...Changing switch circuit 14...T-type flip-flop Applicant Pioneer Co., Ltd. Agent Masu Physician Motohiko Fujimura

Claims (3)

[Claims] (1) A variable gain amplifier that amplifies and outputs a luminance signal while changing the gain according to a gain control voltage, and a predetermined time period at which the average level of the luminance signal obtained after being amplified by the variable gain amplifier is a voltage generating circuit that generates a voltage according to a change after elapse of time; and a switch that selectively outputs either the output of the voltage generating circuit or a predetermined voltage as the gain control voltage alternately at every predetermined time. A frequency separation type single tube color camera characterized by comprising a circuit. (2) The voltage generating circuit includes first and second integrating means;
a luminance signal supply means for supplying the amplified luminance signal to each of the first and second integration means alternately at predetermined time intervals; and a level between the outputs of the i1 and second integration means. 2. The frequency separation single-tube color camera according to claim 1, further comprising a differential amplifier that generates a voltage according to the difference. (3) The frequency separation method monotube color camera according to patent roadbed range items 1 and 2, wherein the predetermined time is l horizontal scanning time.