JPS6030290A - Signal processing circuit of color video camera - Google Patents

Abstract

PURPOSE:To improve color unevenness and color noise, and exclude a feeling of physical disorder from a photographed picture by detecting a low-luminance component which is lower than a specific level from an image pickup signal, and attenuating the gain of a chrominance signal according to the level of the detection signal. CONSTITUTION:A video signal right before entering an AGC circuit 5 has the chrominance signal removed through a filter 32 and is inputted to a highlight detecting circuit 23 for detecting a highlight signal which is higher than a specific level and a low luminance detecting circuit 33 for detecting a luminance signal which is lower than a specific level. The detected highlight signal and low luminance signal are summed up by an adding circuit 35 and impressed as a control signal to a gain control circuit 28. Consequently, attenuation effect which is largest at a black level part is obtained within the control range of the low luminance detection signal and attenuation effect which is gradually less up to a detection point is obtained, so color unevenness and color noise are suppressed effectively as a part becomes so dark that the color unevenness and color noise are conspicuous.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a signal processing circuit for a color video camera, and particularly to a signal processing circuit for a color video camera, which reduces color unevenness and color noise that are noticeable in achromatic images or dark areas of images, and improves image quality. This invention relates to improved signal processing circuits.

[Background of the invention]

FIG. 1 is a block diagram schematically showing a signal processing circuit of an immediate-carrier frequency separation type single-tube video camera, which has been widely used as a home-use tube color video camera. In this figure, 1 is a lens device, 2 is an iris am
, a is an image pickup tube. Brightness (
Y) The signal is a baseband signal, and the color signal is arranged on the light guide surface of the image pickup tube at opposite inclinations to the vertical direction.
A set of color stripe filters (e.g. red cut filter,
Determined by the configuration of the blue cut filter). The red (river, back (B)) color signals are respectively extracted as frequency-multiplexed carrier color signals that are quadrature-modulated.The waveform shown in the figure is an example of the signal waveform obtained when photographing a black and white gray scale chart, and the shaded area is a carrier color signal, and a carrier wave signal is also obtained in proportion to the luminance 4g.The extracted signal passes through a preamplifier 48, is controlled to a rated level by an output control circuit (AGC) 5, and is sent to a terminal 8. The circuit 6 is an AGC obtained by inputting the luminance signal (Y), a detection circuit for generating an iris training voltage, S, and a switching circuit.First, when the amount of light incident on the lens l is relatively small, A control voltage is applied to the AC+C circuit 5 such that the gain attenuates from the maximum gain state as the amount of incident light increases, and after completing the predetermined gain control, when the amount of light incident on the lens increases further, the iris jDA82 is An fB control voltage that gradually closes the iris from the open state is applied to the iris drive circuit 7 to control the light n incident on the image sensor 3. In this way, the level of the video signal obtained from the terminal 8c is controlled. The amount of incident light is controlled to a predetermined rated level over a wide range.The video signal obtained at the terminal 8 is passed through a low-pass filter 9 (for example, cutoff frequency fc: 3 MHz).
The luminance signal is passed through a low-pass filter 10 (e.g. fc
500KHz), the low-frequency components of the luminance signal are filtered by a bandpass filter 11 (for example, a bandpass of 3.58±0.5MHz).
) to separate the carrier color signals. Separated shine [
The signal (Y) undergoes γ processing in a gamma (ry) abstraction circuit 12 and is input to a color encoder 23 (Y'). On the other hand, the carrier color signal separated by the bandpass filter 11 is 1lt
Based on the principle of vertical correlation of the iI image, the signals of the passing *tJ@ of the delayed gland (I) 11) L) 13 during one horizontal scan are processed by the summation circuit 15 and the subtraction circuit 18, respectively, as 〃IJn, The signal is subtracted and separated into the conveyance red signal and the conveyance red signal No. 1. Thereafter, amplitude detection is performed by detection circuits 16 and 19, respectively, to obtain red (R) No. 18 and blue (B) signals. Separation.

The detected H and J1 signals are respectively sent to the gamma correction circuit 17.
．． 20 and input to one input terminal of color difference matrix circuits 21 and 22, respectively.

On the other hand, the luminance low-frequency component separated by the low-pass filter IO is gamma-corrected by the comma correction circuit (rYL) 14 and input to the other input terminal of the color difference matrix circuits 21 and 22, and output from the circuit 21 and 22. Color difference (IK-
Y'LI B'-Y'L'&Toku60 Color M4R No. IC
-Y'L and B'-'Y'L are input to the color encoder 40.

1i'-Yυ is a modulating circuit 24, and W-Y'L is a modulating circuit 25, where subcarriers (
358MHz) SC1 and 8C2 are balanced modulated, and then added in the adder circuit 26 to produce the N'l'SC carrier color I1.
I'm using the number. Transport color No. 4M has base clip circuit 2
7. The signal is input to the signal processing circuit 30 via the color killer circuit 28. The luminance signal gY' is also input to the circuit 30, and further processed by blanking, white clipping, synchronization signal addition, burst signal addition, etc., and sent to the output terminal 3.
Add NTSU +y to 1.

When a highlight No. 18 occurs that is approximately 2 to 3 times higher than the short-circuit level of the luminance signal, the color killer circuit 28 detects multiplexed signals superimposed on the highlight portion due to insufficient dynamic range of the circuit. Since the transmitted signal is destroyed, it is no longer possible to take out the prefectural color sending signal to the terminal 8, and as a result, the color difference 1d B'-Y'L, lze Y'
This is to prevent the balance of L from being disturbed and the highlighted area to become greenish, resulting in the production of unnaturally colored urine. In other words, highlight Hakushichi detection [gIlli23 detects a highlight that is about 2 to 3 times higher than the rated level, and during the period in which the older brother of cough supply No. 6 occurs (as shown in the operation of bJ, N'L '8C carrier color signal is suppressed (original control) and only one signal is used.

Next, (9) of the base clip circuit 27 will be explained.

The base clip circuit 27 is used to reduce color unevenness N1 color noise CN, etc. that are noticeable in achromatic images. In other words, as shown in the input/output characteristics of Figure 2 (a),
7 non-linearly suppresses a relatively small level below the threshold level vTH.

Note that achromatic colors, for example, No. 11. When photographing an achromatic subject, such as a clay scale chart that changes stepwise from black to white, as shown in the slant diagram in the figure W, the color difference signal B
'-Y'L, ■4! - Y'L is more perfect than zero 7, the white balance is perfect, color unevenness occurs and it is blurry, but the color signal (
B/, lc/) and the luminance signal (Y'ri's dark m 7Jl et al. 8E1) Tracking error, shading that occurs in the dark part of Y'L caused by the sensitivity difference due to the deflection of the image pickup tube, or B', An error component is generated in the color difference signal due to the shape ink generated in le, resulting in color unevenness.Due to the nature of the image pickup tube, the above-mentioned tracking error occurs more often in dark areas.

On the other hand, color noise is visually noticeable in dark areas, and
As the captured image becomes darker and the gain of the AGC circuit 5 increases, the S/N ratio decreases and color noise increases. As mentioned above, color unevenness and color noise are more noticeable in dark areas or in dark photographed images, and the amount of force and strain is large. Therefore, in the method shown in FIG.
If the threshold value VTu 'E in Figure 2 (a) is added to make the color noise less noticeable, it will be difficult to obtain a sufficient improvement effect when engraving dark areas or dark objects, and under any circumstances However, if you increase the VTH'a on the pillar plate where color unevenness or color noise is not a problem, conversely, the chromatic color 1111i4
The color signal information of 12 is also greatly suppressed, and the 6 saturation of bright areas is also lost, causing the inconvenience that the entire image feels unnatural.

(Objective of the invention) Book @ 1: The object is to improve the drawbacks of the above-mentioned prior art,
To provide a signal processing circuit that can uniformly improve unevenness and color noise in both bright and dark areas of an achromatic image, and does not give a continuous effect to block shadows.

[Summary of the invention]

In order to achieve the above object, the present invention first focuses on relatively bright parts of an achromatic image, suppresses color unevenness and color noise to the minimum necessary level, and then uses AGC@ Detects a luminance signal at a predetermined level relative to the rated level (level during iris operation) of the luminance signal before the iris operation, for example, a luminance signal that is about % to 5 from the black level, and uses the detected luminance signal to
As the black level increases, the gain of the carrier color signal is attenuated to improve color unevenness and color noise, and the gain control circuit is configured as described above.
Share % illite color killer circuit 288 and easily realize it.

[Embodiments of the invention]

Below, Example 71 of non-invention! - This will be explained using FIGS. 3 and 4. In Figure N3, the same symbols as in Figure 1 indicate the same circuits and functions.

In order to explain the present invention in detail, as an achromatic photographic signal, as shown in the waveform chart T in this figure, a highlight extending beyond the rated level (YT) next to the clay scale signal GS that changes from black to white will be used. Assume that the signal HL exists. The video signal immediately before (or before) the AGC circuit 5 is
A highlight detection circuit 2 that detects a highlight signal of a predetermined level (YWH) or higher (for example, 2 to 3 times the rated level or higher) after the carrier color signal is removed by the filter 32.
3 and a low-luminance detection circuit 33 that detects a luminance signal from black (low-luminance signal) below a predetermined level, which is the main part of the present invention, for example, a luminance signal from black (low-luminance signal) at a height of about a month of the rated level. Detect signal and low brightness signal. After that,
The adder circuit 35 adds the signal and uses the added signal as a control signal to control the carrier color signal gain control circuit (color killer circuit) 28.
and gain control. FIG. 4 shows the relationship between the control signal US applied to the circuit and the control characteristics.

As shown in this figure, the required attenuation (
The operating point is set to obtain γB). With this setting, in the control range (YBL) based on the low luminance detection signal, the greatest attenuation effect is obtained at the black level portion (VB), and a gradually smaller attenuation effect is obtained at the detection point. Since the brightness portion shown by the broken line is clipped, the gain is not controlled for bright brightness of YBL or higher, and the more color unevenness and color noise are noticeable in dark areas, the more effective the color unevenness and color noise will be. oppressed.

On the other hand, in the fourth part, as mentioned above, the base clip N path (low saturation suppression circuit) 27 takes into account the color unevenness component, which is quantitatively smaller than the dark part ζ, and suppresses color unevenness and color noise at the minimum necessary level. Since it is possible to suppress -(), there is no problem of greatly reducing the saturation in a chromatic image.In addition, depending on the highlight detection signal (YWK,), the signal may be abnormally large as explained in the conventional example in FIG. The gain is greatly attenuated in the highlight portion to prevent the highlight from being colored green.Of course, the gain control circuit is effectively shared here, but it may be provided separately.

Next, the reason why it is extremely effective to obtain the low luminance detection signal from the video signal before AGCI gl 5 will be described below. A state where the subject illuminance is relatively bright, that is, iris mechanism 2
In the operating region of , the input level of the preamplifier 40 is kept constant, so the video signal is maintained at a predetermined rated level before and after the AGC circuit 5, and the S/N is determined by the noise generation I4 of the preamplifier circuit. S/N
is kept constant. However, as the subject illuminance gradually decreases (darkens), the iris becomes open, and as it becomes even darker, A (J Ctv enters the operating range and A
The GC circuit is controlled to increase the gain from the maximum gain attenuation to keep the output of the AGC circuit 5 constant. That is, A
When entering the GC operating range, the level of the video signal input to the preamplifier 4 decreases as the subject illuminance decreases, resulting in a decrease in S/N and, as a result, color noise becomes noticeable in proportion to the illuminance.

At the same time, the video signal level before AGCl path 5 decreases from the predetermined rated level Y as the subject illuminance becomes low (as the illuminance of the subject becomes low), so as shown in the lower waveform diagram of FIG. In other words, with a low S/N ratio of 1, the operation gradually brings about a gain attenuation effect from the brightness level area to the black level area, resulting in a color noise suppression effect over the entire screen. The effect of improving image quality is significant.

At this time, the saturation of the brightness part of the mourning color image also gradually decreases.
However, the image content is such that 87N of the photographic screen itself has decreased completely, so the effect is not a problem and there is no unnatural feeling.

FIG. 5 shows a highlight (high brightness) signal detection circuit 23, a low brightness signal horizontal use circuit 33, and an addition circuit 3, which are the main parts of the present invention.
This is a specific circuit example of No. 5. In Figure 5, transistor Q
l, Q2. Q3. Q4, constant current source circuit 11. Diode D1. Resistance 1. ■Also 2. The highlight signal detection circuit 23 is configured by R4. A bias voltage VWH is applied to the base of the transistor Q2 to set a level for slice detection of highlight signals of a predetermined level (for example, 2 to 3 times the rated value) or higher, and a video signal is input to the base of the transistor Ql to exceed VWll. , transistor Q1 turns on and 1. The current is changed by a Hi-flow mirror circuit consisting of DI, R2, R3, and Q3, and is amplified by a ratio of 4, and a highlight signal having the same polarity as the human input is detected at the emitter of the transistor Q4. On the other hand, transistors (upper 6 + Q7 + Qs + Q9, constant current source circuit ■2, diode D3, resistor 1 is also 101) Lll, lL12, R1
4 and R13, the low brightness summer signal detection circuit 33 is similarly configured. A bias voltage VB is applied to the base of the transistor Q7 to determine a clip level for obtaining a low luminance signal below a predetermined level (for example, rated luminance level 73). A video signal is input to the base of transistor Q6, and when it becomes less than VB, transistor Q7 becomes 0, Nl,
Similarly, the low luminance detection signal is amplified by the ratio R14/R1o and is output to the emitter of the transistor Q9. Resistance 6. The adder circuit 35 is configured by the transistor Q5. Diode D2 and resistor l are also 7,
I(, 8, R9 are current sinking DC level shift circuits, and by setting 7.■78.J(, 9), the operating point of the control voltage can be arbitrarily selected.

Although not described in detail in this embodiment, in a frequency separation type color photo camera, the luminance n1ffi and
This improves the tracking of the R signal and B signal to improve the bonoid balance from dark to bright areas.In other words, the luminance at a predetermined level (M) is divided into 3 to 4, and each of the divided signals is In response, processing means are often adopted to control the gain of the red (A) and blue (transfer) signals to improve tracking with the luminance signal from the dark level to the bright level. .

In such a case, the low luminance detection IU used in the present invention,
The low-luminance component of the above tracking bucket signal is commonly turned off.
It is possible to implement the present invention extremely easily.

〔Effect of the invention〕

According to the present invention, color unevenness that is noticeable in achromatic images can be eliminated without reducing the saturation of chromatic images. You can get similar visual improvement effects. Furthermore, the effect of improving color noise, which becomes noticeable in dark areas or as the subject illuminance decreases, is also increased. According to the present invention, the 1I111 quality does not feel unnatural or strange, and the effect of improving image quality is extremely large.

[Brief explanation of the drawing]

Figure 1 is a block configuration diagram showing an example of the signal processing LU path of a conventional color video camera, Figure 2 is a characteristic diagram for explaining the No. 1 processing circuit of Mukai, and Figure 3 is a block diagram showing an example of the signal processing LU path of a conventional color video camera. Block diagram illustrating the main parts of the signal processing circuit used,
FIG. 4 is a characteristic diagram for explaining the present invention, and FIG. 5 is a circuit diagram showing an example of a specific circuit for realizing the main part of the present invention. 1... Lens 2... Iris mechanism 3... Shooting (7
1. rR signal low frequency component extraction filter 1
1... Carrier color signal extraction band, filter 12.14,
17.20... Gamma correction circuit 13... IkiDL
15...Addition circuit 16.19...Detection circuit 18
...Reducing field circuits 21, 22...Color difference matrix L
! Circuit 23...Color encoder 24.25-...1'#7RA circuit 26 ・)tu
11. @Route 27...Low saturation suppression (base clip)
Circuit 28...Limited system # (color killer) circuit 30...
・Signal processing circuit 32... Carrier color signal suppression filter 33... Low luminance signal detection circuit 35... Calculation circuit

Claims (1)

[Claims] (In a recolor video camera, a low luminance component below a predetermined level of a luminance signal is detected from a video signal obtained by imaging, and a color difference signal is modulated and transmitted in response to the level of the detected signal. A signal processing circuit for a color video camera characterized by controlling the gain of a gain control circuit provided in the color 4i path. (2) The above low-luminance signal component is generated before the automatic gain control (AGC) circuit of the color video camera. The signal processing circuit according to claim 1 of Patent H is characterized in that it detects the low luminance component from the video signal, and detects the high luminance component at a second predetermined level or higher. i'F is characterized in that the gain of the gain control circuit is controlled by a signal obtained by adding the detected signals of both components. (4) The above gain control circuit controls the gain of the carrier chrominance signal using divided signals obtained by dividing the luminance signal into multiple levels, corrects the tracking of the luminance signal and the chrominance signal, and moves from a dark area to a bright area. Claim 1, characterized in that the IHA processing for improving the white balance is performed, and the low luminance area component of the division No. 16 and the low luminance detection signal below the predetermined level are made common. (The signal processing circuit according to any one of (3) to (3) above.