KR0139363B1 - Backlight Compensation Circuit of Camera - Google Patents

Abstract

The present invention relates to a backlight compensation circuit of a camera. In particular, when the backlight compensation function is performed, the aperture is opened to the maximum to prevent the luminance signal from being clipped and to correct the luminance signal in units of pixels of the image pickup device to obtain a perfect backlight compensation effect. In the video camera, it is equipped with a microcomputer to determine the aperture position from the set value before opening the aperture to the maximum in the backlight compensation condition, and the luminance signal captured by the image pickup device is compared with the average luminance signal value and the input luminance signal value. And a luminance signal increasing / decreasing unit for increasing or decreasing the pixel unit to be applied to the digital signal processing unit.

Description

Backlight Compensation Circuit of Camera

1 is a conventional circuit diagram,

2 is an internal circuit diagram of a digital signal processor;

3 is a screen division diagram,

(B) shows an embodiment of the shooting screen;

4 is an aperture control circuit diagram,

5 is a circuit diagram of the present invention.

6 is a detailed circuit diagram of the present invention;

7 is a flowchart of the present invention.

* Explanation of symbols for the main parts of the drawings

1: subject 10; lens

20: imaging device 30: data converter

40: digital signal processing unit 50: memory

60: microcomputer 70: iris control part

80: hall voltage detector 90: luminance signal increase and decrease

91: Subtractor 92: Adder

93: multiplexer

The present invention relates to a backlight compensation circuit of a camera. In particular, when the backlight compensation function is performed, the aperture is opened to the maximum to prevent the luminance signal from being clipped and to correct the luminance signal in units of pixels of the image pickup device to obtain a perfect backlight compensation effect. I would have to.

The conventional video camera captures light incident from the subject 1 through the lens 10 as shown in FIG. 1 by the CCD imager 20 and converts the light into an image signal by the data converter 30. .

The video signal of the data converter 30 is applied to the digital signal processor 40 to be processed and then applied to a recording block (not shown) as a video signal.

At this time, the digital signal processor 40 is operated by the control of the microcomputer 60 and the microcomputer 60 issues a control command to the digital signal processor 60 by an internal program operation according to a key input.

The digital signal processor 40 is composed of a white clip unit 41 for clipping a digital luminance signal of one pixel unit as shown in FIG. 2, a luminance signal gain controller 42, and a setup unit 43. The memory 50 stores the average value of the overall luminance signal among the image signals passed through the converter 30 and the average value of the luminance signals of each of the screens I, III, and III divided as shown in FIG.

That is, the photographed subject screen is divided into I, III and III areas as shown in FIG. 3A to store the average luminance signal average value and the total luminance signal average value for each of the I, III and III areas in the memory 50. .

The microcomputer 60 reads the average value of the luminance signal stored in the memory 50, determines whether the backlight compensation condition is applied according to an internal program, and controls the aperture control unit 70 according to the set value to set the aperture control voltage to the set value. By increasing or decreasing, the aperture is opened or closed.

That is, if the average value of the luminance signal in region I is lower than the average value of the entire luminance signal and the average value of the luminance signal in region I is higher than the average value of the luminance signal in region II or III, it is determined that the backlight mode is used to control the aperture to be opened. Control to close

As such, the backlight is compensated by controlling only the aperture, and thus, when the luminance signal changes suddenly in the I, II, and III areas within the screen, the backlight is not properly corrected.

For example, window 2 and window 3 as in (b) of FIG.

If there is a wall (4) between and the subject (1) in front of the wall (4), if you take a picture of this, the average value of the luminance signal of the region I in the divided screen as shown in (a) of FIG. Since it is much smaller, the conditions of backlight compensation are established.

When the backlight compensation condition is satisfied as described above, the microcomputer 60 controls the aperture control unit 70 to open the aperture as much as possible.

Then, the brightness of the window (2) and (3) part of the screen to be photographed is clipped and the screen becomes unnatural and the part of the subject (1) becomes brighter due to the increase in the brightness signal level to some extent but feels dark in the full screen state. .

This phenomenon occurs when only the aperture is opened to the maximum and the luminance signal is not corrected when the backlight compensation condition is established. Previously, when the backlight compensation was performed, the screen was unnaturally photographed as described above.

The present invention has been made in view of the above, and stops at a certain range before opening the iris as much as possible under the backlight compensation condition, thereby preventing the luminance signal from being excessively clipped and the image pickup device in the luminance signal processing portion of the digital signal processing unit. The logic to increase or decrease the luminance signal in units of pixels is configured to maximize the backlight correction effect by adding the correction value compared with the average luminance signal level of the entire screen in units of pixels.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

4 is an aperture control circuit diagram of a camera, and the light passing through the lens 10 is captured by the imaging device 20 and then applied to the digital signal processor 40 through the data converter 30 shown in FIG. Lose.

The amount of light passing through the lens 10 is controlled by an aperture (not shown) and the aperture is opened or closed by using an aperture driving motor by the control voltage of the aperture control unit 70.

The aperture control unit 70 controls the opening and closing of the aperture by the control command of the microcomputer 60.

The opening and closing of the iris are configured to change the resistance value of the slide resistance, and the resistance value is detected by the hall voltage detector 80 as a hall voltage and applied to the microcomputer 60.

Therefore, the microcomputer 60 recognizes the current of the aperture opening state by recognizing the hole voltage, and in the present invention, the aperture is opened under the backlight correction condition, but the hall voltage is checked by the microcomputer 60 to check the hole voltage to a maximum range before opening. Only open the aperture until

FIG. 5 is a circuit diagram of the present invention, and the present invention provides a luminance signal increasing / decreasing unit 90 that can increase or decrease the luminance signal level by one pixel at the luminance signal input terminal of the luminance signal processing portion of the digital signal processing unit 40 of the existing camera. Installation is configured.

Here, the digital signal for one pixel picked up by the image pickup device is input to the luminance signal increasing / decreasing unit 90 in 8 bits.

In addition, the digital signal processing unit 40 includes a white clip unit 41 for clipping the luminance signal of one pixel unit whose signal level is increased or decreased in the luminance signal increasing / decreasing unit 90;

A luminance signal gain controller 42 for controlling the gain of the luminance signal passing through the white clip portion 41;

The setup unit 43 outputs the output of the luminance signal gain control unit 42 as an 8-bit digital luminance signal in units of one pixel.

6 is a detailed circuit diagram of the present invention.

The luminance signal input of the one pixel photographed is applied to the input of the multiplexer 93, the adder 92 and the subtractor 91, and another input of the adder 92 is obtained by subtracting the average value of the luminance signal from the overall luminance signal of the screen. The correction value set according to the present invention is applied, and the output of the adder 92 is applied to another input of the multiplexer 93 and the average value of the luminance signal of the screen is applied to another input of the subtractor 91. The subtractor 91 selects the switching operation of the multiplexer 93 according to the result of subtracting the signal average value.

That is, the present invention provides a subtractor 91 for subtracting the average value of the luminance signal from the luminance signal input, an adder 92 for adding the correction value and the luminance signal input set according to the value obtained by subtracting the input luminance signal from the average luminance signal value of the entire screen; And a multiplexer 93 for switching and outputting the output of the adder 92 and the luminance signal input according to the output of the subtractor 91.

This invention is described with reference to the flowchart of FIG.

First, the microcomputer 60 determines the backlight compensation condition by obtaining the average luminance signal of the entire screen and the average luminance signal of each of the I, II, and III divided regions.

Determination of the backlight compensation condition of the microcomputer 60 is a known function of the existing camera.

If it is not a backlight compensation condition, the luminance signal picked up by the image pickup device is recorded as it is.

The microcomputer 60 may recognize how much the current aperture is opened by recognizing the hall voltage detected by the hall voltage detector 80. The microcom 60 may check the average value of the luminance signal when the backlight correction condition is not used to open an optimum state of the aperture. To control the closing.

This is a method of adjusting aperture in a general camera.

Previously, the backlight compensation function was performed only under the condition of opening and closing the aperture by using the aperture control function that was acquired when the backlight compensation condition was established.

However, when the backlight compensation condition by the aperture adjustment is performed, the part that was bright before the backlight compensation was performed by opening the aperture as much as possible (high brightness part) became brighter and became closer to the clip level. The part which was dark before the correction (low brightness part) becomes a little brighter by opening of the aperture, but the high brightness part becomes brighter and feels relatively dark.

Therefore, when the backlight compensation is performed by only opening and closing the aperture, the above-described phenomenon occurs, resulting in an inadequate luminance on the screen.

In the present invention, in order to prevent the phenomenon that the luminance signal is clipped by the maximum aperture in the backlight compensation condition, the aperture stops before the maximum opening time and the luminance signal is corrected by one pixel unit so that a perfect backlight correction effect is achieved. To get it.

That is, when the backlight compensation condition is satisfied, the microcomputer 60 issues a control command to the aperture control 70 to drive the aperture driving motor and recognizes the opening of the aperture as a hall voltage so that the aperture stops at a predetermined value before the aperture is opened to the maximum. Control the iris drive motor.

The subtractor 1 subtracts the average luminance signal of the entire screen and the luminance signal input for one pixel, and generates a carry when the average luminance signal of the entire screen is larger than the luminance signal input for one pixel. If the overall luminance signal average value is smaller than the luminance signal input for one pixel, no carry is generated.

When a carry occurs in the subtractor 91, the multiplexer 93 selects an output of the adder 92 and applies it to the digital signal processor 40. When a carry does not occur in the subtractor 91, the multiplexer 93 selects the output of the adder 92. In this case, the luminance signal input is selected and applied to the digital signal processor 40.

Here, the adder 92 adds a correction value to the original luminance signal applied by the image pickup device, and the correction value is set according to the magnitude of the luminance signal average minus the luminance value of the entire screen. .

As described above, the present invention compares the average value of the luminance signal and the luminance signal input value of the entire screen. If the average luminance signal value of the entire screen is large, the luminance signal plus the input luminance signal correction value is selected. The backlight compensation effect can be fully pursued.

Claims (2)

In a video camera, a microcomputer is configured to determine the aperture position at a set value before opening the aperture to the maximum under backlight correction conditions, and the luminance signal captured by the image pickup device is increased and decreased in units of pixels by comparing the average luminance signal value with the input luminance signal value. And a luminance signal increasing / decreasing portion to be applied to the digital signal processing portion. 2. The luminance signal increasing / decreasing unit according to claim 1, wherein the luminance signal increasing / decreasing unit adds a subtractor (91) for subtracting the average value of the luminance signal from the luminance signal input, and an adder for adding the correction value and the luminance signal input set according to the value obtained by subtracting the input luminance signal from the average luminance signal value of the entire screen. And a multiplexer (93) for switching and outputting the output of the adder (92) and the luminance signal input in accordance with the output of the subtractor (91).