JPS61198894A - Automatic focus detector - Google Patents

Abstract

PURPOSE:To attain automatic focus detection and adjustment from a video signal without using a special optical system and a photoelectric element by providing a gate signal generating circuit and a gate circuit outputting a chrominance signal from a video amplifier when the gate signal is inputted so as to input the chrominance signal through the gate circuit. CONSTITUTION:Only when the incident luminous intensity of the 3 primary colors is equal in a video signal, the gate circuit 6 is opened and a 3-primary color photoelectric output is fed to a comparison discrimination circuit 7. Then a green light signal output is large, red and blue signal outputs are small and equal nearly to each other at focusing, and when the focus is at front focus, the blue incident light is focused on the photoelectric plane, the blue output is large and the green and red lights are fogged, then the photoelectric output is small. In case of rear focus, the red incident light is focused on the photoelectric plane, the red output is large and the blue and green lights are fogged, then the photoelectric output is small. Thus, the focusing, front focus or rear focus is detected depending on the output ratio of the three primary colors from the comparison discriminating circuit 7, a driver 8 discriminates the focusing state from the detected outputs to move the lens in the focusing direction thereby applying focus adjustment automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic focus detection device for a video camera, and more particularly to a simple automatic focus detection device for a video camera that uses an imaging device through a lens having chromatic aberration. This invention relates to a detection device.

``Prior art'' When two types of light beams with different wavelengths pass through an objective lens and pass through a bisihole provided at the focal plane of each light beam, the amount of each passing light changes when the light beams with each wavelength are in focus. A method of detecting the focus position based on the chromatic aberration of the lens has been proposed (Japanese Patent Publication No. 59-16247), which detects the focus by using the coincidence point of the Ryokawa forces.

``Problem to be solved by the invention'' However, according to this method, a light receiving element must be provided at the focal position of each spectral beam, and if there is a difference in the size of each spectral beam, the accuracy will deteriorate accordingly. Become.

"Means for Solving the Problem" In order to solve such problems, the present invention provides an imaging device that captures a subject image through an objective lens with appropriate chromatic aberration and outputs the image as an electrical signal, and a future improvement. In a video signal generation device that does not require relatively high precision, it consists of a video amplifier that amplifies the video signal of the video amplifier, and an encoder that generates an NTSC signal from the output of the video amplifier
A gate signal generation circuit that inputs a chroma signal (a signal containing only color components) from an encoder and generates one or more rectangular wave outputs with a width corresponding to the achromatic portion in each frame of a video signal, and this gate signal. A gate circuit that passes and outputs the color signal from the video amplifier when input is input, and a color signal that has passed through the gate circuit is input, and when the green signal is the largest and the red and blue signals are small and approximately equal. An automatic focus detection device that generates a focus signal is provided.

1. The present invention uses the above-described means to detect focus by changing the ratio of the nearly equal green, red, and blue components contained in the achromatic signal depending on whether or not the three colors are in focus. It is something to do.

"Example" The present invention will be described in detail below using the figures. Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a signal waveform of each part thereof, and Fig. 6 is a comparison diagram of the magnitude of six primary color signals in in-focus and out-of-focus states. . In Fig. 1, 1 is a photographing lens with chromatic aberration to the extent that it does not affect the resolution of the image, 2 is an imaging device such as an image pickup tube or a semiconductor image sensor, and when focusing, green light p; The arrangement is such that the focus is on the surface. 6 is a video amplifier that amplifies the electric signal from the imaging device, and 4 is an encoder that generates an NTSC signal, and these are known video signal generators. 5 is a gate signal generation circuit which inputs a chroma signal, which is a signal containing only color components, from the encoder 4 and generates a rectangular wave output of a portion corresponding to an achromatic portion in each frame of the video signal as a gate signal; 7 is a gate circuit that passes the six primary color signals of green, red, and blue from the video amplifier 6 when the gate signal is input, that is, when the achromatic color signal is generated from the encoder 4. A comparison judgment circuit compares the thickness of the three primary color signals input from 4 and determines focus, front focus, or rear focus based on the relationship of their sizes. 8 is a comparison judgment circuit that determines focus according to the output of the comparison judgment circuit. 9 is a motor that drives the lens.

Figure 2 shows the signal waveforms of each part in Figure 1, and (mu) is the NT
The waveform of one frame of the SC signal, (g) is the waveform of the color difference modulation signal of only the color components in the NTSC signal, that is, the chroma signal, and CG) is the waveform of the envelope-detected chroma signal.
The part is a color signal part, and the part m is an achromatic part. (The ship is a gate signal waveform having a width of a component corresponding to the achromatic portion m in the envelope detection waveform.

The operation in such a configuration will be explained next.

Assuming that the lens is in the focus position now, of the incident light from the subject, the green light will form an image on the imaging surface, the red light will be focused behind the imaging surface, and the blue light will be focused behind the imaging surface. Since the focus is on the front, both red and blue light become blurred.

Therefore, if the intensities of the incident lights of these three primary colors are equal, the output light from the imaging device will have a large output of green light and a small output of red light and blue light. When the incident light is colored, the photoelectric outputs of the three primary colors are different, so this relationship does not exist. According to the configuration shown in FIG. 1, the gate circuit 6 is opened only when the incident light intensity of the achromatic color, that is, the three primary colors in the video signal is equal, and the three primary color photoelectric outputs are applied to the comparison judgment circuit 7 through the gate circuit 6. , when in focus, the green light signal output is large, and the red and blue signal outputs are small and almost equal (Figure 3 (a)); when the front focus is on, the blue incident light is focused on the photocathode, The output of the blue light is large, and the green and red lights are blurred, so their photoelectric output is small (Figure 3 (b)).When the rear focus is on, the red incident light is focused on the photocathode, The light output is large, and the blue and green lights are blurred, so their photoelectric output is small.

Therefore, it is possible to detect focus, front focus, or rear focus from the output ratio of the six primary colors of the comparison/judgment circuit 7. The driver 8 determines the in-focus state based on these detection outputs, moves the lens in the in-focus direction, and automatically adjusts the focus. By inputting the output from the comparison/judgment circuit 7 to a display device (not shown), it is possible to display in-focus, front focus, and rear focus from the three states mentioned above. Note that the comparison/judgment circuit 7 is configured using, for example, a CPU, and input voltages of red, green, and blue are respectively vR and VG.
, VB, when in focus, that is, vG>vRkiVB, outputs of 0 and 0 are sent to the two output lines to the driver,
When the front pin, that is, vR>VB, outputs 1.0, and when the rear pin, that is, VB>vR, outputs 0 and 1. When the input is 00, the driver 8 outputs 0 to the motor 9, and when the input is 1.0, the output to the motor 9 is 0.
A current in the forward direction is supplied to the motor 9 to drive the lens backward, and when the input is 0 or 1, a current in the reverse direction is supplied to the motor 9 to drive the lens forward. Focusing drive is performed in this way.

According to this device, the blue and red parts of the video signal will be out of focus, but when the video signal is displayed, the blue and red parts will be out of focus compared to the green part when observed with the naked eye. The effect of blurring is small, and in the case of videos, the effect of blurring is much smaller than that of still photos, so automatic focus detection and automatic focus adjustment can be performed to a degree that does not cause any practical problems.

"Effects of the Invention" As explained above, according to the present invention, in addition to providing the lens with appropriate chromatic aberration, a special optical system and light! This has the effect that automatic focus detection and adjustment can be performed from a video signal without using an element.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a diagram of signal waveforms of each part thereof, and Fig. 6 is a comparison of the magnitude of photoelectric output of six primary colors when in focus, front focus, and rear focus. It is a diagram. 1...Lens 2...Imaging device 6...Video amplifier 4...
...Encoder 5...Gate signal generation circuit 6
......Gate circuit 7...Comparison judgment circuit
8...Driver applicant Kazuo Inamori, representative of Kyocera Corporation Figure 1 Figure b Gate date Figure 2 (b) -[FC] 3 Figure (Q) (b) (C)

Claims (1)

[Claims] An imaging device that converts the light distribution of a subject image into an electrical signal through a lens having chromatic aberration, a video amplifier that amplifies a video signal from the imaging device, and an encoder that generates an NTSC signal from the output of the video amplifier. a gate signal generation circuit that receives a chroma signal from the encoder and generates an output corresponding to an achromatic portion in each frame of the video signal; and a gate input from the gate signal generation circuit. A gate circuit outputs a color signal inputted from the video amplifier at a certain time, and the color signal from the gate circuit is inputted, and in-focus is detected when the green signal is the largest and the red and blue signals become smaller. An automatic focus detection device featuring: