JP3363477B2 - Imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an image pickup apparatus including a still video camera and a movie video camera using a solid-state electronic image pickup device.

[0002]

BACKGROUND ART In recent years, a so-called CCD camera using a CCD sensor as a solid-state electronic image pickup device has become widespread. With the trend toward miniaturization of this CCD camera, miniaturization of the built-in lens, diaphragm, CCD sensor, etc. has been demanded.

However, these lenses, diaphragms and CCDs
Along with the miniaturization of the sensor, the influence of the diffraction of light at the aperture opening of the lens becomes large, and the problem that the resolution deteriorates has arisen.

Table 1 shows a diaphragm aperture value (F number) and a spatial frequency characteristic (modulation transfer function) (hereinafter referred to as MTF; MTF = Mo) in a 1/4 inch CCD sensor (effective screen size 3.6 mm × 2.7 mm).
dulation transfer function). In Table 1, S is a standardized spatial frequency.

[0005]

[Table 1]

FIG. 7 is a graph of Table 1. The resolution at the time of designing the 1/4 inch CCD in Table 1 and FIG. 7 is 1000 TV lines (= 185.3 lines / mm).

As can be seen from Table 1 and FIG. 7, the larger the aperture value (F number) of the diaphragm, the greater the influence of light diffraction, and the sharper the reduction in resolution. For example, FNO.
With the 32 aperture, the response H (S) of the CCD with respect to the amount of light passing through the aperture of the aperture becomes approximately zero at the position of about 330 TV lines.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image pickup apparatus capable of taking a clear image even if the lens, diaphragm and solid-state electronic image pickup element are downsized.

In order to achieve the above object, an image pickup device according to the present invention comprises an image pickup optical system including a diaphragm and a solid-state electronic image pickup device which converts an optical image incident through an aperture of the diaphragm into a video signal and outputs the video signal. In the image pickup device, a luminance signal extraction circuit for extracting a luminance signal component from a video signal output from the solid-state electronic image pickup device, a contour enhancement circuit for performing a contour enhancement process on the luminance signal output from the luminance signal extraction circuit, A variable gain amplifier circuit that amplifies the output signal of the contour emphasis circuit, and a gain in the variable gain amplifier circuit,
According to the aperture value of the diaphragm, the aperture value of the diaphragm is increased as the aperture value is increased, and the frequency response of the solid-state electronic image pickup device with respect to the amount of light passing through the aperture of the diaphragm is controlled to be substantially the same regardless of the aperture value of the diaphragm. The gain control means is provided with a synthesizing circuit for synthesizing the luminance signal output from the luminance signal extracting circuit and the signal output from the variable gain amplifying circuit.

In the above image pickup apparatus, the gain of the variable gain amplifier circuit increases as the aperture value of the diaphragm is increased by the gain control means, and the frequency response of the solid-state electronic image pickup device with respect to the amount of light passing through the aperture of the diaphragm is irrespective of the aperture value. It is controlled so that it is kept almost constant. Then, the luminance signal extracted from the video signal by the luminance signal extraction circuit and subjected to the contour enhancement processing by the contour enhancement circuit is amplified by the variable gain amplification circuit whose gain is controlled as described above.

Therefore, even when the level of the video signal from the solid-state electronic image pickup device is lowered due to the diffraction of light in the diaphragm, the gain for amplifying the brightness signal whose contour is emphasized as the aperture value of the diaphragm at that time increases. By increasing, it becomes possible to compensate for the drop in the level of the video signal corresponding to the aperture value of the diaphragm.

In a preferred embodiment of the present invention,
The gain control means controls the gain of the variable gain amplifier circuit so that the frequency response is kept substantially constant in the range of about 1 TV line to about 200 TV lines.

This is most effective if the level drop compensation using the edge-enhanced luminance signal as described above is performed within a range of up to about 200 TV resolutions at which humans visually feel the sharpest. Because there is.

As described above, according to the image pickup device of the present invention, the solid-state electronic image pickup device such as a CCD is downsized, the influence of diffraction of light in the aperture is increased, and the video signal output from the solid-state electronic image pickup device is increased. Even if the level of is reduced, it is possible to capture a clear image by performing edge enhancement corresponding to the aperture value of the diaphragm.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail based on the embodiments shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention.

In FIG. 1, an image pickup optical system 10 is an image pickup lens.
11, aperture 12 and CCD sensor (solid-state electronic image sensor) 13
The video signal output from the CCD sensor 13 is input to the color separation circuit (luminance signal extraction circuit) 15 via the preamplification circuit 14. The color separation circuit 15 separates the video signal into a luminance signal (Y signal) and a chromaticity signal (C signal).
The luminance signal output from the color separation circuit 15 includes a gamma correction circuit 16 for luminance signal, a horizontal edge enhancement circuit (edge enhancement circuit) 17, and a vertical edge enhancement circuit (edge enhancement circuit) 18.
Entered in.

A signal obtained by horizontal edge enhancement by the horizontal edge enhancement circuit 17 and a signal obtained by vertical edge enhancement by the vertical edge enhancement circuit 18 are added to each other by a first synthesizing circuit 19. Are synthesized.
This combined signal is amplified by a variable gain amplifier circuit (hereinafter referred to as AGC circuit) 20. It is given to the second synthesis circuit 21.

In the second combining circuit 21, the combined signal from the AGC circuit 20 and the luminance signal gamma-corrected by the gamma correction circuit 16 are added together and combined.

The chromaticity signal (C signal) output from the color separation circuit 15 is applied to the chromaticity signal gamma correction circuit 22 to be gamma-corrected, and then the matrix circuit 23 applies the color difference signals RY, It is converted into BY and input to the modulation circuit 24.

The color difference signals R-Y and B-Y are modulated by the modulation circuit 24 and then applied to the third synthesizing circuit 22. In the third synthesizing circuit 25, a synchronism signal generating circuit (not shown) is applied. The synchronization signal and the combined signal provided from the second combining circuit 21 are added. The modulation circuit 24, the third synthesizing circuit 25 and the synchronizing signal generating circuit constitute an NTSC encoder. Then, an NTSC video signal is output from the third synthesis circuit 25.

The CPU (gain control means) 30 is a photometric element.
The aperture value (F number) of the diaphragm is determined based on the photometric value of 33, and a command signal is output to the iris control circuit 31 which controls the diaphragm 12 of the imaging optical system 10. In response to this command signal, the iris control circuit 31 controls the aperture 12 so that the aperture value of the aperture 12 becomes the value set by the CPU 30. The CPU 30 also sets the AG corresponding to the set opening value.
The gain of the C circuit 20 is searched from the LUT (look-up table) 32, and the gain is set to that gain.
20 gain control.

The gain of the AGC circuit 20 stored in the LUT 32 is set as follows.

FIG. 2 shows MT at a resolution of 200 TV lines.
The relationship between F response H (S) and aperture value (F number) is measured and plotted. FIG. 3 is a plot of the reciprocal of the function obtained from FIG. The horizontal axis of FIG. 3 represents the aperture value of the diaphragm, and the vertical axis represents the gain of the AGC circuit 20. The LUT 32 stores the gains corresponding to the aperture values obtained from the function shown in FIG.

As described above, the reason why the gain is set based on the resolution of 200 TV lines is that it is around 200 TV lines of resolution that humans visually feel the sharpest.

The AGC circuit 20 amplifies the combined contour emphasizing signal given from the first combining circuit 19 according to the gain set by the CPU 30. That is, A
The contour enhancement signal β output from the GC circuit 20 increases as the resolution increases as shown in FIG.
The signal has a magnitude that takes a maximum value near 0 TV lines and then decreases, and the level increases as the aperture value increases.

Therefore, the luminance signal α having the characteristic shown in FIG. 4 and the contour enhancement signal β from the AGC circuit 20 having the characteristic shown in FIG. , The resolution is as shown in FIG.
Up to 200 TV lines, it is possible to obtain an MTF characteristic in which the CCD response with respect to the amount of light passing through the aperture of the aperture is almost constant regardless of the aperture value of the aperture.

As described above, by amplifying the contour emphasis signal corresponding to the aperture value, it is possible to eliminate the influence of light diffraction at the aperture of the diaphragm even when a small solid-state electronic image pickup device is used. it can.

It is not necessary to strictly control the gain of the edge-enhanced signal at a resolution of 200 TV lines, and a resolution of 200 T is required.
It may be around V lines. Furthermore, it suffices to go up to near the sharpness at which humans visually feel the sharpest.

In the above embodiment, the aperture value of the diaphragm 12 is CP.
Although the automatic exposure CCD camera which is automatically controlled by the U30 and the iris control circuit 31 has been described, the present invention describes a method of manually setting the aperture value of the diaphragm C
It goes without saying that it can be applied to a CD camera.
In the case of a CCD camera in which the aperture value of the aperture is manually set, the CPU 30 detects the aperture value of the aperture that has been set, and based on this, the same amplification control of the contour emphasis signal as described above is performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an aperture value and an MTF response in 200 TV lines with a resolution of 1/4 inch CCD.

FIG. 3 is a graph showing a relationship between an aperture value and a gain of an AGC circuit.

FIG. 4 is a graph showing a change in the level of the luminance signal gamma-corrected with the aperture value as a parameter with respect to the resolution.

FIG. 5 is a graph showing a change in the level of the contour emphasis signal after amplification with respect to the resolution.

6 is a graph showing an MTF characteristic of a combined signal obtained by adding a luminance signal having the characteristic shown in FIG. 4 and an edge enhancement signal having the characteristic shown in FIG.

FIG. 7 is a graph showing the MTF characteristic of a 1/4 inch CCD.

[Explanation of symbols]

12 aperture 13 CCD (solid-state electronic image sensor) 17 Horizontal edge enhancement circuit (edge enhancement signal circuit) 18 Vertical direction edge enhancement circuit (edge enhancement circuit) 19 First synthesis circuit 20 AGC circuit (variable gain amplifier circuit) 21 Second synthesis circuit 30 CPU (gain control means) 31 Iris control circuit 32 LUT

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 5/222-5/257 G02B 7/11 H04N 9/68

Claims (2)

(57) [Claims] 1. An imaging device comprising an imaging optical system including a diaphragm and a solid-state electronic imaging device for converting a light image incident through an aperture of the diaphragm into a video signal and outputting the video signal. Luminance signal extraction circuit for extracting a luminance signal component from a video signal, a contour enhancement circuit for subjecting the luminance signal output from the luminance signal extraction circuit to contour enhancement processing, and a variable gain amplification circuit for amplifying the output signal of the contour enhancement circuit. , The gain in the variable gain amplifier circuit is increased as the aperture value of the aperture increases according to the aperture value of the aperture, and the frequency response of the solid-state electronic image pickup device with respect to the amount of light passing through the aperture of the aperture becomes the aperture value of the aperture. Regardless of the gain control means for controlling so as to be substantially the same, the luminance signal output from the luminance signal extraction circuit and the variable gain Combining circuit for combining the signals output from the width circuit, an imaging device provided with a. 2. The gain control means controls the gain of the variable gain amplifier circuit so that the frequency response is kept substantially constant in the range of about 1 TV line to about 200 TV lines of resolution. The image pickup apparatus according to claim 1.