JPS5838030B2 - False signal removal method for single tube color television camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for combining, for example, two stripe filters and mounting them on a single image pickup tube, and extracting each primary color from a single carrier imaging output signal at a frequency related to the repetition period of the stripe filter stripes. This invention relates to a method for removing false signals occurring in the output video signal of a single-tube color television camera that separates and extracts signals.

The stripe filter used in this type of single-carrier frequency separation single-tube color television camera is made of cyan and white, and has a width that provides appropriate resolution, as shown in Figure 1. A stripe filter in a direction diagonal to a horizontal scanning line is made of yellow and white and has the same width as the stripe filter in the orthogonal direction, and the way the stripes of both filters overlap is reversed between adjacent scanning lines. Based on the periodic arrangement of cyan stripes that block red light and yellow stripes that block blue light, the image of the incident light transmitted through the filter is imaged. A red signal R and a blue signal B are separated and extracted from the output signal by signal processing similar to that of sampling at a period related to the above-described periodic arrangement.

Such sampling signal processing utilizes the above-mentioned inversion of the overlapping of both stripes for each horizontal scanning period.
As shown in the figure, the imaging output signals of adjacent scanning lines ■ and scanning lines ■ are added to an adder 2 and a subtracter 3 using a delay element 1 for one horizontal scanning period (1H), and the sum is red. The signal and the difference blue signal are respectively taken out.

However, in the filter having the above-described structure, since the combination of stripes is different between alternate scanning lines, the transmitted light image C changes in color and contrast between alternate scanning lines.
Therefore, when an incident light image that changes sharply in the vertical direction is captured, false signals may occur at the boundaries of the image plane due to the overlap with the above-mentioned periodic changes in color and contrast for each scanning line. Become.

In order to remove such false signals, conventionally, for example, as described in Japanese Patent Laid-Open No. 49-62029 filed by the applicant, a carrier color difference signal shaped from the color signals separated and extracted as described above is used. A method has been used to electrically correct the camera output signal by averaging signals that are sequentially delayed by one horizontal scanning period, but such electrical methods cannot sufficiently eliminate the above-mentioned false signals. Furthermore, the addition of such a correction circuit would impair the features of single-tube color television cameras, such as light weight and low power consumption.

On the other hand, as a method for optically preventing the generation of the above-mentioned false signals, the above-mentioned false signals are detected in the imaging output of the red signal and blue signal extracted by taking the sum and difference of the imaging output signals at the scanning line period. In order to prevent the appearance of high-frequency components that contribute to the generation of light, for example, as shown in FIG. An optical low-pass filter 4 such as a phase type diffraction grating is inserted at an appropriate distance d between the lens 4 and the image pickup tube 6, and the pitch of the diffraction grating is set to a value close to an integral multiple of the wavelength of the green light. , and set the direction of the checkered stripes in the vertical direction orthogonal to the scan line, so that only the red and blue lights are diffracted in the scan line direction as shown, and the red light and blue light are blurred in the scan line direction. It is known to cause only a certain portion of the low frequency range to pass through.

On the other hand, as an optical two-dimensional low-pass filter for blurring a two-dimensional image, there is one in which the above-mentioned diffraction grating is arranged in both the horizontal and vertical directions, and a filter in which the diffraction grating is arranged in both horizontal and vertical directions, as shown in FIG. Although it is known that only the intersection points of the diffraction gratings are left in a circular shape or the like, such conventional two-dimensional optical low-pass filters have not been designed to have different pass characteristics depending on the direction.

Note that there are optical low-pass filters that utilize the birefringence of quartz plates, etc., but they do not work satisfactorily on polarized incident light such as reflected light;
It has drawbacks such as inability to impart wavelength selectivity.

As mentioned above, phase-type diffraction gratings are suitable for imparting wavelength selectivity to transmitted light. Produces a significant beam of light in the direction perpendicular to the grid pattern relative to the point.

Regarding the prevention of such light beams, Japanese Patent Laid-Open No. 50-136048 filed by the applicant describes, for example, as shown in FIG. A method for preventing the above-mentioned light beams from occurring due to overlapping diffraction patterns by dispersing the direction of the diffraction pattern is described, but no consideration was given to the case of constructing an optical two-dimensional low-pass filter. .

An object of the present invention is to solve the above-mentioned conventional problems, and to reduce the required low cost in the horizontal and vertical directions by using a simple optical means instead of an electrical means involving a complicated circuit structure. An optical two-dimensional low-pass filter is used which exhibits band-pass characteristics, is easy to impart wavelength selectivity, and does not produce highlight beams in any direction. An object of the present invention is to provide a false signal removal method for a single tube color television camera using a single carrier frequency separation method using a combination of stripe filters.

That is, the false signal removal method of the present invention separates and extracts each primary color signal by disposing a plurality of stripe filters, each having stripes that intersect in different directions with respect to the scanning line, on the light incident surface of the image pickup tube. In a single-tube color television camera, an optical two-dimensional low-pass filter consisting of a two-dimensional diffraction grating in which the pitch, width, and thickness of the grating are different in the vertical and horizontal directions is used. It is characterized by the addition of a filter.

The present invention will be explained in detail below with reference to the drawings.

As mentioned at the beginning, a single-carrier frequency separation type single-tube color television camera uses a combination of two types of stripe filters to periodically and selectively extract red and blue signals. , due to the interference between brightness changes and hue changes in the scan line period in the vertical direction for only the red and blue images that occur based on the combination of stripe filters and steep level changes in the vertical direction in the incident light image. Therefore, as an optical low-pass filter to sufficiently prevent the occurrence of such false signals,
Although a phase-type diffraction grating is most suitable because it can appropriately impart wavelength selectivity, it is conventional to use a diffraction grating only in the direction perpendicular to the horizontal scanning direction of the screen. If band-passing is attempted, a sufficient removal effect cannot be obtained due to the causes of false signals mentioned above.

On the other hand, in the method of the present invention, as shown in FIG.
The phase-type diffraction gratings configured in this array and combination are placed in front of the image pickup tube in the same manner as shown in the third figure, but the pitches pH and pv of the diffraction gratings in the horizontal and vertical directions, and the width of the gratings are WH and W■ and the grating thickness δH
and δV are set to appropriate values, taking into account the stripe filters for separating each primary color and the spectral characteristics of the image pickup tube. , blue (B), and green (G), and the two primary colors red (R) and blue (B) are the same as before, only in the direction perpendicular to the scanning line. The configuration is such that the high frequency range is reduced to some extent, and the primary color green (G) has a transmission characteristic as flat as possible.

Therefore, the optical transfer function (OTF) of the phase-type diffraction grating
As shown in FIG. 3, a phase-type diffraction grating is placed in front of the light-receiving surface of the image pickup tube 6 at a distance d, and the pitch of the grating is p, the width is W, and the thickness is δ. Then, if the wavelength of the incident light is λ, the obtained optical transfer function (OTF
) is expressed by 1-2° (1-cosδ) p , and the cutoff spatial frequency at that time is /λ4.

Such optical transfer function and cut-off spatial frequency are
It was set to suit the periodic changes in the vertical direction of brightness and hue in certain portions of the red and blue extracted signals that cause the generation of false signals mentioned above, as well as the periodic changes in the horizontal direction accompanying these changes. Examples of specifications of a phase-type composite diffraction grating as an optical low-pass filter according to the present invention are shown below.

Horizontal direction: Pitch of grating pH=0.3 Width of grating "H=0.072ffiI!l Thickness of grating δH=540nmX->=270nm Vertical direction: Pitch of grating py=0.2mm Width of grating"v = 0.1 mm Grating thickness δy = 5 4 0 nmX 2 = 10
Distance between the 80 nm diffraction grating and the light-receiving surface: d=8im For the phase-type diffraction grating of the present invention method when such specifications are provided, its horizontal optical transfer function (OT
FIG. 7 shows how F) changes, and FIG. 8 shows how the optical transfer function (OTF) changes in the vertical direction.

Note that the illustrated transfer characteristics are based on the dimensions of the light receiving surface, that is, the imaging screen on the image pickup tube target, for example, 10.3 mm
7. This is an example where s= and settings are made in consideration of the spectral characteristics of each primary color separation stripe filter and image pickup tube.

As is clear from the characteristics illustrated above, in the phase-type diffraction grating according to the present invention, the optical transfer function in the horizontal direction has a Takagi-decreasing characteristic for all the three primary colors R, G, and B, and the optical transfer function in the vertical direction The function has a characteristic of lowering the high frequency range only for the two primary colors (red (R) and blue) related to the stripe filter, and has a substantially flat characteristic for green (G).

In the horizontal and vertical phase type diffraction grating according to the above-mentioned method of the present invention, the grating pattern can be undulated in the same way as in the past in order to remove the light beam caused by the incident light spot of the highlight. By undulating the grating, the direction of phase diffraction can be spread in all directions of 360°, and the generation of light beams can be completely suppressed.

At this time, the mode of the waviness of the lattice stripes, that is, the period of the waviness and the depth of the waviness, are appropriately changed depending on the difference in the degree of phase diffraction in each of the horizontal and vertical directions.

FIG. 9 shows an example of a diffraction grating according to the present invention constructed as described above.

In the example shown in Figure 9, the lattice is undulated in the form of a series of sequentially inverted arcs, and the angles of the undulation arcs are set to 280° and 80° for the horizontal and vertical lattice stripes, respectively. However, the diffracted light is uniformly dispersed over 36σ, and no light beams are produced even when photographing a high-brightness subject.

Furthermore, by imparting undulations to the gratings in both the horizontal and vertical directions, the optical transfer function in each direction is further reduced in the examples shown in FIGS. 7 and 8 as compared to the examples shown in the figures. However, in the diffraction grating according to the present invention, in order to avoid deterioration of the vertical green optical transfer function due to the waviness of the horizontal grating, the period qH of the waviness of the horizontal grating is set as follows. It is necessary to set the frequency fH at which the optical transfer function becomes a minimum due to the waviness to be higher than the frequency fV at which the optical transfer characteristic in the vertical direction becomes a cutoff.

That is, when the diffraction grating is given arcuate undulations as in the example shown in Figure 9, the period q of the undulations in the horizontal direction is
H is set to maintain the relationship qH≧2λ·d−fv with respect to the wavelength λ, the distance d to the light receiving surface, and the above-mentioned vertical frequency fV.

Note that the period qv of the vertical waviness is also preferably set to maintain the opening ratio of q≧2λ·d−fH in the same manner as described above.

In order to manufacture a horizontal and vertical phase type diffraction grating having the above-described structure, for example, horizontal and vertical gratings can be sequentially deposited on a glass substrate by mask deposition. At this time, it is not necessary to position the horizontal grating and the vertical grating with respect to each other, so it can be manufactured easily.

As is clear from the above description, according to the present invention, optical low-pass filters having wavelength characteristics that differ depending on two-dimensional directions are easily manufactured and added to the incident surface of the image pickup tube, thereby forming stripes. The single carrier frequency separation method using a filter can easily and completely eliminate the generation of false signals that are characteristic of single-tube color television cameras.
Moreover, even when a high-brightness subject is imaged, no beams are produced at all, and in addition, an extremely high-quality color imaging screen can be obtained without reducing resolution in the vertical direction.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the schematic structure of a stripe filter used in a single-tube color television camera with single carrier frequency separation method, Fig. 2 is a block diagram showing the mode of image pickup output signal processing, and Fig. 3 4 is a diagram showing an example of the schematic configuration of an optical two-dimensional low-pass filter, and FIG. 5 is a diagram showing the configuration of a conventional phase-type diffraction grating. Diagram showing an example of a schematic structure, No. 6
The figure is a diagram showing an example of the structure of a phase-type diffraction grating according to the removal method of the present invention, FIG. 7 is a characteristic curve diagram showing an example of its horizontal optical transmission characteristic, and FIG. FIG. 9 is a characteristic curve diagram showing an example of an optical transfer function, and FIG. 9 is a diagram showing another example of the structure. 1... IH delay element, 2... Adder,
3... Subtractor, 4... Keiwei lens, 5
...Phase type diffraction grating, 6... Image pickup tube.

Claims (1)

[Claims] 1. A plurality of stripe filters, each having stripes that intersect in different directions with respect to the scanning line, are arranged on the light incident surface of the image pickup tube to separate and extract each primary color signal. In a single-tube color television camera, an optical two-dimensional low-pass filter consisting of a two-dimensional diffraction grating in which the pitch, width, and thickness of the grating are made different in the vertical and horizontal directions is used. A false signal removal method for a single-tube color television camera, which is characterized by being added to the light incidence surface of the image pickup tube. 2. Claim 1, characterized in that the optical two-dimensional low-pass filter is configured to remove a high frequency portion of the red and blue optical images only in the vertical direction.
False signal removal method for a single-tube color television camera as described in . 3. The optical two-dimensional pass filter is constructed with a two-dimensional diffraction grating that imparts to transmitted light a phase change having a period that is an integral multiple of the wavelength of green light only in the vertical direction. 2. False signal removal method for a single tube color television camera according to item 2. 4. The optical two-dimensional low-pass filter is constructed by the two-dimensional diffraction grating in which the horizontal and vertical gratings are provided with undulations having mutually different periods and depths. A false signal removal method for a single-tube color television camera according to scope 3.