JPH0572500A - Phase grating filter - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an excellent color false signal removal performance by separately performing optical low-pass filtering on the long wavelength side and the short wavelength side when removing a color false signal by a phase grating. It is intended to provide a phase grating filter. [Structure] First, low-pass processing is applied only to long-wavelength components of light
Optical filters 1 and 2 and second optical filters 3 and 4 that perform low-pass processing only on the short-wavelength component of the light.
The light that has passed through the optical filters 1 and 2 and the second optical filters 3 and 4 is subjected to low-pass processing selectively for long-wavelength components and short-wavelength components as an overall characteristic, and intermediate wavelength components are Passes without low-pass treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase grating filter which removes aliasing distortion that occurs during image pickup in an image pickup device such as a CCD video camera.

[0002]

2. Description of the Related Art In an image pickup device such as a CCD video camera, aliasing distortion occurs when a subject is spatially sampled by an image pickup device. In order to remove this aliasing distortion, unnecessary high frequency components are removed in advance by an optical low-pass filter before the incident light enters the image sensor. Recently, a phase grating has been used as the optical low pass filter.

The phase grating filter is an optical low-pass filter that utilizes the diffraction of light and is made of resin or the like.
Cost reduction can be expected. Another characteristic of the phase grating is color selectivity. Color selectivity means that low-pass processing can be selectively applied only to a specific wavelength, and it may be effective depending on the color separation filter used in the image pickup apparatus.

FIG. 4 is an arrangement diagram showing an arrangement example of color separation filters to which a phase grating filter is applied. In FIG. 4, color filters 30, 31, 32 indicate color filters arranged on the image pickup device. The green filter is arranged diagonally,
The red filter and the blue filter are arranged every other pixel. When the color filter shown in FIG. 4 is used, the red and blue signals are spatially sampled at half the frequency of the green signal, so that the folding signals of the red and blue signals are generated at half the frequency of the green signal. Therefore, by selectively subjecting only the red and blue signals to low-pass processing, a high-resolution video camera can be constructed by producing a luminance signal from the high-frequency component of the green signal.

FIG. 3 is a two-dimensional frequency characteristic diagram showing available frequency bands when a phase grating filter is used. In FIG. 3, the horizontal axis represents the horizontal frequency and the vertical axis represents the vertical frequency. The frequency bands of the red and blue signals are (0,0), (fh1,0), (fh1, fv) by the phase grating.
1), (0, fv1), the green signal is (0,
Since the triangular areas of 0), (fh2,0), and (0, fv2) can be used, the luminance resolution can be wide.

[0006]

By the way, FIG. 2 is a configuration diagram showing a configuration example of a conventional phase grating filter. As shown in FIG. 2, in the conventional example, for example, a phase grating 8 having a refractive index N5 and a phase grating 9 having a refractive index N6 are combined. FIG. 6 is a material characteristic diagram of a conventional phase grating filter. As shown in FIG. 6, with respect to the dispersion of the refractive index N5, the refractive index N6
Is selected so that the refractive index becomes the same near the green signal wavelength. As a result, the green signal 2
The lattice pattern between the materials does not appear, the lattice pattern appears only for the red and blue signals, and the color selectivity appears. However, in reality, it is very difficult to optimally select the phase grating 8 and the phase grating 9.

FIG. 8 is a spatial frequency characteristic diagram showing the color selectivity of the conventional phase grating filter. As shown in FIG. 8, the frequency characteristics of the red signal and the blue signal are often not uniform, and the use of the phase grating filter of the conventional example has a problem that the color balance of the video camera output is lost.

These problems are particularly noticeable when constructing a high quality video camera. That is, there is a difficulty in that the required color signal band is not uniform even if the color false signal is removed using the phase grating.

The present invention solves the problems of the conventional phase grating filter described above, increases the degree of freedom in selecting the phase grating material while using the phase grating, and eliminates the unevenness of the color signal band while performing the desired spurious signal suppression. The object is to provide a phase grating filter that can be used.

[0010]

DISCLOSURE OF THE INVENTION The present invention is a phase grating filter using a phase grating, wherein a first optical filter for subjecting only a long wavelength component of light to low-pass processing and a short wavelength component of light are provided. A second optical filter that performs low-pass processing is provided, and the light that has passed through the first optical filter and the second optical filter is selective to a long wavelength component and a short wavelength component as an overall characteristic. Is a phase grating filter that is configured to pass low-pass processing and pass the intermediate wavelength component without being subjected to low-pass processing.

[0011]

In the present invention, the light that has passed through the first optical filter and the second optical filter is subjected to the low-pass processing selectively for the long-wavelength component and the short-wavelength component as a comprehensive characteristic,
The intermediate wavelength component passes through without being subjected to low frequency processing. Therefore, it is possible to configure a high-quality video camera because the output color signal band can be aligned and an ideal frequency characteristic can be achieved while maintaining the color selectivity by the phase grating.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the phase grating filter according to the present invention will be described below with reference to the drawings.

FIG. 1 is a side view of the phase grating filter of this embodiment as seen from the side with respect to the optical axis. In FIG. 1A, the first optical filter is formed by adhering a first phase grating 1 and a second phase grating 2. Further, the second optical filter is configured by adhering the third phase grating filter 3 and the fourth phase grating filter 4 together. FIG. 5 is a material characteristic diagram of these phase grating filters. Figure 5
In (a), the refractive index characteristic N1 of the first phase grating 1 and the refractive index N2 of the second phase grating 2 intersect on the short wavelength side. Therefore, the low-pass processing is selectively performed on the long wavelength side. Further, in FIG. 5B, the refractive index characteristic N3 of the third phase grating and the refractive index characteristic N4 of the fourth phase grating intersect on the long wavelength side. Therefore, the low-pass processing is selectively performed on the short wavelength side. FIG. 7 is a spatial frequency characteristic diagram showing the color selectivity of the phase grating filter of the present invention. As shown in FIG. 7, since the frequency characteristics of the red signal and the blue signal are the same, the color balance of the output signal is not lost.

FIG. 1B is a side view showing a phase grating filter of another embodiment. As shown in the figure, the first optical filter is composed of the first phase grating 5 and the second phase grating 6, and the second optical filter is the second phase grating 6 and the third phase filter.
, And the second phase grating 6 is shared. Even in this case, it is possible to provide the same characteristics as those of the phase grating filter as shown in FIG.

The phase grating of each part in the above phase grating filter is manufactured by cutting or press glass method.
The phase grating filter can be made of resin or glass material.

When the red and blue signals are low-pass processed by the phase grating filter of the present invention, either color signal may be low-pass processed first.

In the above embodiment, the case where the red signal and the blue signal are selectively subjected to the low-pass processing based on the relationship of the color filter array shown in FIG. 4 has been described. Any combination of signals, green signals and green signals may be selected.

[0018]

As described above, in the phase grating filter of the present invention, in the phase grating filter using the phase grating, the first optical filter for performing the low-pass processing only on the long-wavelength component of the light and the short wavelength of the light. Second low-pass processing for wavelength components only
The light having passed through the first optical filter and the second optical filter is subjected to low-pass processing selectively for long-wavelength components and short-wavelength components as an overall characteristic, Since the wavelength component passes through without being subjected to the low frequency processing, the output color signal band is uniform and the overall characteristic is improved. That is, a high quality image pickup device using a phase grating can be constructed. Further, since the phase grating can be made of resin or the like and is inexpensive, it can contribute to the cost reduction of the imaging device.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a phase grating filter of the present invention as viewed laterally with respect to an optical axis.

FIG. 2 is a configuration diagram showing a configuration example of a conventional phase grating filter.

FIG. 3 is a two-dimensional frequency characteristic diagram showing available frequency bands when a phase grating filter is used.

FIG. 4 is an arrangement diagram showing an arrangement example of color separation filters to which a phase grating filter is applied.

FIG. 5 is a material characteristic diagram of the phase grating filter of the present invention.

FIG. 6 is a material characteristic diagram of a conventional phase grating filter.

FIG. 7 is a spatial frequency characteristic diagram showing the color selectivity of the phase grating filter of the present invention.

FIG. 8 is a spatial frequency characteristic diagram showing color selectivity of a conventional phase grating filter.

[Explanation of symbols]

 1 ... 1st phase grating 2 ... 2nd phase grating 3 ... 3rd phase grating 4 ... 4th phase grating

Claims (1)

[Claims] 1. A phase grating filter using a phase grating, wherein low-pass processing is applied only to long-wavelength components of light.
Optical filter and a second optical filter that applies low-pass processing to only the short-wavelength component of light, and the light that has passed through the first optical filter and the second optical filter has an overall characteristic. A phase grating filter characterized in that low-pass processing is selectively applied to long-wavelength components and short-wavelength components, and intermediate-wavelength components are allowed to pass without low-pass processing.