JPH0511219A - Diffraction grating for video camera - Google Patents

Abstract

PURPOSE:To provide the diffraction grating for the video camera which has a response value improved in an area on an OTF except at the trap points of a color false signal and a brightness false signal and also has small light wavelength dependency. CONSTITUTION:The diffraction grating which is used for the video camera having a solid image pickup element so as to improve the picture quality includes 1st gratings arrayed in a 1st direction and 2nd diffraction gratings arrayed in a 2nd direction, and those 1st direction G1 and 2nd direction G2 cross each other at an angle other than 90 deg..

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to diffraction gratings, and more particularly to
The present invention relates to improvement of a diffraction grating used for improving image quality in a video camera having a solid-state image sensor.

[0002]

2. Description of the Related Art Referring to FIG. 4, a conventional diffraction grating is shown in a plan view and a sectional view. This diffraction grating has a disc shape as a whole, and includes a first grating arranged along the first direction G1 and a second grating arranged along the second direction G2. I'm out. These first lattice directions G1
And the second lattice direction G2 are orthogonal to each other. In the plan view in which the diffraction grating is represented by a circle, the H direction (horizontal direction) and the V direction (vertical direction) correspond to the H direction and V direction of the solid-state image sensor, respectively. The cross-sectional view shown on the lower right side of the circular plan view shows the cross section along the direction orthogonal to the direction G1 of the first grating. The cross-sectional view shown on the lower left side of the plan view is the direction G of the second lattice.
2 shows a cross section along a direction orthogonal to 2. As can be seen from these cross-sectional views, the diffraction grating of FIG. 4 has the grating pitch P1 and the grating step a in the first grating and the grating pitch P2 and the grating step a in the second grating.

Referring to the graph in FIG. 5, an OTF (optical transfer fun) of a diffraction grating as shown in FIG.
ction: Response function) is shown. In each graph in FIG. 5, the horizontal axis represents the spatial frequency F (lp / mm: l
(p represents a line pair), and the vertical axis represents the response value. This OT is usually used for designing a diffraction grating.
F is used to determine the characteristics of the diffraction grating.

The diffraction grating for a video camera must first suppress two false signals, a color false signal and a brightness false signal, which are generated in the solid-state image sensor in the H direction. for that reason,
The diffraction gratings are designed to have a response value of 0 at the spatial frequencies corresponding to their spurious signals and trap those spurious signals. For example, in FIG. 5A, the diffraction grating has a response value of 0 at the trap spatial frequency Hc of the OTF in the H direction in order to suppress the color false signal in the H direction, and suppresses the luminance false signal in the H direction. It is designed to have a response value of 0 also at another trap spatial frequency Hy for the purpose. Further, in FIG. 5B, the diffraction grating is designed to have a response value of 0 at the trap spatial frequency Vcy of the OTF in the V direction in order to suppress the color false signal and the brightness false signal in the V direction. In the V direction, since the color false signal and the luminance false signal correspond to the same spatial frequency,
It can be blocked by one trap point Vcy. The spatial frequency of the trap point as described above is a value determined from the pixel pitch of the solid-state image sensor.

[0005]

The diffraction grating for improving the image quality of the video camera as described above needs to have a response value of 0 at the trap point, but has a high response value at other spatial frequency regions. It is desired to have. Generally, OTF also depends on the wavelength of light, but it is desirable to minimize the light wavelength dependency.

However, as described above, in the prior art diffraction grating, the first grating direction G1 and the second grating direction G
The angle formed with 2 was fixed at 90 °. This is because conventionally, the technique for evaluating the characteristics of the diffraction grating by including this angle as a parameter of the OTF was unclear.
That is, in the prior art, the control of the characteristics of the diffraction grating was mainly performed by adjusting only the grating pitch and the grating step, so that the response value in the region other than the trap point was improved and the optical wavelength dependence was reduced. Could not be fully achieved.

In view of the above problems of the prior art, the present invention provides a video having an improved response value in a region other than the trap point of the false color signal or the false brightness signal on the OTF and having a small light wavelength dependence. The purpose is to provide a diffraction grating for a camera.

[0008]

A diffraction grating according to the present invention, which is used for improving image quality in a video camera having a solid-state image pickup device, includes a first grating arranged along a first direction and a second grating. A second grating arranged along the direction, wherein the first direction and the second direction intersect each other at an angle other than 90 °.

[0009]

According to the present invention, not only the lattice pitch and the lattice step but also the angle formed by the first lattice direction and the second lattice direction is 9
Since the angle is adjusted to a value other than 0 °, in the characteristics of the diffraction grating, it is possible to easily improve the response value in a region other than the trap point of the color false signal or the brightness false signal on the OTF, and the light wavelength dependence. Can also be small.

[0010]

1 is a plan view of a diffraction grating according to an embodiment of the present invention. Also in this figure, V
The direction and the H direction correspond to the V direction and the H direction of the solid-state image sensor, respectively. However, in the diffraction grating of the present embodiment, unlike the conventional diffraction grating, the first grating direction G1 and the second grating direction G2 intersect at an angle other than 90 °. When designing such a diffraction grating, the characteristics of the diffraction grating are mainly judged by utilizing OTF. In the following discussion of OTF, a diffraction grating including a sinusoidal grating will be described, but the present invention can also be applied to other diffraction gratings.

Referring to FIG. 2, there is shown an OTF in the H direction decomposed for each component of the first grating in the G1 direction and the second grating in the G2 direction in the diffraction grating of this embodiment. In each graph in FIG. 2, the horizontal axis represents the spatial frequency F (lp / mm)
And the vertical axis represents the response value. Figure 2
In (A), the OTF obtained by converting the grating pitch of the first grating in the G1 direction into the grating pitch in the H direction is shown. In this example, the first grating G1 is designed to trap the color false signal Hc in the H direction. On the other hand, in FIG. 2B, the OTF obtained by converting the grating pitch of the second grating in the G2 direction into the grating pitch in the H direction is shown, and the false luminance signal Hy in the H direction is trapped. Is designed to. Then, in FIG. 2C,
The total OTF in the H direction obtained by the combination of the first grating G1 and the second grating G2 is shown in FIG.
2 is obtained by multiplying the response values of FIGS. 2A and 2B at the corresponding spatial frequency. The characteristic of the diffraction grating in the H direction is finally determined by the total OTF in the H direction.

Referring to FIG. 3, the first grating G in the diffraction grating
O in the V direction decomposed for each component of 1 and the second lattice G2
TF is shown. The horizontal axis and the vertical axis of each graph in this figure are the same as those of each graph in FIG. In FIG. 3A, the OTF obtained by converting the lattice pitch of the second lattice G2 into the lattice pitch in the V direction is shown. In this example, the second grating G2 is designed to trap the color false signal and the luminance false signal Vcy in the V direction (in the V direction, the color false signal and the luminance false signal correspond to the same spatial frequency. ing). On the other hand, FIG. 3B shows the OTF in the V direction by the first grating G1. This OTF
In the above, by changing the angle θ1 formed by the first grating G1 and the H direction shown in FIG. 1, the OTF represented by the solid line curve to the OTF represented by the one-dot chain line or the broken line is changed.
Can be changed to In FIG. 3C, the second
The total OTF in the V direction obtained by the combination of the grating G2 and the first grating G1 is shown, and the response value in FIG. 2C is shown in FIG.
It is obtained by multiplying the response values of (A) and (B) by each other.

As can be seen from FIG. 3, if the variation cycle of the response becomes long as in the OTF shown by the broken line curve in FIG. 3B, the V direction shown in FIG. In the total OTF, the light wavelength dependency is reduced, and the response value is improved while the spatial frequency F changes from 0 to Vcy.

[0014]

As described above, according to the present invention, the OTF
It is possible to provide a diffraction grating for a video camera, which has an improved response value in a region other than the trap points of the color false signal and the brightness false signal and has a small light wavelength dependency.

[Brief description of drawings]

FIG. 1 is a plan view showing a diffraction grating according to an embodiment of the present invention.

FIG. 2 is a graph showing an OTF in a H direction in a diffraction grating according to an exemplary embodiment of the present invention.

FIG. 3 is a diagram showing an OTF in a V direction in a diffraction grating according to an embodiment of the present invention.

FIG. 4 shows a prior art diffraction grating for a video camera.

FIG. 5 OT in the H direction in a prior art diffraction grating
It is a graph which shows an example of F.

[Explanation of symbols]

 H Horizontal direction of solid-state image sensor V Vertical direction of solid-state image sensor a Step of diffraction grating G1 Direction of first grating G2 Direction of second grating F Spatial frequency

Claims (1)

Claim: What is claimed is: 1. A video camera having a solid-state imaging device, the diffraction grating being used for improving image quality, the diffraction grating being a first diffraction grating arranged along a first direction. And a second grating lined up along a second direction, wherein the first direction and the second direction intersect with each other at an angle other than 90 °. Diffraction grating.