JPS6320988A - Color image pickup device - Google Patents

Abstract

PURPOSE:To permit the respective image points of a color image pickup to be faithfully color-separated by using the image formation optical system of a one-sided telecentric system and permitting a main beam which is made incident on an image pickup element from the side of an object (original) to be vertical to an image pickup surface. CONSTITUTION:The color separation filter of an inorganic multilayer thin film is provided on the image pickup surface of a lenear image sensor 13. The one- sided telecentric system lens is used in an image formation lens 12. With such a constitution, light flux 15A-15C with respect to the image formation lens 12 from points A-C which are set apart in a main scan direction of an original surface 11 are converted into parallel light fluxes 15a-15c by the image formation lens 12. Main beams 16a-16b outgoing on the side of the lenear image sensor 13 from the image formation lens 12 are vertically and equally made incident on the apertures (a)-(c) of the lenear image sensor 13. Although the inorganic multilayer thin film filter whose wave length transmission characteristic converts in accordance with an incident angle is used for a color separation, a uniform color separation is executed by color separation filters in respective apertures.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color imaging device in which a color separation filter is provided on an imaging surface.

2. Description of the Related Art In recent years, with the development of semiconductor technology, high-performance imaging devices based on various photoelectric conversion methods have been developed. for example,
In facsimile machines, CCD (Charge
One-dimensional solid-state imaging systems using linear image sensors (Coupled Devices) have been put into practical use, and two-dimensional solid-state imaging plates have been put into practical use in television input systems, achieving high speed, high reliability, compactness, and low cost. In recent years, a method of providing a color separation filter corresponding to each pixel has been mainly adopted.

As shown in FIG. 2, the conventional imaging device of a facsimile machine has an imaging lens 2 and a linear image sensor 3, which constitute an imaging optical system, which are arranged opposite to the document surface 1. The scanned portion (X-axis) of the document surface 1 illuminated by a band-shaped light source such as a fluorescent pair is imaged by the lens 2 onto the aperture row (y-axis) of the photoelectric conversion section of the linear image sensor 3. ing. The following methods are known for colorizing the scanner section of such a facsimile.

1) The spectrum of the light source is approximately field (8), green (q), blue (B
) A light source switching method that processes image sensor output by switching three types of light sources consisting of three color areas in a field sequential or scanning line sequential manner.

11) The light source that spreads over the white spectrum range is continuously lit, and each aperture (pixel unit) of the image sensor is provided with, for example, a row of R, G, and B color filters at the top of the dot, so that color separation signals are sent serially to each aperture of the image sensor. method to obtain.

111) A method similar to light source 11), but using multiple rows of image sensors, providing a predetermined color separation filter for each row, and extracting color separation signals corresponding to each row.

In the imaging system of a television camera, an imaging surface is provided behind the imaging lens 2 as in FIG. 2, and photoelectric conversion is performed by electronic two-dimensional scanning. In a single-chip solid-state imaging device, a color filter is provided in an opening corresponding to each pixel of a two-dimensional solid-state imaging device, and the color signal is extracted as a color signal.

Among the above conventional examples, a method of forming a color separation filter in the form of a thin film on an image sensor is considered to be a promising technology in the future in terms of reliability, precision, and economy.

Problems to be Solved by the Invention However, when a thin film-like color separation filter is formed on the imaging surface of a solid-state imaging device and an image is captured using a conventional imaging lens, there is a problem in that distortion of spectral characteristics occurs depending on the image height.

This problem arises for the following reasons. That is, when an image is captured using a conventional imaging lens as shown in FIG. 2, a light beam 4A from a point A at the center of the document 1 passes through the imaging lens 2 and then enters the aperture of the image sensor 3 as shown by a light beam 4a. The light beam 4B from point B on the document l passes through the imaging lens 2 and then enters the aperture obliquely as shown by the light beam 4b.

In this way, the angle θa formed with the optical axis of the luminous flux incident on each pixel aperture of the linear image sensor 3 changes depending on the pixel position, and the range of the angle θa is generally from 0 to 2O2.
It extends back and forth. On the other hand, multilayer thin film filters are generally designed (standard) based on the angle of incidence as shown in Figure 3.
For this reason, when a color separation filter consisting of a multilayer thin film filter is formed on the imaging surface of a linear image sensor, the spectral characteristics differ depending on the angle θa formed by the light beam incident on each aperture, and the above-mentioned This results in distortion of the spectral characteristics. This problem can be said to be an unavoidable constraint due to the design principle in which the filter characteristics are controlled based on the interference effect of the thin film.

The present invention has been made in view of the above-mentioned problems, and is a solid-state image sensor equipped with a color separation filter on the imaging surface, in particular, an inorganic multilayer thin film color separation filter that can be expected to have high reliability is applied to the solid-state image sensor. An object of the present invention is to provide a color imaging device that can obtain uniform color separation characteristics even when using a solid-state imaging device configured as a chip.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method in which the light beam incident on the solid-state imaging device side provided with the color separation filter is perpendicular to the principal ray of the imaging optical system. As shown in FIG.

Function: As described above, the present invention uses a one-sided telecentric system for the imaging system that projects onto the imaging surface, thereby making it possible to arrange the principal ray to be vertically incident on each pixel aperture of the solid-state imaging device. Since each chief ray is equally perpendicular to the color separation filter provided on the image sensor,
Color separation characteristics do not become non-uniform from place to place.

Example The present invention will be explained in detail below.

FIG. 1(a) shows an embodiment in which the present invention is applied to a photoelectric conversion section of a color facsimile, in which 11 is a document surface, 12 is an imaging lens constituting an imaging optical system, and 13 is a two-dimensional solid-state image sensor. The device is a linear image sensor.

The imaging surface of the linear image sensor 13 is provided with a color separation filter made of an inorganic multilayer thin film. Imaging lens 1
2, a one-sided telesend link lens is used.

With this configuration, a point A distant from the document surface 11 in the main scanning direction
, B, C to the imaging lens 12
5B and 15C are light beams 15a parallel to the imaging lens 12.
, 15b, 15c, and are emitted from the imaging lens 12 to the linear image sensor 13 side.
b, 16c are apertures a, b of the linear image sensor 13,
Normal incidence equal to c. As a result, even though an inorganic multilayer thin film filter whose wavelength transmission characteristics change depending on the incident angle is used for color separation, uniform color separation is performed by the color separation filter of each aperture.

Here, the maximum lens diameter of the imaging lens 12 may be about the same size as the size S of the LSI image sensor 13 used as an image sensor, and it is larger than that of a conventional non-tele heptagonal lens. Although it is somewhat large, it can be designed and manufactured to such an extent that it does not pose a problem in practical use, so it has very good compatibility as a reduction imaging optical system using an image sensor.

As image sensors, CCDs with a pixel pitch of 14 μm to 7 μm and approximately 1,700 to 5,000 pixels have already been put into practical use (
5WAX = approximately 35 areas).

FIG. 1(b) shows the existence of an angle ε between the incident light beam 15a other than the principal ray and the principal ray 16a. However, the angle ε is distributed equally for each principal ray, and the value of ε is, as a general example, approximately, so there is little variation in the spectral characteristics as shown in FIG.

It is clear from the previous example that good color separation characteristics can be obtained using exactly the same design principle for a two-dimensional image sensor configured as a television camera, and the present invention can also be applied to that case. It is possible.

In the above embodiments, a case has been described in which a multilayer thin film filter is used as a color separation filter provided on the imaging surface, but the present invention is not limited to this case, and other color separation filters can also be used. For example, it is also possible to use an on-chip organic filter that uses a gelatin film as a dye dispersion medium, and in this case as well, it is possible to suppress unnecessary interference effects that occur depending on the angle of incidence of the light beam and achieve a uniform color. Decomposition is possible.

Effects of the Invention As is clear from the above explanation, the present invention uses a single-sided telecentric imaging optical system to provide a configuration in which the chief ray entering the image sensor from the object (original) side is perpendicular to the imaging surface. This has the effect that each image point is faithfully color-separated in color imaging in which a color separation filter is provided on the imaging surface.

[Brief explanation of drawings]

FIG. 1 (aJ is a side view showing the main parts of a color imaging device according to an embodiment of the present invention, and FIG. 1 (bl is a diagram schematically showing a light beam incident on one image sensor aperture in the embodiment) , FIG. 2 is a side view showing the main parts of a conventional general imaging device, and FIG. 3 is a graph showing the characteristics of a multilayer thin film filter.

Claims (2)

[Claims] (1) It has a one-dimensional or two-dimensional solid-state image sensor equipped with a color separation filter on its imaging surface, and an imaging optical system that projects an image onto the imaging surface of this solid-state imaging device, and this imaging optical system is installed on one side. A color imaging device characterized by being configured as a telecentric system. (2) The color imaging device according to claim 1, wherein the color separation filter is composed of a multilayer thin film.