JPH0432374A - Electronic image pickup device - Google Patents

Abstract

PURPOSE:To improve the resolution by providing an image pickup optical system and a video signal process circuit forming a video signal for displaying a video image similar to an object based on an output signal from the image pickup element to the image pickup device. CONSTITUTION:The image pickup lens system 1 is a so-called anamorphic optical system and forms an image of a character A being an object in a way that its longitudinal direction is more expanded than the lateral direction. The image is received by an image pickup element 2 having a square photoelectric conversion plane, in which photoelectric conversion is processed. A prescribed processing is applied to an output signal obtained from the image pickup element 2 by a video process circuit 3 and displayed on a monitor 4 with a correct aspect ratio. Thus, the light utilizing efficiency of the light made incident through the image pickup lens system 1 for the image pickup element 2 having a square photoelectric conversion plane is highest and when the area for one picture element is kept same, the number of picture elements is maximized. Thus, the image pickup area is increased and high resolution processing of the electronic image pickup device is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to electronic imaging devices such as electronic still cameras and video cameras.

[Conventional technology]

Visual information in today's highly information-oriented society mainly takes the form of printed matter (prints) and electronic images (television, etc.), and a huge amount of this visual information is used in a variety of situations and will continue to grow in the future. The amount is on the rise. Printed matter has its limits when it comes to sorting, arranging, storing, and transmitting this vast amount of visual information at high speed, so we have no choice but to use electronic video. However, it cannot be denied that the image quality, especially the resolution, of electronic images is lower than that of printed materials.

This low resolution is mainly due to the fact that the number of pixels of the image sensor is too small. For example, currently 4.8mmX6
．． 490 x 670 pixels are arranged on a 4mm imaging surface, but increasing the number of pixels by reducing the size of each pixel is close to the limit, so measures such as installing a microlens for each pixel to increase the amount of light are being taken. Currently, attempts are being made to maintain the S/N ratio at a high level. Therefore, 35
-The path to increasing pixel density to the level of full-size silver halide film is difficult. Another way to increase the density of pixels is to increase the imaging area by forming a thicker image of the object, but this method inevitably requires a larger optical system, so it is difficult to make it more compact. This would go against the flow of time.

[3] Problems that the Invention Attempts to Solve] By the way, the shape of the imaging surface of the image sensor currently has an aspect ratio of 3:4 based on the NTSC standard, and future high-definition television standards will further increase the aspect ratio. is predicted to increase. Lens systems compatible with these must ensure optical performance at least within the circumscribed circle of the imaging surface (rectangle). In a rectangular imaging surface with the same area, the larger the aspect ratio, the larger the radius of its circumscribed circle, and the corresponding lens system must be larger.

On the other hand, when using optical systems of the same size, the larger the aspect ratio of the imaging surface, the smaller the number of pixels must be, which is not efficient. That is, when using optical systems of the same size, the light receiving area is maximized when the imaging surface is square, so if the size of each pixel is the same, the number of pixels can be maximized. Since the number of pixels in the vertical direction is determined by the standard, horizontal resolution can be improved by allocating the increased number of pixels in the horizontal direction. However, even if the imaging surface is configured to be square, the reproduction screen has an aspect ratio of 3:4 according to the NTSC standard, and must be higher than this according to the high-definition television standard.

In view of the above-mentioned points, an object of the present invention is to provide an electronic imaging device in which the number of pixels is increased and resolution is improved without increasing the size of the optical system by using an optical system that is not rotationally symmetrical as a photographing lens.

[Means and effects for solving the problem] The electronic imaging device of the present invention uses an imaging lens system that has different imaging magnifications in the xz section and the yz section when two axes are optical axes in an xyz three-dimensional coordinate space. An imaging optical system that forms an image of an object and receives the image with an image sensor having a photoelectric conversion surface substantially perpendicular to the optical axis, and an image that is substantially similar to the object based on an output signal from the image sensor. The present invention is characterized by comprising a video signal processing circuit that forms a video signal for displaying.

FIG. 1 is a conceptual diagram showing the principle of the present invention.

The photographing lens system 1 is a so-called anamorphic optical system, and forms an image of the object, the letter A, by elongating it in the vertical direction more than in the horizontal direction. This image is received by an image sensor 2 having a square photoelectric conversion surface and charged and converted. The output signal obtained from the image sensor 2 is subjected to predetermined processing in the video processing circuit 3, and displayed on the monitor 4 with the correct aspect ratio.

Generally, the image circle of the photographing lens system 1 is the image circle of the image sensor 2.
This is the circumscribed circle of the rectangular photoelectric conversion surface, but the square has the largest area among the rectangles inscribed in an image circle of the same size. Therefore, an image sensor with a square photoelectric conversion surface has the highest utilization efficiency of light incident through the photographic lens system, and if the area of each pixel is the same, it can maximize the number of pixels, which improves resolution. It is advantageous in this respect. However, among the normal television standards, the aspect ratio of the screen should be determined based on ergonomics, so it is not desirable to change the shape of the screen arbitrarily.

Therefore, in the present invention, the aspect ratio a defined by the usual standard:
b (for example, 3:4 according to the NTSC standard) with an analog ratio of 1/'a:1/b (1/' according to the N'FSC standard)
A square image is formed using a photographing lens system having a ratio of 3:1/4=4:3), and this image is received by an image sensor 2 having a square photoelectric conversion surface. The number of pixels in the vertical direction of the image sensor is the number of scanning lines (N'f'S) defined by the normal standard.
If the number of pixels is determined according to the C standard (525 lines), the number of pixels in the horizontal direction will increase, and the horizontal resolution can be improved. In this case, the photographic lens system 1 forms an image by elongating the vertical direction more than the horizontal direction compared to a normal photographing lens system having the same image circle, so each pixel is formed into an elongated shape in the vertical direction. For example, the density of pixels in the horizontal direction can be increased without changing the area of one pixel.

The number of pixels in the vertical direction is determined according to the standard, so if normal signal processing is performed after photoelectric conversion, it will be the same as the subject.
A reproduced image with a high horizontal resolution and an aspect ratio of :b (3:4 in NTSC) can be obtained.

〔Example〕

Next, an example of a photographic lens system used in the present invention will be described.

Anamorphic optical systems include those that use lenses with different radii of curvature in two directions orthogonal to each other, and those that use prisms, but those that use lenses are used here.

FIG. 2 is a cross-sectional view of the lens system of this embodiment, with (A) showing the cross section in the horizontal direction and (B) showing the cross section in the vertical direction. As is clear from the figure, this lens system consists of, in order from the object side, a lens group I that has positive refractive power, and a second lens group II that has negative refractive power and moves along the optical axis for zooming. , a third lens group (■) that has a positive refractive power and moves along the optical axis for zooming, and a fourth lens group (■) that has a positive refractive power and has an imaging function. An aperture stop S is provided between the lens group and the fourth lens group. The plane plate arranged behind the fourth lens group is a filter such as an infrared cut filter or an optical low-pass filter. This lens system includes lens elements that have different focal lengths in the horizontal scanning direction and vertical scanning blade height of the image sensor 2, and the imaging magnification in the vertical direction is larger than that in the horizontal direction, but the focal position remains unchanged in either direction. Since they must be approximately equal, the following points need to be taken into consideration.

When an anamorphic lens is composed of a toric surface or the like, the focal lengths of the vertical and horizontal sections of the photographing lens system 1 differ due to the contribution of the partial system sandwiched between the toric surface closest to the object side and the toric surface closest to the image side. The image points of this partial system may be made to substantially coincide on both cross sections. However, in this type of subsystem, there is only one type of conjugate point common to both cross sections. Therefore, this subsystem should not move during focusing, and focus adjustment should always be performed using another subsystem closer to the object than this subsystem, so that the object point position with respect to this subsystem is always fixed. There must be.

Also, if the azimuth (tilt around the optical axis) of a partial system that includes lens elements with different focal lengths in two directions changes, the direction in which the image is distorted will not be constant and it will become very difficult to see. It is better not to rotate around the optical axis.

Based on the above considerations, in this example, an anamorphic lens element is provided in the fourth lens group that does not move during zooming, focusing, etc.

In addition, in a zoom lens, if an anamorphic lens element is installed in the part that contributes to zooming, it becomes difficult to maintain a constant zoom ratio in two directions, so from this point of view as well, it is recommended to include an anamorphic lens element in the fixed lens group. It is a good idea to set one up.

Lens data for this example is shown below.

rx = 22.9782 dx -1,5nl-1,84866νl -23,7
8r 2 = 16.5102 d2-0.3 r 3 - 17.8333 d5 = 4.7 n2-L72916 ν2-
54.88r4-ω d4-variable r5・37.6803 d5-0.9 n3 =1.6968 νs
-56,49r 6 = 8.9793 d6-2.58 r2-13,43148 d7 = 0.8 n4"1.617 ν4"8
2.79r@ -52,3345 d8-variable r, -28,918 d9 = 1.7 r xo''' ω dlo-variable rl, -a Co (aperture d xx = 1.8 r 12- 29.4596 d+2 -2.1 r 13--14.4996 d 13-0.33 r 14-- 9.1605 614-4.4237 r 15- 15.0204 dl;-0,4 r□6- 17.2834 d 16 - 3.85 r 1-10,5496 dl7-0.2 r 18- 61.6049 dlg-2, t r□9=-28,462:J n 5 =1.84668 n6 -1.80518 n 7 -1.80518 nB =1.58913 =1.65844 ν5 -23.78 Shiro ``25.43 Schiff -25,43 νa -60,97 Shi9 -50.86 d 19-13.8 Rhz= 14.1276 Dxz"dt2 R□3--13.1097 Dx3-dl3 R Eng4--10.9672 D x4- d 14 N7- n7R', i
s= 11.0472 D engineering=-dl5 R16-17,0453 px6-aig R17-- 13.7064 D17-dxF R engineering a" 278.7502 Dxs-dxs R□e=-53,4914 D19-dl9 r2o -(X) d20- 1.6 r21ga c.

s-rig n 10-1.51633 Si1o-84. i59-
ng Nb=n6 V6- Shiro ■7 arrangement ]ノ 7 Vs-ν8 ■, -ν9 dl1-4.4 r22' ω d 22- 0.5 r231 l a: as-0,6 r 24- (1) n xx-1,54771 n 12-1.51633 ν, □-62.83 ν□2”64.15 f LX= 10.3~2B, 19, f r-Y
= 13.74~34.92.

Fx 7. '2.7, FY/3.6,
I H=4.7 However, r+, R, + is the radius of curvature of each lens surface, d+, II)+ is the distance between each lens surface, n l ,
NJ is the refractive index of each lens, νl, VJ is the Atsube number of each lens, ftxsfLy is the focal length of the entire system in the horizontal and vertical directions, respectively, Fx, FY are the f-numbers of the lens system in the horizontal and vertical directions, respectively, and IH is image height,
f-, fs, and ft are the focal lengths of the entire system in wide, standard, and telephoto conditions, respectively.

[Effects of the Invention] According to the present invention, an object image is formed at a ratio different from the original aspect ratio of the system, and this image is received by an image sensor having a square imaging surface, thereby reducing the imaging area. It can be made larger and has a great effect on increasing the resolution of electronic imaging devices.

[Brief explanation of drawings]

Claims (1)

[Claims] In the xyz three-dimensional coordinate space, when the z-axis is the optical axis, an image of the object is formed by an imaging lens system with different imaging magnifications in the xz and yz sections, and this image is converted into a photoelectric conversion surface that is approximately perpendicular to the optical axis. and a video signal processing circuit that forms a video signal for displaying an image substantially similar to an object based on an output signal from the image sensor. Characteristic electronic imaging device.