JPH0467836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an electronic camera using a one-dimensional image sensor (hereinafter referred to as a line sensor).

[Prior Art and its Problems] Currently, various video cameras with built-in two-dimensional image sensors and electronic still cameras that capture still images are provided. In these video cameras or electronic still cameras, it is difficult to increase the number of pixels in the two-dimensional image sensor itself, and the vertical resolution is low because these images are formed based on so-called standard television signals. Because of the limitation in the number of scanning lines, it is difficult to obtain images with high resolution, such as silver halide photography, and in this respect, there is a demand for improvement in image quality.

On the other hand, line sensors having as many as 5,000 pixels per line have been used in facsimile devices and document image input devices that similarly require images with high resolution. Since these devices usually use still images or documents drawn on flat paper as the input image medium, the intensity of the light source can be kept constant, and the line Scanning in the direction of movement can be achieved by mechanically and relatively moving the sensor or the input image medium at a constant speed.

In this way, focusing on the fact that a line sensor can easily have a high number of pixels, a line sensor using this line sensor as an image pickup element for an electronic still camera has already been proposed, for example, in Japanese Utility Model Application Publication No. 35679/1983.
In this idea, the subject light passing through the lens is reflected by a rotating mirror that rotates around an axis perpendicular to the optical axis, which is located behind the lens, and forms an image on the line sensor. Two-dimensional scanning of the subject image is performed by scanning in the direction and scanning in the direction orthogonal to the line direction by rotating a rotating mirror.

However, in this type of electronic still camera, where the scanning speed of the line sensor and the rotational speed of the rotating mirror are constant, there is a dynamic range (dynamic range) within which an appropriate exposure can be obtained when the light intensity (brightness) of the subject changes. ) becomes narrower, and in order to deal with this problem, for example, if the rotation speed of the rotating mirror is slowed down according to the light intensity of the subject, the so-called high-speed shutter will not work, and if the rotation speed is increased, the exposure will be insufficient. It was hot.

[Object of the Invention] The present invention has been proposed in view of the above points, and its purpose is to use a line sensor that can increase the number of pixels per scanning line, so that the horizontal direction of the line sensor can be increased. A high-resolution, high-definition image is obtained by scanning and, in the vertical direction, by sampling a number of lines greater than the number of scanning lines of a standard television signal through a rotating mirror. An object of the present invention is to provide an electronic camera that can expand the dynamic range by changing the rotational speed of the line sensor and the charge accumulation time of the line sensor according to the light intensity of the object.

[Structure of the Invention] In order to achieve the above object, the present invention provides a rotating mirror that forms an optical image incident from a lens on a line sensor in accordance with an exposure control signal determined based on the light intensity of the optical image. The line sensor is rotated at a corresponding rotation speed, and the charge accumulation time of the line sensor is controlled in accordance with the exposure control signal.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. First, FIG. 1 shows the main parts of an electronic camera according to the present invention. In the figure, 1 is a lens, and a rotating mirror 4 is disposed on the optical axis of the lens.
This rotating mirror 4 is connected to a shaft 3 of a motor 2 that is perpendicular to the optical axis, and is rotatable around this shaft 3. A focusing plate 5 is provided above the rotary mirror 4, and a pentaprism 6 and a magnifying glass 7 are disposed close to the focusing plate 5, as in a well-known single-lens reflex camera. A photometric element 8 is attached to an appropriate position of the pentaprism 6, and a well-known exposure control circuit 9 is connected to this photometric element 8.

A rotation speed control circuit 10 and a charge accumulation time control circuit 11 are connected in parallel to the output side of the exposure control circuit 9, and an output terminal of the rotation speed control circuit 10 is connected to a motor drive circuit 12. On the other hand, the output terminal of the charge accumulation time control circuit 11 is connected to a line sensor drive circuit 13, and this line sensor drive circuit 13 has a self-scanning sensor disposed on the opposite side of the focusing plate 5 etc. via the rotating mirror 4. A line sensor 14 as a type photoelectric element is connected. Here, the line sensor 14 may be of either MOS type or CCD type. A well-known signal processing circuit 15 is connected to the output side of the line sensor 14. Note that 16 in the figure indicates an output terminal of the signal processing circuit 15.

Next, this operation will be explained. Light transmitted through the lens 1 is reflected by the rotating mirror 4 which is stationary at the initial position, and is imaged on the focusing plate 5. The brightness of this optical image is detected by the photometric element 8, converted into an electrical signal, and input to the exposure control circuit 9. The exposure control circuit 9 calculates the brightness based on this photometric amount to obtain a predetermined exposure. Determine time T. A signal representing this exposure time T is input to the rotation speed control circuit 10 and the charge accumulation time control circuit 11, respectively, and depending on the magnitude of this exposure time T, the motor drive circuit 1
The rotational speed ω of the motor 2 and thus the rotating mirror 4 via the line sensor drive circuit 13 and the charge accumulation time Te of the line sensor 14 via the line sensor drive circuit 13 are controlled.

On the other hand, the charges accumulated in the line sensor 14 via the rotating mirror 4 are input to the signal processing circuit 15.
The signal is converted into an appropriate signal form and output from the output terminal 16. Here, the form of the output signal may be analog or digital, and even if the signal for one screen is output in serial form, a group of signals divided into a plurality of blocks is output from the plurality of output terminals 16. It is also possible to do so.

FIG. 2 shows the relationship between the exposure time T determined by the exposure control circuit 9, the brightness of the optical image (image illuminance I), the rotational speed ω of the rotating mirror 4, and the charge accumulation time Te. Now, assume that the aperture size of lens 1, that is, the aperture value, is constant, and the exposure time T
is set to be inversely proportional to the image illuminance I.
At this time, the charge accumulation time Te of the line sensor 14
is controlled to be equal to the exposure time T. Here, if the time required to read out the charges accumulated in the line sensor 14 is ts, then the rotational speed ω of the rotating mirror 4 is such that the image illuminance I is above a certain value and the exposure time T<ts. When the relationship exists, it is desirable to set it to a constant value ω ₀ as shown in the figure, and when the image illuminance I is below a certain value and the exposure time T≧ts, it is desirable to control it so that it is inversely proportional to the exposure time T. . In other words, theoretically, it would be ideal if the rotational speed ω is always inversely proportional to the exposure time T, but there are physical limits to changing the rotational speed, and Even if there is a time difference between the part and the final scanning line part, there is no practical problem as long as there is no sense of discomfort, so there is no need to increase the rotational speed ω more than necessary.
In addition, in the case of T≧ts, it is necessary to rotate the rotating mirror 4 slowly as the exposure time T increases in order to eliminate blurring of the optical image during charge accumulation, so the rotation speed ω is set in inverse proportion as shown in Fig. 2. It is necessary to control it.

In this way, by appropriately setting the rotational speed ω of the rotating mirror 4 and increasing the number of scans by the line sensor 14 during the entire scanning period, it is possible to obtain an image with high definition.

Next, FIG. 3 shows the amount of charge accumulated in the line sensor 14 and the video output read out in this embodiment. When T<ts, as shown in FIG. A video output is obtained with a readout time ts every time the scanning of
Between each scan, the video output waveform becomes continuous,
The charge accumulation time Te becomes shorter as the image illuminance I increases. Therefore, during the period ts-Te, the charges generated in the line sensor 14 are discharged to a charge discharge region (not shown) in the line sensor 14, or
Alternatively, the driving of the line sensor 14 is controlled so as to prevent the generation of the charge itself.

Further, in the case of T≧ts, as shown in FIG. 3B, after the charges are read out during the period ts, the readout is interrupted, resulting in intermittent video output. on the other hand,
As shown in the figure, charge is continuously accumulated during the period T-ts.

The operation of the rotating mirror 4 is as shown in FIG. 4, and as shown in FIG.
The light passing through is reflected by the rotating mirror 4 and guided to the finder system 17 consisting of a focusing plate 5, a pentaprism 6, a magnifying glass 7, etc., and the rotating mirror 4 also functions as a reflecting mirror for optical image observation. ing. The rotating mirror 4 rotates from position a in the direction of the arrow in the figure, and scanning of the optical image starts from position b in b of the figure. At position c, the central portion of the optical image is scanned, and the rotating mirror 4 further rotates to a scanning end position (not shown). Thereafter, the rotating mirror 4 is controlled to either continue to rotate in the same direction and stop at position a, or to rotate in the opposite direction and return to position a. Here, it goes without saying that the line sensor 14 may be placed at any position as long as the light reflected by the rotating mirror 4 is incident thereon.

Next, FIG. 5 is a flowchart showing the operation of this embodiment. First, when a power switch (not shown) is turned on, photometry is started by the photometry element 8. Next, when the optimum exposure time T is calculated by the exposure control circuit 9, this exposure time T is compared with a predetermined charge readout time ts, and as described above, if T<ts, a constant rotational speed ω ₀
If T≧ts, the rotating mirror 4 rotates at a rotational speed ω that is inversely proportional to T. When the charge accumulation time Te is determined according to this exposure time T, scanning by the line sensor 14 starts,
The video signal is read out sequentially. When the required number of scans is completed, the rotating mirror 4 returns to its original position.

[Effects of the Invention] As described above, according to the present invention, a two-dimensional image with high definition can be created using a one-dimensional image sensor that can have a higher number of pixels than a two-dimensional image sensor and is relatively inexpensive. In addition, the dynamic range is substantially expanded even when the light intensity of the optical image of the object changes, so that good images based on proper exposure can always be obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a configuration diagram of the main parts, Figs. 2 and 3 A and B are illustrations of operation, and Fig. 4 A and B are illustrations of operation of the rotating mirror. Figure 5 is a flowchart. 1... Lens, 2... Motor, 3... Axis, 4...
...Rotating mirror, 5... Focusing plate, 6... Pentaprism, 7... Loupe lens, 8... Photometric element, 9...
...Exposure control circuit, 10...Rotation speed control circuit, 1
1...Charge accumulation time control circuit, 12...Motor drive circuit, 13...Line sensor drive circuit, 14...
...Line sensor, 15...Signal processing circuit, 16...
...Output terminal, 17...Finder system.

Claims (1)

[Scope of Claims] 1. A lens into which subject light is incident, a one-dimensional image sensor on which an optical image of the subject is formed,
In an electronic camera that photoelectrically converts the optical image into an electric video signal using a rotating mirror that moves the optical image in a direction perpendicular to the running direction of the one-dimensional image sensor, means for detecting the light intensity of the optical image. and a rotation speed control circuit that changes the rotation speed of the rotating mirror according to the light intensity, and a charge accumulation time control circuit that changes the charge accumulation time of the one-dimensional image sensor according to the light intensity. An electronic camera characterized by: 2. Claim 1, comprising an exposure control circuit that determines the exposure time according to the light intensity of the optical image, and changes the rotational speed of the rotating mirror and the charge accumulation time of the one-dimensional image sensor according to the exposure time. Electronic camera as described in section. 3. The electronic camera according to claim 1, wherein the rotation speed of the rotating mirror is set to be constant when the light intensity of the optical image is equal to or higher than a predetermined value. 4. The electronic camera according to claim 1, wherein the rotating mirror also serves as a reflecting mirror for guiding light to an optical finder system for observing an optical image.