JPH11122540A - Ccd camera, controller for ccd camera and sensitivity adjustment method for ccd camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CCD camera that is capable of reading an image at a high speed with high S/N and the sensitivity adjustment method while keeping a luminous quantity of an image constant automatically at the selection of a binning pixel number. SOLUTION: The CCD camera 1 has a CCD 11 and a control section 12 and an electronic shutter and a binning function are controlled in response to an external control signal. A controller 2 of the CCD camera 1 is provided with an A/D converter 21 that converts image data photographed by the CCD 11 into digital data and a sensitivity control means 22 consisting of a control CPU 23, a memory 24 and an input output IF 25. The control CPU 23 obtains an exposure time to keep an apparent luminous quantity per one pixel in the photographed image constant by referring to a table stored in the memory 24 and provides an output of an electronic shutter control signal to the control section 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CCD camera, and more particularly, to a CC camera having a binning function capable of high-speed photographing.
Related to D camera.

[0002]

2. Description of the Related Art In a normal CCD camera, it takes one field period (1/60 second) to photograph one screen. In order to increase the speed, a binning method is used in which luminance information of a plurality of pixels, that is, accumulated charges are simultaneously read to shorten the time required to read the entire image in exchange for resolution.

[0003]

In a general CCD,
Since each pixel accumulates charge as image information between the charge reading and the next charge reading, the charge accumulation period, that is, the exposure time corresponds to the frame rate which is the screen update period. By executing the binning, the frame rate is shortened and the exposure time is also shortened. However, since the charge transfer time itself from the pixel is not shortened, for example, 4 (2)
X2) Even when pixels are read out at the same time, the frame rate cannot be reduced to ４, but is reduced to about １ ／. As a result, since the exposure time is not sufficiently reduced, the total amount of charge accumulated in a plurality of pixels constituting one apparent pixel by binning becomes larger than the amount of accumulated charge of each pixel before binning, and the reading is performed. When the amount of charge per pixel of the output image, that is, the amount of light increases, and the imaging target is sufficiently bright, the amount of light may be saturated by binning.

As a technique for preventing this saturation, there is a technique in which the saturation charge amount of the transfer register for adding the accumulated charges is made larger than that of each pixel. However, in order to increase the number of binning pixels, the saturation of the transfer register is increased. It is necessary to make the charge amount extremely larger than the saturation charge amount of each pixel, and the transfer portion becomes large. Further, when the saturated charge amount is extremely large, when the number of binning pixels is small, the actual accumulated charge amount to be transferred becomes smaller than the saturated charge amount of the transfer register, and the S / N ratio is deteriorated. . Therefore,
This technique is not preferable when it is desired to change the number of binning pixels.

On the other hand, there is a technique for suppressing the light amount of an image acquired by a CCD during binning. For example,
There are techniques for limiting the amount of light incident on the CCD by installing an aperture and the like, and techniques for controlling the exposure time itself of the CCD.
As a technique for controlling the exposure time of the CCD, there is an electronic shutter for controlling the charge accumulation time of a pixel. However, conventionally, every time the number of binning pixels is switched, the light amount is adjusted manually or by a gain control or the like. .

In view of the above problems, the present invention enables high-speed, high-S / N-ratio image reading while automatically keeping the image light amount constant even when the number of binning pixels is switched during the binning operation. It is an object to provide a CCD camera and a method of adjusting the sensitivity thereof.

[0007]

The CCD camera of the present invention has a CCD consisting of two-dimensionally arranged image pickup pixels, and has a binning function for simultaneously reading out charges of a plurality of adjacent pixels as information of one pixel. In a CCD camera, an electronic shutter that controls each image pickup pixel to change the charge accumulation time as an exposure time, and an image pickup corresponding to one pixel of a read image by controlling the exposure time of the electronic shutter according to the number of binning pixels. And a sensitivity control unit for keeping the sum of the accumulated charge amounts of the pixels at a certain value or less.

According to this, by executing the binning function of simultaneously reading out the charges of a plurality of adjacent pixels as information of one pixel, the reading time of the entire screen, that is, the frame rate is shortened, and the time resolution is improved. Can be. At this time, since the charges of the pixels read out simultaneously by binning are added, the charge amount, that is, the light amount of the image may be saturated in the charge transfer path of the CCD as it is. However, according to the present invention, the electronic shutter is controlled so that the sum of the accumulated charge amounts of the imaging pixels corresponding to one apparent pixel of the imaging screen is kept to be equal to or less than a certain value in accordance with the number of binning pixels. Is changed, the electric charge does not saturate due to binning even when the photographing target is sufficiently bright.

Further, the CCD camera control device of the present invention comprises:
A binning function for simultaneously reading out the charges of a plurality of adjacent pixels as information of one pixel by an external control signal;
CCD capable of controlling an electronic shutter that controls each of the imaging pixels and changes the charge accumulation time that is the exposure time
A CCD camera control device for controlling a camera, the control device transmitting a control signal for controlling an exposure time of an electronic shutter according to a set number of binning pixels, and calculating a charge amount of an imaging pixel corresponding to one pixel of a read image. It is characterized by comprising sensitivity control means for keeping the sum below a certain value.

[0010] According to this, similarly to the above-mentioned CCD camera, the accumulated charge of the imaging pixel corresponding to one apparent pixel of the imaging screen is obtained by using a CCD camera capable of externally controlling the binning function and the electronic shutter. The electronic shutter is controlled so that the sum of the amounts is kept below a certain value, and the charge accumulation time of each pixel is changed. Therefore, even when the object to be photographed is sufficiently bright, the charges are not saturated by binning.

The CCD camera or the sensitivity control means of the CCD camera control device has a memory, and uses a correspondence table or a correspondence function between a predetermined number of binning pixels and an exposure time recorded in the memory. The exposure time of the electronic shutter may be controlled.

The accumulation time for keeping the sum of the accumulated charge amounts of the imaging pixels corresponding to one pixel of the imaging screen constant is determined according to the light quantity and the number of binning of the imaging target. The storage time corresponding to the number of binnings is measured in advance, and these are stored in the memory of the apparatus in a table or a function format, and the storage time corresponding to the set number of binnings is calculated to control the electronic shutter. , It is possible to control to automatically change the accumulation time in accordance with the change in the number of binning.

Further, according to the sensitivity adjusting method of the CCD camera of the present invention, the charge storage time, in which the sum of the stored charge amounts of all the image pickup pixels corresponding to one pixel of the read image becomes substantially the same, is determined in advance according to the number of binning pixels. A step of obtaining from the correspondence table or the correspondence function between the set number of binning pixels and the charge accumulation time, and a step of controlling the electronic shutter to read out the charge accumulated in the charge accumulation time obtained in the above step from each pixel, It is characterized by having.

According to this, the total sum of the electric charges read out from all the pixels corresponding to one pixel on the screen is always kept below a certain value.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. This device is a CCD camera 1 for taking images.
And a CC for externally controlling the imaging operation of the CCD camera 1
It comprises a D camera control device 2 and a display / recording device 3 for displaying and / or recording images taken by the CCD camera 1.

The CCD camera 1 comprises a CCD 11 and a control unit 1
Consists of two. Among them, the CCD 11 is an imaging element in which imaging pixels are two-dimensionally arranged, and a binning function for simultaneously adding and outputting accumulated charges of a plurality of adjacent pixels according to a timing signal from the outside, and a CCD function for a partial area of the screen. A sub-array function for outputting only image information as effective image information,
An electronic shutter function for controlling the charge accumulation time of each pixel is provided. The control unit 12 includes an electronic shutter control unit 13 that outputs an electronic shutter control signal for controlling the electronic shutter function, and a binning control unit 14 that outputs a timing signal for controlling the binning sub-array function. It operates according to the control signal.

The CCD camera control device 2 includes an A / D converter 21 for digitally converting image data picked up by the CCD camera 1 and a control means 22 for sending a control signal to the control unit 12 of the CCD camera 1. This control means 2
Reference numeral 2 denotes a control CPU 23 for calculating the operation timing and the like of the electronic shutter of the CCD 11, a memory 24 in which data serving as a basis of the calculation or an arithmetic expression and the like, and data such as a photographing pattern are transmitted from the outside to the control CPU 23. Input / output interface 25.

Here, the binning sub-array operation of the CCD 11 will be briefly described with reference to FIG. FIG.
FIG. 3 is a diagram schematically showing an arrangement of imaging pixels. This C
In the CD 11, pixels of 507 lines × 757 columns are arranged, and among these, effective pixels contributing to shooting are 49 pixels.
Pixels of 4 lines × 656 columns. And binning
During sub-array operation, a specific _Dy line × _Dx
The image information of a pixel area (hereinafter, referred to as a sub-array area) of a column is represented by n × n pixels as one apparent pixel, ie,
Image information is read out as pixels of (D _y / n) lines × (D _x / n) columns.

Since the readout of the stored charge utilizes the charge self-transfer function which is a feature of the CCD, only the stored charge in the sub-array area cannot be taken out to the transfer register, and all pixels need to be scanned. . Specifically, the accumulated charges in the area where the image information is unnecessary, that is, the areas above and below the sub-array area shown in FIG. 2 are also temporarily transferred to the horizontal transfer register and then discharged. In addition, for lines including the sub-array region, vertical binning is performed by adding electric charges when the lines are transferred to the horizontal transfer register. The horizontal binning is performed by taking out the electric charges of each column from the horizontal transfer register and adding them at that time. At this time, the accumulated charges of the pixels outside the sub-array region are discharged without being output as an image.

The transfer of the stored charge in the portion where the image information is unnecessary can be greatly shortened as compared with the readout of the stored charge in the sub-array region where the image information is required, but the transfer time is reduced to 0. Can not be. Therefore, since a certain amount of time is required for charge transfer in these unnecessary areas and charge transfer for charge addition during binning, this becomes an overhead, and the frame rate increases as the apparent number of pixels changes due to the binning function. It will not be shortened. As a result, when the exposure time is made to match the frame rate, the amount of light received by the pixel determined by (exposure time) × (the number of pixels included in one apparent pixel) increases, so that one apparent pixel The total amount of accumulated charges increases as the number of binning pixels increases. For this reason, when the subject is sufficiently bright, an increase in the number of binning pixels causes an increase in the amount of received light more than necessary, which may exceed the saturation charge of the transfer path.

In order to prevent this, in the present embodiment, the sensitivity of the pixels of the CCD 11 is adjusted using an electronic shutter. Hereinafter, the operation will be specifically described with reference to FIGS. 1, 3, and 4. FIG. FIG. 3 is a flowchart of the sensitivity adjustment, and FIG. 4 is a timing chart of the exposure method.

As shown in FIG. 1, the number of binning pixels,
The photographing pattern data such as the sub-array operation is transmitted to the CCD camera controller 2 via the input / output interface 25.
(S1 in FIG. 3). To the control CPU 23, a control signal indicating an operation state such as the current number of binning pixels of the CCD camera 1 is sent from the control unit 12 of the CCD camera 1. Further, the CCD 11
The luminance information of the image area is also sent from the A / D converter 21 which has converted the image data obtained in step 1 into a digital form.

Based on the number of binning pixels to be set, the current number of binning pixels, and luminance information of the image area, the control CPU 23 refers to a table or an arithmetic expression stored in advance in the memory 24 and determines that the luminance is substantially the same. Exposure time is determined. Details of the tables or arithmetic expressions stored in the memory 24 will be described later. At the same time, the frame rate in the photographing pattern is obtained, and the operation timing of the electronic shutter for making the exposure time of each pixel coincide with the previously obtained exposure time is obtained (S2 in the figure).

Then, the operation timing is transmitted to the control unit 12 of the CCD camera 1 together with the control signal of the binning operation (S3 in FIG. 3). The control unit 12 acquires an image while controlling the electronic shutter based on the control signal (S4 in FIG. 4). Each pixel of the CCD 11 is normally shown in FIG.
As shown in (1), charge is accumulated and recorded between exposure timing signal pulses corresponding to the frame rate (in this example,
10 ms). However, in the present embodiment, as shown in FIG. 2B, when the electronic shutter control signal pulse comes, the electric charge accumulated in the pixel is released, so that the exposure timing is changed from the electronic shutter control signal pulse to the exposure timing. The charge can be accumulated only for the time between signal pulses. In other words, the exposure time can be further reduced. In the example of FIG. 2B, by transmitting an electronic shutter control signal pulse shifted by 6 ms from the exposure timing signal pulse, the electric charge accumulated up to that point is discarded. The exposure time is set to 4 ms before the exposure timing signal pulse.

As a result, the apparent brightness per pixel output from the CCD 11 is kept substantially constant, so that the exposure time automatically follows the change in the number of binning pixels, and the speed is always high and the S / N ratio is high. Images can be captured.

The inventor of the present application measured an apparent change in the amount of light per pixel when the number of binning pixels was changed. The measurement compares the apparent luminance per pixel in the number of binning pixels for two states with different amounts of light incident on the CCD and three states of a dark state without a light source using an LED as a light source. Table 1 and FIG. 5 show the measurement results of the luminance change. Table 2 shows the ratio of the luminance to the change in the number of binning pixels.

[0028]

[Table 1]

[Table 2] It can be seen that as the number of pixels increases, the luminance increases and the rate of the increase also increases. Therefore, if the exposure time of the pixel is reduced to the reciprocal of this ratio with respect to the frame rate, the amount of received light becomes the same. Table 3 shows the reduction ratio of the exposure time to the frame rate.
Here, the unit is%.

[0029]

[Table 3] By storing the correspondence of the exposure time to the luminance change in the memory 24 in the form of a table or a function in advance,
As described above, the sensitivity adjustment at the time of the binning operation can be automatically performed.

If the table stored in the memory 25 can be rewritten by the control CPU 23 via the input / output interface 25, the sensitivity can be adjusted according to the light wavelength of the subject.

In the above description, the case where the CCD camera and the camera control device are separate devices has been described as an example. However, the sensitivity adjustment device of the present invention may be incorporated in the control unit of the CCD camera.

[0032]

As described above, according to the present invention, the exposure time is controlled by the electronic shutter so that the apparent amount of received light per pixel at the time of binning is always the same. Thus, it is possible to capture an image at a high S / N ratio. In addition, operability is improved because it is not necessary to adjust the aperture according to the change in the number of binning pixels.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a schematic view of a pixel area of the CCD of FIG. 1;

FIG. 3 is a flowchart of a sensitivity adjusting operation of the apparatus of FIG. 1;

FIG. 4 is a timing chart of an exposure operation of the apparatus of FIG.

FIG. 5 is a diagram illustrating a change in luminance with respect to the number of binning pixels.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... CCD camera, 2 ... CCD camera control device, 3 ... Display / recording device, 11 ... CCD, 12 ... Control part, 21 ... A
/ D converter, 22: sensitivity control means, 23: control C
PU, 24 ... memory, 25 ... input / output interface.

Claims (5)

[Claims] 1. A C comprising imaging pixels arranged two-dimensionally.
A CCD camera having a CD and having a binning function for simultaneously reading out charges of a plurality of adjacent pixels as information of one pixel, comprising: an electronic shutter for controlling each of the imaging pixels to change a charge accumulation time which is an exposure time thereof; A CCD camera comprising: a sensitivity control unit that controls an exposure time of the electronic shutter according to the number of binning pixels to maintain a sum of accumulated charge amounts of imaging pixels corresponding to one pixel of a readout image to be equal to or less than a certain value. 2. The apparatus according to claim 1, wherein the sensitivity control unit has a memory, and uses a correspondence table or a correspondence function between a predetermined number of binning pixels and an exposure time recorded in the memory, or an exposure time of the electronic shutter. Claim 1 for controlling
The described CCD camera. 3. A binning function for simultaneously reading out the charges of a plurality of adjacent pixels as information of one pixel by an external control signal, and an electron for controlling each of said imaging pixels to change a charge accumulation time which is an exposure time thereof. A CCD camera control device for controlling a CCD camera capable of controlling a shutter. The CCD camera control device transmits a control signal for controlling an exposure time of the electronic shutter according to a set number of binning pixels, and corresponds to one pixel of a read image. A CCD camera control device comprising sensitivity control means for keeping the sum of the accumulated charge amounts of the imaging pixels to be kept below a certain value. 4. The electronic device of claim 1, wherein the sensitivity control means has a memory, and uses a correspondence table or a correspondence function between a predetermined number of binning pixels and an exposure time recorded in the memory. 4. The CCD camera control device according to claim 3, wherein a control signal for controlling an exposure time of the shutter is transmitted. 5. C comprising imaging pixels arranged two-dimensionally.
A sensitivity adjustment method of a CCD camera having a CD and having a binning function of simultaneously reading out charges of a plurality of adjacent pixels as information of one pixel, wherein an imaging corresponding to one pixel of a read image is performed according to the number of binning pixels. Obtaining a charge accumulation time in which the sum of the accumulated charge amounts of the entire pixel is substantially the same from a preset table or a correspondence function of the number of binning pixels and the charge accumulation time; Reading out the electric charge accumulated during the electric charge accumulation time obtained in the step.