JPH07236093A - Image pickup device - Google Patents

Abstract

PURPOSE:To provide an image pickup device capable of reducing the remaining correction and the deviation of correction and producing an image of high resolution by accurately correcting the offset amount due to the dark current of the solid-state image pickup element. CONSTITUTION:The device is provided with a solid-state image pickup element 13a which outputs the picture data corresponding to the picked up optical image. It is also provided with a storage means (offset memory 20) storing the correction data measured to correct the offset amount due to the dark current for each picture element of the solid-state image pickup element 13a and an offset correction means (driving circuit 20 and adder 19) correcting the picture data of the solid-state image pickup element 13a based on the correction data stored in the storage means. Further, the offset correction amount is changed according to the image pickup time, the temperature of the solid-state image pickup element, picture element value, the location of the picture element. When the picture element value is high, the replacement of the picture element value itself is performed. The offset correction is performed based on the analog amount. Further, the correction and the change of data is performed according to the presence of the picture element value dependent area in the characteristic of the correction data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus used in an X-ray diagnostic apparatus or the like, and more particularly to an image pickup apparatus using a solid-state image pickup element such as CCD (Charge Coupled Device) as an image pickup element for picking up an optical image. .

[0002]

2. Description of the Related Art Conventionally, for example, there is a medical X-ray fluoroscope as a device equipped with this type of imaging device. In this X-ray fluoroscope, the X-rays that have passed through the subject are converted into optical signals by an image intensifier (II), and the optical signals are incident on the image pickup apparatus. In the image pickup device, an optical signal is converted into an electric signal by the solid-state image pickup element of the TV camera. Then, a perspective image is displayed on the monitor based on the electric signal output from the image pickup apparatus.

In the solid-state image sensor, an effective pixel area for actually photoelectrically converting a subject image and a light-shielded pixel area called optical black are included in the light-receiving element arranged in the light-receiving portion. is doing. While the dark current is output from the optically black pixel area, the dark current from the effective pixel area is directly superimposed on the output current of each pixel in the effective pixel area as an offset component, so this offset is corrected. There is a need.

There are various methods for this offset correction. As one of them, there is a method of previously detecting the position of a defective (scratch) pixel whose dark output is a certain level or higher from the dark image and replacing the pixel value of the defective pixel with the pixel value of an adjacent pixel. As another method, for example, Japanese Patent Laid-Open No. 2-16
As described in Japanese Patent No. 4184, a dark output is stored in a memory at a timing at which an optical image is not incident on a solid-state image sensor,
A method is also known in which this stored value is subtracted from the output of the solid-state image pickup device when an optical image is incident, thereby performing offset correction for each pixel by digital processing.

[0005]

However, the above-mentioned conventional Hofset correction has various unsolved problems as follows.

First, in the method of substituting the pixel value of an adjacent pixel, when a defective pixel is caused by a variation in dark current, the solid-state image sensor is used in a high temperature state or is used in an image capturing mode with a long image capturing time. Since the number of defective pixels is inevitably increased (that is, the light accumulation time is long), simple replacement of pixel values is not sufficient, and there is a large amount of uncorrected pixels, resulting in deterioration of the image spatial resolution. . Further, although the components other than the dark current are normal signal components, the normal signal information is discarded by the replacement, and there is a problem that the amount of information obtained from the image is reduced.

On the other hand, the method of subtracting the dark output from the light incident output has the following disadvantages such as low correction accuracy.

First, when a solid-state image sensor in which the correction amount for each pixel depends on the pixel value is used, the pixel value characteristic for each pixel address is expressed as shown in FIG. In the figure, when the pixel address is plotted on the horizontal axis and the pixel value is plotted on the vertical axis, and when the conditions such as temperature and light accumulation time are changed from Condition 1 to Condition 2, the average level of pixel values changes from Graph 1 to Graph 2. It shows how it changes to. As a result, the variation for each pixel also changes (for example, increases) from variation 1 to variation 2.
The correction characteristic for this solid-state image sensor is usually expressed as the graph shown in FIG. The pixel value (= average level of light intensity) is plotted on the horizontal axis, and the variation (= correction amount) is plotted on the vertical axis, representing the “pixel value-variation” characteristic of a pixel. As can be seen from this characteristic, in the range from the pixel value = 0 (that is, dark output) to a certain value PVd (pixel value dependent region Rp), the variation value also gradually increases from a certain initial value, and the pixel value PVd After that, the variation value is constant. In the case of a solid-state image sensor having such characteristics, the pixel-value-dependent region Rp has a different correction amount from the dark output, so that accurate offset correction can be performed when the incident light level falls within the pixel-value-dependent region Rp. There is an inconvenience that it cannot

On the other hand, as described above, even when the correction amount for each pixel does not depend on the pixel value, that is, when the solid-state image pickup device having the flat characteristic without the pixel value dependence region Rp in FIG. Since the imaging time changes,
The amount of correction required also changes. However, as described above, it is not possible to perform accurate correction simply by subtracting the correction amount of the constant value that is the dark output. That is, the light accumulation time of the image sensor changes according to the image capture mode, and the correction amount for each pixel depends on the light accumulation time, but the dark output accumulation time does not always match the image accumulation time. This is because a large correction amount cannot be obtained.

Further, as described in Japanese Patent Laid-Open No. 2-164184, when performing offset correction by digital processing, it is necessary to assign a bit length to the correction amount (positive or negative) of each pixel. The effective bit length (dynamic range) is reduced. For example, assuming that the dynamic range is 4096 (= 12 bits) and the correction amount is -100, the effective bit length is 4096-100 = 39.
It becomes 96.

The present invention has been made in view of the above-mentioned problems of the prior art. Even when the image pickup device is used in a high temperature state or the image pickup time is long, the correction remaining (correction variation) is reduced and the space is reduced. A first object is to prevent deterioration of resolution. A second object is to prevent a decrease in the amount of information obtained from the image. Furthermore, a third object is to perform highly accurate offset correction even when using a solid-state image sensor of the type in which the correction amount for each pixel depends on the pixel value. Furthermore, a fourth object is to perform more accurate offset correction when a solid-state image sensor of a type in which a correction amount for each pixel does not depend on a pixel value is used and the imaging time changes. To do.

[0012]

In order to achieve the above object, an image pickup apparatus according to the present invention comprises a solid-state image pickup element for outputting image data composed of pixel values corresponding to a picked-up optical image. Further, the solid-state imaging device is configured to store pre-measured correction data for correcting an offset amount caused by a dark current for each pixel of the solid-state imaging device, and the solid-state imaging based on the correction data stored in the storage device. An essential part is that an offset correction means for correcting the image data from the element for each pixel is provided.

In particular, in the image pickup device according to the invention as defined in claims 2 to 4, the characteristic of the correction data with respect to the pixel value has a pixel value dependent region depending on the pixel value, and the correction data is stored in the image pickup device. It is the data measured at the time of shipment.
For example, the correction data is data measured at the time of shipment by making a light amount having a pixel value corresponding to a region other than the pixel value dependent region enter the solid-state imaging device. Further, based on one or a combination of one or a plurality of parameters of an imaging time for which the optical image is continuously incident on the solid-state image sensor, a temperature of the solid-state image sensor, a pixel value of the image data, and a position of the pixel. A correction data changing means for changing the correction data is added.

Particularly, in the image pickup apparatus according to the invention of claim 5, a judging means for judging whether or not the correction data changed by the correction data changing means exceeds a reference value for each pixel, and this judging means. When it is determined that the above correction data exceeds the reference value, the replacement means for replacing the pixel value of the pixel to be determined with the pixel value obtained from the pixel values of the neighboring pixels is added. Further, in the image pickup device according to the invention of claim 6, a replacement address memory means for storing in advance an address required to replace the image data, and a pixel position of an object to be imaged by the solid-state image sensor is the replacement address memory. A replacement means for replacing the pixel value of the pixel with the pixel value obtained from the pixel value of the neighboring pixel when the replacement address stored in the means is added.

Particularly, in the image pickup apparatus according to the invention of claim 7, the offset correction means converts the correction data into an analog amount, and a conversion data of the analog amount of the D / A converter. And an adder for adding the analog amount of image data of the solid-state image sensor, and A / A for converting the addition result of the adder into a digital amount.
Equipped with a D converter.

On the other hand, in the image pickup device according to the present invention, the characteristic of the correction data with respect to the pixel value does not depend on the pixel value, and the correction data causes an optical image to enter the solid-state image pickup element. It is the output data in the dark when measured in the non-lighted state. For example, the dark output data is data measured in the frame period immediately before the image capturing,
Correction data changing means for changing the dark-time output data based on the image pickup time during which the optical image is continuously incident on the solid-state image pickup element is added.

Particularly, in the image pickup apparatus according to the invention of claim 10, the judging means for judging for each pixel whether or not the correction data changed by the correction data changing means exceeds a reference value, and this judging means. When it is determined that the correction data exceeds the reference value, a replacement unit that replaces the pixel value of the pixel to be determined with the pixel value obtained from the pixel values of the neighboring pixels is added. According to an eleventh aspect of the present invention, a replacement address memory unit that stores in advance an address that needs to replace the image data, and a pixel position of an object to be imaged by the solid-state image sensor is the replacement address memory. A replacement means for replacing the pixel value of the pixel with the pixel value obtained from the pixel value of the neighboring pixel when the replacement address stored in the means is added.

According to the twelfth aspect of the present invention, the offset correction means includes a D / A converter that converts the correction data into an analog amount, the analog amount conversion data of the D / A converter, and An adder for adding the analog amount of image data of the solid-state image sensor is provided, and an A / D converter for converting the addition result of the adder into a digital amount is provided.

[0019]

According to the present invention, the offset correction is performed on the basis of the previously measured correction data for each pixel. At this time, in the case of a solid-state image sensor having a correction amount characteristic having a pixel value dependent region, the correction data is collected with an incident light amount corresponding to the outside of the region at the time of shipment, and the correction amount characteristic solid state having no pixel value dependent region is collected. In the case of an image sensor, dark output is collected as correction data. In this way, since the collection time and the collection state are changed according to the correction amount characteristic, highly accurate offset correction can be performed with a simple configuration.

In the inventions according to claims 4 to 6, 10 and 11, the correction amount is any one or any combination of the imaging time, the temperature of the solid-state imaging device, the pixel value and the pixel position. And / or a mode of adding a correction for replacing the pixel value itself when the pixel value is equal to or higher than a predetermined level (or when the position of the image pickup pixel reaches a replacement address measured in advance) Therefore, it is possible to reduce the correction variation and the uncorrected portion, which makes it possible to perform the offset correction with higher accuracy and reduce the artifacts.

Further, according to the invention described in claims 7 and 12, offset correction is performed with the analog amount being maintained, and thereafter,
Since it is converted into a digital amount, the dynamic range of the A / D converter is expanded.

Further, in the invention according to claim 9, when there is no pixel value dependent region, the dark output data (correction data) collected immediately before the image pickup is changed based on the image pickup time.
It becomes real-time correction data that captures the temperature change of the solid-state image sensor, and it is not necessary to consider the influence of such temperature change on the offset correction.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. The following embodiments apply the image pickup apparatus according to the present invention to a medical X-ray diagnostic apparatus.
Of course, it can be applied to other devices such as a medical endoscope device.

(First Embodiment) A first embodiment will be described with reference to FIG.

The X-ray diagnostic apparatus shown in FIG. 1 includes an X-ray tube 10 that irradiates an object P with X-rays, and an image intensifier (hereinafter, referred to as an intensifier) that receives the X-rays that have passed through the object.
(Referred to as “I.I.”) 11.
I. Optical system 12 and TV camera 1 provided on the output side of 11
Equipped with 3. The TV camera 13 is C in this embodiment.
A solid-state image sensor 13a is provided, in which light-receiving elements made of CDs are two-dimensionally arranged corresponding to each pixel.

The X-ray tube 10 is connected to the X-ray tube via a high voltage generator 14.
It is connected to the X-ray controller 15 and can emit X-rays in response to the X-ray exposure signal S1 output from the X-ray controller 15. In addition, I. I. Reference numeral 11 is for inputting X-rays transmitted through the subject P and converting the X-rays into an optical signal corresponding to an optical image. The optical signal is an optical system 1 including a lens or the like.
The solid-state image pickup device 13a of the TV camera 13 is irradiated with the light through 2. The optical signal with which the solid-state image sensor 13a is irradiated is converted into an image signal of a corresponding electric quantity in each of the light receiving elements corresponding to each pixel. The solid-state image sensor 13a receives the drive signal Sd and the pixel address signal Sa sent from the drive circuit 16 and performs the above-mentioned opto-electric conversion.

The output side of the TV camera 13 is further provided with a 2-input adder 19 via an amplifier 17 and an A / D converter 18.
Is connected to one input end. As a result, the image signal output from the TV camera 13 is amplified and then A / D converted into image data Di in a digital amount, and the adder 19
To enter.

On the other hand, the other input terminal of the adder 19 is connected to the output side of the offset memory 20, and the pixel address signal Sa from the drive circuit 16 is input to the input side of the offset memory 20. It is like this. The offset memory 20 includes the solid-state image sensor 13a.
Offset data D as a correction amount determined for each pixel of
Off (a positive or negative value for each pixel) is stored in advance. The offset data Doff is for correcting the dark output, and is collected and stored in advance before use of the device, such as when the device is shipped. It should be noted that, at the time of collecting the offset data, the “correction amount-pixel value” characteristic of the solid-state image sensor 13a has a pixel value dependence region Rp in which the correction amount (= variation) depends on the pixel value as shown in FIG. If there is, an optical image of a pixel value that avoids the pixel value dependent region Rp is made incident on the solid-state image pickup device 13a and collected.

The offset memory 20 outputs the offset data Doff of the address designated by the pixel address signal Sa to the adder 19 in synchronization with the arrival of the image data Di from the solid-state image pickup device 13a. There is.

As a result, the adder 19 adds the two input data and sends the added data to the CRT (cathode ray tube) 22, which is a TV monitor, via the D / A converter 21 in the subsequent stage. As a result, the X-ray fluoroscopic image is displayed on the CRT in real time.

Further, the X-ray diagnostic apparatus is provided with a controller 23 for managing the entire apparatus through the X-ray controller 15 and the drive circuit 16 and an input device 24 for allowing the controller 23 to manually input necessary information. There is.

As described above, in this embodiment, X-rays are radiated from the X-ray tube 10 to obtain an X-ray fluoroscopic image, while a dark output is output to the solid-state image pickup device 13a having no pixel value dependent region Rp. ,
Further, the offset output value is measured in advance for each pixel in the solid-state image sensor 13a having the pixel value dependent region Rp, and this measured value is used as the offset data Doff. Then, the offset data Doff is added (when the offset data Doff is positive) or subtracted (when the offset data Doff is negative) to the image data Di output from the solid-state image sensor 13a for each pixel, and automatically. Correct the offset. As a result, the offset data required for canceling the actual dark current can be satisfactorily acquired for each pixel regardless of the presence or absence of the pixel value dependent region Rp, and the offset amount can be corrected with high accuracy, and the pixel in the offset correction can be corrected. It is possible to satisfactorily eliminate the variation between them. As a result, the resolution of the image does not decrease and the S / N ratio of the image can be improved.

(Second Embodiment) Second Embodiment FIGS. 2 and 3
It will be described based on. The same or equivalent constituent elements as those of the above-described embodiment are designated by the same reference numerals, and the description thereof is simplified or omitted (the same applies to the third and subsequent embodiments).

The second embodiment also considers the image pickup time (the time during which the optical image is continuously incident on the solid-state image pickup element).

As shown in FIG. 2, the X-ray diagnostic apparatus according to the second embodiment is provided with an offset data generation circuit 30 in place of the offset memory of FIG. The generation circuit 30 is made to supply the pixel address signal Sa from the drive circuit 16 and the imaging time information Stime from the controller 23. Therefore, the controller 23 refers to the imaging time data stored in advance according to the imaging mode (perspective mode / imaging mode (long-time exposure mode / short-time exposure mode)) designated via the input device 24. Then, the imaging time information Stime is supplied.

As shown in FIG. 3, the offset data generating circuit 30 has a coefficient memory 31 for receiving the imaging time information Stime and one input end connected to the memory reading side of the coefficient memory 31. A two-input multiplier 32,
Offset memory 33 for receiving the pixel address signal Sa
And the read side of the offset memory 33 is connected to the other input terminal of the multiplier 32. The output terminal of the multiplier 32 is connected to one input terminal of the adder 19 as in the first embodiment.

In the offset memory 33, the offset data Dof for each pixel collected in the same manner as in the first embodiment.
f ^* is stored in advance. Therefore, the offset
The memory 33 multiplies the offset data Doff ^* corresponding to the address specified by the pixel address signal Sa by the multiplier 32.
Output to. On the other hand, the coefficient memory 31 stores in advance coefficients corresponding to the length of the imaging time, and the imaging time information Stime
The coefficient Ctime corresponding to that in FIG.
Output to 2. That is, when the switching of the imaging mode is instructed from the input device 24, the shooting time information Stime is also switched, and the coefficient Ctime is automatically changed to a value corresponding to the length of the shooting time.

The multiplier 32 receiving the offset data Doff ^* and the coefficient Ctime thus generated is
The multiplication of “Doff = Doff ^* × Ctime” is performed, and the final offset data Doff is calculated for each pixel. This offset data Doff is added to the pixel data Di in the adder 19 and subjected to the same offset correction as described above.

Therefore, according to this embodiment, during fluoroscopy, offset correction due to dark current is corrected pixel by pixel.
In addition, since the length of the imaging time is taken into consideration, the correction variation is not affected by the length of the light accumulation time, even if the shooting time is a long time such as a long exposure mode or a short shooting time. It is possible to perform high-accuracy offset correction with less noise.

The offset data generating mechanism in this embodiment may be constructed as shown in FIG. That is, the offset memory of the offset memory circuit 34 stores in advance offset data for a plurality of frames that can be selected according to the length of the imaging time, and according to the imaging time information Stime and the pixel address signal Sa. The offset data Doff can be read directly for each pixel.

(Third Embodiment) A third embodiment will be described with reference to FIGS.

The third embodiment also considers the operating temperature of the solid-state image pickup device.

TV camera 13 of the X-ray diagnostic apparatus shown in FIG.
Is provided with a temperature sensor 39 for detecting the temperature of the solid-state image sensor 13a. The temperature sensor 39 is composed of, for example, a thermistor, a thermocouple, a semiconductor sensor,
It is arranged, for example, in the vicinity of a. As a result, the temperature sensor 39 outputs to the controller 23 a temperature detection signal (for example, a change in resistance value) Ctemp substantially corresponding to the operating temperature of the solid-state image sensor 13a.

While the controller 23 controls the X-ray exposure, it periodically inputs the temperature detection signal Ctemp, and normally operates the gradually changing operating temperature of the solid-state image pickup device 13a by, for example, a table lookup. The element temperature information Stemp corresponding to the calculation result is output to the offset data generation circuit 40.

The offset / data generating circuit 40 has a coefficient memory 41 and a multiplier 3 as shown in FIG.
2. The offset memory 33 is provided. The coefficient memory 41 stores in advance a coefficient Ctemp (see FIG. 8) corresponding to the magnitude of the operating temperature of the solid-state image sensor 13a, and outputs the coefficient Ctemp corresponding to the temperature value of the input element temperature information Stemp to the multiplier 32. To do. The pixel data signal Sa is also supplied to the offset data generation circuit 40. Therefore, the offset data generation circuit 40 generates the offset data Doff based on the element temperature information Stemp and the pixel address signal Sa, as in the second embodiment.

Therefore, the operating temperature of the solid-state image pickup device 13a, which changes from moment to moment, is measured one by one, and the offset correction in which the correction amount corresponding to this temperature value is also added is performed for each pixel. As a result, even when the operating temperature of the solid-state imaging device 13a rises due to an increase in operating time of the device itself or an increase in environmental temperature, it is possible to prevent the accuracy of offset correction from being lowered due to such a temperature change, and to prevent correction variations. It is possible to obtain a high-quality perspective image while maintaining a small amount of highly accurate offset correction.

The offset data generating circuit 4
0 has a configuration in which the coefficient memory 41 and the offset memory 33 are provided side by side, but like the one shown in FIG. 5, an offset memory circuit storing offset data Doff for a plurality of frames different for each temperature is provided. The element temperature information Stemp and the pixel address signal Sa may be supplied to the offset memory circuit.

(Fourth Embodiment) Furthermore, a fourth embodiment is shown in FIG.
~ It demonstrates based on FIG.

In the fourth embodiment, the amount of light incident on the solid-state image pickup device, that is, the pixel value is taken into consideration to perform more appropriate offset correction. Depending on the type of solid-state image sensor, as shown in FIG. 22, an appropriate correction amount (variation of pixel value: see FIG. 21) changes according to the pixel value. In the process of transferring charges on the solid-state image sensor, transfer residuals occur. However, since the degree of the transfer residuals depends on the amount of transferred charges, the correction amount changes as described above.

In order to deal with this change in the correction amount, the X-ray diagnostic apparatus shown in FIG. 9 is provided with an offset data generation circuit 50, and the generation circuit 50 is supplied with the pixel address signal Sa from the drive circuit 16 in the same manner as described above. A / D converter 1 for inputting and converting the output of the TV camera 13 into a digital amount
The output of 8 is input as the pixel value information Spx.

The offset data generation circuit 50 is shown in FIG.
As shown in, the coefficient memory 51 for supplying the pixel value information Spx and the offset memory 51 for supplying the pixel address signal Sa
A memory 33 and a multiplier 32 that multiplies the read data of both memories 51 and 33 are provided, and the multiplication result D of this multiplier 32
Off is supplied to the adder 19 as in the above embodiment. As shown in FIG. 11, the coefficient memory 51 has a coefficient C corresponding to designated pixel value information Spx (incident light amount).
px is output (for example, when the pixel value increases, the coefficient Cpx also increases, and conversely, when the pixel value decreases, the coefficient Cpx also decreases).

Therefore, the offset data generation circuit 5
Offset data Dof supplied from 0 to the adder 19
Since f is corrected for each pixel according to the pixel value, the output "Di + Doff" of the adder 19 is also corrected according to the pixel value. Therefore, since the offset correction due to the dark current is performed in consideration of the pixel value, the highly accurate offset correction with a small correction variation is performed.

(Fifth Embodiment) Furthermore, a fifth embodiment is shown in FIG.
2 and FIG. 13.

The fifth embodiment considers the position of each pixel of the solid-state image pickup device. The appropriate correction amount for each pixel changes depending on the position of the pixel. This is because the transfer residual of the charge occurs in the process of transferring the charge on the image pickup element, and the degree of the transfer residual changes depending on the length of the transfer path.

As shown in FIG. 12, the X-ray diagnostic apparatus of this embodiment receives a pixel address signal Sa and converts the pixel address into a transfer path length TL 60.
And an offset memory 61 for outputting a correction amount Doff corresponding to the converted transfer path length TL. As shown in FIG. 13, the offset memory 61 has an offset correction amount D that decreases as the transfer path length TL increases.
The off characteristic data is stored in advance, and the correction amount Doff corresponding to the transfer path length TL instructed by the conversion circuit 60 can be read. The offset data Doff read from the offset memory 61 is sent to the adder 19. Other configurations are similar to those of the first embodiment.

Therefore, according to the present embodiment, a more accurate offset correction is carried out by changing the correction amount for each pixel position, and the spatial resolution is lowered and the S / N ratio is caused by the difference in the residual charge transfer. It is possible to prevent a decrease in the ratio and obtain a high-quality perspective image with little correction variation.

(Sixth Embodiment) FIG. 14 shows the sixth embodiment.
~ It demonstrates based on FIG.

The sixth embodiment relates to the improvement of the correction amount collection time, and the pixel value dependence region Rp as shown in FIG.
It can be applied to a solid-state image sensor having a correction amount characteristic that does not have.

The X-ray diagnostic apparatus according to this embodiment is shown in FIG.
As described above, the offset data generation circuit 70 that inputs the imaging time information Stime and the pixel address signal Sa output from the controller 23 and the drive circuit 16, and the two switching ends that switch according to the switch switching signal S2 from the controller 23. and an electronic switch 71 having a and b. The electronic switch 71 is interposed between the offset data generation circuit 70 and the A / D converter 18 and the adder 19 on the output side of the solid-state image sensor 18. That is, the common end c of the electronic switch is connected to the output end of the A / D converter 18, one switching end a is connected to one input end of the adder 19, and the other switching end b is offset. Reaching the data generation circuit 70. The electronic switch 71 switches to the switching end b side when the switch switching signal S2 is on, and switches to the switching end a side when the switch switching signal S2 is off.

The offset data generating circuit 70 includes a coefficient memory 31 which inputs the photographing time information Stime and outputs a corresponding coefficient Ctime, and a two-input multiplier 32 which receives the coefficient Ctime as one input, and also includes a pixel An offset memory 72 for inputting the address signal Sa is provided. The offset memory 72 is further supplied with a write / read control signal _{SW / R} for controlling the write mode from the controller 23 to the memory 72 and the read mode from the memory 72. Corresponding to this writing / reading, the image data Di is input to the data writing input end of the offset memory 72 via the switching end b of the electronic switch, while the data reading end is input to the multiplier 32. It is configured to reach the other input end.

The controller 23 outputs the image pickup time information Stime according to the image pickup mode to the offset data generation circuit 70, and turns on (switching end b side) and off (switching end a side) the switch switching signal S2. ), A write / read control signal _{SW / R} which is turned on (during writing) and turned off (during reading) is output. The controller 23 is adapted to perform X-ray exposure and offset correction as shown in FIG. 16, for example, depending on the imaging mode.

The other structure is similar to that of the second embodiment.

The operation of this embodiment will be described with reference to FIG. In a certain imaging mode 1 (for example, short-time exposure mode), the switch switching signal S2 and the write / read control signal S _{W / R} are set to ON whenever the X-rays are not exposed (FIG. 16 ( d) (e)). This allows
Since the switch path of the electronic switch 71 is on the side of the switching end b, the output end of the A / D converter 18 is connected to the offset memory 72, and the offset memory 72 is always immediately preceding, that is, one frame before. The image data Di is regularly written as offset data. This allows
The offset data in the offset memory 72 is updated every frame and becomes the latest data.

At time t _{0, the} imaging mode is the mode 2 now.
(For example, long-time exposure mode) has been commanded, but X-ray exposure has not been commanded yet (see (f) of the same figure). As a result, the interval of the frame signal VD is changed (for example, becomes longer: see (a) in the figure), and the latest offset is delayed by one frame for each frame related to this new imaging time.
Data is written in the offset memory 72 (e.g., image data Di in a frame F _n is as offset data, are written in the next frame F _{n + 1).}

In this state, at time t ₁ , when the X-ray irradiation signal S1 for instructing the start of X-ray irradiation is turned on (see FIG. 9A), the start time t of the next frame F _{n + 1} is started. in fact, after X-ray exposure is started (see FIG. (c)), the time in which the image data Di of the frame F _n is completed writing to the offset memory 72 corresponding to the oN X-ray emitting signal S1 at _1a t
_{At 1b} , both the switch switching signal S2 and the write / read control signal SW _{/ R} fall off in synchronism this time (see (d) and (e) in the same figure). As a result, the switch path of the electronic switch 72 changes to the opposite switching end a side, and the offset memory 72 changes to the read state.

As a result, the latest offset data Doff ^* of the pixel corresponding to the pixel address signal Sa is read from the offset memory 72, and this data Dof is read.
f ^* is a coefficient C according to the shooting time information Stime at that time
Time is multiplied and the final offset data Doff
Is calculated. Now, the conversion data D of the A / D converter 18
Since i is supplied to the adder 19, the latest offset data Doff is added to or subtracted from the converted data Di. This offset correction is performed for each pixel.

After that, when the X-ray irradiation signal S2 is turned off at time t ₂ , the actual X-ray irradiation is also ended in synchronization with this. However, the OFF state of the switch switching signal S2 and the write / read control signal SW _{/ R} is maintained until the next frame when the image data of the frame related to the end of the exposure is output from the solid-state image sensor 13a, and the image capturing mode is set. The X-ray image that has been offset-corrected according to the above is displayed on the CRT 22.

Then, at the time t ₃ when the image processing frame ends, the switch switching signal S2 and the write / read control signal S _{W / R} are turned on, and as described above, the latest image data Di is offset. The data is sequentially written in the offset memory 72.

As described above, in the case of the solid-state image pickup device having no pixel value dependent area, the offset data collected at the timing immediately before the image pickup in which the optical image is not incident can be utilized, and the offset data can be changed even if the image pickup time changes. It is possible to perform near real-time offset correction corresponding to the length of the imaging time. As a result, while the highly accurate offset correction can be performed, the correction amount is collected under the temperature of the solid-state image sensor at the time when the image is actually taken, so that it is possible to respond to the temperature of the solid-state image sensor as described above. There is an advantage that the correction becomes unnecessary and the element configuration and the correction process become simple.

(Seventh Embodiment) Furthermore, a seventh embodiment is shown in FIG.
This will be described with reference to FIGS. The seventh embodiment relates to a countermeasure when the absolute value of the offset correction amount Doff is large.

As described above, the method of correcting the offset correction amount Doff according to the image pickup time, the element temperature, the pixel value, and the pixel position is very superior, but it may include a slight error. Even if the ratio of the correction error is small, if the absolute value of the offset correction amount Doff is large, a considerable error may remain in the corrected image data "Di + Doff". In such a case, the artifact is generated. Can also cause Therefore, the present embodiment has an object to provide an image with few artifacts even when the absolute value of the offset correction amount Doff is large.

The X-ray diagnostic apparatus shown in FIG.
Between the pixel address signal Sa from 6 and the offset correction amount Doff from the offset data generation circuit 30 to determine the replacement pixel address Sa ^* and between the adder 19 and the D / A converter 21. And a replacement circuit 81 that replaces the pixel value of the determined replacement pixel address Sa ^* .

As shown in FIG. 18, the replacement address determining circuit 80 has an absolute value circuit 82 for calculating the absolute value of the offset correction amount Doff, an output of the absolute value circuit 82, and a predetermined reference value De of the offset correction amount. Comparator 83 for comparing
And a gate circuit 84 which opens and closes in response to the comparison result of the comparator 83. The comparator 83 has an offset correction amount Doff.
When the absolute value of is less than or equal to the reference value De, the output is kept off, but when it exceeds the reference value De, it is turned on. The gate circuit 84 is opened (OFF) while the output of the comparator 83 is OFF, and blocks the pixel address signal Sa.
When the output of the comparator 84 is on, it is closed (on) and the pixel address signal Sa is passed. As a result, the comparator 8
At the pixel address at which the output of 3 is turned on, the gate circuit 84 supplies the pixel address signal Sa at that time to the replacement circuit 81 as the replacement pixel address Sa ^* .

The replacement circuit 81 has a data register, a writing / reading circuit, etc., and replaces the pixel value when the replacement pixel address Sa ^* is instructed, for example, with the pixel value of one adjacent pixel. For this replacement, a method of calculating an average value from pixel values of a plurality of adjacent pixels and replacing the average value can also be adopted. When the replacement pixel address Sa ^* is not instructed, the replacement circuit 81 supplies the output of the adder 19, that is, the offset-corrected image data “Di + Doff” to the D / A converter 21 of the next stage as it is.

Other configurations and functions are the same as those of the second embodiment.

As described above, when the absolute value of the offset correction amount Doff generated by the offset data generation circuit 30 exceeds the reference value De, the pixel address thereof is automatically determined by the replacement address determination circuit 80. The pixel data of the image data of such a pixel address is replaced by a replacement circuit 81 in relation to an adjacent pixel, and a pixel value that may include a relatively large offset error is processed accurately. As a result, an image with few artifacts can be provided, and a double prevention measure is applied to the correction of the dark output by offset correction by addition (subtraction) and replacement, and the reliability thereof becomes extremely high.

In this embodiment, regardless of whether or not the absolute value of the correction amount Doff is larger than the reference value, the offset correction by addition (subtraction) is once performed, and then the replacement is performed if necessary. However, a switching circuit is inserted between the offset data generation circuit 30 and the adder 19 so that the offset correction by addition (subtraction) is not performed when the absolute value of the correction amount Doff is larger than the reference value. You can also

In the above embodiment, the image pickup time is used as the offset correction parameter, but dark output for each pixel collected in advance (first embodiment), the temperature of the solid-state image sensor (third embodiment), pixel The same can be applied to the value (fourth embodiment) and the pixel position (fifth embodiment).

A modification of the seventh embodiment is shown in FIG.
As shown in the figure, in this X-ray diagnostic apparatus, the pixel address signal Sa is replaced by the replacement address determination circuit 80 described above.
Only the replacement information memory 86 is provided. In this replacement information memory 86, the address where the image data needs to be replaced is measured before the device is used, such as when the device is shipped, and the replacement address is written. Therefore, when the pixel address signal Sa corresponds to the stored replacement address, the replacement command signal Scd = ON is sent from the replacement information memory 86 to the replacement circuit 81, and the image data is replaced in the same manner as described above. Pixel address signal S
When a does not correspond to the stored replacement address, the replacement command signal Scd = OFF, and the replacement operation is not performed.
This function enables the replacement operation with a simpler configuration.

(Eighth Embodiment) Further, an eighth embodiment is shown in FIG.
It will be described based on. This embodiment relates to the mounting position of the offset correction mechanism.

The X-ray diagnostic apparatus shown in FIG. 20 is obtained by changing the position of the offset correction mechanism of the one shown in FIG. 1 according to the first embodiment. Specifically, the amplifier 17, the 2-input analog adder 90, the amplifier 91, the A / D converter 92, the digital processing circuit 93, and the A / D conversion are provided between the output side of the TV camera 13 and the CRT 22. The device 21 is inserted in this order. On the other hand, on the read side of the offset memory 20 for reading the offset correction amount Doff, another D / A converter 94 and an amplifier 95 are provided in this order, and the output end of the amplifier 95 is connected to the adder 90.

As a result, the offset correction amount Doff of the digital amount read corresponding to the pixel address signal Sa is obtained.
Is converted into an analog quantity by the D / A converter 94,
It reaches the adder 90. Since the image data of the analog amount as it is is supplied to the adder 90 for each pixel, the adder 90
Then, the offset correction "Di + Doff" of the analog amount is performed. This correction result is then returned to a digital amount by the A / D converter 92 and then subjected to necessary digital processing by the digital processing circuit 93. After that, the image data is D /
The A converter 21 converts the analog image signal back to CRT
22 is displayed.

As described above, the offset correction is performed with the analog amount as it is before being converted into the digital amount.
It is possible to effectively use all the bit lengths of the D / D converter 92 as image data, and avoid the problem that the effective bit length is reduced by the offset correction as described above. it can.

Note that this embodiment is not limited to the configuration in which the offset correction is performed based on the offset data Doff for each pixel collected at the time of shipment, and the offset correction based on the imaging time (second embodiment), Offset correction based on temperature of solid-state image sensor (third embodiment), offset correction based on pixel value (fourth embodiment), offset correction based on pixel position (fifth embodiment), offset correction by replacement (seventh embodiment) Example) can be carried out in the same manner.

Although the offset correction parameters (imaging time, element temperature, pixel value, pixel position) are individually set in the above-described second to fifth embodiments, these parameters are explained. , I.e. imaging time,
It is also possible to use any of the element temperature, the pixel value, and the pixel position as a parameter that is appropriately combined and to implement the parameter. Also, offset correction related to those parameters,
The offset correction by replacement may be appropriately combined and implemented.

[0086]

As described above, according to the present invention,
An appropriate amount of the offset amount due to the dark current of the solid-state image sensor depending on whether or not the correction amount has a pixel value dependent region (for example, when there is a pixel value dependent region, it is measured in advance at the time of shipment, etc. Corrected by the offset correction amount for each pixel, mode for changing the correction amount by any one or any combination among the parameters of the imaging time, the temperature of the solid-state image sensor, the pixel value, and the pixel position, the pixel value Is above a predetermined level, a mode in which correction for replacing the pixel value itself is added, a mode in which offset correction is performed with the analog amount and then converted into a digital amount, etc. If there is no pixel value dependent region, dark output data (correction Data) for each pixel, the dark output data (correction data) collected immediately before imaging based on the imaging time, the pixel value itself when the pixel value is above a predetermined level. Since the correction is performed in the mode of adding the replacement correction, the mode of performing the offset correction as it is in the analog amount and then converting it into the digital amount, the correction remaining and the correction variation are significantly reduced to improve the spatial resolution and the artifact. It is possible to obtain a high quality image with an improved S / N ratio due to the reduction of the noise, prevent the deterioration of the information obtained from the image, and effectively use the bit length of the A / D converter. The dynamic range of can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing an offset data generation circuit according to a second embodiment.

FIG. 4 is a graph illustrating a qualitative relationship between an imaging time and a coefficient.

FIG. 5 is a block diagram showing another example of an offset data generation circuit.

FIG. 6 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a third embodiment of the present invention.

FIG. 7 is a block diagram showing an offset data generation circuit according to a third embodiment.

FIG. 8 is a graph illustrating a qualitative relationship between temperature and coefficient of a solid-state image sensor.

FIG. 9 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a fourth embodiment of the present invention.

FIG. 10 is a block diagram showing an offset data generation circuit according to a fourth embodiment.

FIG. 11 is a graph illustrating a qualitative relationship between pixel values and coefficients.

FIG. 12 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a fifth embodiment of the present invention.

FIG. 13 is a graph illustrating a qualitative relationship between a transfer path length and an offset correction amount.

FIG. 14 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a sixth embodiment of the present invention.

FIG. 15 is a block diagram showing an offset data generation circuit and offset data fetching in a sixth embodiment.

FIG. 16 is a timing chart illustrating the operation of the sixth embodiment.

FIG. 17 is a block diagram showing a schematic configuration of an X-ray diagnostic apparatus according to a seventh embodiment of the present invention.

FIG. 18 is a block diagram of an offset data generation circuit and a replacement address determination circuit according to a seventh embodiment.

FIG. 19 is a block diagram of an offset data generation circuit and a replacement address determination circuit according to a modification of the seventh embodiment.

FIG. 20 is a block diagram showing the schematic arrangement of an X-ray diagnostic apparatus according to the eighth embodiment of the present invention.

FIG. 21 is a graph illustrating variation of pixel values when conditions such as temperature and storage time are used as parameters.

FIG. 22 is a characteristic diagram of pixel value-variation (correction amount) for explaining the pixel value dependence region.

[Explanation of symbols]

 13 TV camera 13a Solid-state image sensor 16 Drive circuit 18 A / D converter 19 Adder 20 Offset memory 23 Controller 30, 40, 50, 70 Offset data generation circuit 34 Offset memory circuit 39 Temperature sensor 60 Path length conversion circuit 61 offset memory 71 electronic switch 80 replacement address determination circuit 81 replacement circuit 86 replacement information memory 90 adder 92 A / D converter 94 D / A converter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01L 31/09 7630-4M H01L 31/00 A (72) Inventor Nobuo Kobayashi Shimoishigami, Otawara City, Tochigi Prefecture 1385-1 Stock company Toshiba Nasu factory (72) Inventor Mikito Hayashi 1385-1 Shimoishi, Otawara city, Tochigi prefecture 1385 Stock company Toshiba Nasu factory (72) Inventor Kunio Shiraishi 1385 Shimoishigami, Otawara city, Tochigi prefecture Number 1 within Toshiba Medical Engineering Co., Ltd.

Claims (12)

[Claims] 1. An image pickup apparatus having a solid-state image pickup device for outputting image data composed of pixel values corresponding to a picked-up optical image, for correcting an offset amount caused by a dark current for each pixel of the solid-state image pickup device. And storage means for storing the previously measured correction data, and offset correction means for correcting the image data from the solid-state image sensor for each pixel based on the correction data stored in the storage means. Image pickup device. 2. The characteristic of the correction data with respect to the pixel value has a pixel value dependent area depending on the pixel value, and the correction data is data measured and stored before the use of the imaging device. The image pickup apparatus according to claim 1. 3. The image pickup apparatus according to claim 2, wherein the correction data is data measured by causing a light amount having a pixel value corresponding to a region other than the pixel value dependent region to enter the solid-state image pickup device. 4. At least one or more of an imaging time during which the optical image is continuously incident on the solid-state image sensor, a temperature of the solid-state image sensor, a pixel value of the image data, and a parameter of the pixel position. The image pickup apparatus according to claim 3, further comprising a correction data changing unit that changes the correction data based on a combination of. 5. A judging means for judging for each pixel whether or not the correction data changed by the correction data changing means exceeds a reference value, and this judging means determines that the correction data exceeds the reference value. At this time, a replacing means for replacing the pixel value of the pixel to be judged with the pixel value obtained from the pixel values of the pixels in the vicinity thereof is added.
The imaging device described. 6. A replacement address memory means in which an address required to replace the image data is stored in advance, and a pixel position of an object to be imaged by the solid-state imaging device matches a replacement address stored in the replacement address memory means. The image pickup apparatus according to claim 4, further comprising: a replacement unit that replaces a pixel value of the pixel with a pixel value obtained from pixel values of neighboring pixels. 7. The offset correction means converts a D / A converter for converting correction data into an analog amount, conversion data of the analog amount of the D / A converter, and image data of the analog amount of the solid-state image sensor. And an adder for adding, and A for converting the addition result of this adder to a digital value
The image pickup apparatus according to claim 4, 5 or 6, further comprising a / D converter. 8. The characteristic of the correction data with respect to the pixel value is a characteristic that does not depend on the pixel value, and the correction data is dark output data measured in a state where the optical image is not incident on the solid-state image sensor. 1. The imaging device according to 1. 9. The dark output data is data measured in a frame period immediately before image pickup, and the dark output data is obtained based on an image pickup time during which the optical image is continuously incident on the solid-state image pickup element. 9. The image pickup apparatus according to claim 8, further comprising a correction data changing unit for changing. 10. A judgment means for judging for each pixel whether or not the correction data changed by the correction data changing means exceeds a reference value, and this judgment means determines that the correction data exceeds the reference value. 10. The image pickup apparatus according to claim 9, further comprising a replacement unit that replaces the pixel value of the pixel to be determined with the pixel value obtained from the pixel values of the neighboring pixels. 11. A replacement address memory means for storing in advance an address required to replace the image data,
Substitution means for substituting the pixel value of the pixel with the pixel value obtained from the pixel values of the neighboring pixels when the pixel position of the image pickup target by the solid-state image pickup device coincides with the substitution address stored in the substitution address memory means. 10. The image pickup apparatus according to claim 9, further comprising: 12. The offset correction means converts a D / A converter that converts the correction data into an analog amount, conversion data of the analog amount of the D / A converter, and image data of the analog amount of the solid-state image sensor. 11. An adder for adding and an A / D converter for converting the addition result of the adder into a digital amount are provided.
Alternatively, the imaging device according to item 11.