JP3667383B2 - X-ray TV camera device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an X-ray TV camera device, and more particularly, to an X-ray TV camera device with little image quality deterioration even when an input signal level is lowered.
[0002]
[Prior art]
The X-ray TV camera apparatus converts X-rays that have passed through a subject into an optical image by an image intensifier, and then captures the optical image with a TV camera and displays it on a monitor screen. The configuration of a conventional X-ray TV camera device is shown in FIG.
[0003]
6, X-rays emitted from the X-ray tube 101 pass through the subject 102 and enter an image intensifier (hereinafter abbreviated as II) 103. I. I. Reference numeral 103 denotes incident X-rays that are converted into visible light by a phosphor, and an image of the visible light is captured by the TV camera 105 through the optical system 104. In addition, I.I. I. A part of the visible light output 103 enters the photomultiplier tube 106, the intensity of which is converted into an electric signal, and is transmitted to the automatic brightness adjustment (ABC) circuit 116.
[0004]
An analog image signal photographed by the TV camera 105 is amplified to an appropriate signal level inside the camera control unit 107, and then converted into an analog-digital signal and output as a digital image signal to the image acquisition system 109 of the diagnostic apparatus main body 108. Is done. The image acquisition system 109 reduces the noise of the image signal by digital signal processing and stores it in the image memory 110. The image stored in the image memory 110 is displayed on the screen of the monitor 112 by the image processing system 111 performing image processing according to the designation of the window level and window width. The image stored in the image memory 110 is written and stored from the image storage system 113 to the image file device 114 such as an optical disk device.
[0005]
The automatic brightness adjustment circuit 116 sends a signal to the high voltage control circuit 117 based on the detection signal of the photomultiplier tube 106, and the high voltage control circuit 117 receives the X-ray imaging conditions inputted from the console 115 and the automatic brightness. A high voltage supplied from the high voltage supply circuit 118 to the X-ray tube 101 and its current value are controlled by a signal from the adjustment circuit 116. Thus, when the input to the photomultiplier tube 106 decreases, the automatic brightness adjustment mechanism increases the X-ray intensity and increases the I.D. I. Control is performed so that the fluorescence output 103 becomes constant.
[0006]
In such a conventional automatic brightness adjustment mechanism (hereinafter abbreviated as ABC mechanism), the exposure amount of the subject is limited. Therefore, when the subject's body thickness is particularly thick, the X-ray attenuation amount Is large, I.I. I. The amount of X-ray incident on the I. The output level of the video signal obtained by photographing the fluorescent screen with a TV camera falls within a predetermined level. For this reason, there are a method of controlling the automatic aperture (also referred to as auto iris) of the TV camera based on the video signal level and a method of controlling the gain of the camera by automatic gain control (hereinafter abbreviated as AGC).
[0007]
[Problems to be solved by the invention]
However, even if a method of controlling the automatic aperture of the TV camera based on the video signal level or a method of controlling the gain of the camera using the AGC is used, the I.C. I. If the amount of X-rays incident on the I. The image on the fluorescent screen becomes an image with a lot of quantum noise, and there is a problem that the image quality is remarkably lowered and the diagnostic ability is deteriorated.
[0008]
In view of the above problems, the object of the present invention is to exceed the control range of the ABC mechanism. I. It is to provide an X-ray TV apparatus capable of reducing image noise even when the amount of X-ray incident on the screen is reduced.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray TV camera apparatus according to claim 1 of the present invention provides a rolling average signal obtained by weighted averaging an input image signal and an image signal stored in a frame memory at a predetermined ratio. A recursive filter that outputs and uses the rolling average signal as a new frame memory storage signal, a moving image detection circuit that detects a motion amount of the input image signal based on a comparison between the input image signal and the rolling average signal, and A coefficient generation circuit that generates an input image signal coefficient and a rolling average signal coefficient based on a signal level and the amount of motion; a first coefficient multiplication circuit that multiplies the input image signal and the input image signal coefficient; A second coefficient multiplication circuit for multiplying the rolling average signal by the rolling average signal coefficient; An addition circuit for adding a multiplication result of the first coefficient multiplication circuit and a multiplication result of the second coefficient multiplication circuit and outputting a signal; detecting a signal level of the output signal; And a level detection circuit for transmitting to the coefficient generation circuit.
[0010]
The X-ray TV camera apparatus according to claim 2 is the X-ray TV camera apparatus according to claim 1, wherein the coefficient generation circuit increases the rolling average coefficient and the signal level when the absolute value of the motion amount is small. If smaller, the coefficient is generated so as to increase the rolling average coefficient.
[0012]
[Action]
With the above configuration, in the first aspect of the present invention, the recursive filter weights and averages the input image signal and the rolling average signal stored in the frame memory up to one frame before at a predetermined ratio, thereby rolling the image signal. A signal is output, and the contents stored in the frame memory are updated with this rolling average signal.
[0013]
The level detection circuit detects the signal level of the input image signal and transmits the signal level to the coefficient generation circuit. The moving image detection circuit receives the input image signal and the rolling average signal, and detects the amount of motion of the image based on the difference between the two.
[0014]
The coefficient generation circuit is a circuit for generating a coefficient that weights and averages the input image signal and the rolling average signal. When the absolute value of the motion amount is small, the coefficient of the rolling average signal is increased to reduce the noise. When the absolute value of the motion amount is large, the coefficient of the rolling average signal is reduced to improve the followability to the input image. Furthermore, if the input signal level is small even if the amount of motion is the same, the coefficient of the rolling average signal is increased to enhance the noise reduction effect.
[0015]
The first coefficient multiplying circuit and the second coefficient multiplying circuit respectively multiply the input image signal, the input image signal coefficient, the rolling average signal, and the rolling average signal coefficient, and the multiplication results are added by an adder circuit to obtain a weighted average. Is obtained as an output image signal.
[0016]
In the invention according to claim 2, the recursive filter weights and averages the input image signal and the rolling average signal stored in the frame memory up to one frame before at a predetermined ratio, and outputs the rolling average signal of the image signal. In addition, the stored contents of the frame memory are updated with this rolling average signal.
[0017]
The level detection circuit detects a signal level of an output image signal, which will be described later, and transmits the signal level to the coefficient generation circuit. The moving image detection circuit receives the input image signal and the rolling average signal, and detects the amount of motion of the image based on the difference between the two.
[0018]
The coefficient generation circuit is a circuit for generating a coefficient that weights and averages the input image signal and the rolling average signal. When the absolute value of the motion amount is small, the coefficient of the rolling average signal is increased to reduce the noise. When the absolute value of the motion amount is large, the coefficient of the rolling average signal is reduced to improve the followability to the input image. Furthermore, if the input signal level is small even if the amount of motion is the same, the coefficient of the rolling average signal is increased to enhance the noise reduction effect.
[0019]
The first coefficient multiplying circuit and the second coefficient multiplying circuit respectively multiply the input image signal, the input image signal coefficient, the rolling average signal, and the rolling average signal coefficient, and the multiplication results are added by an adder circuit to obtain a weighted average. Is obtained as an output image signal.
[0020]
【Example】
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a main configuration of a first embodiment of an X-ray TV camera apparatus according to the present invention, and corresponds to the invention described in claim 1.
[0021]
In FIG. 1, digitized input image signals 11 are connected to a gain adjustment circuit 1, a level detection circuit 2, a moving image detection circuit 4, and a multiplication circuit 7, respectively. The level detection circuit 2 detects the level of the input image signal 11 (addition value or addition average for the image) and generates a level signal 12. The gain adjustment circuit 1 adjusts the signal level of the input image signal 11 based on the level signal 12 and outputs the adjusted signal level to the recursive filter 3. The recursive filter 3 is a circuit that includes a frame memory and outputs a rolling average signal 13 as shown in FIG. 2 described later.
[0022]
The moving image detection circuit 4 obtains a difference in signal intensity between the input image signal 11 and the rolling average signal 13 for each pixel. The result obtained for each pixel is output as a motion amount signal corresponding to each pixel. The coefficient generation circuit 5 is a circuit that generates a coefficient for weighted averaging of the rolling average signal and the input image signal. The coefficient k of the rolling average signal (0 ≦ k <1) and the coefficient 1-k of the input image signal are used as pixels. Occurs every time. The coefficient generation circuit 5 includes a look-up table using a read-only memory. Based on the motion amount signal 14 and the level signal 12, coefficients k and 1-k as shown in the graph of FIG. Occur.
[0023]
The coefficient multiplication circuits 6 and 7 multiply the input image signal 11 and the coefficient 1-k, and the rolling average signal 13 and the coefficient k, respectively. The outputs of the coefficient multiplying circuits 6 and 7 are added by an adding circuit 8 to obtain an output image signal 15.
[0024]
FIG. 2 is a block diagram showing a detailed configuration of the recursive filter 3. In FIG. 2, if the subscript (t) is the frame time, the subtracter 21 subtracts the read signal F (t−1) from the frame memory 24 from the input signal A (t), and the coefficient multiplication circuit 22 is added to the subtraction result. Is multiplied by the coefficient h, and the multiplication result and the read signal F (t−1) of the frame memory 24 are added by the adder 23 to obtain an output signal F (t). That is, the output signal F (t) is expressed by Equation (1).
[0025]
[Expression 1]
F (t) = F (t−1) + h × {A (t) −F (t−1)} (1)
Since the normal coefficient h (0 <h ≦ 1) is selected as h = 1/2 ^m (m is a positive integer), the coefficient multiplication circuit simply shifts the subtraction result by m bits.
[0026]
As is clear from equation (1), in the recursive filter, even if the frame memory is updated infinitely, the frame memory is not saturated. When the noise component of the input signal is shot noise, the SN ratio of the stationary portion is improved to about (2 / h−1) ^1/2 when t is sufficiently larger than 1 / h.
[0027]
Further, it is possible to adopt a recursive filter configuration as shown in FIG. In FIG. 3, the input signal A (t) is multiplied by a coefficient h (0 <h ≦ 1) by a coefficient multiplier 31. On the other hand, the read output of the frame memory 34 is multiplied by a coefficient 1-h by a coefficient multiplier 33. The outputs of the coefficient multipliers 31 and 33 are added by an adder 32 to become an output F (t), and the stored contents of the frame memory 34 are updated by this output F (t). Also in this case, the output signal F (t) follows the equation (1), but the coefficient h and the coefficient 1-h can be controlled by the signal level detected by the level detection circuit which is the gain control signal of AGC. Become.
[0028]
FIG. 4 is a graph showing the coefficient k generated by the coefficient generation circuit 5 in FIG. In FIG. 4, the X-axis direction is an image motion amount indicated by the motion amount signal, and the Y-axis direction is a rolling average signal coefficient k.
[0029]
The input image signal coefficient 1-k is a distance from the graph of y = 1 to the coefficient k in the -Y direction. When the absolute value of the amount of motion is small, the coefficient of the rolling average signal is increased to increase the noise reduction effect.When the absolute value of the amount of motion is large, the coefficient of the rolling average signal is decreased to reduce the coefficient to the input image. Increase followability. Furthermore, when the level signal 12 is small even when the amount of motion is the same, as shown by the broken line graph, the coefficient k of the rolling average signal is increased to enhance the noise reduction effect.
[0030]
According to the first embodiment, an area where the image motion is large is an image having a high ratio of the input image signal 11, and an area where the motion is small is an image having a high ratio of the rolling average signal.
[0031]
FIG. 5 is a block diagram showing a main configuration of a second embodiment of the X-ray TV camera apparatus according to the present invention, and corresponds to the invention described in claim 2. In FIG. 5, the digitized input image signal 11 is connected to the recursive filter 3, the moving image detection circuit 4, and the multiplication circuit 7, respectively. The recursive filter 3 is a circuit that includes a frame memory as shown in FIG. 2 and outputs a rolling average signal 13.
[0032]
The moving image detection circuit 4 compares the input image signal 11 and the rolling average signal 13 to detect the motion amount of the input image and outputs it as a motion amount signal 14. The coefficient generation circuit 5 is a circuit for generating coefficients: k and 1-k for weighted average of the input image signal and the rolling average signal for each pixel, and is configured by a look-up table using a read-only memory. Based on the quantity signal 14 and a level signal 12 from the level detection circuit 2 described later, coefficients k and 1-k as shown in FIG. 4 are generated.
[0033]
The coefficient multiplication circuits 6 and 7 multiply the input image signal 11 and the coefficient 1-k, and the rolling average signal 13 and the coefficient k, respectively. The outputs of the coefficient multiplying circuits 6 and 7 are added by the adding circuit 8 and then the level is adjusted by the gain adjusting circuit 1 to become an output image signal 16. The level detection circuit 2 adds (or adds and averages) the output of one image from the addition circuit 8 to generate a level signal 12 and transmits it to the gain adjustment circuit 1 and the coefficient generation circuit 5.
[0034]
The difference between the second embodiment and the first embodiment is that the gain adjustment circuit 1 and the level detection circuit 2 are provided on the output side of the image signal processing. The response speed is slower than that, but since feedback control is performed, there is an advantage that a relatively stable image with little luminance change can be obtained.
[0035]
【The invention's effect】
As described above, according to the present invention, since the input signal and the rolling average signal are weighted and averaged based on the level of the image signal and the motion of the image, the I.V. I. Even if the amount of X-rays incident on the light source decreases, the noise of the image can be reduced, and at the same time, it is fed back to the rolling average signal that generates the output image level information. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main configuration of a first embodiment of an X-ray TV camera device according to the present invention.
FIG. 2 is a block diagram illustrating a configuration example of a recursive filter.
FIG. 3 is a block diagram illustrating another configuration example of the recursive filter.
FIG. 4 is a graph illustrating an example of coefficients by a coefficient generation circuit according to an embodiment.
FIG. 5 is a block diagram showing a main configuration of a second embodiment of the X-ray TV camera apparatus according to the present invention.
FIG. 6 is a block diagram showing a conventional example of an X-ray TV camera device.
[Explanation of symbols]
1 gain adjustment circuit 2 level detection circuit 3 recursive filter 4
Movie detection circuit 5 Coefficient generation circuit 6, 7 Coefficient multiplier 8 Adder

Claims (2)

A recursive filter that outputs a rolling average signal obtained by weighted averaging the input image signal and the image signal stored in the frame memory at a predetermined ratio and uses the rolling average signal as a new frame memory storage signal;
A moving image detection circuit for detecting a motion amount of the input image signal based on a comparison between the input image signal and the rolling average signal;
A coefficient generation circuit for generating an input image signal coefficient and a rolling average signal coefficient based on the signal level and the amount of motion;
A first coefficient multiplication circuit for multiplying the input image signal and the input image signal coefficient;
A second coefficient multiplication circuit for multiplying the rolling average signal by the rolling average signal coefficient;
An addition circuit for adding a multiplication result of the first coefficient multiplication circuit and a multiplication result of the second coefficient multiplication circuit and outputting a signal;
An X-ray TV camera apparatus comprising: a level detection circuit that detects a signal level of the output signal and transmits the signal level to the coefficient generation circuit. 2. The coefficient generation circuit according to claim 1, wherein the coefficient generation circuit generates a coefficient so as to increase a rolling average coefficient when an absolute value of a motion amount is small and to increase a rolling average coefficient when a signal level is small. X-ray TV device.

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