JPH05111479A - X-ray television device - Google Patents

Abstract

PURPOSE:To enable executing of adequate image processing by digitizing all video signals without generating white drop-outs and black collapses even with a high-contrast subject. CONSTITUTION:The min. value of the video output of a TV camera 15 is detected and a small offset alpha is applied to the video signals in accordance with this value. Such video signals are applied to a nonlinear amplifier 27. The max. value of the output of the nonlinear amplifier 27 is then detected and the output of the nonlinear amplifier 27 is amplified according to this value so as to be converged in the input range of an A/D converter 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray television device used in the fields of medical treatment and the like.

[0002]

2. Description of the Related Art First, a simplified construction of a conventional X-ray television apparatus is shown in FIG. 2 and its operation will be briefly described. X emitted from the X-ray tube 10 and transmitted through the subject 11.
The line forms a visible image on the projection plane of the image tube (Image Intensifier = II) 12. This image is taken by a television (TV) camera 15, and a display device (CRT) is used.
Etc.) 21. Here, in many cases, the image captured by the TV camera 15 is an A / D converter (AD
After being converted into digital data by C) 18, the image processing circuit 19 performs various image processing such as contour enhancement. The image data subjected to the image processing is converted into an analog video signal again by the D / A converter (DAC) 20 and sent to the display device 21.

Here, the brightness of a predetermined range on the projection surface of the image tube 12 is set so that the image displayed on the display device 21 always has an appropriate brightness even if the X-ray transmittance of the subject 11 is different. The photo pickup 17 for detecting the
3, the X-ray controller 16 appropriately determines the operating conditions (tube current and tube voltage) of the X-ray tube 10 based on the brightness data.

[0004]

The feedback control of the X-ray condition by the X-ray controller 16 in the conventional X-ray television apparatus is such that the average luminance is constant within a predetermined range including the center of the screen. Therefore, if the X-ray conditions are set so that the brightness of the image is appropriate for a flat (low contrast of X-ray transmittance) subject, the subject thickness of the lung field or the like is significantly different (contrast of contrast is low). When a (high) subject is projected, a thin portion causes whiteout (halation) and a thick portion causes blackout.
On the contrary, if the X-ray condition is determined with reference to a region where the subject thickness is significantly different, when a flat subject is projected, the contrast is remarkably lowered and the details are destroyed.

The problem that the contrast becomes low when a flat subject is projected can be solved by a process of emphasizing the contrast of a target portion by a non-linear amplifier. However, if whiteout (halation) or blackout occurs, particularly when the X-ray television apparatus includes an image processing circuit, a part of the image data is subjected to A / D conversion performed in the preceding stage. Will be lost, and appropriate image processing cannot be performed.

The present invention has been made in order to solve such a problem, and an object of the present invention is not to cause overexposure or underexposure of a subject even if the subject has a high contrast. An object is to provide an X-ray television device capable of converting a video signal into digital data.

[0007]

SUMMARY OF THE INVENTION The present invention, which has been made to solve the above problems, captures an image formed on an image tube with a television camera and outputs a video signal generated by the television camera to a non-linear amplifier and In an X-ray television device that digitizes through an A / D converter, a) is provided between a television camera and a non-linear amplifier, detects the minimum value of a video signal output by the television camera, and then detects the minimum value. Offset means for adding a video signal to the non-linear amplifier based on the following, and b) is provided between the non-linear amplifier and the A / D converter, detects the maximum value of the output of the non-linear amplifier, and detects the maximum value. Maximum width adjusting means for amplifying the output of the non-linear amplifier according to
It is characterized by having.

[0008]

The offset means detects the minimum value of the video signal output by the television camera and adds an offset to the video signal based on the minimum value. The offset here is preferably set so that the minimum value of the video signal coincides with a predetermined reference point (usually the zero point) of the non-linear amplifier, or slightly above the reference point. As a result, black crushing is prevented.

The offset added video signal is given a predetermined contrast characteristic by a non-linear amplifier. The output of the non-linear amplifier is sent to the A / D converter,
Since the portion exceeding the maximum input level of the A / D converter is overexposed (halation), the maximum width adjusting means detects the maximum value of the output of the non-linear amplifier, and the maximum value is the maximum input of the A / D converter. The output of the non-linear amplifier is amplified (attenuated) so that it is below the level. Therefore, the video signal of the image captured by the television camera is converted into digital data by the A / D converter without causing whiteout (halation) and blackout.

[0010]

1 shows the basic construction of an X-ray television apparatus according to an embodiment of the present invention. In the X-ray television apparatus of this embodiment, between the TV camera 15 and the A / D converter 18 of the conventional X-ray television apparatus shown in FIG.
An offset circuit 26, a non-linear amplifier 27, and a linear variable gain amplifier 30 are provided, and a circuit 24 that detects the minimum value of the video signal output of the TV camera 15 and an offset amount of the offset circuit 26 is set based on the detected minimum value. A circuit 25, a circuit 28 for detecting the maximum value of the output of the non-linear amplifier 27, and a circuit 29 for adjusting the gain of the linear variable gain amplifier 30 based on the detected maximum value are provided. Here, the minimum value detection circuit 24, the offset adjustment circuit 25, and the offset circuit 26 configure the offset means, and the maximum value detection circuit 28, the gain adjustment circuit 29, and the linear variable gain amplifier 30 configure the maximum width adjustment means. ..

The operation of the X-ray television apparatus of this embodiment is as follows. The object 1 generated by the X-ray tube 10
The X-rays transmitted through 1 form a visible image on the projection surface of the image tube (II) 12. A photo pickup 17 provided inside the optical system 13 detects the average brightness (within a predetermined range) of the screen of the image tube 12 and outputs the signal as X.
Send to the line controller 16. The X-ray controller 16 changes the tube current and the tube voltage of the X-ray tube 10 according to a predetermined procedure to set the intensity and wavelength of the output X-ray to appropriate values, as in the above-described conventional apparatus. As a result, the average brightness within the predetermined range of the transmitted X-ray image projected on the projection surface of the image tube 12 is always kept constant. The TV camera 15 is the image tube 1
The image on the projection plane 2 is photographed and output as a predetermined video signal.

In this way, although the average brightness of the projection surface of the image tube 12 in a predetermined range is kept constant,
When the X-ray transmittance of the subject 11 is largely different (that is, when the contrast is very strong), the video signal generated by the TV camera 15 is converted into digital data by the A / D converter 18. At this time, whiteout (halation) or blackout may occur partially. That is, the image data is fixed to the maximum value or the minimum value in the portion exceeding the convertible range of the A / D converter 18. This is similar to the case where the image data is lost in that portion (area), and the image processing circuit 19 cannot perform correct image processing.

In order to avoid such a problem, the X-ray television apparatus according to this embodiment performs the following processing before inputting the video signal generated by the TV camera 15 to the A / D converter 18. Give. First, TV camera 1
The video signal generated by the reference numeral 5 is applied to the offset circuit 26.
And the minimum value detection circuit 24.
The minimum value detection circuit 24 detects the minimum value Vmin of the video signal for one screen, and the value Vmin is used as the offset adjustment circuit 2.
Send to 5. Here, the minimum value Vmin detected by the minimum value detection circuit 24 is not the entire surface of one screen but the image processing circuit 19
Therefore, it is desirable to set the minimum value within the range (effective visual field) in which image processing is performed. Further, it may be set to the minimum value of a part (particularly focused part) whose range is further limited (FIG.
(A)).

This minimum value Vmin is the offset adjustment circuit 2
Sent to 5. The offset adjustment circuit 25 uses this minimum value V
The offset amount α of the video signal in the offset circuit 26 is set based on min. Here, the offset amount α may be zero, but it is desirable to set it to a predetermined small value in order to have a margin. As a result, all the video signals within the effective visual field are amplified by the non-linear amplifier 27 to a predetermined level, and are converted into digital data by the A / D converter 18.

The video signal (FIG. 5B) given the offset α by the offset circuit 26 is amplified by the amplifier 27 having a non-linear amplification characteristic. The nonlinear amplifier 27 used in this embodiment is a logarithmic type (LO
G) It has an amplification characteristic, but this is to increase the contrast of a portion which is a portion to be noticed but whose contrast cannot be read because the contrast is low, so that the portion to be noticed can be photographed more clearly. .. In addition,
Besides the logarithmic type, various types of nonlinear amplifiers can be used depending on the object to be photographed, and for example, a two-stage linear type as shown in FIG. 4 can also be used.

The output of the non-linear amplifier 27 (FIG. 5 (c)) is sent to the linear variable gain amplifier 30 and linearly amplified there, but at the same time, it is also sent to the maximum value detection circuit 28.
The maximum value detection circuit 28 detects the maximum value Vmax of the output of the non-linear amplifier 27 (again, it is desirable to detect the maximum value within the effective field of view or within a further limited area), and the value Vmax is adjusted to the gain adjustment circuit. Send to 29. The gain adjustment circuit 29 uses the non-linear amplifier 2 based on the maximum value Vmax.
The gain of the linear variable gain amplifier 30 is set so that the output of No. 7 falls within the input range of the A / D converter 18. The gain here is that the output of the non-linear amplifier 27 is A / D.
It is preferable to set it to be equal to the upper limit of the input range of the converter 18, or to set it within the range with a slight margin (β) as shown in FIG. As a result, all the video signals are converted into digital data by the A / D converter 18 without causing white crushing (halation).

The gain signal thus set by the gain adjusting circuit 29 is sent to the linear variable gain amplifier 30,
The linear variable gain amplifier 30 outputs the output of the non-linear amplifier 27 to
It is linearly amplified with the set gain and sent to the A / D converter 18.

The operation after the A / D converter 18 is the same as that of the above-mentioned conventional apparatus, and the digitized image data is subjected to various kinds of image processing by the image processing circuit 19, and D
It is displayed on the screen of the CRT 21 via the / A converter 20.

[0019]

In the X-ray television apparatus according to the present invention, the image signal is amplified in consideration of not only the average brightness of the image formed on the image tube but also the maximum and minimum values. A video signal of an image captured by a television camera is converted into digital data by the A / D converter without causing whiteout (halation) and blackout. Therefore, when various kinds of image processing are performed based on the data digitized by the A / D converter, the data is not lost, so that appropriate image processing can be performed. Further, even when the display is simply performed on the display device, it is possible to display an appropriate image without blown-out highlights and underexposure on the screen of the display device and with an appropriate contrast. Moreover, since such processing is automatically performed without bothering the operator, it is possible to reduce the photographing time and the exposure dose.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an X-ray television device that is an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional X-ray television device.

FIG. 3 is a graph showing the amplification characteristic of a logarithmic amplifier, which is a type of nonlinear amplifier used in the X-ray television apparatus of the embodiment.

FIG. 4 is a graph showing the amplification characteristics of a two-stage linear nonlinear amplifier which is another nonlinear amplifier.

FIG. 5 is a graph showing a state of a video signal at each stage of the X-ray television device according to the embodiment.

[Explanation of symbols]

10 ... X-ray tube 11 ... Subject 12 ... Image tube (II) 13 ... Optical system 15 ... TV camera 16 ... X-ray controller 17 ... Photo pickup 18 ... A / D converter 19 ... Image processing circuit 20 ... D / A converter 21 ... Display device (CRT) 24 ... Minimum value detection circuit 25 ... Offset adjustment circuit 26 ... Offset circuit 27 ... Non-linear amplifier 28 ... Maximum value detection circuit 29 ... Gain adjustment circuit 30 ... Linear variable gain amplifier

Claims (1)

[Claims] 1. An X-ray television apparatus for photographing an image formed on an image tube by a television camera and digitizing a video signal generated by the television camera through a non-linear amplifier and an A / D converter, comprising: a) An offset means provided between the television camera and the non-linear amplifier, detecting the minimum value of the video signal output by the television camera, and adding an offset to the video signal based on the minimum value to give the non-linear amplifier, b) a maximum width adjusting means which is provided between the non-linear amplifier and the A / D converter, detects the maximum value of the output of the non-linear amplifier, and amplifies the output of the non-linear amplifier according to the maximum value. An X-ray television device characterized by the above.