JPH0669447B2 - X-ray image processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for processing a video signal of an X-ray image obtained by an X-ray television camera, and more particularly to an image processing apparatus for noise reduction.

[Prior art]

In an X-ray fluoroscopy system using an X-ray television camera, the X-ray dose cannot be increased in order to suppress X-ray exposure to a subject, and it is inevitable that the resulting fluoroscopic image contains noise.

Therefore, conventionally, noise reduction is performed by image processing in which an afterimage effect is given to a video signal through a recursive filter (temporal recursive filter).

As shown in FIG. 2, the recursive filter uses a frame memory (1) that stores an image for one frame, and the image of the previous frame stored in this is stored in a multiplier (2) with the value S of each pixel ( 1-A) times (where 0 <A <1) is added to each pixel I of the image obtained at the present time in the adder (3).
Is multiplied by A in the multiplier (4), 1A + S (1-A) is calculated (weighted average), and the result is rewritten in the frame memory (1) to form a recursive filter.

Here, A is called the coefficient of the recursive filter. The larger the value of A, the weaker the effect of the recursive filter and the shorter the afterimage (when A = 1, the afterimage is not added),
On the contrary, the smaller the value, the stronger the effect of the recursive filter and the longer the afterimage, and the noise reduction effect increases.

[Problems to be Solved by the Invention]

In the above recursive filter, the noise is reduced as the value of A is reduced and the effect of the recursive filter is enhanced.
/ N ratio improved However, for a moving image, the afterimage effect appears as an image shift (movement blur), and the image quality deteriorates due to a reduction in resolution and contrast, which is rather difficult to see.

On the contrary, if the value of A is increased to suppress the motion blur and the effect of the recursive filter is weakened, there is a conflicting problem that the afterimage effect is not given, the noise reduction effect is small, and the S / N is not improved.

Since the degree of the afterimage effect of the recursive filter changes depending on the value of A, it may be possible to adjust the value of A according to the magnitude of the motion of the subject while observing the fluoroscopic image, but this is extremely difficult. It is the work of.

In view of the above, the present invention reduces the afterimage effect according to the magnitude of the motion of the subject or does not add the afterimage so that noise reduction due to the afterimage effect can be performed as the motion becomes smaller, An object is to provide an X-ray image processing device.

[Means for solving problems]

The X-ray image processing apparatus according to the present invention provides a motion detection means for obtaining the sum of one screen (one frame) of the difference value for each pixel between the image signal passed through the recursive filter and the current image signal, and an output of this detection means. Accordingly, there is provided a means for determining, for each frame, the mixing ratio of the next image (next frame) of the current image signal and the image signal that has passed through the recursive filter.

[Action]

The image signal from the X-ray fluoroscopic image system can be passed through a recursive filter to obtain a predetermined afterimage effect with a plurality of images before that, and an optimum noise reduction suitable for a stationary subject can be obtained. Can improve the S / N ratio.

The motion detecting means compares the current image signal with the image signal of the image that has passed through the recursive filter (hereinafter referred to as recursive filter image) for each pixel, detects the difference value, and detects the difference value for one frame. Calculate the sum. The means for determining the mixing ratio determines the mixing ratio between the current image signal of the next frame and the image signal passed through the recursive filter based on the output of the motion detecting means.

Therefore, when the movement of the subject is large, the output of the motion detection means (the sum of the difference values) becomes large, the ratio of the current image of the output images becomes large, and a perspective image that is not affected by the afterimage is obtained, while When the movement is small or there is no movement, the output of the movement detection means (sum of difference values)
Becomes smaller, the ratio of the recursive filter image in the output image becomes larger, and noise reduction due to the afterimage effect of the recursive filter is performed more.
The N ratio is improved.

〔Example〕

An explanation will be given below based on FIG. 1 showing a block diagram of one embodiment of the present invention.

In the figure, a video signal of an X-ray fluoroscopic image obtained from an X-ray television camera is converted into a digital signal through an A / D converter (5), sent to a multiplier (4) and multiplied by A. It is input to the post-adder (3). The frame memory (1) thus stores the video signal of the frame at the previous time point, which is read out by the multiplier (2) (1-A).
It is multiplied and input to the adder (3).

The output of the adder (3) is multiplied by (1-B) in the multiplier (6) and sent to the adder (7) and to the subtractor (8) which constitutes the motion detector (13).

The output of the A / D converter (5) is sent to the subtractor (8), multiplied by B in the multiplier (9), and sent to the adder (7). The output of the adder (7) is sent to the frame memory (1) to update the memory for each pixel and D
The A / A converter (10) is passed through the A / A converter (10) to be converted into an analog signal and output to a television monitor device (not shown).

Here, the signal of a certain pixel of one frame sent from the camera at a certain time is I, and the frame memory at this time (1)
If the signal of the same pixel as that stored in S is S, the output P of the adder (7), that is, the above pixel signal of the frame memory (1) rewritten by the output of this adder (7) is P = IB + { IA + S (1-A)} (1-B).

The current video output from the A / D converter (5) and the output of the adder (3) (output through the recursive filter) are sent to the subtractor (8), and these are subtracted for each pixel,
The absolute value of the difference value is detected. The output of the subtractor (8) is given to an arithmetic circuit (12) via a non-linear processing circuit (11) that constitutes a motion detector in cooperation with the subtractor, and the sum of absolute values of the difference values for one frame is calculated. The total value calculated is changed according to the magnitude of the motion of the subject during one frame. If the motion of the subject is large, the sum value will be large, and if it is small, the sum value will be small.
When the subject is stationary, the total value is zero.

Therefore, the values of the multiplication coefficients (1-B) and B given to the multipliers (6) and (9) are changed according to the total value. That is, when the input image data from the A / D converter (5) is a still image or the magnitude of motion is small, the output of the arithmetic circuit (12) becomes small, and in this case, the multiplier (9)
The value of the coefficient B of is small (where 0 <B <1), that is, the coefficient (1-B) of the multiplier (6) is large. (However, 0 <
1-B <1) Therefore, the ratio of the recursive filter image to the output image is increased and the S / N ratio is improved.

Conversely, if the input image data is a moving image, the multiplier (12)
Output (a value indicating the total amount of movement of the entire screen) becomes large.
In this case, the value of the coefficient B of the multipliers (6) and (9) is increased (0 <B <1) to increase the ratio of the current image to be output.

That is, when the motion of the input image data is large due to the motion of the subject, the ratio of the current image to be included in the output image is increased, the afterimage is suppressed, and when the motion is small, the ratio of the recursive filter image to be included in the output image is increased. As a result, the afterimage effect is increased, noise reduction is performed thereby, and the S / N ratio is greatly improved. In addition, specifically, the sum of the absolute values of the difference values at a certain frame (at a certain time point) is calculated, and the coefficients of the multipliers (6) and (9) in the next frame are changed. That is, the mixing ratio of the recursive filter image and the current image is changed in frame units (standard television system, 525 lines / 60 Hz, 33.3 msec unit).

[Modified Example]

(1) Look-up tables can be used as the multipliers (2) and (4).

If a look-up table is used, the coefficient A of the recursive filter is added so as to add an appropriate afterimage to the site while taking into consideration the preference of the observer while viewing the site of the subject and the perspective image displayed on the monitor. The value of can be selected and set.

(2) The multipliers (6) and (9) in which the value of the coefficient B is set by the output of the motion detector are the sum of absolute values of the difference values for one frame, the pixel value of the current image, the recursive filter image. You may use the look-up table which inputs each pixel value of.

In this way, the nonlinear processing circuit (11) of the embodiment can be omitted.

(3) The motion detector detects the absolute value of the difference value of each pixel between the current image signal and the image signal that has passed through the recursive filter. However, it detects the positive or negative difference value, You may make it detect the sum total in 1 frame of it.

〔effect〕

According to the X-ray image processing apparatus of the present invention, the mixing ratio of the current Masato and the recursive filter image automatically changes depending on the motion state for a subject whose motion increases or decreases. That is, when the movement becomes large, the afterimage effect is suppressed or the afterimage effect is not given, and when the movement becomes small, the afterimage effect is given, and optimum noise reduction is performed to improve the S / N.

As a result, an X-ray fluoroscopic image effective for diagnosis can be obtained regardless of the size of the motion of the subject.

Also, the sum of the difference values for each pixel in one frame, that is, 1
The total amount of motion of the frame (that is, the entire screen) changes the mixing ratio (ratio) between the current image of the next frame and the image that has passed through the recursive filter. An image is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. (1): Frame memory, (2) (4) (6) (9):
Multiplier (3) (7): Adder, (5): A / D converter (10): D / A converter, (13): Motion detector ((8) ... subtractor, (11) …… Non-linear circuit, (12)…
(Arithmetic circuit)

Claims (1)

[Claims] 1. A recursive filter for applying an afterimage effect between a plurality of images, a mixing means for mixing a current image signal and an image signal passed through the recursive filter, and a current image signal and an image signal passed through the recursive filter. Motion detecting means for obtaining the sum of the difference values for each pixel of one screen (one frame), and the mixing ratio of the next image (next frame) of the mixing means based on the output signal of this motion detecting means for one screen ( X-ray image processing apparatus, characterized in that the frame memory of the recursive filter is rewritten by the output of the mixing means.