JPH0833922B2 - Image noise reduction device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an image noise reduction apparatus suitable for reducing noise in an X-ray fluoroscopic image and obtaining an easily viewable image.

2. Description of the Related Art Since X-ray fluoroscopic images inevitably contain quantum noise, it has been conventionally performed to reduce this by image processing. Conventionally, a recursive filter device is used to reduce quantum noise. This will be described with reference to the drawings. In FIG. 3, X-rays are emitted from the X-ray tube 1 toward the subject 2, and the X-rays passing through the subject 2 enter the image intensifier 3. In this way, the transmitted X-ray image is converted into a visible light image,
A video signal is obtained by the camera 4. If this video signal is sent to the TV monitor 8 as it is, an X-ray fluoroscopic image can be observed, but the image displayed in this way has a lot of quantum noise, and details cannot be seen. Therefore, the recursive filter device 6 is used. The recursive filter device 6 comprises two amplitude converters (Look Up Table) 61, 62, an image memory 63 and an adder 64. The video signal is converted into a digital signal by the A / D converter 5, and then the amplitude converter 61
Then, its amplitude is uniformly converted to 1 / K times (K is a recursive filter coefficient). Adder 64 in the previous frame
The image signal output from the image memory 63 is stored in the image memory 63, and its amplitude is uniformly converted to (1-1 / K) times by the amplitude converter 62. The adder 64 is one of these two amplitude converters 61,
The output signal of 62 is added for each corresponding pixel, and the addition result is written in the image memory 63. The input signal from the TV camera 4 in the current frame (jth frame) is Ij, and the adder 64
Of the output signal I'i of the adder 64 one frame before (i-th frame),
Since it is stored in 63, I'j is represented by I'j = (1 / K) Ij + (1-1 / K) I'i. In the recursive filter device 6, since the images of the previous frame are added at a predetermined ratio in this way, quantum noise is reduced. That is, since quantum noise occurs randomly, different frames do not overlap and are not enhanced by such addition, whereas signal components overlap between multiple frames and are enhanced by such addition. This is because the noise is relatively reduced. Therefore, the output signal of this recursive filter device 6 is
If converted into an analog signal through the D / A converter 7 and sent to the TV monitor 8 for display, a clear X-ray fluoroscopic image without quantum noise can be observed.

[Problems to be Solved by the Invention]

However, in the case of the recursive filter device, it is inevitable that an afterimage will occur in the image of a moving part because of the principle of adding the images of the previous frame. As the recursive filter coefficient K is increased and the quantum noise reduction effect is increased, the image in the still portion becomes easier to see, but the afterimage becomes more noticeable and the image in the moving portion becomes harder to see. An object of the present invention is to provide an image noise reduction device capable of reducing quantum noise and suppressing the occurrence of an afterimage in a moving part.

[Means for Solving the Problems]

To achieve the above object, in the image noise reduction device according to the present invention, a recursive filter device, a subtractor for performing a subtraction between the recursive filter image obtained from the original image through the recursive filter device and the original image, An image filter device for extracting an afterimage from the image output from the subtractor, and an adder / subtractor for adding / subtracting the output image of the image filter device and the recursive filter image are provided.

[Action]

The recursive filter image is obtained by reducing quantum noise from the original image, but has an afterimage for a moving object. Therefore, if the subtraction between the recursive filter image and the original image is performed, the afterimage of the recursive filter image and the quantum noise of the original image are extracted. This afterimage consists of spatial low-frequency components, and quantum noise contains a lot of spatial high-frequency components.Therefore, by utilizing this difference in properties, an appropriate image filter device that extracts only spatial low-frequency components can be used. Only the afterimage can be extracted. By adding and subtracting the image and the recursive filter image of only the afterimage thus obtained, the recursive filter image is obtained by reducing the quantum noise and adding the afterimage from the original image as described above, and thus the afterimage component of the recursive filter image. You can cancel only. Therefore, an image with reduced quantum noise and no afterimage can be obtained.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, A / from the TV camera 4
The signal (original image) that has passed through the D converter 5 is sent to the recursive filter device 6 and the subtractor 9. The recursive filter device 6 includes 1 / K and (1-1 / K) amplitude converters 61 and 62, an image memory 63, and an adder 64. The subtractor 9 subtracts the recursive filter image from this original image, and the output image is sent to the adder 11 after being filtered by the image filter device 10. The adder 11 adds the output image of the image filter device 10 and the recursive filter image. Here, the recursive filter image is one in which the quantum noise of the original image is reduced, but has an afterimage in a moving portion. Therefore, in the subtractor 9,
Subtracting this recursive filter image from the original image means canceling other signals except the quantum noise of the original image and the residual image of the recursive filter image. In other words, such subtraction extracts the quantum noise of the original image and the afterimage of the recursive filter image. By the way, included in the output signal of the subtractor 9,
Examining the quantum noise component and the afterimage component, it can be seen that the former contains many high components and the latter is low components in the spatial frequency. Therefore, by utilizing the difference in the spatial frequency components and extracting only the low frequency components, the afterimage is extracted. Therefore, as the image filter device 10 for performing the spatial filter processing on the image output from the subtractor 9, for example, a median filter or a Hadamard filter 21 as shown in FIG.
And a threshold processor or a non-linear processor 22 may be used. Alternatively, although not shown, a low-pass filter process such as a smoothing process device may be used. In this way, the image having only the afterimage obtained from the image filter device 10 is added to the recursive filter image in the adder 11. However, since the afterimage is given a negative sign in the subtractor 9, the recursive image is obtained by this addition. Only the afterimage component in the filter image will be canceled (when the subtractor 9 is B-A instead of A-B, the afterimage is subtracted from the recursive filter image.
It is necessary to use a subtractor instead of the adder 11). Therefore, the afterimage included in the recursive filter image is removed, so that an image with reduced quantum noise and no afterimage can be obtained. The signal of this image is D / A
Converted to analog signal by converter 7 and TV monitor 8
Sent to A circuit for edge enhancement may be added to the output image of the adder 11 so that the image is displayed on the TV monitor 8 as an image with less blur.

【The invention's effect】

According to the image noise reduction device of the present invention, it is possible to obtain an easy-to-see image while suppressing the afterimage of a moving part while having the noise reduction effect equivalent to that of the recursive filter device.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of an image filter device, and FIG. 3 is a block diagram showing a conventional example. 1 ... X-ray tube, 2 ... Subject, 3 ... Image intensifier, 4 ... TV camera, 5 ... A / D converter, 6 ... Recursive filter device, 7 ... D / A converter, 8 ... TV monitor, 9 …
Subtractor, 10 ... Image filter device, 11, 64 ... Adder, 61,
62 ... Amplitude converter, 63 ... Image memory, 21 ... Median filter or Hadamard filter, 22 ... Threshold processing device or non-linear processing device.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G06F 15/62 390 A

Claims (1)

[Claims] 1. A recursive filter device, a subtractor for subtracting between a recursive filter image obtained from an original image through the recursive filter device and the original image, and an afterimage extracted from the image output from the subtractor. And an adder / subtractor that performs addition and subtraction of the output image of the image filter device and the recursive filter image.