JPH0647035A - Image processing system - Google Patents

Abstract

PURPOSE:To eliminate a noise while suppressing the blurring of an image caused by a motion. CONSTITUTION:This system consists of a recursive filter circuit constituted of multipliers 15, 16 an adder 17 and a frame memory 12, a noise coefficient calculating circuit for which the image data of the previous frame delayed by a frame memory 11 and the image data of the present frame are inputted and a recursive filter coefficient calculating circuit 14 for deriving a recursive filter coefficient in accordance with the noise coefficient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus suitable for performing noise removal processing on an image displayed on a television monitor in an X-ray television system.

[0002]

2. Description of the Related Art In an X-ray television system, normally, as shown in FIG.
X-rays that pass through the subject 42 are image inspectors 43
The resulting visible image is converted into a video signal by the TV camera 44, converted into a digital signal by the A / D converter 45, passed through the recursive filter circuit 46, and subjected to image processing. Image data of the D / A converter 47
Then, the signal is returned to an analog signal and sent to the television monitor device 48 to display an X-ray fluoroscopic image.

The recursive filter circuit 46 is for smoothing video data in the time direction, thereby removing image noise.

[0004]

However, in the conventional image processing by such a recursive filter circuit, if the recursive filter coefficient is increased to increase the noise removal effect, the image of a fast-moving portion is blurred. There is.

In view of the above, an object of the present invention is to provide an image processing apparatus improved so that noise can be removed while suppressing blurring of an image due to motion.

[0006]

In order to achieve the above object, in the image processing apparatus according to the present invention, the recursive filter means is compared with the image data of the current frame and the image data of the previous frame to reduce the noise of the image. It is characterized by having means for obtaining the component and motion component for each pixel, and means for controlling the recursive filter coefficient for each pixel according to these noise component and motion component.

[0007]

Since the noise component and the motion component of the image are obtained for each pixel and the recursive filter coefficient is controlled for each pixel according to these, when the motion component is small, the recursive filter coefficient of the pixel is determined. The noise removal effect can be increased by increasing the value, and on the other hand, for other pixels, when the motion component is large, the recursive filter coefficient of the pixel is decreased to give priority to preventing the blur due to the motion rather than the noise removal effect. be able to. In this way, the recursive filter coefficient is dynamically controlled for each pixel according to the noise component and the motion component obtained for each pixel, so that the noise removal effect and the prevention of the blur due to the motion can be achieved for each part of the image and for each part. It can be optimally balanced over time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an image processing apparatus according to an embodiment of the present invention. The image processing apparatus according to this embodiment is used instead of the recursive filter circuit 46 in FIG. 4, and the recursive filter coefficient is a noise. And a recursive filter circuit to which a function of dynamically controlling each pixel according to a motion state is added.

In FIG. 1, digital image data In representing the nth frame of a video signal of an X-ray fluoroscopic image is input to and stored in a frame memory 11.
The digital image data In-1 one frame before is read out and sent to the noise coefficient calculation circuit 13. The noise coefficient calculation circuit 13 stores the current digital image data In
The noise coefficient Pn (x, y) at the pixel (x, y) is also sent by the digital image data In of the current frame and the delayed digital image data In-1 of the previous frame. Is calculated.

The noise coefficient Pn (x, y) is expressed by Pn (x, y) = ΔDn (x, y) -ΔMn (x, y). Here, ΔDn (x, y) is expressed by the following mathematical formula 1,

[Equation 1] It is the average error between In (x, y) and In-1 (x, y) in the vicinity of each pixel (x, y) (template of W × W pixels).

That is, as shown in FIG. 2, ΔDn (x, y) is the pixel 32 at the position (x, y) when the position of each pixel on the screen 31 is represented by the XY coordinate system. The average error between the current frame and the frame immediately before the current frame for W × W local regions 33 in the vicinity of is obtained.

On the other hand, ΔMn (x, y) is expressed by the following mathematical formula 2,

[Equation 2] It is the difference between the average values of In (x, y) and In-1 (x, y) in the vicinity of each pixel (x, y) (template of W × W pixels).

Therefore, the noise coefficient Pn (x, y) is the difference between the average error ΔDn (x, y) and the average difference ΔMn (x, y).

Here, when there is no movement in the vicinity of the pixel (x, y), ΔMn (x, y) = 0 and Pn (x, y) = ΔDn (x, y), but ΔDn (x , Y) is a value proportional to the magnitude of random noise, so the noise coefficient Pn (x, y) is also a value proportional to the magnitude of random noise.

On the other hand, when there is motion near the pixel (x, y), ΔMn (x, y) becomes a value proportional to the amount of motion, and this is ΔDn corresponding to random noise.
Since it is subtracted from (x, y), the noise coefficient Pn (x, y) has a smaller value as the motion increases.

A noise coefficient Pn having such a property
(X, y) is sent to the recursive filter coefficient calculation circuit 14, and the recursive filter coefficient K is obtained. For example, the calculation circuit 14 has a conversion table for obtaining the recursive filter coefficient Kn (x, y) from the noise coefficient Pn (x, y). As the conversion table, a simple proportional type as shown in A of FIG. 3, a proportional type with a dead zone as shown in B of FIG. 3 and an exponential function type as shown in C of FIG. 3 are considered. To be

The recursive filter coefficient K thus obtained
From n (x, y) 1 / {Kn (x, y)} and 1-1 /
{Kn (x, y)} is obtained, and the former is sent to the multiplier 15 and digital image data In (x,
y) is multiplied, and the latter is sent to the multiplier 16 and is multiplied by the processed digital image data I′n−1 (x, y) stored in the frame memory 12 one frame before.

The outputs of these multipliers 15 and 16 are the adder 1
Digital image data I′n after being added and processed in 7
(X, y) is obtained and written in the frame memory 12.

The above operation is repeated for each pixel and each frame. The multiplier 15 multiplies the image data of the current frame by 1 / {Kn (x, y)}, and the multiplier 16 multiplies the image data after processing in the previous frame stored in the frame memory 12 by 1-1. / {Kn (x, y)}
Is repeated for each pixel and for each frame, which is exactly the function of a normal recursive filter. Here, the recursive filter coefficient Kn (x, y) is dynamically changed for each pixel and for each frame according to the noise coefficient Pn (x, y) obtained for each pixel. By such dynamic control of recursive filter coefficient, the recursive filter coefficient is increased to increase the noise removal effect in an area with large noise and small movement, and conversely, the recursive filter coefficient is increased in an area with small noise and large movement. You can make it smaller to prevent blurring due to movement.

Although the embodiment applied to the X-ray television system has been described above, it goes without saying that the image processing apparatus of the present invention can also be applied to other cases where it is necessary to remove image noise.

[0021]

As described above, according to the image processing apparatus of the present invention, the recursive filter coefficient is dynamically controlled for each pixel in accordance with the noise and the situation of the motion. Image noise can be effectively reduced while preventing blurring.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing pixels and local regions for explaining the operation of the embodiment.

FIG. 3 is a graph showing conversion characteristics between a noise coefficient P and a recursive filter coefficient K in the example.

FIG. 4 is a block diagram of a conventional example.

[Explanation of symbols]

 11, 12 Frame memory 13 Noise coefficient calculation circuit 14 Recursive filter coefficient calculation circuit 15, 16 Multiplier 17 Adder 41 X-ray tube 42 Subject 43 Image intensifier 44 Television camera 45 A / D converter 46 Recursive filter circuit 47 D / A converter 48 TV monitor device

Claims (1)

[Claims] 1. A recursive filter means, a means for obtaining a noise component and a motion component of an image for each pixel by comparing the image data of the current frame and the image data of the previous frame, and the noise component and the motion component An image processing apparatus according to claim 1, further comprising means for controlling the recursive filter coefficient for each pixel.