JPH0647036A - Image processing system - Google Patents

Abstract

PURPOSE:To suppress the blurring of an image caused by a motion, and also, to effectively eliminate noises extending over the whole of a screen. CONSTITUTION:From the image data of the present frame, a recursive filter coefficient at every picture element is controlled in accordance with average luminance in the vicinity of its picture element and also, in accordance with a motion coefficient derived from a relation between the image data of the previous frame and the present frame, the image data from a space filter processing circuit 21 are switched by a switching circuit 20.

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, a noise removing effect is uniformly generated in a bright place and a dark place of the image, and therefore, the effective noise removing is practically performed. There is a problem that you cannot do it. That is, the image pickup tube of the television camera has a characteristic that a lot of noise is present in a dark portion and the noise is conspicuous. Nevertheless, even in a dark place, noise is removed to the same extent as in a bright place. Noise in dark places cannot be removed effectively.

In addition, conventionally, there is another problem that an image is blurred when there is motion. That is, since the image processing by the recursive filter is smoothing of the image data in the time direction, if the recursive filter coefficient is increased to increase the noise removal effect, the image of a fast-moving portion is blurred.

In view of the above, the present invention enhances the noise removal effect in the dark portion of the image and reduces the noise removal effect in the bright portion to suppress the blurring of the image. An object of the present invention is to provide an image processing apparatus capable of obtaining an image having a uniform S / N ratio without blur.

[0007]

In order to achieve the above object, in the image processing apparatus according to the present invention, the recursive filter means and the recursive filter coefficient for each pixel from the image data of the current frame are used as the average luminance in the vicinity of the pixel. According to the motion component of each pixel obtained from the relationship between the image data of the current frame and the image data of the previous frame, It is characterized by having means for using spatially filtered data.

[0008]

The average brightness in the vicinity of a certain pixel is obtained, and the recursive filter coefficient for the pixel is controlled according to the average luminance. As a result, the recursive filter coefficient can be increased in the dark portion of the image to enhance the noise removal effect. On the other hand, in the bright portion of the image, noise is originally small, so that the recursive filter coefficient is reduced to reduce the noise removal effect and the blurring of the image due to motion is prevented. Further, when the movement becomes large, the recursive filter processing, which is the processing in the time direction, is changed to the processing in the spatial direction, and the noise is removed by the processing in the spatial direction while preventing the image from being blurred due to the movement.

[0009]

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 in place of the recursive filter circuit 46 in FIG. Each of them comprises a recursive filter circuit to which a dynamic control function is added, a noise removal processing circuit in the spatial direction, and a switching circuit for switching these circuits.

In FIG. 1, digital image data In representing the nth frame of a video signal of an X-ray fluoroscopic image is input to a local average value calculation circuit 13, and the local average value Mn (x, y) in each pixel (x, y). y) is calculated. As shown in FIG. 2, this local average value Mn (x, y) is obtained by comparing the pixel 32 at the position (x, y) in the screen 31 with W pixels × W pixels in the vicinity thereof. It is an addition average value (average brightness) of the pixel data of the local region 33 extracted by the template, and is represented by the following mathematical formula 1.

[Equation 1]

This local average value Mn (x, y) is sent to the recursive filter coefficient calculation circuit 15 to obtain an appropriate recursive filter coefficient Kn (x, y) for each pixel. That is, this recursive filter coefficient calculation circuit 1
5 has a conversion table for obtaining the recursive filter coefficient Kn (x, y) from the local average value Mn (x, y). This conversion table is of a simple inverse proportional type as shown in A of FIG. It is desirable to select an inverse proportional type with dead zone as shown by B in FIG. 3 and an inverse exponential type as shown by C in FIG.

The recursive filter coefficient K thus obtained
From n (x, y) 1 / {Kn (x, y)} and 1-1 /
{Kn (x, y)} is obtained, the former is sent to the multiplier 17, and the digital image data In (x,
y) is multiplied, and the latter is sent to the multiplier 18 and is multiplied by the processed digital image data I′n−1 (x, y) of one frame stored in the frame memory 12.

The outputs of these multipliers 17 and 18 are the adder 1
Digital image data I'n after addition and processing in 9
(X, y) is obtained and written in the frame memory 12. The function of the recursive filter is achieved by repeating the above operation for each pixel and for each frame.

Thus, the recursive filter coefficient Kn
Since (x, y) is small when the local average value Mn (x, y) is large and is large when the local average value Mn (x, y) is small, the noise removing effect is small in a bright portion, The noise removal effect becomes large in the dark part. Generally, bright areas have less noise, while dark areas have more noise, so by varying the degree of noise removal effect according to the brightness, it is possible to respond to the original noise level. This makes it possible to obtain a uniform S / N ratio on the entire surface of the image.

On the other hand, the frame memory 11 stores the image data of each frame and outputs the image data of the immediately preceding frame. That is, the image data In-1 one frame before the current image data In of the nth frame is obtained from the frame memory 11 with a delay of one frame. This image data In-
1 is input to the local average value calculating circuit 14 having the same configuration as the above-mentioned local average value calculating circuit 13, and the local average value Mn−
1 (x, y) is obtained.

The local average values Mn (x, y) and Mn-1 (x, y) from these local average value calculation circuits 13 and 14 are
It is sent to the motion coefficient calculation circuit 16. The motion coefficient calculating circuit 16 calculates the motion coefficient ΔMn (x, y) for each pixel by ΔMn (x, y) = Mn (x, y) −Mn−1 (x, y). This motion coefficient ΔMn (x, y) is calculated as pixel (x,
It shows the temporal change of the local average value Mn (x, y) for y), and has a strong correlation with the movement of the subject image near that pixel.

The motion coefficient ΔMn (x,
The switching circuit 20 is switched according to y). That is, when the motion coefficient ΔMn (x, y) exceeds a predetermined threshold value, the switching circuit 20 is switched from the frame memory 12 side to the spatial filter processing circuit 21 side. The spatial filter processing circuit 21 performs spatial filter processing such as convolution processing on the image data In of the current n-th frame with a template of N pixels × N pixels, and smooths the image in this frame in the spatial direction. The obtained image data is obtained.

The image data from the spatial filter processing circuit 21 is sent to the multiplier 18 instead of the image data from the frame memory 12 by the switching of the switching circuit 20. Therefore, when the motion becomes larger than a certain amount, the process in the time direction is switched to the process in the space direction, and it is possible to remove noise without blur due to the motion.

It should be noted that, when the movement becomes larger than a certain level, the processing in the time direction is not completely switched to the processing in the spatial direction by the switching circuit 20, but the processed image in the temporal direction and the processed image in the spatial direction are not changed. It is also possible to gradually change the ratio with. That is, a weighting addition circuit (not shown) for weighting and adding the image data from the frame memory 12 and the image data from the spatial filter processing circuit 21 is provided instead of the switching circuit 20,
This weighting addition circuit is controlled according to the motion coefficient ΔMn (x, y), and the weight of the image data from the spatial filter processing circuit 21 is increased as the motion coefficient ΔMn (x, y) increases.

Further, 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 for each pixel is dynamically controlled according to the brightness of the image to enhance the noise removal effect in a dark area with a lot of noise. , The noise removal effect is reduced in bright and originally low noise areas to prevent blurring due to motion, and the spatially processed data is used when motion is large, which results in dark and fast moving areas. However, it is possible to remove noise without blur due to motion, and it is possible to obtain an image having a uniform S / N ratio without blur due to motion on the entire screen.

[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 a conversion characteristic between a local average value M 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, 14 Local average value calculation circuit 15 Recursive filter coefficient calculation circuit 16 Motion coefficient calculation circuit 17, 18 Multiplier 19 Adder 20 Switching circuit 21 Spatial filter processing circuit 41 X-ray tube 42 Subject 43 Image intensity Fire 44 TV 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 controlling a recursive filter coefficient for each pixel from image data of a current frame according to an average luminance in the vicinity of the pixel, and a means for spatially filtering the image data of the current frame. ,
An image processing apparatus comprising: means for using the above spatial filtering processing data according to a motion component for each pixel obtained from the relationship between the image data of the current frame and the image data of the previous frame.