JPH04115673A - Picture processor - Google Patents

Abstract

PURPOSE:To improve an S/N by detecting the movement of a picture from the mutual comparison of an original picture, a recursive filter processing image and a time moving average processing image, switching and outputting the recursive filter processing image and the time moving average processing image every respective picture elements. CONSTITUTION:The output picture (original picture) of an A/D converter 5 is defined as (a), the output picture of a recursive filter processing circuit is defined as (b) and the output picture of a moving average processing circuit is defined as (c). An original picture (a) and a picture (b) are inputted to a comparator 16, besides, the picture (b) and a picture (c) are inputted to a comparator 17, outputs (d) and (e) of the comparators 16 and 17 are inputted to a detector 18 and it is detected whether the (d) and the (e) are same or not. A multiplexer 15 selects the picture (b) when the detected result of the detector 18 is the same and selects the picture (c) when it is not the same and a selected picture (f) returned to an analog signal through a D/A converter 19 and is displayed by a monitor television 20. Thus, noise is reduced on the moving picture and an S/N is improved.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image processing device, and particularly to an image processing device that reduces noise in an image.

[Conventional technology]

A recursive filter is usually used to reduce image noise. This recursive filter can achieve a great noise reduction effect when the image is still, but when the image is moving, an afterimage occurs, and the image of the moving object moves with a trail. The result is an image that looks like there is someone there. Therefore, conventionally, the motion of an image of a moving object is detected, and in order to suppress afterimages, the coefficient of a recursive filter is controlled to be close to 1 so that the image becomes close to the original image. There are cases where the coefficients of the recursive filter are controlled by detecting motion for each pixel, and cases where the coefficients of the recursive filter are uniformly controlled for all pixels on the entire screen.

[Problem to be solved by the invention]

However, simply controlling the coefficients of the recursive filter in this way causes problems such as a decrease in the S/N ratio. In other words, when detecting movement for each pixel and controlling the coefficients of the recursive filter, pixels with a lot of movement will approach the original image, and the S/N ratio will drop significantly compared to pixels with little movement. do. Moreover, this difference in the S/N ratio between pixels appears on the image and looks like an afterimage, or only noise becomes noticeable. Furthermore, if the coefficients of the recursive filter are uniformly controlled for all pixels on the entire screen, the coefficients of the recursive filter will approach 1 for the entire screen in frames with rapid movement, resulting in almost no noise reduction effect.
The S/N ratio will decrease. In view of the above, the present invention provides an image processing device that can improve the S/N ratio even for moving images while suppressing afterimages of moving images and suppressing deterioration of resolution due to movement. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the image processing device according to the present invention includes means for performing recursive filter processing on the original image, means for performing temporal moving average processing on the original image, and means for performing a temporal moving average processing on the original image. Image movement is detected by comparing the image with the recursive filter process and the temporal moving average process image, and the recursive filter process image and the temporal moving average process image are calculated for each pixel according to the detection results. It is characterized by having means for switching and outputting each time.

[For production]

Both recursive filter processing and temporal moving average processing can provide a noise reduction effect. However, for moving images, in the former case the afterimage falls quickly but lasts for a long time, while in the latter case the afterimage falls slowly but disappears in a short time. Therefore, it can be said that the former has good resolution for motion but poor afterimage characteristics, and the latter has poor resolution for motion but good afterimage characteristics. Therefore, by switching between the recursive filter processed image and the temporal moving average processed image for each pixel according to the movement, it is possible to take advantage of the characteristics of each and compensate for the drawbacks. As a result, it is possible to suppress the afterimage of a moving image, suppress a decrease in resolution with respect to the movement, reduce noise in a moving image, and improve the S/N ratio.

【Example】

Hereinafter, an embodiment in which the present invention is applied to noise reduction of X-ray TV images will be described in detail with reference to the drawings. In FIG. 1, from X-ray tube 1 to X! ! is subject 2
The X-rays are irradiated toward the object 2 and transmitted through the subject 2, and then enter the image intensifier 3. The incident X-ray image is converted into an optical image in the image intensifier 3, and the optical image is converted into a video signal by the TV right camera. This video signal is converted into a digital signal by an A/D converter 5, and then sent to a cursive filter processing circuit, which is comprised of a look-up table 6.7, an adder 8, and a frame memory 9. The lookup table 6.7 is a pixel value conversion circuit composed of, for example, ROM or RAM, and the lookup table 6 converts the pixel value to 1/K, and the lookup table 7 converts the pixel value to 1-1/K. converted. This K is a coefficient of the recursive filter. Further, the output of this A/D converter 5 is input to a moving average processing circuit constituted by a large number of frame memories 10, 11, 12, an adder 13, and a divider 14. Frame memories 10, 11, and 12 store the images of several previous frames, and the adder 13 adds the images of these multiple frames and the image of the current frame, and then the number of frames added. Moving average processing is performed by dividing by n. n is the number of integrated sheets to be moved. Let a be the output image (original image) of the A/D converter 5, b be the output image of the recursive filter processing circuit, and C be the output image of the moving average processing circuit. A comparator 16 compares the original image a and the image
are input and these comparisons are made. Here, it is assumed that the output d of the comparator 16 is + (plus) when a is larger than b, and - (minus) when a is smaller than b. Further, the image C and the image C are input to the comparator 17, and the two are compared. The output e of this comparator 17 is +(plus) when b is larger than C, and -( when b is smaller than C).
minus). The outputs d and e of the comparators 16 and 17 are input to the detector 18, which detects whether d and e are the same. The multiplexer 15 operates based on the detection result of the detector 18, and selects image C if they are the same, and selects image C if they are not the same. The image f selected in this way is returned to an analog signal via the D/A converter 19, and is sent to the monitor television 20.
is displayed. Here, a case where a bright object moves and a case where a dark object moves will be specifically explained with reference to FIG. 2. The video signal of one scanning line of the original image a is shown as A in FIG. 2, and it is assumed that this moves in the direction of the arrow (to the left) as the object moves to the right. When the coefficient K of the recursive filter is set to 2, the output image of the recursive filter processing circuit becomes as shown in FIG. 2B. Further, when the moving integral number n is 3, the output image C of the moving average processing circuit becomes as shown in FIG. 2C. Therefore, the output signals d and e of the comparators 16 and 17 are respectively in the second diagram. It will change like E. Then, if d and e are the same, the image is selected, but if they are different, the image C is selected, so the output image f of the multiplexer 15 becomes as shown in FIG. 2F. Therefore, the afterimage falls earlier (than the moving average processed image @C) and disappears earlier than the moving average processed image C (than the recursive filter processed image). Become,
Image tailing is further reduced, and afterimages are suppressed. Since the afterimage falls quickly, it is possible to prevent a decrease in resolution for movement. This is true even when a dark object is moving. This can be easily understood by inverting black and white. In the case of recursive filter processing, the improvement effect of the S/N ratio is 101og(2K -1> [dB], and in the case of moving average processing, it is l Q logn [dB]. Therefore, as described above, If n is determined, the same S/N ratio improvement effect will be obtained, and even if each pixel is switched to either image, the S/N ratio will not change, and the image will have a uniform S/N ratio. In general, it is desirable to set n so that the S/N ratio improvement effect is the same for recursive filter processing and moving average processing, but depending on the image (for example, when moving In some cases, it is better not to be equal (depending on the speed and brightness). Also, in the above example, the 2 input using comparators 16 and 17
Although two images are compared, it is of course possible to calculate the difference value between them.

【Effect of the invention】

According to the image processing device of the present invention, the S/N ratio is improved by taking advantage of the noise reduction effect of recursive filter processing and the noise reduction effect of temporal moving average processing, and the resolution of recursive filter processing with respect to movement is improved. It is possible to take advantage of the advantages of good afterimage characteristics for images with movement due to temporal moving average processing. As a result, as well as suppressing afterimages for moving dragons, it also prevents the resolution from decreasing due to movement.3. /N
An image with improved ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a time chart for explaining the operation. 1...XT tube, 2...Subject, 3...Image intensifier, 4...TV right camera 5...A/
D converter, 6.7... Lookup table, 8.1
3... Adder, 9. 10-12... Frame memory, 14... Divider, 15... Multiplexer, 16
．． 17...Comparator, 18...Detector, 19...D
/' A converter, 2o...Monitor TV.

Claims (1)

[Claims] (1) Means for performing recursive filter processing on the original image, means for performing temporal moving average processing on the original image, substantial original image, recursive filter processed image, and temporal moving average processed image The invention is characterized by comprising means for detecting movement of the image from a mutual comparison with the image, and switching and outputting a recursive filter-processed image and a temporally moving average-processed image for each pixel according to the detection result. Image processing device.