Television – Image signal processing circuitry specific to television – Noise or undesired signal reduction
Reexamination Certificate
1997-07-24
2001-03-20
Kostak, Victor R. (Department: 2711)
Television
Image signal processing circuitry specific to television
Noise or undesired signal reduction
C382S275000
Reexamination Certificate
active
06204891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the temporal filtering of the noise in an image of a sequence of digital images as well as to a device for carrying out this method.
The invention can be used notably for the processing of medical images formed in an X-ray fluoroscopy mode by means of a system which utilizes a low-intensity X-ray beam and produces a sequence of noisy digital images of low contrast which must be filtered so as to remove the noise without degrading the details.
The temporal filtering operation consists in smoothing, as a function of time, a monodimensional signal which is referred to as a temporal signal and consists of the digitized intensity values of a pixel having a given location in the images of the sequence.
2. Description of Related Art
A temporal filtering method of this kind is already known from the publication by R. E. KALMAN entitled “A new approach to linear filtering and prediction problems”, published in “Transactions of the ASME”, Journal of Basic Engineering, Series 82D, pp. 35-45, 1960.
Kalman filtering is defined by a recursive equation which yields the filtered intensity of a current pixel of an image of the sequence as a function of hypotheses made a priori, as a function of the intensity of the pixel having the same location in the preceding image of the sequence, and as a function of a factor which is called a Kalman gain.
This equation can lead to several recursive algorithms. In one of these algorithms the Kalman gain is a function of the difference between the noisy intensity observed at a given instant and the filtered intensity observed at the preceding instant for a pixel of given location. If an intensity discontinuity occurs due to a movement or a noise peak, therefore, the temporal signal is smoothed ahead of the discontinuity, but not after the discontinuity. Therefore, this algorithm is not suitable for dealing with this type of intensity discontinuity.
It is a problem that, due to the very low intensity of the fluoroscopic X-ray beam, the images of the sequence are extremely noisy and frequently contain noise peaks.
It is another problem that, due to the fact that each image of the sequence is separated from the next image by a small time interval, an important event, for example the displacement of a small tool such as a catheter, may occur from one image to another. The filtering of the image in which the movement of this small object occurs should not distort or erase this object.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a temporal filtering method for the reduction of the noise in the successive images of a sequence of digital images, which method:
operates strictly in real time, which means that it produces the filtered current image as from the appearance of said current image observed, immediately and without image delay, irrespective of the image rate in the sequence;
is capable of eliminating the noise peaks;
does not erase or distort the small objects in motion.
The problem of real-time elimination of noise peaks is solved by means of a method for the temporal filtering of the noise wherein at a given pixel location a combination is formed of a temporally filtered sample of the last instant but one, whereto a first weight has been assigned, and a noisy sample of the last instant modified by a second weight which is a function of a probability value concerning absence of a noise peak in this sample. The problem of eliminating the noise without distorting the small objects in motion is solved by means of such a method. Further, a device for carrying out this filtering method offers the advantage that it can be simply put into operation and that it provides, strictly and exactly in real-time, effective temporal noise filtering with suppression of the noise peaks.
REFERENCES:
patent: 4682230 (1987-07-01), Perlman et al.
patent: 4807033 (1989-02-01), Kusen et al.
patent: 4897724 (1990-01-01), Veldhuis
patent: 5142537 (1992-08-01), Kutner
patent: 5414472 (1995-05-01), Hwang
patent: 5442407 (1995-08-01), Iu
R.E. Kalman, “A New Approach to Linear Filtering and Prediction Problems”, published in “Transactions of the ASME”, Journal of Basic Engineering, Series 82D, pp. 35-45, 1960.*
Ari Nieminen et al, “A New Class of Detail Preserving Filters for Image Processing” in IEEE Transactions on Patterns Analysis and Machine Intelligence, Vol. PAI9, No. 1, Jan. 1987.
Kostak Victor R.
Renfrew Dwight H.
U.S. Philips Corporation
LandOfFree
Method for the temporal filtering of the noise in an image... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the temporal filtering of the noise in an image..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the temporal filtering of the noise in an image... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467450