WO1998011718A1 - Procede pour la reduction du bruit d'un signal image - Google Patents

Procede pour la reduction du bruit d'un signal image Download PDF

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Publication number
WO1998011718A1
WO1998011718A1 PCT/DE1997/001859 DE9701859W WO9811718A1 WO 1998011718 A1 WO1998011718 A1 WO 1998011718A1 DE 9701859 W DE9701859 W DE 9701859W WO 9811718 A1 WO9811718 A1 WO 9811718A1
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WO
WIPO (PCT)
Prior art keywords
image signal
input
signal
images
delayed
Prior art date
Application number
PCT/DE1997/001859
Other languages
German (de)
English (en)
Inventor
Aishy Amer
Hartmut Schröder
Udo Bremer
Original Assignee
Siemens Aktiengesellschaft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Aktiengesellschaft filed Critical Siemens Aktiengesellschaft
Publication of WO1998011718A1 publication Critical patent/WO1998011718A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/21—Circuitry for suppressing or minimising disturbance, e.g. moiré or halo

Definitions

  • the invention relates to a method for noise reduction of an image signal according to the preamble of patent claim 1.
  • the object of the invention is to provide a method for noise reduction of an image signal, which provides better results when there is movement in the image signal.
  • the image content of images of the feedback image signal is converted to the movement phase of the images of the input image signal using motion vectors.
  • the detection areas created by the movement are replaced in the feedback path by image portions of the input image, which are subjected to a local noise reduction.
  • an incorrect movement determination is taken into account.
  • smaller errors lead to a disproportionately larger weighting factor k, that is to say a disproportionately higher weighting of the input path compared to the feedback path.
  • a fallback mode is provided in which only the image on the input side is locally reduced in noise.
  • the method works in a motion vector error-tolerant manner with non-linear filter control and a non-linear fallback mode which is influenced by the threshold value.
  • To correct the motion vector field it is advantageous to carry out a homogenization of the motion vectors within the moving object. If the original and homogenized motion vector is used in parallel, two vectors are optionally available, of which the one that delivers the lower error is selected for motion compensation.
  • FIG. 1 shows a circuit diagram for carrying out the method according to the invention
  • Figure 2 characteristic curves for the reduction factor k and F igur 3 is a diagram considering a homogenization ⁇ overbased motion vector.
  • the basic circuit diagram of FIG. 1 has an input connection 1, to which an image signal S is fed, the
  • the image signals S, G comprise a sequence of images, for example zeilenver- k ammten fields or frames for noise reduction, a recursive filtering is performed.
  • This means that the output signal G - as described in more detail below - is delayed frame-wise and is linked to the input channel by means of an adder 3.
  • the fed-back image signal is weighted in a multiplier 4 with the factor 1-k, the signal S in the input channel is weighted in a multiplier 5 with the factor k. By changing k, the relation of the input path to the feedback path is set.
  • a memory device 20 is provided for the image-wise delay of the noise-reduced image signal G on the output side within the feedback loop.
  • the embodiment shown relates to image signals S, G with interlaced fields.
  • the device 20 then has two field memories 21, 22 which are connected in series n rows.
  • the image memory 22 then contains a field delayed twice by one field duration, which is supplied as the image signal G * via a connection 23 to the multiplier 4 of the feedback path.
  • the fields fed back to adder 3 for linking have the same raster position in comparison to the field S on the input side.
  • the fed back fields are motion-compensated depending on the existing movement.
  • the motion information is onnection at a A 7 fed.
  • a signal D is present at connection 7, which contains a motion vector field for the input field.
  • T his means that for each pixel the displacement rela t iv to the position of the corresponding Jardinpu kts is indicated in the previous field.
  • Motion vector fields can be obtained in various conventional ways. For example, a motion vector field can be determined on the receiver side by forming the spatial difference of the pixels of two fields.
  • the motion vector field can, however, also be transmitted on the transmitter side, which is the case in particular in the case of motion-based coding methods by means of prediction, for example according to the MPEG standard.
  • the motion vector field can contain a motion vector for each pixel or for image blocks composed in blocks. The former variant is used in the exemplary embodiment.
  • detection areas which result from the different movement of objects in an image are taken into account in the method according to the invention. If there is a detection area, this is indicated by a corresponding identifier for each pixel or for each block by a signal F at connection 6.
  • the motion compensation i.e. the conversion of the feedback signal G to the movement phase on the input side by means of the motion vectors present in the motion vector field is carried out by means of the image memories 21, 22.
  • Pixels m as a function of the displacement vectors in the vector field D.
  • the image memory is written nonlinearly with the pixels of the noise-reduced output signal G to be compensated as a function of the respective displacement vectors of the vector field D.
  • the pixels are written to the position in the image memory that is assigned to them by the motion vector.
  • the motion compensated t en image points are read out linearly.
  • the image memory therefore has a partial image memory 21a which is designed as an image memory with random access.
  • the large beta e of this section is determined by the maximum possible V ektorverschiebung.
  • a memory part 21b is provided which can be linearly addressed.
  • the image memory 22 is organized accordingly.
  • a multiplexer 24 or 25 is provided on the output side of the image memories 21, 22.
  • the output of the respectively assigned image memory and correspondingly prepared pixels of the input image signal S are fed to the multiplexer.
  • the switching control of the multiplexers 24, 25 takes place by means of the signal F m as a function of the detection areas. If there is a detection area, the pixels of this detection area are filled with pixels from the preferably locally noise-reduced input image S.
  • the pixels fed to the multiplexer 25 at the connection 26 are already in the correct grid.
  • the pixels supplied to the multiplexer 24 at the connection 27 are to be converted by a linear raster interpolation 28 to the raster of the field read out from the image memory 21. For raster interpolation, averaging of the image lines immediately adjacent to the image line to be generated is expediently suitable.
  • the pixel signals fed to the raster interpolation 28 or the connection 26 are preferably generated from the input signal S by a local noise reduction 29. In contrast to a temporal feedback, this noise reduction only works locally within a single field of the input signal S. It is expedient to calculate a centrally weighted average value with pixels of a neighborhood including the pixel currently being viewed that are homogeneous with the input pixel.
  • the neighborhood pixels are those in horizontal, vertical and in two diagonal directions ver t ei t l are. If the absolute difference of a neighboring point b i ld of a neighborhood to the central center pixel within a predetermined Wert Schl ⁇ is, this means that this neighbor pixel not beyond an edge l IEGT It is called homogeneous.
  • the two Nachbarsent- points are homogeneous and that of the homogeneity is optimum for all four directions with respect to this direction ge f reasons, so ng the neighboring sheep m that direction ex- pandiert until either a maximum defined size of the
  • Neighbor sheep or an inhomogeneity is achieved. Those pixels that lie within the expansion range in the direction found are center-weighted If no direction is found to be homogeneous, the neighborhood is searched for as large a number of similar points as possible and these are averaged with the weighted current point If no homogeneous neighboring point is found, the current input image point is output unchanged from the device 29 so that the sharpness of the image is not reduced.
  • the central weighting of the image points is expediently carried out as a function of an estimated noise power described below.
  • a device 30 takes account of incorrect motion vectors in order to reduce their negative effects on the image quality.
  • An error measurement is carried out by determining the difference between the field on the input side and the feedback, motion-compensated field G * at the output 23 of the memory device 20 in a subtractor 31.
  • the difference signal is rectified in a device 32 and smoothed in a low-pass filter 33, on which the error signal V to be processed is present on the output side. Since the input image signal as the reference signal is subject to the noise disturbance to be reduced, the deviation becomes zwec preferably not k separately for each pixel, son ⁇ d ren picture b ereichrii determined.
  • the area is central to those pixel to be arranged, the noise is reduced just we d.
  • the measurement of the deviation takes place as a linear development center-he d values of the differences between the Referenzsentpun kt s and the collocated compensated pixels.
  • the error signal V is evaluated in a device 34 with a characteristic curve. The weighting factors k and 1-k result from this. Since the measured deviation only depends on the image signals themselves, motion vector errors are only corrected if there is a pixel error. Motion vector errors that do not produce a pixel error have no visible effect.
  • the characteristic curve formed in block 34 is expediently also made dependent on the noise power contained in the input image sequence S.
  • the amplitude of the evaluation characteristic curve of block 34 must be adjusted.
  • a device 35 therefore carries out a noise level estimation with respect to the input image signal S. Homogeneity considerations are carried out, the pixels lying within a neighborhood being regarded as the more homogeneous the less the amplitude of the neighboring pixels deviate from the center pixel. The homogeneity measures determined in this way for a large number of smaller neighborhoods are then summed up and standardized within a larger neighborhood. The larger neighborhood that was determined to be the most homogeneous is used to calculate the noise power contained.
  • the characteristic curve is made dependent on the noise level estimate determined in this way.
  • V mapping rule
  • FIG. 2 shows two curve curves 34b and 34c which are different depending on the noise level estimate.
  • the block 34 executes the characteristic curve shown in FIG. 2, a reduction factor k being taken directly from an input value of the error! Signal V by means of the noise-dependent characteristic curves 34a, b, c.
  • a fallback mode is advantageously provided. This is activated when the error signal V exceeds a threshold value. Then, instead of the temporally noise-filtered signal output by the adder 3, the locally noise-filtered signal output by the device 29 is switched through to the noise-reduced image signal G at the output 2.
  • a multiplexer 40 is provided, to which the output of the adder 3 or the output of the device 29 is alternatively fed and which is connected on the output side to the connection 2.
  • the multiplexer 40 is controlled by a threshold detector 41, to which the error signal V is fed.
  • the threshold value detector 41 is preferably also controlled by the detection signal F. If the error signal V exceeds the threshold value within a detection range, the temporally noise-reduced signal is nevertheless preferred and the output of the adder 3 is switched through in the multiplexer 40. This takes into account that the high error indicated by the error signal V is essentially due to the local noise reduction in the detection area.
  • the motion-compensated image storage device 20 can also be designed for the temporary storage and motion compensation of progressive images.
  • the image memories 21, 22 are connected in parallel, in that the image memory 21 receives the upper half of the progressive image, the image memory 22 the lower half of the progressive image.
  • a raster interpolation 28 is not required.
  • the image of the input image signal S just processed is bmarized, that is to say the brightness pixel values of the corresponding input image are compared with a threshold value, so that a binar image is generated.
  • the binarization is not sensitive to noise.
  • Edges are determined from the binary image by a shape-preserving edge detection. The edges are then linked together to form closed contours. Objects can be reconstructed from this.
  • An output signal generated by the reconstruction indicates the object affiliation of the pixels of a neighborhood of the current pixel to the object to which this current pixel belongs.
  • the majority of motion vectors within an object can be assumed to be correct and it can be expected that only some of the motion vectors are defective, especially in the peripheral areas of objects, the minority of incorrect vectors can be corrected without error if they refer to the majority motion vector within the Object boundaries adjusted, eg replaced.
  • the reliability of determining a correct majority motion vector decreases. Faulty vectors can be determined by object-based vector homogenization because, for example, a faulty majority vector is calculated on the basis of a too small object size. It is therefore advisable to use an error signal both for a motion vector that is actually fed with the motion compensated image and for an image motion compensated with the majority motion vector.
  • the motion-compensated image signal that supplies the minimum error signal is used for the time filtering for feedback.
  • FIG. 3 A circuit section taking into account the use of a homogenized motion vector is shown in FIG. 3.
  • the motion-compensated memory 40 which corresponds to the memory 20 in FIG. 1, generates two motion-compensated output image signals G * 1, G * 2, one of which is motion-compensated according to FIG. 1 by the motion vector field D, the other by the homogenized motion vector DH.
  • devices 41, 42 which correspond to elements 31, 32, 33 of FIG. 1, an error signal VI or V2 is calculated in each case by forming the difference with the image signal S on the input side.
  • the minimum error signal which corresponds to the error signal V of FIG. 1 and is supplied to the movement device 34 is determined in a device 43 from the error signals VI, V2.
  • a switch 44 is controlled, which forwards that of the image signals G * l, G * 2 as signal G * to the recursive filter 3, 4, 5, which has provided the minimum of the error signals VI and V2.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Picture Signal Circuits (AREA)

Abstract

Procédé pour la réduction du bruit d'un signal image au moyen d'un filtre récursif (3, 4, 5), dans lequel le signal image réinjecté (G*) est transféré, avec support du vecteur déplacement, sur la phase déplacement du signal image à l'entrée (S). Avantageusement, lors d'erreurs de transfert, la récursion est réduite (k, 1-k). Une réduction locale du bruit (29) est prévue pour des domaines de détection et pour un mode relâchement.
PCT/DE1997/001859 1996-09-11 1997-08-27 Procede pour la reduction du bruit d'un signal image WO1998011718A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE1996136952 DE19636952C2 (de) 1996-09-11 1996-09-11 Verfahren zur Rauschreduktion eines Bildsignals
DE19636952.5 1996-09-11

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WO1998011718A1 true WO1998011718A1 (fr) 1998-03-19

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KR100687645B1 (ko) 2002-06-25 2007-02-27 마쯔시다덴기산교 가부시키가이샤 움직임 검출 장치 및 그것을 이용한 잡음 제거 장치
DE102004060829B4 (de) * 2004-12-17 2013-02-28 Entropic Communications, Inc. Verfahren und Vorrichtung zur Reduktion von Rauschen in einem Bildsignal

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JPS5537018A (en) * 1978-09-08 1980-03-14 Nippon Hoso Kyokai <Nhk> Moving correction noise lowering system
US4296436A (en) * 1978-08-21 1981-10-20 Hitachi, Ltd. Noise reducing system
US4500911A (en) * 1981-05-25 1985-02-19 Nippon Hoso Kyokai Noise reduction apparatus
DE4221236A1 (de) * 1992-06-27 1994-01-05 Thomson Brandt Gmbh Verfahren und Vorrichtung zur Rauschreduktion für Videosignale
JPH07288719A (ja) * 1994-04-18 1995-10-31 Kokusai Denshin Denwa Co Ltd <Kdd> 動き適応型雑音除去フィルタおよびこれを用いた動き補償フレーム間符号化装置

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EP0581059B1 (fr) * 1992-07-31 1997-09-24 Siemens Aktiengesellschaft Procédé et appareil de réduction de bruit d'un signal TV ou vidéo
JPH06121192A (ja) * 1992-10-08 1994-04-28 Sony Corp ノイズ除去回路
US5510856A (en) * 1994-12-30 1996-04-23 Daewoo Electronics Co., Ltd. Apparatus for determining motion vectors

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US4296436A (en) * 1978-08-21 1981-10-20 Hitachi, Ltd. Noise reducing system
JPS5537018A (en) * 1978-09-08 1980-03-14 Nippon Hoso Kyokai <Nhk> Moving correction noise lowering system
US4500911A (en) * 1981-05-25 1985-02-19 Nippon Hoso Kyokai Noise reduction apparatus
DE4221236A1 (de) * 1992-06-27 1994-01-05 Thomson Brandt Gmbh Verfahren und Vorrichtung zur Rauschreduktion für Videosignale
JPH07288719A (ja) * 1994-04-18 1995-10-31 Kokusai Denshin Denwa Co Ltd <Kdd> 動き適応型雑音除去フィルタおよびこれを用いた動き補償フレーム間符号化装置
US5568196A (en) * 1994-04-18 1996-10-22 Kokusai Denshin Denwa Kabushiki Kaisha Motion adaptive noise reduction filter and motion compensated interframe coding system using the same

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DE19636952A1 (de) 1998-03-12

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