Abstract: This invention presents an approach to first estimate a depth/disparity map using spectrally coded plenoptic camera, and then based on the disparity map the parallax between different spectral channels is rectified. Based on our new technique, we can reconstruct not only multispectral images but also a depth/disparity map. Moreover, the quality of reconstructed spectral images is significantly improved using our parallax rectification.

Abstract: Devices, systems, apparatuses, methods, and other embodiments associated with bit resolution enhancement are described. In one embodiment, an apparatus includes logic configured to produce a high-resolution pixel from a low-resolution pixel. The apparatus includes logic configured to classify the high-resolution pixel as being in a smooth region of an image based on at least one of a gradient value and a variance value associated with the low-resolution pixel. The apparatus includes logic configured to selectively re-classify the high-resolution pixel as not being in the smooth region of the image based on a set of neighboring high-resolution pixels associated with high-resolution pixel. The apparatus includes logic configured to selectively filter the high-resolution pixel based on whether the high-resolution pixel remains classified as being in the smooth region of the image.

Abstract: A band processing circuit which generates image signals corresponding to different frequency bands from an image signal in which signals corresponding to different colors are arranged and which suppresses noise by synthesizing the image signals of the different frequency bands, a sampling circuit which generates image signal corresponding to the colors by sampling the image signal input from the band processing circuit in accordance with a predetermined arrangement, and a luminance/color generation circuit which generates a luminance signal in which aliasing is suppressed using an image signal output from the sampling circuit.

Abstract: Current output pictures of video data are generated utilizing a motion compensated (MC) blended picture and a corresponding non-MC blended picture of the video data. Windows of picture data from a first picture and MC windows of picture data from a MC previously output picture may be partitioned. The partitioned widows are compared and the first picture is blended with the MC previously output picture based on the comparison to, for example, reduce noise and prevent motion trail artifacts. Non-MC windows of picture data from a MC or non-MC previously output picture may be partitioned and compared with the windows of picture data from the first picture. The first picture may be blended with the MC or non-MC previously output picture based on the comparison to reduce motion trail artifacts. A blending factor is determined and utilized to blend the blended pictures to reduce noise and prevent motion artifacts.

Abstract: Some embodiments of the invention provide a media-editing application that performs frame rate conversion detection on a video. For a video that has been converted from one frame rate and format to another frame rate and format, the application detects the conversion method that has been used in the conversion of the video. Some embodiments perform this frame rate conversion detection by detecting patterns of repeating fields and/or frames in a video sequence created by the different conversion processes. Some embodiments compute (i) a frame difference value for each consecutive frames, (ii) a correlation score for the first and second fields of each frame, and (iii) a correlation score for the second field of each frame and the first field of a succeeding frame. Frame difference values are compared with each other to detect repeated frames and correlation scores are compared with each other to detect repeated fields.

Abstract: A method to enhance detail of an image based on noise elimination includes calculating a noise weight corresponding to a probability that a center pixel, located in a block of pixels of a region of the image, is noise by using a difference between the center pixel and a surrounding pixel located in the block of pixels, calculating a first substitution value for the center pixel based on the noise weight; and calculating a second substitution value for the center pixel by using the noise weight and a sharpen filter.

Abstract: An image processing system for processing a target pixel to be processed, which target pixel corresponds to inputted image data, a plurality of pixels including the target pixel being arranged in a matrix manner, includes an NR circuit (106). The NR circuit (106) includes a signal processing process circuit (114) for carrying out subtraction or addition, with respect to a pixel value Aij of the target pixel, of a value equivalent to a noise quantity Er calculated in advance, in a case where the pixel value Aij of the target pixel is larger or smaller, respectively, than a first couple of estimated values Bij and Cij for the pixel value Aij of the target pixel, the first couple of estimated values Bij and Cij being estimated from pixel values of respective pixels adjacent to the target pixel, centered at the target pixel, in a temporal axis or in a spatial axis.

Abstract: An apparatus and a method for adaptive filtering includes an antenna that receives analog video broadcast signal data; an analog-to-digital converter coupled to the antenna and converting the received analog video broadcast signal data to digital video signal data; a frame buffer memory storing the digital video signal data; an instruction memory storing adaptive filtering instructions; and an adaptive filter coupled to the memory and the analog-to-digital converter, wherein the adaptive filter: reads the adaptive filter instructions from the memory; executes the adaptive filter instructions; averages an input pixel with a corresponding pixel stored in the frame buffer memory; calculates a forgetting factor for each pixel in the plurality of pixel values stored in the frame buffer memory; and filters noise from each pixel of the plurality of pixel values stored in the frame buffer memory based on the forgetting factor.

Abstract: A method for suppressing banding and rolling flicker in video acquired by a video camera. The method comprises acquiring a plurality of video frames and assessing an amount of rolling flicker in the plurality of video frames. The method further comprises configuring the video camera to quiet banding and rolling flicker responsive to periodic illumination at a first frequency if the amount of rolling flicker is above a threshold, and, configuring the video camera to quiet banding and rolling flicker responsive to periodic illumination at a second frequency if the amount of rolling flicker is below the threshold.

Abstract: A method of determining field dominance in a sequence of video frames, the method comprising: generating from a first video frame a top field and a bottom field; interpolating the top and bottom fields to produce an interpolated top field frame and an interpolated bottom field frame respectively; correlating each of the interpolated top field frame and interpolated bottom field frame with a second video frame occurring immediately previous to the first video frame in the sequence of video frames and with a third video frame occurring immediately subsequent to the first video frame in the sequence of video frames; and determining from the outcome of the correlation the field dominance of the sequence of video frames.

Abstract: A first sigma filtering circuit sigma filters an image to produce a filtered image. An analysis circuit processes the sigma filtered image to produce an approximation part and a detail part. A second sigma filter circuit filters the approximation part to produce a sigma filtered approximation part. Another analysis circuit process the sigma filtered approximation part to produce a second approximation part and a second detail part. A third sigma filter circuit sigma filters the second approximation part to produce a sigma filtered second filtered approximation part. A first synthesizer synthesizes the sigma filtered second filtered approximation part and the second detailed part to produce a first reconstructed image, and a second synthesizer synthesizes the first reconstructed image and the first detail part to produce a final filtered image.

Abstract: The present disclosure describes a method and apparatus for filtering noise in a video image, comprising receiving a first video image, a second video image and motion information wherein the first image may be an image to be filtered and the second image may be a filtered image wherein the second image may be temporally related to said first image.

Abstract: A motion detection method includes steps of receiving a previous frame and a current frame, calculating a pixel value difference of a target pixel between the previous frame and the current frame to determine a temporal pixel difference, calculating pixel value differences between the target pixel and surrounding pixels of the target pixel in the previous frame and the current frame, respectively, to determine a spatial pixel difference, and dividing the temporal pixel difference by the spatial pixel difference to determine a motion value of the target pixel.

Abstract: An analog video receiver implemented in an integrated circuit device. The analog video receiver includes an amplifier to amplify an analog video signal having a desired carrier frequency, and a mixing circuit to mix the amplified analog video signal with a complex sinusoid having a frequency substantially equal to the carrier frequency.

Abstract: A horizontal direction component pixel extractor extracts a pixel of interest and a horizontal direction component pixel thereof from an input video signal. A vertical direction component pixel extractor extracts the pixel of interest and a vertical direction component pixel thereof from the input video signal. A threshold setter sets a threshold value from the pixel of interest and the vertical processing direction component pixel thereof. A non-linear smoother non-linearly smoothes the pixel of interest using a horizontal processing direction component pixel in accordance with the set threshold value, thereby generating a video signal. A flat rate calculator calculates a flat rate in a vertical direction of the pixel of interest using a vertical processing direction component pixel. A mixer mixes the input video signal and the generated video signal using the flat rate, thereby outputting a horizontal direction smoothed video signal.

Abstract: A noise reduction circuit outputs a signal corresponding to a voltage difference between two different signals. The noise reduction circuit includes: an amplifier circuit for amplifying the two different signals at different timings; and a voltage difference detection circuit for detecting a voltage difference between the two different signals amplified by the amplifier circuit. The noise reduction circuit accumulates, a predetermined number of times, an electric charge corresponding to the voltage difference detected by the voltage difference detection circuit and combines the accumulated electric charges to output a resultant electric charge.

Abstract: A noise reduction apparatus includes a subtracter receives a motion video signal and finds a difference signal indicative of a difference from a motion video signal preceding by 1 frame and from which noise is removed, a first multiplier executes multiplication so as to increase/decrease the difference signal corresponding to the motion video signal, a second multiplier detects an mount of motion of the motion video signal and executes multiplication so as to increase/decrease the difference signal from the subtracter in accordance with the amount of motion, an arithmetic unit subjects the increased/decreased difference signal from the second multiplier to addition/subtraction with the motion video signal, and a memory unit stores the noise-free motion video signal in a memory area and supplies to the subtracter as a 1-frame-preceding noise-free motion video signal.

Abstract: A video noise reduction system for reducing video noise in a sequence of video frames. In the video noise reduction system, a temporal filter computes multiple temporal average values for the video frames in different temporal directions. A motion detector computes multiple motion signal values for the video frames in different temporal directions. Finally, a control unit selects one of the temporal average values based on the motion signal values as output.

Abstract: A method of interpolating a given output pixel value when upconverting interlaced video to progressive video includes the step of determining averages for vertically adjacent pixels, left diagonally adjacent pixels, and right diagonally adjacent pixels respectively for the given output pixel and the step of determining differences between the vertically adjacent pixels, the left diagonally adjacent pixels, and the right diagonally adjacent pixels respectively. The method further selects as an interpolated value for the given output pixel among the averages based on a minimal difference of an absolute value among the differences respectively and further constrains the interpolated value to the value of the average of the vertically adjacent pixels if a value of the given output pixel is not between a range of values defined by adjacent pixels above and below the given output pixel or if the selected minimal difference is not unique.

Abstract: The present invention provides a solid-state imaging device which compensates a field curvature which occurs due to an aberration of the optical imaging system and surely receive light incident with a wide angle. Each pixel (pixel size of 2.2 ?m square) in a solid-state imaging device includes a light-transmitting film with the first effective refractive index distribution and a light-transmitting film with the second effective refractive index distribution, a light-receiving element, a wiring, a wavelength selection filter, and a Si substrate. A pixel (1) is a pixel placed an approximate center of the solid-state imaging device. A pixel (n) is a pixel placed in the periphery of the solid-state imaging device, and a pixel (n-x) is a pixel that are placed between the pixel (1) and the pixel (n). The light-transmitting film of each pixel has approximately same effective refractive index distribution. ?0, which is a main light angle on the light-receiving element side, is approximately same.

Abstract: A system and system for performing adaptive recursive noise reduction with still pixel detection on a video stream is presented. After processing a field pixels that were modified are stored in the field so that processing of later fields uses the modified pixels. Furthermore, the system uses novel still pixel detection routines that include multiple thresholds and multiple windows of pixels so that noise reduction is only performed on still pixels.

Abstract: A method of attenuating noise contained in an image signal according to the extent of the movement of the image signal based on the amount of noise, and an apparatus therefor are provided. This method includes measuring the amount of noise in an image signal by accumulating an offset between an input image signal and a delayed output image signal for a predetermined time, detecting the extent of the movement of the input signal based on the amount of noise measured, and forming an output image by controlling the specific weight of the input image signal and the delayed output image signal according to the detected movement.

Abstract: To determine the noise contained in a picture, it is proposed first to determine homogeneous picture regions of the picture (100-102) and then to measure the high-frequency signal component in these homogeneous picture regions (BR). The measurement of the high-frequency signal components is here averaged over many measurement points, i.e. over many homogenous picture regions (BR), and is processed into a noise figure (NOISE_SUM) (103-104). In this way, the quality of the picture can be measured directly in the picture content.

Abstract: A method and system for processing an image recorded by an imaging device may include: a) providing an image having an array of adjacent elements each corresponding to a respective part of the image and having a respective intensity value associated therewith; b) processing the intensity values to determine an intensity contrast value for each respective element according to differences in intensity values between respective adjacent elements; c) determining a depth value for each element corresponding to the distance between the imaging device and at least part of an image forming object represented in the image by the respective element; d) processing the depth values to determine a depth contrast value for each respective element according to differences in depth values between respective adjacent elements; and, processing the intensity contrast values and depth contrast values to identify at least one area of the image corresponding to one or more respective objects in the image being processed.

Abstract: A spatio-temporal joint filter and a spatial joint filter for noise reduction are disclosed. The spatio-temporal joint filter includes a spatial joint filter including the first and second sub filters having different characteristics and includes a temporal joint filter. When the present invention is adequately used, an edge/detail region of an image is well preserved, an aggressive noise reduction is performed on a flat region, and the temporal flicker problems are eliminated. Additionally, it has an intrinsic motion compensation effect by using the spatio-temporal correlation between the adjacent frames.

Abstract: The invention relates to a method and apparatus for detecting asymmetry in transient signals and to a method and apparatus for correcting such asymmetry.

Abstract: A system and method are provided for calculating a target pixel for scaling an image comprising a plurality of source pixels. A contour is determined in the image using at least one of a first set of predetermined parameters. A filter tap configuration is adaptively selected from a predefined set of filter tap configurations in accordance with the determined contour. The predefined set of configurations includes a plurality of non-linear filter tap configurations. The target pixel is calculated by selectively convolving ones of the plurality of source pixels along a locus of the selected filter tap configuration with a weighting factor, and combining the convolved pixels.

Abstract: A method and system of noise filtering is provided. The pixels of a first filter mask are separated into groups based on luminance . . . The sizes of each group is determined and a largest group is selected. The distance of each group of pixels from the largest group is also calculated. Pixels in groups that are small compared to the largest group and far from the largest group are tagged as noisy. After tagging the noisy pixels, additional filtering can be applied to the pixels of first filter mask without degradation from the tagged pixels.

Abstract: An adaptive median filter (40) provides dynamic detection and correction of digital image defects which are caused by defective or malfunctioning elements of a radiation detector array (20). The adaptive median filter receives (100) lines of pixel values of a digital image that may have defects and a user-defined defect threshold. The lines of pixel values are scanned on a pixel-by-pixel basis using a kernel of n×n pixels, where the kernel contains the candidate pixel being examined (120). Each kernel is numerically reordered (130) and a median value is calculated (140). A defect threshold value is calculated by multiplying the user-defined defect threshold criteria and the candidate pixel value (150). A reference value is calculated by subtracting the candidate pixel value and the median value (160). The reference value is compared to the defect threshold value (170).

Abstract: A camera signal processing apparatus comprises an interpolated pixel data generating means for interpolating, at least on two directions, pixel data based on an imaging signal from a solid-state image sensor in which an imaging light enters through a color filter having a different spectral characteristic for each pixel separately generating interpolated pixel data in the at least two directions; a correlation detecting means for detecting a correlation value indicative of a degree of correlation in each of the at least two directions of the interpolated pixel data; a normalizing means for normalizing the correlation value of each of the at least two directions to generate a normalized value indicative of a relative value of the correlation value of each of the at least two directions; a correcting means for adding a predetermined correction value to the normalized value; a weighting means for weighting the interpolated pixel data in each of the at least two directions by the normalized value and adding toget

Abstract: An image filter circuit which realizes a large-scale median filter as a digital circuit which has not been conventionally constructed without difficulty. The filter circuit has a histogram A update unit 102 which generates a histogram A with upper-bit data of pixels within a matrix, a cumulative adder A104 which searches for a class including a pixel value corresponding to a predetermined rank in ascending order as a target class based on the histogram A, a histogram B update unit 106 which generates a histogram B with lower-bit data of pixels included in the target class, and a cumulative adder B108 which searches for a pixel value of the predetermined rank in ascending order in the matrix. The filter circuit having these constituent elements outputs a median pixel value of the matrix.

Abstract: A video signal including illumination flicker component is integrated at each of unit areas (horizontal lines) in a frame (field) of the video signal. The integrated level at each of the unit areas at the frame and the integrated level at the corresponding unit area of an adjacent frame are averaged. Dividing is effected between results of the averaging and integrating every unit area. It is judged whether flicker exists in the video signal by frequency-analyzing results of the dividing result at the unit areas. The unit area may be plural adjacent lines where flickering are negligible. The averaging circuit may be circulation type of or FIR filter. Threshold level for judging the flicker is changed according to a shutter speed control signal. Flicker compensation may be executed by controlling shutter speed or the AGC according to flicker judging result. A still condition at a block in a frame may be detected from the integration result at plural frames.

Abstract: A method of filtering noise from digital pictures includes selecting a first set of pixels including the union of a pixel of the current picture to be filtered and a second set of pixels temporally and spatially near the pixel. A certain number of extended sums of values assumed by as many pre-established weight functions of the intensity of a selected video component on the first set of pixels is also calculated. The second set of pixels may belong to the current picture or to a preceding picture. Several noise filters for digital pictures are also provided.

Abstract: Correcting deinterlaced video by determining whether the deinterlaced video has comb artifact areas, and correcting the comb artifact areas. The detection of comb artifacts includes comparing the differences in pixel values between adjacent rows with the differences in pixel values of alternate rows. The detection includes calculating comb artifact factors based on the differences, and comparing the median value for a group of pixels with a threshold to determine if there is an comb artifact at the pixel.

Abstract: A apparatus and apparatus for compensating for video insertion loss due to transmission over long twisted pair cable lines is presented. Transmission of video over twisted pair cable is advantageous because of its superior cost advantage over coaxial cable. However, twisted pair cables have significant loss characteristics at the higher frequencies (i.e., broadband) compared to coaxial cables. At a transmitter station, the video signal is amplified in the high frequency region for possible skin effect losses thereby brute forcing the high frequency components to the receiving station. At the receiver station, the video signal is further compensated for diffusion line and skin effect losses. The total skin effect compensation applied in both the transmitter and receiver stations is such that the square root of frequency characteristics of skin effect losses is compensated for.

Abstract: A source coder for video, compression Of H.261 and H.263 is disclosed, including a subtracter, a coding circuit, a predicting circuit, a picture memory with motion compensated variable delay and a filter. The subtracter subtracts an input video frame by a previous predicted frame to obtain a difference. The coding circuit transforms and quantizes the difference to output a coded bit stream. The predicting circuit predicts an error from the coded bit stream. The adder adds the previous predicted frame by the error to output a new predicted frame. The picture memory stores the new compressed frame. The filter is selectively arranged after the picture memory to serve as a loop filter in H.261 mode and arranged before the subtracter to serve as a video-in filter in H.263 mode.

Abstract: The method suppresses noise in a one-dimensional or multi-dimensional signal. A plurality of estimates for the noise-free useful signal are carried out on the basis of a measurement of the noisy signal, and each estimated value for each point is individually assigned a preference. A new estimated value for the useful signal is formed from the individual estimated values by arithmetic averaging weighted by the preference.

Abstract: A method for image enhancement for an interlaced display includes receiving a first group of pixels aligned about an axis, detecting a second group of pixels within the first group of pixels, each pixel of the second group of pixels having a luminous disparity between adjacent pixels less than a first threshold, determining whether each pixel within the second group of pixels is part of a line or edge, the determination including a comparison of luma or chroma disparities between neighboring pixels and filtering each pixel determined to be part of a line or edge.

Abstract: A digital de-emphasis filter for a SECAM decoder for converting a sequence of input image data into filtered image data includes at least one recursion register for storing an auxiliary value that is obtained using an input image data value. An arithmetic circuit uses the auxiliary value and a newly input image data value to generate a new auxiliary value, which replaces the contents of the recursion register, and a filtered image data value. To determine the achromatic value in addition to performing de-emphasis filtering, the filter is provided with a device for storing and outputting a value representative of an estimated value of the achromatic value of the SECAM signal, and a first switch for applying and registering the output estimated value into the recursion register at the beginning of each burst gate period of the SECAM signal.

Abstract: A VGA to analog video converter is useful e.g. for displaying video and/or graphics data from a computer onto a large screen television or television monitor. The RGB video signals output from the personal computer are first converted to digital form. The analog-to-digital converter which does this is clocked by a clock signal generated by a phase-locked loop using the horizontal synchronizing signal from the personal computer. The digital RGB signals are then converted to a YCbCR format. A flicker filter eliminates the flickering appearing on the TV monitor by operating on the luminance (Y) component. The YCbCr signals are encoded into NTSC or PAL Standard, and output in composite analog video or S-VHS format. A color subcarrier synthesizer generates the color subcarrier signal to generate an accurate subcarrier frequency for the video output signals. An analog-to-digital clock phase adjustment is used to ensure that the input RGB signals are sampled at the proper instant by the analog-to-digital converters.

Abstract: Post processing of the converted digital bits from an ADC to provide one or more additional bits of resolution. The additional bits of resolution will be accurate for data which is locally correlated, such as image data. For a particular digital sample, a curve (such as a straight line) is fitted through adjacent samples to determine an expected value for the current sample. The actual digital sample is compared to the expected value to determine whether it is within a threshold of the expected value. The value of an additional bit of resolution is set based upon whether the sample is within the threshold.

Abstract: A method and system for combining a set of n still image frames into a single reduced noise still image. The invention reduces visible noise, along with some television color artifacts, in still images captured from a video stream by combining data from multiple video frames. Each frame comprises an XY array of picture element (pixel) data. In the preferred embodiment, each pixel includes data defining an intensity level as well as color values. A weighted average of several frames of video is taken to generate a single still output frame. The weighting is determined adaptively in order to reduce inter-frame motion artifacts. The resulting output has substantially less visible noise than a simple unweighted average. The algorithm is much faster and simpler to implement than true multi-pixel motion estimation, which is not really necessary in a series of nominally-still images.

Abstract: A video signal is both spatially and temporally filtered. The output video signal is temporally noise reduced in portions of the image which exhibits little or no motion, and is spatially noise reduced in portions where motion exists. This approach is particularly applicable to reducing film grain noise in video material that originates from images on photographic films, since film grain noise is more correlated spatially than temporally.

Abstract: Method of eliminating interference signals from video signals by means of motion-adaptive transversal filtering, in which the motion is detected in the two-dimensional plane for the purpose of S/N ratio improvement. To this end, the forward and backward-motion signals are combined to a common motion signal and transformed into a polar coordinate signal from which the coefficients for controlling the transversal filter are derived.

Abstract: In a method of filtering data, including the steps of processing (7) data (O) to obtain reduced data, delaying (9) the reduced data to obtain delayed data, interpolating (11, 13) the delayed data to obtain interpolated data (R), and combining (1-5) the interpolated data (R) and input data (I) to obtain filtered data (O), the interpolating step (11, 13) includes the step (13) of providing one delayed data element out of several delayed data elements in dependence upon an input data element (p).

Abstract: A video processing apparatus uses multiple image signal integration and reduction for decreasing noise. A television camera picks up an image of a still object and outputs image signals repetitively. An adder adds each newly outputted signal to the sum of previously outputted image signals stored in a memory and stores each new sum of image signals in the memory. A circuit divides each new sum of image signals by the number of times the adder has performed additions, thereby providing a signal that is displayed on a monitor.

Abstract: In a method of processing a video signal including the steps of providing (13) a delayed signal, and furnishing (11) a filtered signal in response to the video signal and the delayed signal, only a small number of preselected frequency components and/or statistical properties is delayed in the step of providing (13) a delayed signal, in order to reduce a required storage and/or processing capacity.

Abstract: A video processing method and apparatus for processing video frames comprising animated images so as to blur movement of the animated images between successive frames, the method or apparatus comparing a first input frame with the following input frame; identifying moving areas in the first input frame by the comparison; calculating the velocity of the movement of the moving areas between the first and following input frame; summing, only for each input pixel site within the identified moving areas of the input frame, the pixel value of each input pixel site and adjacent pixel values determined according to the calculated velocities and a predetermined aperture type for the input frame; and providing an output frame from at least the summed pixel values and pixel values of areas of the input frame other than the moving area, the adjacent pixel values either being the pixel values of pixel sites in the input frame which are spatially adjacent in the direction of the velocity or predicted temporally adjacent pi

Abstract: Jagged vertical or diagonal transition artifacts in interlaced to line doubled progressive scan converted television signals are detected and areas of the television picture having such artifacts are subjected to vertical averaging such that the resolution of the jagged transitions is reduced, thereby softening, "greying" or "fuzzing" the jagged transitions and causing them to appear smooth. Thus, highly contrasted lines appearing in a sawtooth pattern, which are extremely perceptible, are replaced with a flash of what might be characterized as "fuzziness," which is not perceptible. The eye no longer perceives the jagged artifacts. Moreover, areas of reduced vertical and horizontal resolution, resulting from the vertical averaging, do not create any new artifacts and are not perceived by the eye. Artifacts are detected by comparing pixels in corresponding positions in the scan lines of the line doubled progressively scanned television signal.

Abstract: The system for reducing composite beat, composite second order beat and thermal (snow) noise impairments in a television system digitizes individual frames to apply digitized a grey scale values (v.sub.(i,j)) to the pixels in the frames and then applying a spatial filter to a block of pixels including the then current pixel being processed to determine the pixel (P.sub.(min)) with the minimum grey scale value (v.sub.(min)) and the pixel (P.sub.(max)) in the block with the maximum grey scale value (v.sub.(min)). V.sub.(max) -v.sub.min is compared with a threshold value (v.sub.(T)) and if v.sub.(max) -v.sub.min) >v.sub.(T), the value (v.sub.(i,j)) of the pixel being processed remains unchanged, but if v.sub.(max)-v.sub.(min).notgreaterthan.v.sub.(T), a value (v.sub.(av.)) equal to the weighted average value of pixels in the block is used as the grey scale value v.sub.(R-i,j) for the pixel being processed.