Abstract: An image display apparatus includes a filter which obtains low-frequency image data from input image data, a multiplier which multiplies the low-frequency image data obtained by the filter by a predetermined ratio, and a subtracter which subtracts, from the input image data, the low-frequency image data multiplied by the predetermined ratio to obtain high-frequency image data. In addition, a display control unit displays, in alternate order, the low-frequency image data and the high-frequency image data, and an adjustment unit adjusts the predetermined ratio so as to set a flicker of an image displayed by the display control unit to a predetermined level.

Abstract: A readout frequency of a sensor of a digital image capturing device is set based on a frequency of alternating current (AC) mains so that a readout period of the sensor of the digital image capturing device is not an integer multiple of a flicker period. The flicker period is equal to half of a period of the AC mains. A first image frame and a second image frame are captured using the sensor of the digital image capturing device. The second image frame is captured later in time than the first image frame. Whether flicker has occurred in the first and second image frames due to a periodic fluctuation of light emitted by a light source powered by the AC mains is detected by comparing a brightness of an area of the first image frame to a brightness of a corresponding area of the second image frame.

Abstract: Disclosed herein is an image taking apparatus including an image taking device, a gain adjustment circuit, and a correction circuit. The image taking device operates with timings based on a frame rate determined in advance and the total number of horizontal lines, has an electronic shutter allowing a shutter speed to be adjusted, receives light in a period equal to the shutter speed of the electronic shutter and carries out an opto-electrical conversion process on the light for every horizontal line in order to generate a predetermined signal. The gain adjustment circuit adjusts the gain of the electrical signal received from the image taking device. The correction circuit compares an image taking video signal with a reference video signal to compute a flicker component as a component oriented in the vertical direction of an image represented by the image taking video signal in a flicker correction process of eliminating flickers.

Abstract: Flicker occurs in a flicker-noticeable area consisting of pixels with no pixel value variations. An image processing device (100) includes a variance calculation unit (101) that obtains a variance of an area consisting of a target pixel and neighboring pixels included in a first frame, and changes, according to the variance, the rate at which an error generated at the target pixel through tone level restriction is distributed within the frame and between frames. The image processing device (100) includes an error diffusion unit (113) that distributes the error generated at the target pixel to the neighboring pixels included in the first frame based on an intra-frame error diffusion rate and an intra-frame error distribution weight, and distributes the error generated at the target pixel to a target pixel and neighboring pixels included in the second frame based on an inter-frame error diffusion rate and an inter-frame error distribution weight.

Abstract: The invention relates to a method for processing video pictures, the video pictures consisting of pixels digitally coded, the digital code word determining the length of the time period during which the corresponding pixel of a display is activated, wherein to each bit of a digital code word a certain activation duration called sub-field is assigned, the sum of the duration of the sub-fields according to a given code word determining the length of the time period during which the corresponding pixel is activated, said method comprising the following steps: detecting the video pictures source mode and the parity between pictures, if the source is in film mode, distributing the total number of sub-fields used for two frame raster in three groups of sub-fields and assigning to a value of a pixel a code word that corresponds to the distribution of the active sub-fields period over the three sub-fields groups, and if the source is in camera mode, distributing the total number of sub-fields used for each frame r

Abstract: A judder detection apparatus, a de-interlacing apparatus using the judder detection apparatus, and a de-interlacing method. The judder detection apparatus includes a judder detector to detect whether a detected pattern that is similar to a judder pattern occurs using predetermined pixel values of even and odd fields sequentially input, a pattern detector to detect whether an input image has a uniform pixel value in every other line of the even and odd fields and whether consecutive lines of the even and odd fields have a blind pattern having a difference from the uniform pixel that is greater than or equal to a threshold value, and a determiner to determine whether the detected pattern that is similar to the judder pattern is a judder based on whether the blind pattern is detected.

Abstract: A display apparatus to receive a picture signal containing information of a picture and to process the picture signal using at least an area distinguishing the picture from another picture includes a motion detector to detect whether there is a motion in the area of the picture signal, a hysteresis generator to output hysteresis information on each area according to a detected result of the motion detector from a previous frame up to a current frame, a moving picture detector to detect whether the picture signal is a moving picture signal or a still picture signal in the area on the basis of the hysteresis information, and a gradation level converter to convert the picture signal corresponding to the area into either a group of gradation levels for a moving picture to display the moving picture signal or a group of gradation levels for a still picture to display the still picture signal according to a detecting result of the moving picture detector.

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: In the case where an input signal is an interlace signal such as NTSC signal, a flicker interference as aliasing interference brought about by the sampling theorem is contained in a region where a vertical frequency component is high. Accordingly, in the conventional processing in which rate of change in gradation is improved by making a drive voltage of liquid crystal at the time of change in gradation larger than normal liquid crystal drive voltage to increase response rate of the liquid crystal panel, interference component is also emphasized. As a result, quality level of a video picture to be displayed on the liquid crystal panel is deteriorated. The invention provides a compensation device capable of improving rate-of-change in gradation at a part where there is no flicker interference and changing rate-of-change in gradation to suppress the flicker at a part where there is any flicker interference.

Abstract: A video processing system is presented that interleaves video data. In accordance with some embodiments of the present invention, data from a first field is placed in a frame and is augmented with pixel values in adjacent alternate rows of the frame with pixel values determined from the pixel values in the first field data and pixel values from the second field data.

Abstract: Plasma Display Panels (PDP) are becoming more and more interesting for TV technology. Due to the larger size of PDPs, with larger viewing angle the large area flicker effect will become more serious in the future, in particular when handling 50 Hz video standards. This invention proposes a different sub-field organisation, with different coding, which reduces large area flicker artefact, and which is characterised by: 1. Grouping of sub-fields (SF) in 2 sub-field groups (G1, G2), of similar structure. 2. Adjusting the starting times of the two sub-field groups to a time raster corresponding to a doubling of the frame repetition rate by adding a first blanking period of a first dedicated length behind the last sub-field of the first sub-field group and a second blanking period of a second dedicated length behind the last sub-field of the second sub-field group.

Abstract: The present invention provides an image signal processing apparatus and a method thereof which perform double-speed conversion on images subjected to telecine conversion and in which a first field is specified based on difference values between pixel signal levels calculated with respect to respective detected pixels, write pixel positions which are shifted from the positions of the detected pixels in the vector directions of motion vectors are calculated in a field following the first field, the calculated write pixel positions are stored in correspondence with the motion vectors, interpolation pixel data is calculated from pixel data read from the first field in correspondence with the stored write pixel positions and motion vectors, and the calculated interpolation pixel data is written into the write pixel positions.

Abstract: The present invention provides an image signal processing apparatus and a method thereof in which each of the fields forming the unit-frame is specified, with respect to the inputted image signal, based on a difference value calculated in signal level between a detected pixel in a current field and a detected pixel at the same position in a field which comes one frame behind the current field, a motion vector for a field which comes two frames behind the current field is detected, with respect to the detected pixel in the current field, the detected pixel is shifted, with respect to the specified first field, in a direction opposite to the motion vector within the range of the detected motion vector, the detected pixel is shifted, with respect to the specified fourth field, in a direction along the motion vector, and the detected pixels is shifted, with respect to the specified second and third fields, so as to make the pixels gradually closer to the pixel position shifted with respect to the fourth field, in

Abstract: A flicker correction apparatus for correcting a flicker component of an image signal obtained by imaging an object using an imaging device is provided. The apparatus comprises an image average calculation section for calculating an average of the image signal, a flicker frequency calculation section for calculating a flicker frequency, a flicker data extraction section for extracting flicker data using the average of the image signal and the flicker frequency, a flicker determination section for determining the presence or absence of a flicker phenomenon using the flicker data, a flicker correction amount calculation section for calculating a flicker correction amount using the flicker data, and a flicker correction section for removing the flicker component of the image data using the flicker correction amount.

Abstract: In order to generate a risk index of stress symptoms triggered by flashing lights on a scan type video display screen, a video signal processor is provided which operates such as to implement temporal filtering and spatial filtering on a video signal applied thereto every field and detect low temporal frequency components while excluding effects due to high spatial frequencies. A risk index generator receives the low frequency components from the video signal processor and determines the risk index based thereon.

Abstract: Thin horizontal lines and edges are vulnerable to flickering on an interlaced monitor. To reduce flickering filtering is adaptively applied to the pixels of lines or edges to reduce the flicker energy or contrast of the pixel to a level less than a threshold energy or contrast necessary for flickering under the local conditions. The flicker energy or contrast is a function of the luminance of the line pixel and vertically adjacent background pixels, the number of intensity transitions in the vertical vicinity of the line, and the line length. Adaptive filtering by the described method is computationally conservative and does not adversely effect the detail in the remainder of the image.

Abstract: An image data conversion processing device including an issue unit, plural line storing units, and a generating unit for converting to a television signal image data stored in plural kinds of developing formats in a storing unit. The image data comprises plural lines, and the television signal comprises a predetermined number of lines. The issue unit issues a transmission instruction of image data to the storing unit in accordance with a period specified by a ratio of the number of lines of the image data to be converted and the number of lines of the television signal. The plural line storing units cyclically store the image data transmitted from the storing unit line by line on the basis of the transmission instruction of the issue unit.

Abstract: At first, average brightness of each of frames of a moving image is calculated by a computer. Following that, a moving average along a time axis is calculated for each of the frames so that moving average brightness is generated as a reference data of brightness. Next, difference data between the average brightness and the moving average brightness are generated. Further, the difference data are grouped based on the signs of the reference data. Then, on the basis of the grouped difference data, it is judged whether an unwanted change of brightness is present. Thus, it is automatically and precisely judged whether the unwanted change of brightness such as a flicker is present in the moving image.

Abstract: A graphics controller for flicker filtering interlaced image data is provided. The graphics controller includes a buffer and a memory region. A flicker filter for reducing a flicker of a display presented through an interlaced scan is also provided. The flicker filter is configured to receive interlaced image data prior to any received image data being stored in the memory region. The flicker filter outputs filtered data defining a pixel. The filtered data is stored in the memory region such that two pixels can be output in one memory access to the memory region. Flicker filter enabling circuitry in communication with the buffer is provided. The flicker filter enabling circuitry is configured to supply an even segment and a corresponding odd segment of the interlaced image data to the flicker filter. An apparatus and methods for processing and storing image data having an interlaced format are also provided.

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: A storage picture generating unit (191) weight-adds an input picture and a storage picture to reduce the noise in a still picture portion. An area extraction unit (193) extracts a class tap from the input picture, while extracting a block from each of the input picture and the storage picture. A feature value detection unit (194) detects the dynamic range and the results of the waveform analysis from the class tap, while detecting the still/moving information of the subject pixel from the block. A class code detection unit (195) generates a class code which is based on the feature value. A table (196) outputs to an estimation calculating unit (198) sets of the prediction coefficients held by the table and which are associated with the class code. An area extraction unit (197) extracts prediction taps from the input picture and the storage picture.

Abstract: An apparatus and method for processing a video signal, and particularly, an apparatus and method for deleting a sawtooth wave are provided in which a sawtooth wave component is detected and with consideration of direction the sawtooth wave is deleted. The sawtooth wave deleting method includes (a) detecting a sawtooth wave component based on an area dispersion value and motion information in each frame in an input video signal; (b) detecting a direction from the pixels of the detected sawtooth wave component; and (c) deleting the sawtooth wave component by outputting an interpolated pixel in the detected direction. According to the apparatus and method, since interpolation of a sawtooth wave component is performed with consideration of the direction so that the sawtooth wave component is effectively deleted, a much smoother image is provided after deinterlacing.

Abstract: A method, a circuit arrangement and a display device which suppresses motion blur due to motion integration carried out along a motion trajectory on the image data, which occurs in matrix type displays in which a motion trajectory is integrated by the viewer and/or the display, includes an inverse integration filtering of the video signal. To avoid de-blurring in image regions where motion cannot be detected, or image is low and to avoid noise modulation, motion estimation as well as further image characteristic are used.

Abstract: The circuit includes a motion detector including a first device for producing pixel motion signals, which have a first state for each pixel which is found to have moved and a second state for each pixel which is found to have been stationary, and a second device for correcting the pixel motion signals in order to produce motion values in such a manner that a state of a pixel which differs from matching states of adjacent pixels is ignored.

Abstract: Lighting flicker in the output of a video imaging device is detected. The video imaging device has a main picture area divided into pixels for producing successive images at a frame rate. A series of signals are produced from at least one additional picture area adjacent the main picture area, with the additional picture area having a size substantially larger than a pixel. Each of the signals is a function of light incident on the additional picture area in a time period substantially shorter than that of the frame rate. A predetermined number of the signals are accumulated to form a series of compound samples, and the compound samples are filtered to detect components indicating the lighting flicker. The filtering is performed using a bandpass filter tuned to the nominal flicker frequency. The compound samples are formed at a sample rate which is a multiple of the nominal flicker frequency, and the filtering is performed by taking the fundamental output component of a radix-N butterfly.

Abstract: Plasma Display Panels (PDP) are becoming more and more interesting for TV technology. Due to the larger size of PDPs, with larger viewing angle the large area flicker effect will become more serious in the future, in particular when handling 50 Hz video standards.

Abstract: In a signal coordinating method and apparatus, a pulse generating circuit receives a VSYNC signal and generates a plurality of critical pulses that define critical time periods from fields can control edges of the VSYNC signal. A determining circuit receives an HSYNC signal and the critical pulses, and generates a trigger signal upon detecting that a line scan control edge of the HSYNC signal appears during one of the critical time periods. A time delay loop introduces a time delay into the VSYNC signal upon receipt of the trigger signal to cause the critical time period to appear after the line scan control edge of the HSYNC signal.

Abstract: Plasma Display Panels (PDP) are becoming more and more interesting for TV technology. Due to the larger size of PDPs, with larger viewing angle the large area flicker effect will become more serious in the future, in particular when handling 50 Hz video standards. This invention proposes a different sub-field organisation, with different coding, which reduces large area flicker artefact, and which includes grouping of sub-fields in two sub-field groups wherein the two sub-field groups are identical in terms of the most significant sub-fields and different in terms of the least significant sub-fields, and a sub-field coding process that distributes luminance weight symmetrically over the two sub-field groups so as to minimize the large area flicker luminance component.

Abstract: The invention deals with the large area flicker effect reduction in display devices like plasma display panels, in which the light output is controlled by small pulses over a whole frame period and the amount of small pulses determine the brightness of the light output. The invention proposes an adaptation of the known principle of sub-field grouping for large area flicker reduction for the specific sub-field coding process called incremental sub-field coding, in which only those sub-field code words are taken for display driving having the characteristic that there is never a sub-field inactivated between two activated sub-fields or never a sub-field is activated between two inactivated sub-fields.

Abstract: A graphics controller for flicker filtering interlaced image data is provided. The graphics controller includes a buffer and a memory region. A flicker filter for reducing a flicker of a display presented through an interlaced scan is also provided. The flicker filter is configured to receive interlaced image data prior to any received image data being stored in the memory region. The flicker filter outputs filtered data defining a pixel. The filtered data is stored in the memory region such that two pixels can be output in one memory access to the memory region. Flicker filter enabling circuitry in communication with the buffer is provided. The flicker filter enabling circuitry is configured to supply an even segment and a corresponding odd segment of the interlaced image data to the flicker filter. An apparatus and methods for processing and storing image data having an interlaced format are also provided.

Abstract: The horizontal synchronization frequency and the vertical synchronization frequency of a television receiver is increased by 3/2 times, so that refresh rate increased 3/2 times. The flicker of the displayed picture is thus reduced.

Abstract: In a method of compensating an image signal (10) having a field frequency of substantially N times a mains frequency, in which N≧2, for AC light source induced fluctuations, the image signal (10) and an average signal representing an average image signal content over a given time period are arithmetically processed (14,16-20,8) to obtain a corrected signal (9), in which at least N−1 differences between at least N−1 respective phases of the corrected signal (9) on the one hand, and a selected phase (ph2) other than the N−1 phases of the corrected signal (9), or an average over N fields of the image signal (10), on the other hand, are integrated (14,16), and in which at least N−1 integrated differences are processed (20) to obtain a correction factor for the image signal (10).

Abstract: A method and apparatus for providing a flicker filter for an interlaced video display. Content is analyzed to determine what type of filter or filter characteristics selected from a plurality of available filters or filter characteristics can provide the better display of the content. Based on this analysis, the filter characteristics are selected and used for flicker filtering the content for display.

Abstract: The invention relates to a device for reducing flicker disturbances in a video signal having a temporal median filter and a filter connected downstream. The temporal median filter serves for compensating for brightness fluctuations in the video signal. The filter connected downstream separates high-frequency signal components from the output signal of the temporal median filter and suppresses high-frequency signal components with a high amplitude.

Abstract: A flicker correction apparatus for correcting a flicker component of an image signal obtained by imaging an object using an imaging device is provided. The apparatus comprises an image average calculation section for calculating an average of the image signal, a flicker frequency calculation section for calculating a flicker frequency, a flicker data extraction section for extracting flicker data using the average of the image signal and the flicker frequency, a flicker determination section for determining the presence or absence of a flicker phenomenon using the flicker data, a flicker correction amount calculation section for calculating a flicker correction amount using the flicker data, and a flicker correction section for removing the flicker component of the image data using the flicker correction amount.

Abstract: An apparatus and method for stretching the black level of an image signal to minimize flicker are provided. A black level stretching apparatus includes a minimum and maximum value extraction unit, and an adaptive black level stretch unit. The minimum and maximum value extraction unit for extracting the minimum and maximum values of each field of an image signal removes impulse noise using at least one low-pass-filter. The adaptive black level stretch unit extracts a tilt point, which delimits a dark region that is stretched, calculates a first gradient, selects the first gradient or a second gradient defined by users according to the dynamic range of the input signal, and stretches the black level of the image signal using the selected gradient. Another black level stretching apparatus includes a minimum value extraction unit, a dark region average value extractor, and a black level stretch unit. The minimum value extraction unit extracts and outputs the minimum value of each field of an image signal.

Abstract: An interlaced television signal is derived from an interlaced 625 line, nominally 50 Hz field rate television signal, the derived television signal having perceived reduced line structure and reduced flicker. The field rate and the number of lines of the derived television signal are increased with respect to the field rate and the number of lines of the original television signal, such that perceived flicker and line structure in the derived television signal is reduced. The increase in the field rate and the increase in the number of lines in the derived television signal results in a horizontal scanning rate that does not substantially exceed twice the horizontal scanning rate of the original television signal while minimizing undesirable motion artifacts.

Abstract: The invention provides an image processing apparatus and method as well as a providing medium by which deterioration of the vertical resolution is prevented and conspicuous appearance of line flickering is suppressed. In order to convert an interlaced video signal having 525 scanning lines into another progressive video signal having 525 scanning lines while maintaining the image size, in an odd-numbered field, a line after conversion is offset by 0.5 H (H is the distance between horizontal scanning lines of the inputted video signal). Consequently, pixel data of each line Oi are produced from pixel data of two lines Ii and Ii+1 before conversion. As a result, pixels of a line on the boundary between white pixels and black pixels have a gray color. In an odd-numbered field, no offset is given, and pixel data of each line I1 of the field before conversion are set as they are as pixel data of each line Oi of the field after conversion.

Abstract: An apparatus and method for converting computer graphics images into a format suitable for display on a TV. A flicker filter is combined with a vertical scaling filter and/or vertical overscan compensation filter to produce an interlaced image formatted for display on a TV, more efficiently than if the processes occurred sequentially. The apparatus and method are not limited to any particular filter sizes or set of filter coefficient values. The apparatus and method may be used as part of a multimedia computer system.

Abstract: A method of characterizing a display having a plurality of color channels, that includes the steps of: visually characterizing the gamma of the display; estimating a colorimetric mixing matrix for the display by determining luminance ratios of the color channels using heterochromatic photometry; and combining these luminance ratios with a chromaticity model for the display channels.

Abstract: An image data conversion processing device including an issue unit, plural line storing units and a generating unit for converting to a television signal image data stored in plural kinds of developing formats in a storing unit. The image data comprises plural lines, and the television signal comprises a predetermined number of lines. The issue unit issues a transmission instruction of image data to the storing unit in accordance with a period specified by a ratio of the number of lines of the image data to be converted and the line number of the television signal. The plural line storing units cyclically store the image data transmitted from the storing unit line by line on the basis of the transmission instruction of the issue unit.

Abstract: A device and method is provided for reducing flicker on a video display. The device may be incorporated into a video surveillance system having a number of cameras, monitors, a keyboard controller, a switch, and a flicker reduction circuit. The flicker reduction circuit processes dual interlaced fields of video data with a field FIFO memory area, a line FIFO memory area, and a logic unit. The field memory area acts as a delay to store the field previous to the field being processed, while the line memory area stores the least recent line input from the field memory area. The logic unit computes the flicker-reduced scan line intensity for a given scan line by averaging the given scan line intensity with the resultant scan line intensity average of the two immediately adjacent scan lines in the complementary field.

Abstract: A method of smoothly displaying field videos in an interlaced display according to the invention. In a currently-exiting interlaced display system, the sequence of a scan timing with a top scan timing, a bottom scan timing, a top scan timing, a bottom scan timing . . . , should be consistent to that of field number with a top field, a bottom field, a top field, a bottom field, . . . In the invention, a top or bottom field can be inserted/skipped right after any one field displayed. During inserting/skipping, a new top field which is created from the bottom field or a new bottom field which is created from the top field, is displayed at a corresponding scan timing, thereby efficiently preventing a TV screen from jitters, resulting in smooth display.

Abstract: A method and apparatus for providing a flicker filter for an interlaced video display. Content is analyzed to determine what type of filter or filter characteristics selected from a plurality of available filters or filter characteristics can provide the better display of the content. Based on this analysis, the filter characteristics are selected and used for flicker filtering the content for display.

Abstract: An image data conversion processing device including an issue unit, plural line storing units and a generating unit for converting to a television signal image data stored in plural kinds of developing formats in a storing unit. The image data comprises plural lines, and the television signal comprises a predetermined number of lines. The issue unit issues a transmission instruction of image data to the storing unit in accordance with a period specified by a ratio of the number of lines of the image data to be converted and the number of lines of the television signal. The plural line storing units cyclically store the image data transmitted from the storing unit line by line on the basis of the transmission instruction of the issue unit.

Abstract: A method and a system for improved filtering of display data is disclosed herein. A display system may be used to separately filter display components of the display data based on frequency content of the display components. The display system can include a display data source, a digital image processor, and a display. The display system receives display data from the display data source. The frequency content of a plurality of display components in the display data is determined by the digital image processor. The digital image processor filters the plurality of display components based on the associated frequency content. In at least one embodiment, display components having lower frequency content are filtered to minimize flicker, while display components having higher frequency content are filtered to maximize resolution. The filtered display data is then transmitted to the display.

Abstract: An image processing display apparatus for converting an image signal of an interlace system into a progressive scanning system and displaying an image, having means for conducting low band frequency passing processing so as to reduce flicker for a vertical direction signal component of a still picture signal component included in a video image signal, and means for synthesizing a still picture signal component to which the low band frequency passing processing is applied and a moving picture signal component included in the above-described video image signal to generate a progressive signal.

Abstract: A device and method for preventing flicker that occurs while displaying image data by attenuating a high-frequency portion of orthogonal transformed color signals of the image data. The present invention is also directed to a computer-readable recording medium on which a program for flicker prevention is recorded.

Abstract: Briefly, in accordance with one embodiment of the invention, a method of reducing flicker in a video image sequence includes the following. Successive video images are temporally filtered. The filter length is adjusted so as to reduce the amount of filtering across temporal discontinuities in the video image sequence.

Abstract: An interlaced television signal is derived from an interlaced 625 line, nominally 50 Hz field rate television signal, the derived television signal having perceived reduced line structure and reduce flicker. The field rate and the number of lines of the derived television signal are increased with respect to the field rate and the number of lines of the original television signal, such that perceived flicker and line structure in the derived television signal is reduced. The increase in the field rate and the increase in the number of lines in the derived television signal results in a horizontal scanning rate that does not substantially exceed twice the horizontal scanning rate of the original television signal while minimizing undesirable motion artifacts.