Showing papers on "Pixel published in 1979"

Photometric Stereo: A Reflectance Map Technique For Determining Surface Orientation From Image Intensity

Abstract: This paper introduces a novel technique called photometric stereo. The idea of photometric stereo is to vary the direction of the incident illumination between successive views while holding the viewing direction constant. This provides enough information to determine surface orientation at each picture element. Traditional stereo techniques determine range by relating two images of an object viewed from different directions. If the correspondence between picture elements is known, then distance to the object can be calculated by triangulation. Unfortunately, it is difficult to determine this correspondence. In photometric stereo, the imaging geometry does not change. Therefore, the correspondence between picture elements is known a priori. This stereo technique is photometric because it uses the intensity values recorded at a single picture element, in successive views, rather than the relative positions of features.

An improved illumination model for shaded display

Abstract: To accurately render a scene, global illumination information that affects the intensity of each pixel of the image must be known at the time the intensity is calculated. In a simplified form, this...

Image segmentation and image models

Abstract: This paper discusses image segmentation techniques from the standpoint of the assumptions that an image should satisfy in order for a particular technique to be applicable to it. These assumptions, which are often not stated explicitly, can be regarded as (perhaps informal) "models" for classes of images. The paper emphasizes two basic classes of models: statistical models that describe the pixel population in an image or region, and spatial models that describe the decomposition of an image into regions.

Television image size altering apparatus

Abstract: In television image size altering apparatus of the type wherein pixels relating to a composite video signal are sampled at a synchronous real time rate and wherein the flow of pixel information is coordinated through a memory by a write control and a read control, the composite pixel information is separated into original pixels relating to each basic component of the video signal. Interpolated pixel values are then derived from the original pixel values at an effective rate less than the synchronous rate when compressing the image size and at an effective rate greater than the synchronous rate when expanding the image size. The interpolated pixel values are then combined into new pixel values relating to a new composite video signal and the new pixel values are presented for display at the synchronous rate to alter the size of the television image.

Geometric Correction, Registration, and Resampling of Landsat Imagery

Abstract: SUMMARYThe geometric distortions introduced by the LANDSAT imaging system are well known. However, the satellite does not provide attitude information with sufficient accuracy to determine the geographical position of each picture element or pixel. Thus, to map the data onto the desired space it is necessary to model a geometric transformation from a set of ground control points. Transformation of a LANDSAT image to a UTM co-ordinate grid to 50 metres accuracy (rms) under optimum conditions has been demonstrated. The main factor limiting the ultimate accuracy of the corrected image is the precision to which ground control points on the UTM maps can be mapped to pixels in the LANDSAT image. Digital correlation methods have been used successfully in image-to-image registration to improve the accuracy by 25%, but for map registration, this requires accurately located ground control photographic chips.Various resampling techniques including sin (Πx)/Πx expansions, cubic splines, and Lagrange polynomials are d...

Method and apparatus for improved digital image processing

Abstract: An improved method and apparatus for digital image processing is disclosed which permits greater efficiency in implementation of digital filtering techniques. In one implementation specially selected small generating kemels, or masks, are sequentially convolved with a data array of pixels representative of a particular image for more efficient restoration, enhancement or other conventional digital image processing techniques. The small generating kernels may be varied for each sequential convolution. in some implementations the output of each sequential convolution may be weighted in accordance with the filtering desired. Means for implementing the method are also disclosed.

Image data processor

Abstract: An image data processor for recognizing the degree of variation in the object in the image by dividing an image plane into a plurality of block regions and by sequentially comparing an input image and a background image for each of the divided block regions. The data to be used for comparing the input image and the background image are either the number of occurences of preset amplitude relationships of the signals which are produced by extracting the signals of plural pairs of picture elements in spacially preset relative position relationships from the output signals of an image pickup device while sequentially shifting the positions of the picture elements and by accomplishing the counting operations for each pair of the picture elements when the picture element extracted is included in a preset block region or the data which are produced by linearly transforming the data of the number of occurences.

System for reducing the visibility of the noise in television pictures

Abstract: A television signal noise reduction system employs a movement detector for automatically selecting one of three parallel processing paths, the first of which passes the video signal without modification and the other two of which calculate different weighted averages of the current pixel and surrounding pixels from the current frame and the previous frame.

Tradeoff between Picture Element Dimensions and Noncoherent Averaging in Side-Looking Airborne Radar

Abstract: An experiment was performed to determine the effect on radar image interpretation of: 1) rectangular instead of square pixels, and 2) spatial resolution in the presence of noncoherent averaging. The result is a proof of the hypothesis that interpretability of images is determined by a "spatial-gray-level (SGL) resolution volume" that is the product of the range resolution, the azimuth resolution, and a gray-level resolution. The last is defined as the ratio of the value exceeded 10 percent of the time to that exceeded 90 percent of the time for a chi-square distribution having twice as many degrees of freedom as the number of independent samples averaged. Since the area of the pixel enters, rather than explicit dependence on range or azimuth resolution, rectangular pixels are as interpretable as square pixels having the same area. The SGL accounts for the effect of reduction in fading on interpretability. The numerical interpretability assigned by experienced image interpreters asked to look for specific classes of targets was found to fall exponentially with increasing SGL volume, with a scale determined by the class of target. The experiment showed that, for most of the tasks assigned to the interpreters, the interpretability is reduced to 37 percent for a fully focussed synthetic-aperture radar (SAR) (1-look) for a 10-m (33-ft) square pixel. With an infinite number of samples averaged, the comparable square-pixel dimension is 48 m (157 ft). This is consistent with results obtained using LANDSAT images of about 60-m resolution.

Electronic rescreen technique for halftone pictures

Abstract: A method for rescreening a halftone image to produce an edge-enhanced halftone copy from a halftone original. The halftone original is scanned by a raster input scanner and the resultant analog voltage is compared to a reference voltage to produce a one bit per pixel bit stream, where a pixel is defined as the smallest image (picture) element discernable by the system. For example, in a raster input scanner using a CCD array, the smallest picture element, pixel, is the analog voltage output of one CCD cell. This voltage subsequently can be converted to a digital gray scale representation requiring a plurality of bits per pixel, or either analog or digital representation can be compared to an analog or digital reference voltage to produce a one bit pixel. A six bit per pixel gray scale output is produced therefrom by adding an integrated value and an edge enhancement value for each input pixel received. The integrated value is calculated by summing the number of one bits in the seven by nine bit section surrounding each pixel. The edge enhancement value is calculated by determining the difference between the number of one bits in the right and left halves, and upper and lower halves, of the six by seven bit section surrounding each pixel. A set of equations is used to process these differences to produce an edge enhancement value which is added to the integrated value. From this six bit per pixel gray scale output the six bit output can be preserved, or a halftone copy can be produced by any well-known process. A simple and inexpensive circuit to perform the above functions at high data rates is also disclosed.

Soft x-ray spectrometric imaging system

Abstract: An apparatus for simultaneously obtaining both non-dispersive and spatially-resolved soft x-ray spectra from a distributed soft x-ray source. A charge coupled device (CCD) camera having a back-illuminated CCD is irradiated by an x-ray source and a mechanical shutter or electronic shutter effect is used to define an integration period for the pixels of the CCD that ensures that the probability of a single pixel receiving more than one photon during the integration period is small. The magnitude of the charge at each pixel over an integration period is stored in a memory device and, after a plurality of integration periods have passed, the stored data for each pixel may be individually analyzed or combined and displayed to image the x-ray source.

Imaging by varying the placement of elements in the pixels

Abstract: A digital laser platemaker for imaging an electrophotographic member by electrostatic techniques using information which is derived from a source of binary data. The binary data may be achieved by scanning a pattern or may be synthesized electrically to represent that which it is desired to reproduce on the electrophotographic member. The binary data is applied to a pixel generator which is constructed and arranged to produce an output in the form of signals for driving an acusto-optic deflector that in turn deflects a laser beam to form a composite of rays. The composite of rays represent the columns of a pattern to be applied to each pixel which is generated, the rows of the pixel being represented by the output of a shaft encoder that is synchronized with the rotation of a cylinder carrying the electrophotographic member. The pixel generator produces hexagonal pixels and the pattern in each pixel represents density information derived from the binary data originally received by the pixel generator. The patterns in the pixels are arranged to prevent undesirable moire effects. The electrophotographic member receives the composite rays from a carriage which moves in synchronism with the rotation of the cylinder and the rate at which the composite rays are applied. The resulting latent image is toned and fused on the cylinder. Thereafter it may be used as the printing plate after certain processing.

Low contrast object extraction device

Abstract: A system for automatic thresholding video data to educe and detect objects of interest from both high and low contrast imagery is disclosured here, which makes an object screening system adaptive to changing scene intensity and contrast levels automatically is disclosed. The real-time adaptive image interval extraction device extracts the edges of an object and simultaneously generates a bright signal for intensity larger than a given threshold. The interval, over which an object may exist, is derived from a logical combination of edge and bright signals. The video data is smoothed by a two-dimensional, weighted average, low pass or smoothing filter and passed through two filters, an edge filter and a bright filter. The edge filter determines the edge intensity magnitude associated between sucessive picture elements or pixels in the scan line of video data. An edge threshold is determined automatically from the average edge intensity of each scan line of data. When the data edge becomes greater than the edge threshold, a logical edge output is produced. In the same manner, the data is also passed through a bright filter which emphasizes data above a given background threshold. The background and threshold is updated on a line by line basis. This produces a logical bright signal when the intensity is above the automatically determined threshold.

An algorithmic approach to controlling search in three-dimensional image data

Abstract: In many three-dimensional imaging applications random shaped objects, reconstructed from serial sections, are isolated to display their overall structure in a single view. This paper presents an algorithm to control an ordered search strategy for locating all contours of random shaped objects intersected by a series of cross-section image planes. Classic search techniques in AI problem solving and software for image processing and computer graphics are combined here to aid program initialization and automate the search process thereafter. Using three-dimensional region growing, this method isolates all spatially connected pixels forming a structure's volume and enters image planes the least number of times to do so. An algorithmic description is given to generalize the process for controlling search in 3-D image data where little core memory is available. Phantom and medical computer tomographic data are used to illustrate the algorithm's performance.

Fractional clock edge smoother for a real-time simulation of a polygon face object system

Abstract: The data base for an aircraft flight simulator provides position data for each vertex of each object face in the gaming area plus color, intensity, etc. for each face. The vertex data is combined with aircraft position data and processed to generate two dimensional display vectors (Vd=Xd+Yd) for each vertex. A display generator converts the Xd portion for each vertex into a series of scanline-edge intersections Xdc which define the leading and trailing intersections between each horizontal scanline and the edges of each face. The MSB portion of the intersection coordinate Xdc of each scanline-edge intersection is compared to the incrementing pixel number as the scan proceeds to determine which pixel contains the intersection. The actual change within each pixel of intensity or color associated with scanning across the edge is determined by the LSB portion of Xdc. Each pixel is subdivided into a set of fractional pixels having progressively delayed START DISPLAY times. The LSB portion identifies the particular start time for each edge-scanline intersection. This increased resolution in the horizontal position of each change in intensity or color correspondingly reduces the horizontal dimension of the "staircase" effect inherent in digital displays. The spacing between adjacent START DISPLAY times may be adjusted to accommodate the "worst case" requirement of clearance between start pulses. The resulting series of nonuniformly spaced start times may then include more start times within a single pixel, further reducing the staircase effect.

Binary correlation video tracker

Abstract: A binary correlation video tracker and a video preprocessor included therein, which function cooperatively to form binary patterns of values for the picture elements (pixels) in a predetermined pixel array of each of a plurality of frames of video gray level information generated by an electro-optical sensor, is disclosed. Histograms are formed for selected pixel arrays in the predetermined array of a video frame in accordance with a set of predetermined gray level values. The formed histograms are combined in accordance with a discriminant function to form a composite histogram from which at least one gray level value of the set is selected. Those pixels of the predetermined array which have gray level values corresponding to the selected at least one gray level value are assigned one of two predetermined values, the other pixels being assigned the other of the two predetermined values, whereby a binary pattern of values for the predetermined pixel array is formed. Accordingly, the video tracker selects a reference binary pattern of pixels from the formed binary pattern of the predetermined pixel array of one video frame. The selected reference binary pattern is used for performing auto and cross-correlation operations in the video tracker in accordance with a binary correlation coefficient function. In the cross-correlations, another reference binary pattern of pixels and position thereof in the predetermined array is derived for each of the video frames generated subsequent the one video frame, the results being used in the computation of tracking errors in the video tracker. In the auto correlations, a maximum autocorrelation value is derived for use in determining when the reference binary pattern may be updated with the another reference binary pattern for further binary correlation processing.

Multiple mode raster scanner

Abstract: An image input terminal (IIT) with automatic document handler for feeding documents to be scanned into registered position on the IIT platen. The IIT includes a pair of multi-element scanning arrays with cooperating scan lamp and optics on a movable carriage disposed in scanning relationship with the platen. Analog image signals generated by the scanning arrays are initially processed in separate channels and then combined into a serial stream. The stream of analog image signals may optionally be thresholded or screened to provide binary level image signals or converted to multi-bit gray scale. A control system including microprocessor provides timing and control signals for synchronizing operation of the scanning carriage, document handler, and image signal reading and processing together with electronic crossover between arrays to avoid loss of data, automatic signal gain and deletion of bad image signals or pixels. On board array alignment apparatus permits adjustment of array focus, skew, height, position and overlap.

Statistical Study of Edges in TV Pictures

Abstract: The present study is devoted to the statistical analysis of edges in still monochrome TV pictures. The visual information carried by the edges is especially important both for image interpretation and for subjective image quality evaluation. Statistical knowledge on edges is helpful to improve image coding techniques significantly as well as processing techniques for scene analysis. After an introduction on nonstationary local statistical models, we describe the parameters of edges and the methods used to measure them. Statistical data collected on these parameters are then presented. The data concern orientation, edge length, edge width, runlength between edges and edge slope probability distributions as well as the measure of orientation continuity along an edge and the relative frequencies of edge pixels and contrasted isolated pixels.

Image Feature Extraction Using Diameter-Limited Gradient Direction Histograms

Abstract: Features extracted by operators which examine diameter-limited gradient direction histograms are important because they describe images of industrial workpieces efficiently and have the potential for rapid computation via special purpose hardware. When such operators are passed over an image in raster fashion, features such as the following are detected: a strong peak in the direction histogram indicating the presence of a relatively straight edge, a second strong direction indicating a corner, a wide direction group indicating a curved edge, and a uniform distribution of directions over the histogram indicating small holes. Diameter-limited optimization can be used to substantially reduce the number of pixels which have been given feature labels by such operators without losing descriptive power. Feature labels for direction histograms having a second strong direction, a wide direction group, or a uniform distribution might be retained only if all other pixels within a circular aperture have a lower bin value. Pixels with a strong direction label might be retained only if all other pixels within a circular aperture and along the gradient direction have a smaller bin value. Tracking can then be applied to the remaining strong direction pixels in the direction perpendicular to the gradient to achieve representation of edges by endpoints. Experimental results indicate that descriptions which are compatible with human interpretation can be achieved.

Method and means for preserving original continuity/discontinuity among same colored pel clusters upon array compression

Abstract: Data manipulation apparatus is described for converting raster-scanned data received, for example, from a scanner 2 at a first picture element (pel) resolution to a second lower pel resolution for display, for example, on a CRT terminal 4. The apparatus includes a scale-changing means 8 which functions to replace selected subgroups of pels in the input image by single pels at its output. The significance of each single pel reflects the presence or absence of a pel representing part of an image object in the associated subgroup of pels. The number of pels in the selected subgroups are determined by the degree of compression required to convert to the lower pel resolution. Prior to scale change, the apparatus functions to modify the input data in order to minimize merging of adjacent image objects as a result of scale change and thereby improve the legibility of the output image at the lower resolution. The scanned data is first supplied to a data sensitive thinner 5 which detects narrow gaps between adjacent objects and selectively detects image object edge pels in order to widen the gap. The selectively thinned scanned data is then supplied to a further thinner 6 which removes excess image pels from selected edges of the image objects. The data from thinner 6 is then supplied to a data sensitive merge inhibit unit 7 which moves selected image object pels from a subgroup in which merging as a result of scale change will occur to an adjacent subgroup where merging will not occur. Removal of a pel by the selective thinner 5, or by the thinner 6 or movement of a pel by unit 7 is inhibited if to do so would result in fragmentation of the associated image object.

Raster display refresh system

Abstract: A raster display refresh system includes a charge coupled device (CCD) circulating refresh memory for maintaining a display of information on a cathode ray tube (CRT) screen. The X and Y address of picture elements to be changed are stored in raster scan sequence in a small random access memory (RAM). Whenever a picture element address in the data register of the RAM equals the X and Y screen address of the scanning beam of the CRT, a corresponding new picture element signal stored in the RAM is substituted for the old picture element signal previously circulating the CCD refresh memory.

Local image restoration by a least-squares method

Abstract: Restoration of individual image points by the method of least squares is investigated. We show that restorations computed point by point appear the same as global restorations produced by Fourier techniques. Moreover, parameters that are related to noise, point-spread functions, or object texture can be varied easily from pixel to pixel, allowing a flexibility that is achieved only with computational difficulty in global restoration techniques. To restore individual pixels, only a few points in their neighborhood, need to be considered, and the matrices that must be inverted are small enough for practical computation. The sizes of these matrices can be reduced especially if the blurring point-spread function has symmetries.

Technique for DC restoration in AC coupled display systems

Abstract: A technique for DC restoration in AC coupled display systems which includesistogramming, more specifically calculation of histogram values, of the difference in gray levels between two adjacent picture lines on a picture element by picture element (PIXEL-by-PIXEL) basis. The gray level obtaining the maximum number of occurrences is considered the mode of the histogram values. This mode used as an addition factor to every PIXEL of one of the lines, to add a predominating background level or DC component thereto, which is used to create the difference of gray levels between the next two adjacent picture lines. This addition sequence is carried on throughout the entire image frame.

Generating smooth 2-D monocolor line drawings on video displays

Abstract: One of the major drawbacks of video display systems for line drawing applications has been the poor image quality they usually produce—“jaggy”, “staircased” line edges, moire patterns in regions of closely spaced lines, even, with some systems, lines disappearing (“falling in”) between pixels. Correcting these effects, with appropriate area-sampling techniques, has generally been too computationally expensive to adopt.A new algorithm is presented which generates precise, smooth images of line drawings and solid polygonal-shaped objects on multi-grey-level pixel-mapped video systems. The method is based on an analysis of boundary conditions at each pixel affected by one or more lines. With this method a number of previously needed steps can be quickly eliminated. The commonality of boundary conditions between adjacent pixels and the coherence of such conditions in a raster-scan ordering of such pixels allows efficient generation of these boundary conditions. A recursive subdivision approach allows handling of arbitrarily complex cases by a simple boundary-analyzing technique. Compared with current line-drawing systems, a video system with this algorithm would also display an improved image with respect to certain common visual effects—e.g., distance modulation of line intensity (which may be desirable), artificial small bright clusters of detail (which is undesirable).Since the software interface to the algorithm may be handled through already-standard graphical subroutines, adoption of the algorithm may be accomplished without burdening graphic system users or graphic system-utilizing software.

A tutorial on compensation tables

Abstract: The generation of computer-shaded pictures requires that a program calculate intensities for each pixel. These intensities are then viewed on a monitor or transferred to film. It is desirable that ...

Halftone implementation apparatus

Abstract: A scanned raster is divided into halftone cells that are, for example, four by four picture elements (pixels) in size, i.e., it takes sixteen picture elements to make one halftone cell. The tone is determined by summing a different and predetermined threshold value for each of the picture elements that comprise a halftone cell. Each of these signals is then sliced at a predetermined value; if the sum of the threshold and the video value is higher than the slicing level, the picture element is transmitted as a "1", and if below the slicing level, it is sent as a "0".

Region Representation: Raster-to-Quadtree Conversion

Abstract: : An algorithm is presented for constructing a quadtree for a binary image given its row-by-row description. The algorithm processes the image one row at a time and merges identically colored sons as soon as possible so that a minimal size quadtree exists after processing each pixel. This method is spacewise superior to one which reads in an entire array and then attempts to build the quadtree. Analysis of the algorithm reveals that its execution time is proportonal to the number of pixels comprising the image.

Moving image scanner

Abstract: An image scanner for scanning a document along a plurality of scan lines and providing a plurality of print control signal pulses in response to the image density of the document along the scan lines includes a means for projecting a moving document image onto a focal plane and a sensor array positioned in the focal plane. The sensor array includes columns of sensors extending parallel to the direction of image movement and a shift register associated with each column for sensors for shifting electrical outputs from the sensors in the direction of image movement. In a line copy mode of operation, the electrical outputs are shifted at the same rate at the rate of movement of the image such that the given pixel on the image is scanned sequentially by each of the sensors in a column. The electrical outputs are compared with a predetermined reference label to produce a print control signal. In a gray scale mode of operation, the outputs from all of the sensors in a sensor column are accumulated to produce an output related to the average image density of the area scanned by the column of sensors. The electrical outputs resulting from successively scanning overlapping image areas are integrated until a predetermined reference level is reached to produce a print control signal.

Low-level processing for real-time image analysis

Abstract: This paper describes a system that detects object outlines in television images in real-time. A high-speed pipeline processor transforms the raw image into an edge map and a microprocessor, which is integrated into the system, clusters the edges and represents them as chain codes. Image statistics, useful for higher level tasks such as pattern recognition, are computed by the micro processor. Peak intensity and peak gradient values are extracted within a programmable window and are used for iris and focus control. The algorithms implemented in hardware and the pipeline processor architecture are described. The strategy for partitioning functions in the pipeline was chosen to make the implementation modular. The microprocessor interface allows flexible and adaptive control of the feature extraction process.

Information forming apparatus

Abstract: The present invention is featured, in the transmission of pixel (picture element) signals grouped into blocks defined in a series of pixel signals, by sending a control signal instead of said pixel signals when the pixel signals contained in a block are all white signals or sending pixel signals after modulation when black signals are present in said block thereby compressing the time required for transmission, also by selecting the maximum amplitude of said control signal larger than the maximum amplitude of said modulated pixel signals thereby enabling identification of said control signals from said pixel signals, and by sending, when the final black pixel signal in a black signal containing block is followed by consecutive white pixel signals, a control signal instead of such white pixel signals thereby achieving further compression of the transmission time.