Showing papers on "Pixel published in 1988"

An improved illumination model for shaded display

Abstract: To accurately render a two-dimensional image of a three-dimensional 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 information is stored in a tree of “rays” extending from the viewer to the first surface encountered and from there to other surfaces and to the light sources. A visible surface algorithm creates this tree for each pixel of the display and passes it to the shader. The shader then traverses the tree to determine the intensity of the light received by the viewer. Consideration of all of these factors allows the shader to accurately simulate true reflection, shadows, and refraction, as well as the effects simulated by conventional shaders. Anti-aliasing is included as an integral part of the visibility calculations. Surfaces displayed include curved as well as polygonal surfaces.

A statistical and geometrical edge detector for SAR images

Abstract: A constant-false-alarm-rate (CFAR) edge detector based on the ratio between pixel values is described. The probability distribution of the image obtained by applying the edge detector is derived. Hence, the decision threshold can be theoretically determined for a given probability of false alarm as a function of the number of looks of the image under study and the size of the processing neighborhood. For a better and finer detection, the edge detector operates along the four usual directions over windows of increasing sizes. A test performed, for a given direction, on a radar image of an agricultural scene shows good agreement with the theoretical study. The operator is compared with the CFAR edge detectors suitable for radar images. >

Image sequence enhancement using sub-pixel displacements

Abstract: Given a sequence of images taken from a moving camera, they are registered with subpixel accuracy in respect to translation and rotation. The subpixel registration allows image enhancement with respect to improved resolution and noise cleaning. Both the registration and the enhancement procedures are described. The methods are particularly useful for image sequences taken from an aircraft or satellite where images in a sequence differ mostly by translation and rotation. In these cases, the process results in images that are stable, clean, and sharp. >

Vehicle detection through image processing for traffic surveillance and control

Abstract: A vehicle detection system for providing data characteristic of traffic conditions includes a camera overlooking a roadway section for providing video signals representative of the field (traffic scene), and a digitizer for digitizing these signals and providing successive arrays of pixels (picture elements) characteristic of the field at successive points in space and time. A video monitor coupled to the camera provides a visual image of the field of view. Through use of a terminal and in conjunction with the monitor, an operator controls a formatter so as to select a subarray of pixels corresponding to specific sections in the field of view. A microprocessor then processes the intensity values representative of the selected portion of the field of view in accordance with spatial and/or temporal processing methods to generate data characteristic of the presence and passage of vehicles. This data can be utilized for real-time traffic surveillance and control, or stored in memory for subsequent processing and evaluation of traffic flow conditions.

Determining optical flow from sequential images

Abstract: An exact method determining the optical flow is presented by means of pixel-based mutual-correlation analysis of dynamic images. The mutual-correlation function is calculated between the temporal brightness change of the target pixel and that of its neighboring 16 (or 8) pixels. The local velocity of the target pixel is determined exactly through logical considerations using a reliable lag time estimated by the quadratic interpolation technique. The validity of the proposed method is confirmed by computer simulation of various dynamic images.

Geometric camera calibration using systems of linear equations

Abstract: Geometric camera calibration is the process of determining a mapping between points in world coordinates and the corresponding image locations of the points. In previous methods, calibration typically involved the iterative solution to a system of nonlinear equations. A method is presented for performing camera calibration that provides a complete, accurate solution, using only linear systems of equations. By using two calibration planes, a line-of-sight vector is defined for each pixel in the image. The effective focal point of a camera can be obtained by solving the system that defines the intersection point of the line-of-sight vectors. Once the focal point has been determined, a complete camera model can be obtained with a straightforward least-squares procedure. This method of geometric camera calibration has the advantages of being accurate, efficient, and practical for a wide variety of applications. >

Autonomous robotic vehicle road following

Abstract: A description is given of the system architecture of an autonomous vehicle and its real-time adaptive vision system for road-following. The vehicle is a 10-ton armored personnel carrier modified for robotic control. A color transformation that best discriminates road and nonroad regions is derived from labeled data samples. A maximum-likelihood pixel classification technique is then used to classify pixels in the transformed color image. The vision system adapts itself to road changes in two ways; color transformation parameters are updated infrequently to accommodate significant road color changes, and classifier parameters are updated every processing cycle to deal with gradual color and intensity changes. To reduce unnecessary computation, only the most likely road region in the segmented image is selected, and a polygonal representation of the detected road region boundary is transformed from the image coordinate system to the local vehicle coordinate system based on a flat-earth assumption. >

State machine controlled video processor

Abstract: A system and method of merging and manipulating pixel information for display on a raster scan monitor is disclosed. The invention operates at speeds imperceptible to the viewer by collecting, in each memory access cycle, the data representing multiple pixels and by performing merge and manipulation functions on pixel groups at video rate under control of control data from a state machine. The state machine allows for unique processing decisions to be made for every pixel group displayed on the monitor.

Motion vector estimation in television images

Abstract: Apparatus for motion vector estimation in a television image using a digitized signal representing the image, comprises a vector filter (36) and a vector calculator (37) for determining motion in the image at points spaced a predetermined number of pixels horizontally and a predetermined number of pixels vertically by a block matching technique, thereby to derive motion vectors, and a sub-pixel motion estimator (39) for refining the selection of the motion vectors by determining a sub-pixel offset representing motion between fields of the image not equal to an integral multiple of the spacing between pixels.

Parallel rendering of smoothly shaded color triangles with anti-aliased edges for a three dimensional color display

Abstract: SIMD computer architecture is used in conjunction with a host processor and coordinate processor to render quality, three-dimensional, anti-aliased shaded color images into the frame buffer of a video display system. The method includes a parallel algorithm for rendering an important graphic primitive for accomplishing the production of a smoothly shaded color three-dimensional triangle with anti-aliased edges. By taking advantage of the SIMD architecture and said parallel algorithm, the very time consuming pixel by pixel computations are broken down for parallel execution. A single coordinate processor computes and transmits an overall triangle record which is essentially the same for all blocks of pixels within a given bounding box which box in turn surrounds each triangle. The individual pixel data is produced by a group of M×N pixel processors and stored in the frame buffer in a series of repetitive steps wherein each step corresponds to the processing of an M×N block of pixels within the bounding box of the triangle. Thus, each pixel processor performs the same operation, modifying its computations in accordance with triangle data received from the coordinate processor and positional data unique to its own sequential connectivity to the frame buffer, thus allowing parallel access to the frame buffer.

Anti-aliasing raster operations utilizing sub-pixel crossing information to control pixel shading

Abstract: A method and apparatus for performing anti-aliasing of rendered lines, text and images displayed by a workstation on a video display. The anti-aliasing is performed by logically dividing each addressable frame buffer pixel into sixteen sub-pixels and generating a gray scale value for the displayed pixel that is a function of the number of sub-pixels crossed by a portion of a rendered image. The invented circuitry is part of the circuitry used for combining source and destination data which forms the displayed image namely, an anti-aliasing mask and filter, adder/subtractor logic, saturation logic and anti-aliasing logic.

Method for enhancing image data by noise reduction or sharpening

Abstract: An image enhancing process promotes either noise reduction or image sharpening on a pixel-by-pixel basis as a function of the recognition of specific patterns of sampled pixel values surrounding each pixel to be enhanced The sampled pixel values are divided into two or more subgroups and the enhanced pixel value is provided to promote either image sharpening or noise reduction as a function of the number of pixel values in the different subgroups and their positions relative to each other in the subgroups

Digital halftoning with minimum visual modulation patterns

Abstract: A digital halftone image is produced by providing a binary bit image pattern having a minimum visual noise for each density level in an image. The patterns are produced by employing a stochastic combinatorial minimization technique and a human visual system modulation transfer function (MTF) weighting function to generate a halftone pattern for each density level of the multi-level digital image signal. A halftone image is produced by modularly addressing these patterns with each pixel value in the image.

Method and apparatus for transmitting compression video data and decoding the same for reconstructing an image from the received data

Abstract: METHOD AND APPARATUS FOR TRANSMITTING COMPRESSED VIDEO DATA AND DECODING THE SAME FOR RECONSTRUCTING AN IMAGE FROM THE RECEIVED DATA For transmitting video data in a block format having predetermined number of pixels in each block arranged in coordinates of one- or two-dimensional configuration, each block is provided with at least one function of a predetermined degree having respective coefficients corresponding to respective terms thereof and defining a plane or curved surface. Parameters are obtained as the coefficients of the selected function to give a value for each of the pixels by performing the function of the respective coordinates, and such parameters are transmitted for each block. At the receiving side, the coordinates of the pixels contained in each block are generated, and the values of the pixels are determined for reconstructing a video image therefrom by performing on the coordinates the function which corresponds to the received parameters.

Depth buffer priority processing for real time computer image generating systems

Abstract: A method is disclosed for determining color information in a computer image generated display in which the display is divided into a plurality of spans and each span comprises a matrix of pixels, each of the pixels being further divided into a matrix of subpixels, which method (or apparatus for performing it) allows overlapping and inner penetrating faces appearing in an image to be resolved without conflict. Faces of objects appearing in an image are resolved by a range ordering process for each span in an image. The faces are reordered into range separable groups in which a range separable group is defined as faces in which the maximum range to the most distant face in a group does not overlap the minimum range of the nearest face in another group. Each range separable group of faces is then processed on a per pixel basis for determining the color contribution of that face or group of faces to each subpixel within a pixel. In one form, the process of identifying the colors contributing to a pixel may be terminated at the end of processing of one group of faces when at least a minimum number of subpixels within a pixel have been identified as covered by faces in the processed group. Where groups of faces cannot be divided into range separable groups, forced separation of groups can be implemented by establishing a predetermined maximum number of faces in a group or by inserting a pseudo-face within a group and breaking the groups at the pseudo-face.

Image reconstruction from linograms: implementation and evaluation

Abstract: The notion of a linogram corresponds to the notion of a sinogram in the conventional representation of projection data for image reconstruction. In the sinogram, points which correspond to rays through a fixed point in the cross section to be reconstructed all fall on a sinusoidal curve. In the linogram, however, these points fall on a straight line. The implementation of a novel image reconstruction method using this property is discussed. The implementation is of order N/sup 2/ log N, where N is proportional to the number of pixels on a side of the reconstruction region. It is demonstrated that the performance of the algorithm is superior to that of the filter backprojection method in computational speed on realistic size problems and is equivalent to filtered backprojection in accuracy of reconstruction. >

Apparatus and method for additive/subtractive pixel arrangement in color mosaic displays

Abstract: A liquid crystal display unit is described in which a first panel of pixel elements is used to control red and green portions of a displayed image using an additive technique while a second panel, having pixels aligned with the first panel pixels, controls the blue portion of the image through subtractive techniques. The resulting display system can provide enhanced brightness, resolution and color characteristics. The display system makes use of the fact that the eye is less sensitive to blue radiation for several visual parameters. As a result of the decreased sensitivity, the second (blue) panel can operate with less stringent requirements.

Motion vector selection in television images

Abstract: Apparatus for processing motion vectors associated with a digital television image comprises a vector filter (36) and a vector calculator (37) for deriving a plurality of motion vectors respectively representing the motion of a pixel in the image, a circuit (101, 104) for testing the accuracy of each motion vector by differencing pixels shifted in dependence on the motion vector from two successive fields of the image to a common position in a field interpolated between the two fields, and a vector selector (103) for selecting a motion vector from the plurality in dependence on the testing.

Color image processing device

Abstract: A color image processing device including a reader for reading an original image for each area containing a predetermined number of pixels of the original image and color-separating the read area into red, green and blue components, a character area detector for detecting whether or not the area read by the reader is a character area constituting a part of a character in the original image for each of the red, green and blue components, and a black character area determinator adapted to determine the area read by the reader to be a black character area constituting a part of a black character in the original image if said area is detected to be the character area for all of the red, green and blue components by the character area detector

Method of representing a perspective image of a terrain and a system for implementing same

Abstract: A method is provided for representing, on a display device screen and in perspective from a given point of observation, the image of a terrain known by the nodes of a given mesh network, in which for each image pixel, the point of intersection is determined of the line which starts from the point of observation and which passes through this image pixel with a surface passing through the nodes and taking on approximately the shape of the ground, and said image pixel is illuminated with the color of the pixel associated with a digitized planimetric map or photograph of the ground.

Halftone image recording method using recording data having a plurality of concentrations for one color

Abstract: A method for halftone image recording, wherein dots are formed using two or more concentrations of ink, to express different image densities. Each picture element may comprise a plurality of cells, different predetermined members and patterns of which are actually printed in, to express different gradations. Different such patterns may be used for each ink concentration. Several such patterns, using only thin ink, may, for example, be used to express lower densities, several others, using only thick ink, for high densities, and still others, using dots of thin ink and dots of thick ink, for intermediate densities. For color image recording, different concentrations and different members of concentrations can be used for different colors.

Active matrix LCD image projection system

Abstract: An active matrix LCD light valve between crossed polarizers, utilizing individual transistors to control each "pixel area" of the LCD and storage elements to store signal data for each pixel, with optically shielded "dead spaces" between pixels to eliminate electric field crosstalk and non-information-bearing light bleed through, is illuminated with a bright independent light source which creates a video image projected via specialized projection optics onto an internal or external screen without distortions, regardless of the angle of projection onto the screen. Use of heat sinks, IR reflective coatings, heat absorbing optics, optional fluid, and a thermistor controlled pixel transistor bias voltage injection servo circuit stabilizes image performance, maintaining accurate color and contrast levels as the LCD changes temperature. In one embodiment of the invention, use of a multi-color LCD with a stepped cavity, producing different thicknesses of LCD for the different wavelengths that pass through it, allows a linear correspondence between the wavelengths passing through the LCD to produce true black, high contrast, and CRT-like color rendition. A dichroic mirror arrangement is used to overlap differently colored pixels and a striped mirror system is used to duplicate and offset the resulting "full color" pixels or a lens system is used to expand existing pixels to fill the "dead spaces" between pixels in the projected image, creating a continuous image with no apparent stripes or dots. A special venetian-blind type of screen is also disclosed and methods for using the system to view three dimensional video are also explained.

Optical characteristics of a deformable-mirror spatial light modulator.

Abstract: Some of the optical characteristics of a recently developed solid-state deformable-mirror spatial light modulator have been investigated. The device is composed of an array of 128 × 128 pixels, with each pixel consisting of four hinged reflective rectangular surfaces. Modulation at video frame rates has been achieved, providing real-time displays in coherent light, which may be useful for a variety of optical processing and computing applications.

Updatable micrographic pocket data card

Abstract: A strip of optical contrast laser recording material (17) is disposed on the wallet-size card (11), and has laser written characters recorded thereon. The characters are formed by a plurality of pixels, similar in nature to the dots forming dot matrix characters, except that the pixels themselves are formed of spots. The spots are disposed in a geometric regular array and are usually written one column at a time until a complete pixel is formed. Machine readable (19) and visually readable characters (23) may be combined on a single data strip.

Method for scene-model-assisted reduction of image data for digital television signals

Abstract: A method for scene-model-assisted reduction of image data for digital television signals, whereby a picture signal supplied at time t is to be coded, whereby a predecessor frame from a scene already coded at time t-1 is present in an image store as a reference, and whereby the frame-to-frame information are composed of an amplification factor, of a shift factor and of an adaptatively acquired quad-tree division structure, and it is provided that, upon initialization of the system, a uniform, prescribed gray scale value or picture half-tone expressed as a defined luminance value is written into the image store of a coder at the transmitter and in the image store of a decoder at the receiver store, and are in the same way for all picture elements (pixels), and both the image store in the coder as well as the image store in the decoder are each operated with feed back to themselves in a manner such that the content of the image store in the coder and decoder can be read out in blocks of variable size, and can be amplified with a factor greater than or less than 1 of the luminance and can be written back into the image store with shifted addresses, whereby the blocks of variable size are organized according to a known quad-tree data structure.

Apparatus and accompanying methods for achieving automatic color balancing in a film to video transfer system

Abstract: Apparatus and accompanying methods for use in a film to video transfer system for achieving automatic color balancing of color images for subsequent display on a color monitor. Specifically, this apparatus first transforms each pixel in an image to be transferred from logarithmic exposure ("log exposure") RGB color values into corresponding printing density values through local averaging, then utilizes a printing density based color correction method to generate a color correction offset value for each of the RGB primary colors, and finally converts the three resulting RGB color correction offset values from the printing density domain back to the log exposure domain wherein each offset value is subsequently used to correct the corresponding red, green and blue color values associated with each of the pixels that collectively forms a subsequent scan of the same image prior to the conversion of each of the color balanced RGB pixel values into analog video form.

Method and apparatus for improving the alignment of radiographic images

Abstract: In a diagnostic process in which two images are made on an image recording medium of the same structure at the beginning and the end of a time interval during which the structure changes, a method is provided for permitting a computing device to improve the alignment of the images as reproduced in the form of pixels on a monitor screen. A particular spatial pattern of marker elements is provided, when each of the images is made, in a particular juxtaposition to the structure being imaged, so that the shadows of the elements arise on the respective images. The computing device can then rotate, translate and alter the scale of one image with respect to the other until the shadows of the elements on one image coincide as closely as possible with those on the other image.

A new chain-coding algorithm for binary images using run-length codes

Abstract: This paper presents a new algorithm for converting a binary image into chain codes using its run-length codes. The basic idea of conventional chain-coding algorithm is to follow boundary pixels by convolving a 3 × 3 window with the image and to sequentially generate chain codes. The proposed algorithm has two phases, namely run-length coding and chain-code generation. We use connectivity information between runs as well as their coordinates in the phase of run-length coding. In the second phase (chain-code generation) the connectivity information extracted in the first phase is utilized for sequentially tracking runs containing the boundary pixels to be followed. This algorithm has an advantage that we can detect easily the inclusion relationship between boundaries at the same time as chain-code generation.