Showing papers on "Pixel published in 1989"

Kalman Filter-based Algorithms for Estimating Depth from Image Sequences

Abstract: Using known camera motion to estimate depth from image sequences is an important problem in robot vision. Many applications of depth-from-motion, including navigation and manipulation, require algorithms that can estimate depth in an on-line, incremental fashion. This requires a representation that records the uncertainty in depth estimates and a mechanism that integrates new measurements with existing depth estimates to reduce the uncertainty over time. Kalman filtering provides this mechanism. Previous applications of Kalman filtering to depth-from-motion have been limited to estimating depth at the location of a sparse set of features. In this paper, we introduce a new, pixel-based (iconic) algorithm that estimates depth and depth uncertainty at each pixel and incrementally refines these estimates over time. We describe the algorithm and contrast its formulation and performance to that of a feature-based Kalman filtering algorithm. We compare the performance of the two approaches by analyzing their theoretical convergence rates, by conducting quantitative experiments with images of a flat poster, and by conducting qualitative experiments with images of a realistic outdoor-scene model. The results show that the new method is an effective way to extract depth from lateral camera translations. This approach can be extended to incorporate general motion and to integrate other sources of information, such as stereo. The algorithms we have developed, which combine Kalman filtering with iconic descriptions of depth, therefore can serve as a useful and general framework for low-level dynamic vision.

Automatic thresholding of gray-level pictures using two-dimensional entropy

Abstract: Automatic thresholding of the gray-level values of an image is very useful in automated analysis of morphological images, and it represents the first step in many applications in image understanding. Recently it was shown that by choosing the threshold as the value that maximizes the entropy of the 1-dimensional histogram of an image, one might be able to separate, effectively, the desired objects from the background. This approach, however, does not take into consideration the spatial correlation between the pixels in an image. Thus, the performance might degrade rapidly as the spatial interaction between pixels becomes more dominant than the gray-level values. In this case, it becomes difficult to isolate the object from the background and human interference might be required. This was observed during studies that involved images of the stomach. The objective of this report is to extend the entropy-based thresholding algorithm to the 2-dimensional histogram. In this approach, the gray-level value of each pixel as well as the average value of its immediate neighborhood is studied. Thus, the threshold is a vector and has two entries: the gray level of the pixel and the average gray level of its neighborhood. The vector that maximizes the 2-dimensional entropy is used as the 2-dimensional threshold. This method was then compared to the conventional 1-dimensional entropy-based method. Several images were synthesized and others were obtained from the hospital files that represent images of the stomach of patients. It was found that the proposed approach performs better specially when the signal to noise ratio (SNR) is decreased. Both, as expected, yielded good results when the SNR was high (more than 12 dB).

Multiple resolution image sensor

Abstract: An image sensor comprised of an array of photo elements (pixels) includes a device for randomly addressing individual pixels and a device for selectively varying the number of pixels which can be read out on any one reading cycle. The random addressing of pixels enables the readout of pixels located in selected regions of interest. Limiting the readout of the images to areas of interest allows an increase in the frame rate of the images. Relatively large groups of pixels can be read out simultaneously and the resulting signals can be merged into superpixel signals to provide high speed data capture, albeit at relatively lower resolution, since there will be a reduced number of data samples in each image. This feature is useful to rapidly scan and analyze a scene being viewed in order to locate an area of interest. Once an area of interest is located, the number of pixels read out on each cycle may be reduced to provide a higher resolution, lower speed, readout of the area of interest.

Subpixel measurements using a moment-based edge operator

Abstract: Recent results in precision measurements using computer vision are presented. An edge operator based on two-dimensional spatial moments is given. The operator can be implemented for virtually any size of window and has been shown to locate edges in digitized images to a twentieth of a pixel. This accuracy is unaffected by additive or multiplicative changes to the data values. The precision is achieved by correcting for many of the deterministic errors caused by nonideal edge profiles using a lookup table to correct the original estimates of edge orientation and location. This table is generated using a synthesized edge which is located at various subpixel locations and various orientations. The operator is extended to accommodate nonideal edge profiles and rectangularly sampled pixels. The technique is applied to the measurement of imaged machined metal parts. Theoretical and experimental noise analyses show that the operator has relatively small bias in the presence of noise. >

A perceptually tuned sub-band image coder with image dependent quantization and post-quantization data compression

Abstract: The authors present a 16-band subband coder arranged as four equal-width subbands in each dimension, It uses an empirically derived perceptual masking model, to set noise-level targets not only for each subband but also for each pixel in a given subband. The noise-level target is used to set the quantization levels in a DPCM (differential pulse code modulation) quantizer. The output from the DPCM quantizer is then encoded, using an entropy-based coding scheme, in either 1*1, 1*2, or 2*2 pixel blocks. The type of encoding depends on the statistics in each 4*4 subblock of a particular subband. One set of codebooks, consisting of less than 100000 entries, is used for all images, and the codebook subset used for any given image is dependent on the distribution of the quantizer outputs for that image. A block elimination algorithm takes advantage of the peaky spatial energy distribution of subbands to avoid using bits for quiescent parts of a given subband. Using this system, high-quality output is obtainable at bit rates from 0.1 to 0.9 bits/pixel, and nearly transparent quality requires 0.3 to 1.5 bits/pixel. >

Massively parallel digital image data processor using pixel-mapped input/output and relative indexed addressing

Abstract: A massively parallel digital image data processor provides a large number of processing elements arranged in a two-dimensional matrix form. Relative indexed addressing among the processing elements is provided, whereby image data may be easily accessed by and shared among all processing elements. A single-instruction/multiple-data (SIMD) architecture provides instructions to the processing elements in parallel in accordance with specific application programs therefor. The processing elements use triple-ported register files for their internal memory which may input and output data independently and simultaneously. The processing elements are memory-mapped into the address space of the processor's embedded computer to simplify addressing thereof. All image data is inputted and outputted in pixel format. All image data is transferred, stored and processed in bit-serial format.

Method and apparatus for non-affine image warping

Abstract: A method and apparatus for two-pass image transformation, providing a general solution to execute arbitrary warping of an image. A bicubic mesh is created, by splines or other suitable means, and is used to create displacement tables for X and Y displacement. Alternatively, the displacement tables can be generated directly. The displacement tables represent the movement of each pixel from an original location in the source image to a new location in the destination image. One of the displacement maps is applied to the source image to create an intermediate image and to the other displacement map to create a resampled displacement map. The resampled map is then applied to the intermediate image to create the destination image. By resampling, compensation for altered location points is done automatically. In this manner, no inversion of the underlying equations and functions is required.

Antialiased ray tracing by adaptive progressive refinement

Abstract: We describe an antialiasing system for ray tracing based on adaptive progressive refinement. The goals of the system are to produce high quality antialiased images at a modest average sample rate, and to refine the image progressively so that the image is available in a usable form early and is refined gradually toward the final result.The method proceeds by adaptive stochastic sampling of the image plane, evaluation of the samples by ray tracing, and image reconstruction from the samples. Adaptive control of the sample generation process is driven by three basic goals: coverage of the image, location of features, and confidence in the values at a distinguished "pixel level" of resolution.A three-stage process of interpolation, filtering, and resampling is used to reconstruct a regular grid of display pixels. This reconstruction can be either batch or incremental.

Separable image warping methods and systems using spatial lookup tables

Abstract: A two-dimensional image is subjected to a three-dimensional effect, such as folding, twisting or rotation, and transformed or warped into a modified output image. By successive one-dimensional resampling along two coordinates and parallel channel processing of transposed input image data with rejection of distorted pixel value data, bottleneck, shear and other distortions are addressed. Complete warping systems, resampling subsystems and related methods are disclosed.

Method for high-quality compression by binary text images

Abstract: The invention relates to a method for the compression and decompression of binary test images. The method distinguishes between large low-frequency areas and small high-frequency areas in the original frame. For the low-frequency areas, a scheme for lossy compression is used, whereas for the high-frequency areas, a scheme permitting lossless compression is applied. The compression/decompression process involves five stages; namely prefiltering to remove all black patches (e.g. by removing all black pixels, except where they belong to a large black segment), fast evaluation of compressibility by partitioning the images into mutually exclusive segments and applying different compression modes to each segment, connectivity-oriented subsampling to reduce the reslolution in horizontal and vertical directions which cause the image to be segmented into blocks and a 1-pixel representation for each block is determined, lossless compression and decompression where the reduced file is compressed by conventional techniques, and reconstruction by sequence reversal so that lossless decompression will retrieve the subsampled file, expansion of the subsampled file through replacement of each pixel by a block having equal value and postfiltering.

Liquid crystal display device for display with grey levels

Abstract: A liquid crystal display device having an arrangement of a plurality of pixel display regions (82) each including a plurality of divided pixels (A-D), and being capable of effecting display with a large number of gray levels. Each of the divided pixels (A-D) is displayed individually and selectively with at least two gray levels. The liquid crystal device further includes pixel electrodes (31-36) for individually and selectively enabling the divided pixels (A-D), and a gray level setting circuit for controlling the sum of the areas of the enabled divided pixels (A-D), thereby setting the gray levels of the pixels. In this device, one pixel display region (82) includes n divided pixels (A-D) and if each pixel (A-D) can be displayed with m gray levels, the areas of the pixels (A-D) are set to form a geometric progression using m as a common ratio, whereby display with mn gray levels for one display region (82) can be effected with high precision.

The pixel machine: a parallel image computer

Abstract: We describe the system architecture and the programming environment of the Pixel Machine - a parallel image computer with a distributed frame buffer.The architecture of the computer is based on an array of asynchronous MIMD nodes with parallel access to a large frame buffer. The machine consists of a pipeline of pipe nodes which execute sequential algorithms and an array of m × n pixel nodes which execute parallel algorithms. A pixel node directly accesses every m-th pixel on every n-th scan line of an interleaved frame buffer. Each processing node is based on a high-speed, floating-point programmable processor.The programmability of the computer allows all algorithms to be implemented in software. We present the mappings of a number of geometry and image-computing algorithms onto the machine and analyze their performance.

Image generator for generating perspective views from data defining a model having opaque and translucent features

Abstract: An apparatus for generating an image from data defining a model including a plurality of opaque and translucent features. The image is intended to represent a view of the model from a predetermined eyepoint and is made up from an array of screen space pixels. The image area is divided into an array of sub-areas each of which covers at least one pixel. For each feature in the model that is potentially visible from the eyepoint, a test is conducted to determine which of the sub-areas is at least partially covered by that feature. For each feature which covers a sampling point, a function of the distance from the eyepoint to that feature at the sampling point is determined. An output for each pixel within a sub-area is produced, the pixel output corresponding to the combined effects of the sampling point outputs for all sampling points which contribute to that pixel, and the pixel outputs are displayed.

Method and apparatus for detecting changes in raster data

Abstract: A method and apparatus which provides for the real time comparison of raster data. The raster data is stored in memory such that raster data corresponding to a specific X-Y coordinate location is consistently written to the same memory location. During the process of storing the data in memory, the data currently stored in the memory is read and compared to the data to be written into the same location in memory. If the data is not the same, the discrepancy and location of the discrepancy is noted in a separate area of memory to be used for subsequent analysis and the the data to be written to that location is immediately written into the memory. The method and apparatus of the present invention is particularly applicable to the video graphics environment wherein the current bit of raster image contained in the frame buffer is compared to the updated raster image and the data changes are noted on a pixel by pixel basis. Utilizing the information gathered on the changed pixels, the video display need only update the changed data, thereby minimizing the amount of data to be transferred and increasing the speed of the system. In a preferred embodiment, the method and apparatus of the present invention is employed to provide an interface between a video adapter such as a video graphics array (VGA) and video display system incompatible with the video adapter such as a windowing system whereby the video output generated by the video adapter is translated and input to the video display system for generation of the display in real time.

Method of and apparatus for displaying a multicolor image

Abstract: A method of displaying a high resolution multicolor image on a lower resolution display. The image comprises a plurality of image pixels containing at least first and second image subpixels having first and second colors. The image is displayed on a display having display pixels comprising at least first and second spatially offset display subpixels capable of displaying the first and second colors, respectively. In the method, the first display subpixel is displayed with an intensity which is a function of the intensities of at least two first image subpixels having positions extending over a first region having an area greater than the area of the first display subpixel. The first region is approximately centered on the position of the first display subpixel. A second display subpixel is displayed with an intensity which is a function of the intensities of at least two second image subpixels having positions extending over a second region having an area greater than the area of the second display subpixel. The second region is approximately centered on the position of the second display subpixel. By using a different centered region for each separate subpixel of a composite RGB display picture element in transforming a high resolution multicolor image to a lower resolution display, higher quality images are produced as compared to using a single region for each composite RGB display picture element.

Printing of pixel locations by an ink jet printer using multiple nozzles for each pixel or pixel row

Abstract: An ink jet printer (60) prints dots (30) of colorant at pixel locations using a printing strategy that reduces the visual impact of improperly operating or inoperable nozzles (18), by using multiple nozzles (18) per pixel location or per pixel In one approach, used either for single color or multicolor images, multiple droplets of colorant of the same color are deposited upon a single pixel location from two different nozzles (18) In another approach, used primarily for multicolor images, different pixels of a single pixel row are printed using a droplets of a single color from different nozzles (18)

Autocorrelation and regularization in digital images. II. Simple image models

Abstract: For pt.I see ibid., vol.26, no.4, p.463-73, July 1988. The variogram function used in geostatistical analysis is a useful statistic in the analysis of remotely sensed images. Using the results derived in Part I, the basic second-order, or covariance, properties of scenes modeled by simple disks of varying size and spacing after imaging into disk-shaped pixels are analyzed to explore the relationship between the image variograms and discrete object scene structure. The models provide insight into the nature of real images of the Earth's surface and the tools for a complete analysis of the more complex case of three-dimensional illuminated discrete-object images. >

A fast and flexible thinning algorithm

Abstract: A fast serial and parallel algorithm for thinning digital patterns is presented. The processing speed is faster than previous algorithms in that it reads pixels along the edge of the input pattern rather than all pixels in each iteration. Using this algorithm, an experiment is conducted and the patterns such as 'X', 'H', 'A', 'moving body', and 'leaf' are tested. The results show that this algorithm is faster, structure-preserving, and more flexible in that it can be done either sequentially or in parallel. >

Quick three-dimensional display

Abstract: A diagnostic imaging system generates a three-dimensional display from a series of two-dimensional slice images. A region of interest, defined from a boundary of interest, is selected from one slice and is extrapolated to subsequent slices. Pixels representative of the boundary of interest are isolated and represented by three vectors having an equivalent entries in each. First and second vectors store data representative of first and second coordinates for pixels within each slice. Entries in the third vector corresponds to physical properties of a specimen at a location defined by corresponding entries in the first and second vectors. Areas representative of boundaries of interest falling between slices are extrapolated from vector data from slices neighboring the area. This is accomplished by a linear interpolation of elements of the set of smaller vectors to a number equivalent to the entries in the neighboring larger vectors. Next, a linear extrapolation between respective elements of the lengthened vector and the longer of the vector is made. Finally, a linear interpolation of the intermediate vector to a number of vector elements intermediate the larger and smaller of the neighboring vectors is made. This process is suitably continued during a preselected number of iterations. Finally, a discretized three-dimensional object represented by all sets of first, second, and third vectors are mapped to pixels of an associated pixel frame.

Interactive visualization of 3D medical data

Abstract: Techniques for rendering 3-D medical data are described. They consist of (1) surface-based techniques, which apply a surface detector to the sample array, then fit geometric primitives to the detected surfaces, and finally render the resulting geometric representation; (2) binary voxel techniques, which begin by thresholding the volume data to produce a three-dimensional binary array; the cuberille algorithm then renders this array by treating 1's as opaque cubes having six polygonal faces; and (3) volume-rendering techniques, a variant of the binary voxel techniques in which a color and a partial opacity are assigned to each voxel; images are formed from the resulting colored, semitransparent volume by blending together voxels projecting to the same pixel on the picture plane. Specialized display devices (stereo viewers, varifocal mirrors, cine sequences, real-time image-generation systems, and head-mounted displays) are described. Topics for future research are identified. >

Image Quality Measure Based On A Human Visual System Model

Abstract: A preliminary image quality measure that takes into account two major sensitivities of the human visual system (HVS) is described. The sensitivities considered are background illumination level and spatial frequency sensitivities. Given a digitized monochrome image, the algorithm produces, among some other figures of merit, a plot of the information content (IC) versus the resolution in units of pixels. The IC is defined here as the sum of the weighted spectral components at an arbitrary specified resolution. The HVS normalization is done by first intensity remapping the image by a monotonically increasing function representing the background illumination level sensitivity, followed by a spectral filtering to compensate for the spatial frequency sensitivity. The developed quality measure is conveniently parameterized and interactive. It allows experimentation with numerous parameters of the HVS model to determine the optimum set for which the highest correlation with subjective evaluations can be achieved. The preliminary results are promising.

Method and apparatus for reading image information formed on material

Abstract: To read a document accurately and produce an image signal faithfully representing the document, an image reading method and apparatus adopts various means, of "latching an average light-shielded signal in a digital form", "using an average light-shielded signal resulting from averaging output signals of a plurality of light-shielded pixels as a black reference signal", "replacing that part of an image signal in which an average light-shielded signal is larger than an effective pixel signal in level with a signal of a zero level", "driving CCD sensors at such timing as to allow effective pixel signals output from the CCD sensors to be continuous in time" and "setting DC offset voltages of signals output from CCD sensors to a predetermined clamp potential."

Field-emitter arrays to vacuum fluorescent display

Abstract: A thin vacuum-fluorescent display utilizing a matrix-addressable array of groups of Spindt-type field-emission emitter tips is described. Development of the display required expanding the cathode fabrication technology to cover 5-in-diameter areas uniformly with field-emitter arrays. Each color element of the display is addressed by a group of a few hundred emitter tips operating in parallel. Electrons emitted from the tips are proximity-focused on each color element. Because each pixel is essentially a miniature cathode-ray tube (CRT), the device has the potential to produce brightness similar to those on a CRT in a panel that is 3.3 in square (8.4 cm) in area and 0.15 in (4 mm) thick. >

A one-pass two-operation process to detect the skeletal pixels on the 4-distance transform

Abstract: A skeletonizing procedure is illustrated that is based on the notion of multiple pixels as well as on the use of the 4-distance transform. The set of the skeletal pixels is identified within one sequential raster scan of the picture where the 4-distance transform is stored. Two local conditions, introduced to characterize the multiple pixels are employed. Since the set of the skeletal pixels is at most two pixels wide, the skeleton can be obtained on completion of an additional inspection of the picture, during which time standard removal operations are applied. Besides being correct and computationally convenient, the procedure produces a labeled skeleton, i.e. a skeleton whose adequacy for shape description purposes is generally acknowledged. >

Pixel interpolator with edge sharpening

Abstract: Methods and apparatus for interpolating existing gray-level pixel data to obtain new pixel values during image reduction and enlargement. A quadratic interpolation equation is used to apply location weighting factors to the density values of neighboring pixels. Edge strength modifying factors are used to modify the weighting factors in the x, y, and diagonal directions. In one embodiment, the modifying factors are set to greater than unity when the corresponding edge strength is greater than a predetermined threshold value. In another embodiment, the modifying factors are a non-linear function of the edge strength. These techniques preserve the sharpness of high contrast edges in the original image.

Bar code location and recognition processing system

Abstract: The present invention provides for a bar code location and recognition processing system. The surface on which the bar code appears is optically scanned and converted to binary digital signals by a digital video processor. The output of the digital video processor is provided to a bar code image processor for location and reading of the bar code. The bar code is located by summing the "black" pixels in segments of predetermined width for each horizontal scan line, and determining the location of the "L" pattern characteristic of a digitized image of a bar code summed in this manner. Reading of the binary data corresponding to the bar code is carried out by summing the "black" pixels in each vertical scan line in a rectangular region generally corresponding to the location of the bar code within the digitized image, selecting a threshold value proportional to the average maxima of these sums, and, by determining which sums substantially exceed and which substantially fall below the threshold values, decode a binary code pattern corresponding to the bar code.

Method for edge enhanced error diffusion

Abstract: A method of dynamically adjusting the threshold level of an error diffusion algorithm to selectively control the amount of edge enhancement introduced into the encoded output. The threshold level is selectively modified on a pixel by pixel basis and may be used to increase or decrease the edge enhancement of the output digital image, thus, more closely representing the original detail and edge sharpness of the continuous tone input image.

Method and apparatus for graphics display data manipulation

Abstract: Special purpose graphics instructions are provided to facilitate hidden surface elimination. A Z-buffer check instruction performs multiple, simultaneous unsigned-integer (ordinal) comparisons of newly computed distance (Z) values with the contents of a Z-buffer. Distances of points to be drawn are compared with corresponding values in the Z-buffer, and appropriate bits of a pixel mask are then set to designate those pixels for which the points to be drawn are closer (smaller) than the Z-buffer values. Previously calculated bits of the pixel mask are shifted so that consecutive Z-buffer check instructions accumulate their results in the pixel mask register. A pixel store instruction utilizes the pixel mask to update only those pixel locations in a frame buffer which correspond to a point on a newly rendered surface closer than the surface represented by the current pixel value.