Showing papers on "Grayscale published in 1993"

Morphological grayscale reconstruction in image analysis: applications and efficient algorithms

Abstract: Two different formal definitions of gray-scale reconstruction are presented. The use of gray-scale reconstruction in various image processing applications discussed to illustrate the usefulness of this transformation for image filtering and segmentation tasks. The standard parallel and sequential approaches to reconstruction are reviewed. It is shown that their common drawback is their inefficiency on conventional computers. To improve this situation, an algorithm that is based on the notion of regional maxima and makes use of breadth-first image scannings implemented using a queue of pixels is introduced. Its combination with the sequential technique results in a hybrid gray-scale reconstruction algorithm which is an order of magnitude faster than any previously known algorithm. >

Interactive computation of holograms using a look-up table

Abstract: Several methods of increasing the speed and simplicity of the computation of off-axis transmission holograms are presented, with applications to the real-time display ofholographic images. The bipolar intensity approach allows for the real-valued linear summation of interference fringes, a factor of 2 speed increase, and the elimination of image noise caused by object self-interference. An order of magnitude speed increase is obtained through the use of a precomputed look-up table containing a large array of elemental interference patterns corresponding to point source contributions from each of the possible locations in image space. Results achieved using a data-parallelsupercomputer to compute horizontal-parallaxonly holographic patterns containing six megasamples indicate that an image comprised of 10,000 points with arbitrary brightness (gray scale) can be computed in under 1 s. Implemented on a common workstation, the look-up table approach increases computation speed by a factor of 43.

Spatially Nonuniform Scaling Functions for High Contrast Images

Abstract: An algorithm is presented that scales the pixel intensities of a computer generated greyscale image so that they are all displayable on a standard CRT. This scaling is spatially nonuniform over the image in that different pixels with the same intensity in the original image may have different intensities in the resulting image. The goal of this scaling transformation is to produce an image on the CRT that perceptually mimics the calculated image, while staying within the physical limitations of the CRT.

Grayscale area openings and closings, their efficient implementation and applications

Abstract: The filter that removes from a binary image its connected components with area smaller than a parameter is called area opening. From a morphological perspective, this filter is an algebraic opening, and it can be extended to grayscale images. The properties of area openings and their dual area closings are recalled. In particular, it was proved in [13] that the area opening of parameter of an image is the supremum of the grayscale images that are smaller than and whose regional maxima are of area greater than or equal to . This theorem is at the basis of an efficient algorithm for computing grayscale area openings and closings. Its implementation involves scanning pixels in an order that depends both on their location and value. For this purpose, the use of pixel heaps is proposed. This data structure is shown to be both efficient and low in memory requirements. In addition, it can be used in the computation of various other complex morphological transforms. The use of these area openings and closings is illustrated on image filtering and segmentation tasks

Direct gray-scale extraction of features for character recognition

Abstract: A method for feature extraction directly from gray-scale images of scanned documents without the usual step of binarization is presented. This approach eliminates binarization by extracting features directly from gray-scale images. In this method, a digitized gray-scale image is treated as a noisy sampling of the underlying continuous surface and desired features are obtained by extracting and assembling topographic characteristics of this surface. The advantages and effectiveness of the approach are both shown theoretically and demonstrated through preliminary experiments of the proposed method. >

Principles and Concepts of Computed Tomography

Abstract: The final CT image is actually made of a grid of tiny squares called pixels. The scale of grays assigned to each pixel represents the attenuation of x-rays by the structures in the tomographic slice. Manipulation of the gray scale allows optimal visualization of all the tissues within the slice. This control over the gray scale and the absence of structure superimposition are the advantages of CT over conventional x-ray techniques. The steps used to acquire the final CT image are collection of data from the patient (recording of transmitted x-ray intensities from many angles), computer processing of data (mathematical calculation of attenuation of each structure in the tomographic slice), image display (assigning of appropriate gray scale to CT image to evaluate all structures), and data storage (recording series of tomographic images on x-ray film and archiving image data for later review). Common image artifacts that must be identified and interpreted as such include aliasing, ring artifacts, beam hardening effect, metal, motion, partial volume averaging, and streaking from out-of-field objects.

A Survey of Quality Measures for Gray Scale Image Compression

Abstract: Although a variety of techniques are available today for gray-scale image compression, a complete evaluation of these techniques cannot be made as there is no single reliable objective criterion for measuring the error in compressed images. The traditional subjective criteria are burdensome, and usually inaccurate or inconsistent. On the other hand, being the most common objective criterion, the mean square error (MSE) does not have a good correlation with the viewer's response. It is now understood that in order to have a reliable quality measure, a representative model of the complex human visual system is required. In this paper, we survey and give a classification of the criteria for the evaluation of monochrome image quality.

High speed, high resolution web inspection system

Abstract: A modular system and method using the system for the high speed high resolution inspection of printed webs are provided. Each module inspects one lane of a printed web for print defects. Each gray scale or bipolar gray scale gradient pixel value of a digitally converted input image is compared to the minimum and maximum threshold values of the image template by a real-time digital signal processor. The image template is created in a secondary non-real-time processor by producing a statistical representation of a number of input images. The image template is desensitized to longitudinal and transverse jitter of the printed web so that jitter is not identified by the system as a print defect. The user is signaled if actual print defects exist and the lanes in which the defects exist are identified.

Method and apparatus for halftoning and inverse halftoning and the transmission of such images

Abstract: A method of and system for rendering a halftone image of a gray scale image by utilizing a pixel-by-pixel comparison of the gray scale image against a blue noise mask is disclosed in which the gray scale image is scanned on a pixel-by-pixel basis and compared on a pixel-by-pixel basis to an array of corresponding data points contained in a blue noise mask stored in a PROM or computer memory in order to produce the desired halftoned image. Both digital and optically implemented halftone methods are disclosed. A method for obtaining the inverse halftone or gray scale image of a halftone image is also disclosed in which the halftone image can be comprised of clustered dots or dispersed dots, and it is not necessary to have knowledge of the screening methods or parameter. A method for transmitting and receiving a gray scale image in a compressed and decompressed manner, respectively, is disclosed for efficient facsimile transmission of images.

Method and system for rapidly transmitting multicolor or gray scale display data having multiple bits per pixel to a display device

Abstract: A method and system for rapidly transmitting multicolor or gray scale display data having multiple bits per pixel to a display device is provided. In a preferred embodiment, the method and system constitutes a software facility. The facility first encodes the image into multiple bit per pixel raster data. The multiple bit per pixel raster data has a number of pixels. Each pixel stores a color value corresponding to the color of a particular region within the image. The facility then associates one or more single bit per pixel raster planes with the multiple bit per pixel raster data. Each single bit per pixel raster plane corresponds to a color value that appears in the multiple bit per pixel raster data. Each pixel of each single bit per pixel raster plane corresponds to a pixel of the multiple bit per pixel raster data, and indicates whether the corresponding pixel in the multiple bit per pixel raster data contains the color value of the single bit per pixel raster plane. The facility then transmits the associated single bit per pixel raster planes to the display device. Each single bit per pixel raster plane is accompanied by one or more instructions to draw the single bit per pixel raster plane in the corresponding color value.

Method and apparatus for converting a halftone image into a continuous tone image

Abstract: A method and apparatus for converting a binary image into a gray scale image includes a pipeline having a number of nearly identical stages. At each stage, modifications occur to provide the gray scale image by following a sequence of steps including: (1) determining a sample mean value representing an averaging of pixel values within a neighborhood containing a selected pixel; (2) determining a weighted variation value representing pixel value variations within the neighborhood; and (3) adjusting the pixel value of the selected pixel toward the sample mean value if the difference between the pixel value and the sample mean value exceeds the weighted variation value. The adjustment to the pixel value is in the direction of the sample mean value. Preferably, the weighting of the variation value is different at each stage. At each stage along the pipeline, low pass filtering is provided to remove high frequency noise generated by the process.

Image restoration using a multilayer perceptron with a multilevel sigmoidal function

Abstract: The problem of restoring a blurred and noisy image having many gray levels, without any knowledge of the blurring function and the statistics of the additive noise, is considered. A multilevel sigmoidal function is used as the node nonlinearlity. The same number of nodes as in the case of a binary image is sufficient for an image with multiple gray levels. Restoration is achieved by exploiting the generalization capabilities of the multilayer perceptron network. For realistic images, training time becomes a major burden. To overcome this, a segmentation scheme is suggested. Simulation results are provided. >

An object attribute thresholding algorithm for document image binarization

Abstract: Document image binarization is not a completely solved problem for unconstrained document images. Binarization algorithms, whether global or local, can easily fail on images with noisy or complex background, or poor contrast. The authors report preliminary results on a new approach to document image binarization, an algorithm based on gray scale histogram and run-length histogram analysis. Experimental results on unconstrained machine printed address blocks from the US letter mail stream show that over 99% of such address blocks can be correctly binarized. >

Method for adaptively thresholding grayscale image data

Abstract: A method of generating a remapping function for use in converting near-photographic document image pixel gray level data lying in a first range of gray level values to higher contrast, background-suppressed pixel gray level data lying in a second more limited gray level range. Global document information, such as a histogram of all the document's original pixels, is used to generate at least one threshold gray level value and to determine the shape of the remapping function on either side of the threshold. Preferably, the remapping function is implemented by a look-up table addressed in accordance with the original pixel data.

Apparatus and method for predicting subjective quality of compressed images

Abstract: An apparatus and method are described for predicting a subjective quality rating associated with a reference image compressed at a given level. My apparatus includes components for, and my method includes steps of, storing a digitized color image representing a reference image in memory and compressing at a given level and decompressing the reference image to produce a processed image. My apparatus and method also entail converting the reference image and the processed image each to a grayscale image and dividing each grayscale image into an array of blocks. My apparatus and method further entail generating a first intensity variance array corresponding to the array of blocks of the grayscale reference image and a second intensity variance array corresponding to the array of blocks of the grayscale processed image. Lastly, my apparatus and method entail generating a variance ratio based on the first and second intensity variance arrays, determining a block variance loss based on the variance ratio, and generating the subjective quality rating indicated by the impairment level which is based on the variance loss.

AC plasma gas discharge gray scale graphic, including color and video display drive system

Abstract: A novel drive system is described for AC plasma (ACP) gas discharge flat bistable matrix panels on which real-time video and computer graphics, both with pixel by pixel gray scale are displayed. The drive scheme increases scan speed, reduces complexity and minimizes circuitry required to operate the video and computer graphics gray scale images on the ACP display through: a) unique application of standard high density memory IC architecture, and b) unique panel drive waveform technique. Flicker is avoided with an interlaced framerate of 46 Hz and non-sequential pixel row scanning. The unique panel drive scheme allows high speed operation to avoid flicker in the ACP panel for real time gray scale video and graphic images. Because of the high speed addressing requirements, the panel waveform techniques apply all of the drive voltages to the ACP panel from the row (Y) axis and only selective cancellation voltage from the column (X) axis. This technique results in ground based data transfer from the memory circuits to the column driver ICs, and eliminates significant level shifting through multiple parallel isolation circuits such as transformers or optical couplers. Avoidance of isolation circuits in the X-axis allows higher speed transfer of data into column drivers. The panel addressing requirements for pixel-by-pixel gray scale is minimized through geometric accumulation of pixel on-time per frame. At least 64 levels of gray scale are provided in standard neon ACP displays with pixel rows of 256, 480 and 512, for example.

Error diffusion: a theoretical view

Abstract: Error diffusion has proven to be a very powerful method of producing binary images that are visually similar to the original grayscale images. It has become so popular that many attempts have been made to improve it. In this paper, two modifications to error diffusion, the serpentine raster and threshold modulation, are analyzed from a theoretical viewpoint. The two analyses reveal the origins of the image quality improvements of the modifications and quantify their benefits.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Threshold selection using second derivatives of the gray scale image

Abstract: It is known that when a bilevel image is blurred, the intensity of the original pixels is related with the sign of the curvature of the pixels of the blurred image. A technique for threshold selection is presented where a partial histogram is constructed solely from the pixels where curvature achieves extrema values. The method is most suitable when low-contrast images with textured backgrounds (but not sparse dot matrices) are a large fraction of the input population. >

Halftoning of image sequences

Abstract: We present an algorithm for the halftoning of greyscale image sequences. This facilitates the display of video sequences on black-and-white visual displays (e.g., high-qualityX-terminals) for multimedia applications. The main problem to be overcome when halftoning sequences is the temporal flicker between successive images. The classical problem of halftoning a static greyscale image may be posed as an optimization problem. We present an iterative algorithm for its solution. At the expense of being slower, our algorithm achieves visual results on static images better than those obtained from classic halftoning algorithms. We extend our static halftoning algorithm to image sequence halftoning. Temporal correlation between the halftoned versions of image sequences is guaranteed by using an incremental algorithm transfering information between the images. This results in binary sequences with relatively little high-frequency temporal noise, a feature that facilitates efficient no-loss compression (1∶4) of the results.

Measuring Root Surface Area and Mean Root Diameter of Peach Seedlings by Digital Image Analysis

Abstract: Using area profile integration software and an image processing system, we reliably estimated total root surface area of intact each (Prunus persica (L.) Batsch.) seedlings by 1) producing high-quality monochromatic video images under preset and constant conditions; 2) determining a threshold gray intensity value that differentiates the finest roots on the image; 3) producing a binary image where all pixels with gray values above the threshold are black; 4) determining the proportion of black pixels on the 480× 512-pixel matrix; and 5) multiplying this two-dimensional root surface value by π to estimate total root surface area. Normalized intensity (an average intensity weighted according to the proportion of the binary image in each gray scale class) was calculated using software that superimposed the video image on the binary image and was used to estimate mean root diameter. Evidence of reliability and examples of the use of both estimates are provided.

Clinical utilization of grayscale workstations

Abstract: The factors influencing the image fidelity of gray-scale monitors and how they are determined through both physical and psycho-physical measurements are discussed. Estimation techniques for the amount of image data to be displayed, both the daily digital image data volume and the estimation of the number of gray-scale display stations required, are also examined. Gray-scale display station hardware and software designs are presented. It is pointed out that exceptional attention must be paid to the details of workstation design, as this is the sole interface of the radiologist to the resources of the digital image management network. >

Optimized algorithms for displaying 16-bit gray scale images on 8-bit computer graphic systems

Abstract: Most personal computers contain 8-bit graphic display hardware, whereas most medical gray scale images are stored at 16-bit per pixel integers. To display medical gray scale images on such computers, the 16-bit image data must be remapped into 8-bit gray scale images. This report presents the algorithms and computer code that allow very rapid 16-bit to 8-bit image data transformation. These algorithms are helpful in allowing personal computers with at least the performance of a Macintosh II (Apple Computer, Cupertino, CA) computer to function as low-end picture archiving communication systems or personal workstations.

System and method for bidirectional adaptive thresholding

Abstract: A bidirectional adaptive thresholding technique for use in an image processing system. An array of pixel sensors scans a grayscale image and generates a set of grayscale image data. A buffer storage connected to the sensors stores the grayscale image data. A forward tracker reads the image data from the buffer storage in a forward direction and provides background and peak forward tracked values. A reverse tracker reads the image data in a reverse direction and provides background and peak reverse tracked values. A threshold level generating circuit generates a threshold level that is a proportional function of either the forward or reverse tracked values based on validity criteria. Thereafter, a thresholding circuit thresholds the grayscale image data using the threshold level to provide binary image data.

Address recognition system based on feature extraction from gray scale

Abstract: This paper reports proof of concept of a design for recognizing postal address blocks. The system must function with varying and unspecified fonts, dot matrix printing, and poor print quality. Our design achieves tolerance to differing contrast and degraded print via grayscale analysis, and omnifont capability by encoding character shapes as graphs. The current prototype, restricted to digits, successfully recognizes degraded numeric fields. There are four major modules. First, the strokes comprising each character are detected as ridges in grayscale space. Our design is tolerant of wide contrast variation even within a single character, and produces connected strokes from dot matrix print. Second, strokes are grouped to produce line segments and arcs, which are linked to produce a graph describing the character. The third stage, recognition by matching the input character graph to prototype graphs, is described in a companion paper by Rocha and Pavlidis. Finally, secondary classification is applied to break near ties by focusing on discriminating features. The secondary classifier is described in a companion paper by Zhou and Pavlidis. Experimental results on 2000 address blocks supplied by the USPS are presented. We also report experiments on subsampling the data, which indicate that the performance at 100 dpi is very close to that at the original 300 dpi.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Two-dimensional display model-based halftoning

Abstract: A model-based printing method and system for generating halftone output images corresponding to gray-scale-coded input signals. Models for individual two-level (e.g., black on white) printer types allow predicted printer error signals to be generated which can be used to modify the gray-scale coded signals in such manner as to produce binary signals which, when applied to the printer, create halftone images of enhanced quality. In an alternative embodiment binary signals are selected which minimize an error function based on the difference between (i) a predicted perceived image corresponding to the gray scale inputs as filtered by an eye-model filter and (ii) the halftone image resulting from filtering of the binary sequence by a filter modeling the printer followed by the eye-model filter.

Human arm modeling for analysis/synthesis image coding

Abstract: Analysis/synthesis image coding is potentially a powerful technique for compressing scenes dominated by the head-shoulder images, as in a videotelephone scene with a closeup of the human upper-body. In this paper, we propose a novel approach to image coding of the human arm, based on kinematic modeling of the human arm and motion analysis of the head-shoulder image sequences. The main characteristics of this approach are that i) it relies on the assumption that the human arm can be modeled as a kinematic linkage connected by movable joints, ii) it approximates the 3-D kinematic arm motion from the 2-D image velocities, and iii) it synthesizes shoulder image sequences from one frame of texture image, the wire-frame arm model, and estimated kinematic motion. We evaluated our approach in simulations involving a grayscale monocular image sequence of a moving arm. >

Optical cellular continuous logic array for gray-scale image processing

Abstract: A new optical cellular continuous-logic array for gray-scale image processing is presented. The array involves two steps of multichannel neighborhood ranked-order operations and interimage threshold decomposition continuous-logic operation. Image processing transforms available from this array include gray-scale morphological transforms, stack–nonstack filters, and gray-scale hit-or-miss transforms. An area-coding technique is used to implement neighborhood operations in a correlation thresholding system. A similar one-channel grayscale-correlation and multithresholding system is used for interimage threshold decomposition continuous logic. Primary experimental results are given.