Showing papers on "Grayscale published in 1991"

Method and apparatus for halftone rendering of a gray scale image using a blue noise mask

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. Application specific modifications of the blue noise mask as well as its use for producing halftoned color images are also disclosed.

Method and system for embedding machine readable digital data in grayscale images

Abstract: The present invention provides a system and method for unobtrusively embedding machine readable digital data of many different types in grayscale images for a wide variety of different purposes. To accomplish that, digital data is written into such an image by means of a low contrast modulation of the grayscale density of background portions and/or certain foreground features of the images, suitably at a spatial frequency and a modulation contrast that cause the resulting grayscale modulation of the image to fall below the perceptual threshold of the ordinary observer who views the image from normal viewing distance. The foreground features that are amenable to having digital data encoded in them are those that nominally have a substantially uniform grayscale density over an appreciable area, such as alphanumeric characters and halftone dot patterns, as well as uniformly shaded lines and blocks.

Digital halftoning using a blue noise mask

Abstract: A new digital halftoning algorithm in which the halftoning algorithm is achieved by a pixelwise comparison of the gray scale image against a non-image array, the blue noise mask, is proposed. The blue noise mask is constructed such that when thresholded at any level, the resulting binary pattern has the correct first order statistics, and also its power spectrum has blue noise (high frequency) characteristics which are visually pleasing. The construction of the blue noise mask is described and experimental results are shown. Results from a psychovisual study are provided where subjects rated halftoned images that have the same first order but different second order statistics. >

Method and system for enhancing the quality of both color and black and white images produced by ink jet and electrophotographic printers

Abstract: A method of gray scale printing of dots of one or more colors into pixels and in a controlled ordered sequence into a plurality of super pixels defined by a given number of said pixels, characterized in that: one or more levels of dot loading (Pg. 29 line 20 et seq.) are used to achieve different values of gray level in a multiple-level gray table. This generic method is applicable to both ink jet and electrophotographic printing species of this invention. In one electrophotographic printing species of this invention, there is disclosed a method of electrophotographic color printing which includes mixing a plurality of colors in a single plane and in dot-next-to-dot (DND) pixels within a plurality of super pixels to produce a color image, whereby the sum or the multi-color dots printed in any super pixel is limited to the number of subdivided individual pixels therein (Pg 28 line 19 et seq.), thereby assuring dot-next-to-dot (DND) always printing of said colors in a single plane. The above method further includes varying the area of each printed color dot within each pixel of a super pixel in order to control the gray scale of a printed color image. Gray scale printing is achieved by controlling the selection of a gray table entry level number (Pg. 29 line 20 et seq.) representative of one of several available entry level numbers corresponding to a plurality of different dot loadings for a corresponding plurality of differently printed super pixels.

Automatic separation of text from background in scanned images of complex documents

Abstract: A system that converts a scanned image of a complex document into an image where text has been preserved and separated from the background. The system first subdivides the scanned image into blocks and then examines each block pixel by pixel to construct a histogram of the gray scale values of the pixels. The histogram is partitioned into a first, middle and last regions. If one or more peaks occur in the first and last regions, and a single histogram peak occurs within the middle region, the pixels are reexamined to determine the frequency of occurrence of pixels having a gray scale level of the middle peak nearby pixels which have a level of a first region peak. If this frequency is high, the middle peak is assumed to be background information. After determining the threshold, the system rescans the block applying the threshold to separate the text from background information within the block.

Method for displaying and printing multitone images derived from grayscale images

Abstract: The method of displaying multitone images beginning with a grayscale original image capable of displaying a specific number of gray levels, which includes the steps of: (1) selecting a plurality of colors from the image, one for each of the multitones, each having a color value; (2) selecting a plurality of transfer functions, one for each of the selected colors; (3) converting each of the shades of gray, using the respective color values and the transfer functions, into a new color value; and (4) displaying the resultant multitone image on a video display terminal using the new color values in place of the shades of gray. The displayed image may be printed using one printing plate for each of the selected colors, and using the same transfer functions to convert the shades of gray to new gray values which are subsequently converted into halftone dots for each printing plate.

Apparatus and method for smoothing regions and enhancing edges in gray scale images

Abstract: An apparatus and method for enhancing image data elements used to form a gray scale image are disclosed. The apparatus includes an adaptive neighborhood mask that is applied to a group of data image elements centered about a selected pixel to segregate the elements into center and surround regions about the selected element or pixel. The mask further modifies the elements with weighting factors to derive a contrast vector for the selected data elements in the adaptive neighborhood. This vector is compared to a smoothing window and a pair of edge enhancement windows to determine whether the selected element requires smoothing or enhancement to more clearly define a surface or an edge, respectively. If the element requires smoothing or enhancing, its gray scale value is modified, otherwise it is not modified. The device performs this task for each data element. The enhanced data is analyzed to determine if further enhancement is possible and, if so, the process continues upon the adjusted data until the enhancement of the image data is maximized. An edge area selector may further enhance the image data elements by selecting a small group of elements at the unterminated end of a detected edge in the enhance image. The selected group is enhanced by adjusting the edge enhancement window or by changing the weighting factors and restoring the gray scale values of the selected group to their unenhanced values.

Sunset: a hardware-oriented algorithm for lossless compression of gray-scale images

Abstract: Sunset is a lossless gray scale compression algorithm designed for a simple hardware implementation based on the prediction error context approach for predictive gray-scale compression. Sunset uses adaptive binary arithmetic coding with neighboring prediction error buckets as compact conditioning contexts for directly encoding the prediction error. A prototype card was built to send or receive either compressed or uncompressed images across the IBM PC/AT bus. A special interface was designed to load the memory buffer of a high resolution color display. The result is a component of a workstation prototype for radiologists and the physician who referred the patient. The Sunset approach handles gray scale images where the bits-per-pel precision is simply an input parameter to the algorithm; the compression algorithm itself is relatively insensitive to this parameter. For hardware simplicity, the error bucket (bin) identifier is determined by a leading-one detector (or priority encoder) circuit on the prediction error so the number of prediction error values per bucket is a power of two. The next less significant bits of the prediction error become the ''extra-bits'' which, when encoded, make the algorithm lossless. The number of extra-bits in a final (catch-all) bucket depends on the bits-per-pel parameter of the uncompressed image.

Accurate estimation of surface normals in 3-D data sets

Abstract: A CT scanner or other medical diagnostic imager (A) generates data which is reconstructed (B) into a three-dimensional image representation that is stored in an image memory (C). Points on a surface (10) of a selected subregion, such as the surface of an internal organ, in the three-dimensional image representation are determined (12) which are visible from and correspond to pixels on a viewing plane (14). For each viewable point on the surface, a mean variation along an x, y, and z-coordinate system with its origin at the surface point in question is determined (20). A covariance matrix whose matrix elements along the diagonal are indicative of a rate of variance along each axis and whose other matrix values are indicative of a rate of variance relative to pairs of axes is defined (20). A rate of most rapid change through the 3D data is determined (22), by eigenvalue decomposition (24) of the covariance matrix. A vector along the rate of most rapid change is normalized (26). Gray scale shading for a pixel of a man-readable display (E) corresponding to the surface point is determined (28). In the preferred embodiment, the gray scale shading is proportional to the cosine of the angle between the normalized vector in a direction of most rapid gray scale change and a light source vector. In this manner, the surface normal to a surface at the points which correspond to each pixel of an image display are efficiently determined and provided with an appropriate gray scale value to make the two-dimensional image display appear as if it were three-dimensional.

Image analysis method

Abstract: A method and device for interpreting and processing medical ultrasound and other video images. The mix of reflection coefficients in pixel windows is measured by determining the range and distribution of pixel gray scale values to establish "echoic texture" characteristics. These characteristics are compared with corresponding characteristics of known tissues. The degree of correlation allows a prediction of tissue characteristics of the examined window.

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.

Method and apparatus for data reduction in a video image data reduction system

Abstract: Reducing the amount of data required to describe a greyscale image is achieved by determining the modal greyscale and giving all pixels within a tolerance level of, for example, ±2 greyscale levels of the modal greyscale, a logic value of 0. This leads to significant data reduction since proportionally very many pixels are effected. The contrast extremes of the image are unaffected however so that the image remains reasonably comprehensible.

Color display control apparatus for controlling display gray scale of each scanning frame or each plurality of dots

Abstract: According to this invention, a panel controller converts display data having 64 gray scale levels for a color CRT output from an RAMDAC into display data having 57 gray scale levels to perform display driving of a color LCD. The panel display controller has a function of generating 7 intermediate pseudo gray scales between the base frames of R, G, and B signals by a frame rate control method in the color LCD having 8 base gray scale levels of each of the R, G, and B signals to generate (180K colors) display data having 57 gray scale levels and a function of generating 3 intermediate pseudo gray scales between the base gray scales of the signals by a dither method to generate (24K colors) display data having 39 gray scale levels. The selection of the frame rate control or the dither method and the selection of the 512-color, 180-K-color, or 24-K-color display are arbitrarily performed, or these selection operations are automatically performed in accordance with a display mode.

Method and apparatus for halftoning of images using grayscale error diffusion

Abstract: Internal moire artifacts found in digital halftoning of photographic images are diffused by rearranging the order of grayscale levels in an original screen pattern cell to generate a new screen pattern cell having a different grayscale order of stored screen pattern pixels. The grayscale order of the original cell is modified by the addition of a bump function at each point in the original cell in order of grayscale. The new grayscale order is stored in the new cell. Adding the bump function at the chosen point in the original cell influences the choice of the next pixel in the grayscale so that the grayscale order in the new cell is, in general, somewhat different from the grayscale order in the original cell. Errors caused by internal moire effects are thus both diffused in the grayscale dimension, and also diffused isotropically in the spatial dimension. The effect of rearranging the order of the grayscale levels in the screen pattern cell is to diffuse the internal moire artifacts in the final halftone to nearby pixels, thereby rendering the internal moire artifacts less noticeable.

Image processing using the HSI color space

Abstract: Traditional interfield spatial filtering in the YIQ color space is compared with new spatial filtering techniques developed using the HSI color space. Results based on an extended version of the CCIR impairment scale are presented. The present experiments are based on renderings of computation grids obtained from the MSU/NFS Engineering Research Center for Computational Field Simulation. It is shown that there are three significant points to be considered when performing spatial filtering in the HSI color space for the purpose of flicker reduction. First, sharpness degradations are normally considered more objectionable than flicker degradations. Second, luminance and intensity filtering are visually equivalent. Third, saturation processing can be used to introduce appropriate colors into the gray scale fringe regions that are generated by intensity processing, but hue processing must be used in conjunction with this to avoid the red fringe effect. Therefore, the marginal improvement in image quality does not normally justify the additional computational effort required. >

Method and apparatus for enlarging gray scale images

Abstract: An image scaler which enlarges gray scale images, comprised of any number of gray scales, by any rational factor expressible as a ratio of integers between 1:1 and 2:1. The scaling method is "data conservative" in that it always keeps all of the original gray scale pixel values of the input image, generating additional pixel values as needed to produce an enlarged output image. The scaler generates an insertion number sequence for determining where to insert vacant pixel storage locations and calculates gray scale values for those newly created vacant locations by interpolating between values of neighboring pixels.

Calibration method for video image reproduction with electronic printer and video monitor

Abstract: A technique for calibrating a cathode ray tube multiformat camera and a video monitor. A video image is corrected on a pixel-by-pixel basis and a gray scale is produced on a photosensitive medium, such as film, and on a monitor with uniform quantization in perceived lightness (i.e., perceived lightness or gray shade varies linearly with digital image code value). Consequently, there is no loss of small-signal and strong-signal structures (detail), and all the image information is recorded on film and clearly displayed on the monitor.

Image processing method and apparatus for converting gray-scale images into binary images

Abstract: A method and an apparatus for converting the gray images inputted from the image pickup elements into binary images without losing the shape information of the gray images. The image processing method comprises the steps of obtaining the maximum values and the minimum values of the density for each horizontal scanning line and each vertical scanning line of the inputted images, obtaining the threshold values from the adjacent maximum values and minimum values, obtaining the two type binary images for each horizontal scanning line and each vertical scanning line with the threshold values, obtaining the composed binary images with the logical product or the logical sum between the respective pixels of the above two type binary images.

Iterated Transform Image Compression

Abstract: : The objectives of this research were to present in a clear manner an algorithm based on iterated transforms that can be used to compress grayscale images and demonstrate the algorithm and present results for various images. The theoretical framework for iterated transform image compression has been generalized to include noncontractive transforms. The method has been used to encode the 512 x 512 8-bpp image of Lena at a compression of 15.9:1 with the decode image having a root mean square error of 6.33 (32.1 dB). Other images have been encoded at various encoding conditions with the resulting compressions ranging from 10:1 to 63:1. It was shown that the relaxation of the contractivity constraint can lead to improvement in the fidelity of decoded images.

A Fast Morphological Filter For Enhancement Of Angiographic Images

Abstract: In this paper we present an algorithm for enhancement of angiogra hic images using morphological opening filter. Opening ora gray-scale image by a gray-scale structuring element(SE) can generate a background image. To remove the background image , we can subtract it from the original image. Usually, there are a large number of computations involved in gray-scale opening operation. We present a skipped SE algorithm which can significantly improve the processing speed, and yet gives excellent enliancement for the angiographic images.

System and method for image enhancement

Abstract: Analog video data input is received by a video capture system and digitised. From the pels of the captured image, a gray scale level histogram is constructed with the system processor, and normalised to established white-black references similar to the contrast control function at image capture time. Peaks likely attributable to image artifacts are limited. The image processor then performs a second order best fit regression of the histogram from which the image is thereafter corrected. An automatic correction of the image contrast is thereby effected, wherein capture artifacts are reduced while retaining those of the image. In an alternate embodiment, instead of limiting peaks, an iterative best fit is performed, wherein the peaks are weighted in a subsequent best fit pass as a function of their distances from the curve fit from a prior best fit pass.

A neural net based architecture for the segmentation of mixed gray-level and binary pictures

Abstract: A neural-net-based architecture is proposed to perform segmentation in real time for mixed gray-level and binary pictures. In this approach, the composite picture is divided into 16*16 pixel blocks, which are identified as character blocks or image blocks on the basis of a dichotomy measure computed by an adaptive 16*16 neural net. For compression purposes, each image block is further divided into 4*4 subblocks and, similar to the classical block truncation coding (BTC) scheme, a one-bit nonparametric quantizer is used to encode 16*16 character and 4*4 image blocks. In this case, however, the binary map and quantizer levels are obtained through a neural net segmentor over each block. The efficiency of the neural segmentation in terms of computational speed, data compression, and quality of the compressed picture is demonstrated. The effect of weight quantization is also discussed. VLSI implementations of such adaptive neural nets in CMOS technology are described and simulated in real time for a maximum block size of 256 pixels. >

Grayscale/resolution tradeoffs in image quality

Abstract: Thls paper describes a metric for predicting thc perceptual similarity bctween a lob7-resolution grayscale character and the higher-resolution binary bitmap that was used to generate the grayscale character. The metric is used to quantify perceptual tradeoffs between the number of graylevels in a character bitmap and the resolution of the sampling grid.

Thresholding method for segmenting gray scale image, method for determining background concentration distribution, and image displacement detection method

Abstract: In a thresholding method for segmenting gray scale image which is less dependent on the concentration distribution of the input image, the threshold in determined as a zero-cross point of a histogram difference between the concentration histograms for the gray scale image within the window at a window position at which the window contains more high concentration region and at a window position at which the window contains more low concentration region. Also, in a method of determining a background concentration distribution from an image having an arbitrarily distributed pattern, the background concentration level is determined as a peak concentration or a mean value concentration of a low concentration section of the histogram difference of the concentration histograms for two associated windows. Also. in an image displacement detection method capable of detecting a displacement of a pattern in a two dimensional image accurately by using only a one-dimensional pattern matching without any period mismatching error even for an image of a repetitious pattern, the discplacements in the vertical and lateral direction which are locally minimum and for which a discrepancy in an oblique direction is minimum are selected as the actual displacements.

Improved image analysis method

Abstract: A method and device for interpreting and processing medical ultrasound and other video images. The mix of reflection coefficients in pixel windows is measured by determining the range and distribution of pixel gray scale values to establish 'echoic texture' characteristics. These characteristics are compared with corresponding characteristics of known tissues. The degree of correlation allows a prediction of tissue characteristics of the examined window.

Rapid Euclidean distance transform using grayscale morphology decomposition

Abstract: A fast and exact Euclidean distance transformation using grayscale mathematical morphology is presented. The large structuring element required for this operation is decomposed into iterative applications of simple 3*3 windows. This is possible because the square of the Euclidean distance matrix is easily decomposable. Non-square pixels can also be used in this application. >

Apparatus for converting resolution and gray scale of document image data

Abstract: An apparatus for converting a resolution and a gray scale of document image data, which includes a latch circuit for setting variable values of image control data, a resolution-converting clock generator for generating resolution-converting clock signals, a clock selector for selecting a pixel clock signal, a unit data detector for detecting byte detecting clock signal according to gray scale conversion as a unit data, an image data converter for gray scale conversion and binary codification of the image data, an image data selector for selecting the gray scale of the image data of the image data converter, and an image data output portion for outputting the image data with the selected gray scale in units of bytes. The image data processing can be performed at high speed, and the resolution and the gray scale control is carried out in the hardware, which allows the apparatus to be highly compatible and also to be widely adapted.

Pattern spectrum morphology for texture discrimination and object recognition

Abstract: The pattern spectrum describes the shape and size of structures in an n-dimensional signal. Measurement of the pattern spectrum is based on morphological operations which use a variety of structuring elements to filter a signal at multiple spatial scales. This paper reports on the use of pattern spectra in the grayscale domain for classifying different textures and in the binary domain for object recognition. The advantage of morphological image processing is that it is based on highly parallel primitive operations which are amenable to large-scale implementation in real-time signal processing hardware.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A neural algorithm for variable thresholding of images

Abstract: A two-stage thresholding for gray scale images is presented in this paper. The first stage is based on a conventional application of the histograms which provides fixed global threshold value. This threshold value is then assigned as the initial state of a set of neurons which will process the image in parallel, in a horizontal scan, producing the binary image at the output. The state of the neurons is updated using the Kohonen self-organizing learning algorithm. This technique has two properties, First it smooths the spike noise, and second the low frequency illumination variation is compensated for and the segmented binary image regions are not affected by lighting conditions. Several examples are processed and presented to show the performance of the algorithm. >