Abstract: The gamma adjustment allows the luminance for the sub-pixel arrangement to match the non-linear gamma response of the human eye's luminance channel, while the chrominance can match the linear response of the human eye's chrominance channels. The gamma correction allows the algorithms to operate independently of the actual gamma of a display device. The sub-pixel rendering techniques disclosed with gamma adjustment can be optimized for a display device gamma to improve response time, dot inversion balance, and contrast because gamma correction and compensation of the sub-pixel rendering algorithm provides the desired gamma through sub-pixel rendering. These techniques can adhere to any specified gamma transfer curve.

Abstract: The present invention provides an inspection technique using a charged particle beam by which a method of setting a condition for optimally charging an object to be inspected without relying on an operator's experience is established and a voltage contrast image with higher efficiency of defect detection than ever before can be obtained. The inspection method comprises the steps of scanning an area on a surface of a substrate having a specific pattern formed thereon with a primary charged particle beam, detecting signals of secondary electrons emitted from the area, forming an image of the area from detected signals, and generating a histogram from the image. All these steps are performed each time a condition of irradiation with the charged particle beam is changed. When two or more separate peaks appear in the histogram, the histogram is determined as an optimal condition for inspection, and inspection is performed based on the image obtained under that condition.

Abstract: An image processing apparatus processes input pixel data and outputs the processed pixel data as output pixel data. The image processing apparatus includes an input reliability calculation section for calculating an input reliability indicating the reliability of the input pixel data, an output reliability calculation section for calculating an output reliability indicating the reliability of the output pixel data, a motion-amount detecting section for detecting the amount of the motion of the input pixel data, a compensation section for compensating the output reliability according to the amount of the motion, and a processing section for processing the input pixel data according to the input reliability and the compensated output reliability and for outputting the output pixel data.

Abstract: A novel apparatus and method for controlling a system with multiple observable variables is disclosed. The apparatus and method disclosed use elements of the bottom-up and top-down strategies of artificial intelligence to provide a control system that is able to learn without a training set of information, and that has an learning process that can handle any amount of input data, i.e., cannot become saturated. The control system disclosed is capable of learning and controlling non linear dynamical systems. The control system is also capable of adding additional observable variables or subtracting existing observable variables to determine the state of the plant or system being controlled.

Abstract: A method in image processing for detection of a change in the scene in an area. The method comprises the steps of recording a digital image of the area using a sensor and transforming the recorded image by an operator. The operator is based on a previous modeling of changes in the lighting in the area and on a modeling of how the sensor depicts the area in grayscale values in the recorded image. The method further comprises the step of comparing the transformed image with a reference image of the area in order to detect a difference that indicates a change in the scene.

Abstract: Image data of a target pixel and peripheral pixels are stored in a memory. Using a most significant bit extractor circuit, 4 most significant bits of data are extracted from each image data. A histogram circuit generates a histogram of the extracted 4-bit data. Referring to the histogram, a data processor circuit (17) replaces the image data of the target pixel with a maximum value of the numbers of pixels having the same level and outputs the processed data. Then, a digit-complementing circuit converts the data output from the data processor circuit to 8-bit data and outputs the converted data. In this manner, a regular image is converted into an image similar to a draft-design image.

Abstract: A method of producing a tone scale function which operates on a source digital image to improve tonal characteristics, includes receiving a source digital image including a plurality of pixels; and producing a tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image, wherein the highlight tone scale segment is defined by a different mathematical function than the shadow tone scale segment; at least one of the highlight tone scale or shadow tone scale segments have at least one inflection point; the highlight tone scale segment is defined for points that are equal to or greater than the reference point; and the shadow tone scale segment is defined for points that are equal to or less than the reference point.

Abstract: A system is disclosed for equalizing the distribution of pixel intensities in an image displayed by an oscilloscope. In a primarily software implementation, the maximum pixel intensity (I) present in the rasterized input image, the maximum available display intensity (P) and the desired image resolution (R) are the input variables which permit the calculation of thresholds or bins to which each pixel is assigned. By iteratively performing the analysis of existing pixel intensities and bin thresholds, the number of pixels in each bin may be optimized to form an equalized histogram. Another implementation of the histogram equalization system utilizes software to optimize a hardware-based histogram collector.

Abstract: There is described an image-processing apparatus for converting a first image data inputted into the image-processing apparatus to a second image data used in a visible-image outputting apparatus, which forms an image so as to make it visible for a human eyesight based on the second image data.

Abstract: Contrast in an image is enhanced by mapping an input intensity value to an output intensity value in accordance with a mapping function. A mean intensity value of the image is determined. Co-ordinates of the mapping function are calculated in accordance with the mean intensity value and a plurality of predefined parameters. The mapping function is applied to the input intensity value for determining the output intensity, wherein the mapping function is generated dynamically for each image.

Abstract: A method and system for performing automated biological identification. The system including a preprocessing module with a histogram transform for locally and globally enhancing biological data such as fingerprints. An enhancement module with a fast smoothing and enhancement function. A feature extraction module with a fingerprint oriented thinning function. A matching module with a resolution-enhanced Hough transform function for fingerprint registration and matching score function.

Abstract: This invention is directed to a system and method for creating characterization information and a correction map from a first display grid that can be transmitted and used by a second display grid. Computer readable instructions embodied in a computer readable medium calibrate a first display grid and create an ICC color profile and correction map from said calibration information, such that an image to be displayed across an entire display grid which is segmented into portions corresponding to each display device in the display grid is displayed with uniform luminance and color across the entire display grid. The invention can then store the correction map and characterization information and send the information to a second display device for it to use. Alternatively, the calibration or characterization information can be associated with an image file and sent to a second location for display.

Abstract: An image processing method comprises an extracting step for extracting a plurality of images of different depths of a 3-dimensional object, the axes forming different angles with the 3-dimensional object, a binary coding step for eliminating a gray level range of the plurality of images obtained by the extracting step, the gray level range containing a small amount of components of the 3-dimensional object, remapping the other portion to a predetermined gray level value range, and putting the plurality of images in binary form, and a step for forming a 3-dimensional image of the 3-dimensional object based on the plurality of images put in binary form by the binary coding step.

Abstract: Optically scanned data forms an image stored in a computer memory represented as an array having at least two dimensions. The stored image is subjected to virtual scanning. Thus a subset of the array is defined as a portion of the image having first and second dimensions. The value of the subset is derived, the subset is then incremented, and the value of the incremented subset is determined. The steps of incrementing and deriving the value of the incremented subset are repeated. The derived values of the data are compared to a calibrated standard, to create adjusted values of data. The adjusted data values, in the case of electrophoresis, represent the scanned sample which has been subjected to electrophoresis. Thereafter, the adjusted data values can be integrated or otherwise processed.

Abstract: A method of recognizing an object based on pattern matching using a gray-scale normalized correlation method includes storing a reference image including a foreground and a background each having a predetermined value of density distribution; inputting an image of the object which includes a foreground and a background each having a predetermined average value of density distribution; storing a function for giving the predetermined values of density distribution of the reference image equal to the predetermined average values of density distribution of the input image, respectively; and obtaining a maximum normalized correlation coefficient between the reference image and the input image using the function.

Abstract: A method and apparatus for adjusting a printer is disclosed. An area is printed over, and sensors are used to collect pixel values over the area. Then, metric criteria are applied against pixel values to determine whether or not to adjust the number-density of dots to improve print quality. The apparatus includes a print means, sensor, and processor. It may also include storage to store the pixel values.

Abstract: An adaptive image tone mapping curve based on perceptual preference guidelines is generated as a sigmoidal function, in which the sigmoidal function parameters (slope and shift) are determined by original image statistics. Tone curves generated for different images each have a smooth sigmoidal shape, so that the tone mapping process does not change the image histogram shape drastically. The sigmoidal function has the form: t ? ( x ) = 100 1 + exp ? ( - ? ? ( x / 100 - ? ) ) , where ? is the slope parameter and ? is the shift parameter. The input value x in the sigmoidal function varies in the range [0, 100], because the tone curve is generated on an L* scale, which has values from 0 to 100.

Abstract: A method and associated device wherein an inverse histogram based pixel mapping step is combined with an edge enhancement step such as unsharp masking. In such an arrangement the inverse histogram based pixel mapping step improves the performance of the unsharp masking step, serving to minimize the enhancement of noise components while desired signal components are sharpened.

Abstract: A brightness control apparatus comprising a probability density function (PDF) calculator to calculate a PDF based on pixel values of respective pixels of an input image signal, a first setter to set an upper limit value and a lower limit value with respect to the pixel values that are equal to or smaller than a predetermined level in the PDF, and a brightness value controller to calculate a cumulative distribution function for the PDF controlled by the upper and lower limit values set by the first setter, and calculating brightness levels corresponding to the input image signal based on the calculated cumulative distribution function. The brightness control apparatus controls the brightness of an image signal so as to prevent it from becoming unnecessarily bright or dark when compensating the brightness of an image signal, while also preventing degradation of contrast.

Abstract: To produce a black body angiographic image representation of a subject (42), an imaging scanner (10) acquires imaging data that includes black blood vascular contrast. A reconstruction processor (38) reconstructs a gray scale image representation (100) from the imaging data. A post-acquisition processor (46) transforms (130) the image representation (100) into a pre-processed image representation (132). The processor (46) assigns (134) each image element into one of a plurality of classes including a black class corresponding to imaged vascular structures, bone, and air, and a gray class corresponding to other non-vascular tissues. The processor (46) averages (320) intensities of the image elements of the gray class to obtain a mean gray intensity value (322), and replaces (328) the values of image elements comprising non-vascular structures of the black class with the mean gray intensity value.

Abstract: An apparatus and method are provided to equalize a histogram using a cumulative distribution function (CDF) of an image. A model parameter estimator estimates parameters from the image using a Gaussian model. An error function storing unit stores error function values based on a Gaussian distribution. A CDF calculator calculates a CDF using one of the error function values from the error function storing unit and the estimated parameters. A histogram equalizer performs histogram equalization using the CDF.

Abstract: Image data provided from a scanner is simultaneously supplied to page memory and a reference value calculating section. The reference value calculating section creates a density histogram of the document image on the basis of image data corresponding to a predetermined number of image lines and calculates a set of correction reference values for pixel density correction using the density histogram. A range correcting section corrects pixel density indicated by the image data on all the image data read out from the page memory by using the set of correction reference values. The predetermined number of image lines is a fraction of all the image lines of the document image read by the scanner.

Abstract: A bistable electro-optic display has a plurality of pixels, each of which is capable of displaying at least three gray levels. The display is driven by a method comprising: storing a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level; storing data representing at least an initial state of each pixel of the display; receiving an input signal representing a desired final state of at least one pixel of the display; and generating an output signal representing the impulse necessary to convert the initial state of said one pixel to the desired final state thereof, as determined from said look-up table. The invention also provides a method for reducing the remnant voltage of an electro-optic display.

Abstract: A system and process for generating High Dynamic Range (HDR) video is presented which involves first capturing a video image sequence while varying the exposure so as to alternate between frames having a shorter and longer exposure. The exposure for each frame is set prior to it being captured as a function of the pixel brightness distribution in preceding frames. Next, for each frame of the video, the corresponding pixels between the frame under consideration and both preceding and subsequent frames are identified. For each corresponding pixel set, at least one pixel is identified as representing a trustworthy pixel. The pixel color information associated with the trustworthy pixels is then employed to compute a radiance value for each pixel set to form a radiance map. A tone mapping procedure can then be performed to convert the radiance map into an 8-bit representation of the HDR frame.

Abstract: A money identifying method and a device which can identify money with high precision and quickly by optimally binarizing a surface image of the money. The center coordinates and radius of subject coin C are extracted by a coin shape extraction section from the surface image of the subject coin C obtained by an area sensor, and an effective threshold calculation range is extracted by a threshold calculation range extraction section 107 from the extracted center coordinates and radius of the coin. Further, a density histogram is created by a histogram generation section 108 on the basis of the threshold calculation range, an optimum binary threshold value is calculated from the density histogram by a binary threshold calculation section according to a discriminating analysis, and the optimum binary threshold value is used to binarize an image for identifying the subject coin C.

Abstract: A calibration and correction procedure for a fingerprint scanner. The calibration and correction procedure performs an automatic calibration procedure and gray level linearity procedure. The automatic calibration procedure includes a brightness function to correct for distortions in brightness, a focus check function to identify when the fingerprint scanner is out of focus, and a geometric distortion function to correct for imperfect linearity in the geometry of the fingerprint scanner. The gray level linearity procedure corrects for linear distortions in brightness and contrast of gray levels.

Abstract: A computer with a monitor viewable program executes to display a histogram of image data on the monitor. The monitor contemporaneously displays a screen image viewed on a monitor of the histogram, and displays a digital or analog control element that controls both compression and expansion of midtones. Activation of the midtone compression/expansion element alters the displayed image according to effects of programs underlying the control of the element. This histogram display and element are associated on a single logical screen display in which at least one other image data modification effect is present on the screen image as an addressable image data modification effect.

Abstract: On the basis of a discrimination parameter for discriminating more detailed brightness in an image, the brightness of the image is discriminated, and the optimum degree of correction component is set for the image, thereby performing a more faithful reproduction of the image indicated by image data. Therefore, a highlight point being a brightness value associated with a cumulative frequency of reaching a predetermined value is calculated in a high-brightness area on the basis of a histogram obtained with respect to the number of pixels of a brightness value indicated by the image data, and the image is discriminated in its entire brightness on the basis of the highlight point. On the other hand, a ratio of the cumulative frequency in a predetermined low-brightness area to the number of all the pixels in the histogram is calculated. On the basis of the calculated ratio and the discriminated brightness, a gamma value indicating degree of correction the brightness value to a value of more light image is defined.

Abstract: In a scanning electron microscope, slimming is reduced by reducing a frame count. As the frame count is reduced, the amount of detected secondary electrons decreases, so that a probe current amount is increased to emit an increased amount of detected secondary electrons. A primary electron beam is scanned on a sample, a histogram is created, and the histogram is second-order differentiated to calculate a level of halftone at which a sample image changes in contrast, and to calculate the probe current amount. By adjusting the frame count suitable for the calculated probe current amount, and the contrast suitable for the sample image, the slimming of the sample is limited, and a highly visible sample image is generated for length measurement.

Abstract: An apparatus and a method as well as a storage device of the present invention transform intensity levels with consideration of both features of the intensity levels in an input image and human visual characteristics, wherein the present invention includes the steps of inputting wider dynamic range digital image data, generating a histogram of intensity levels of the image data, generating a histogram equalization LUT by cumulating the histogram, generating a visual characteristics LUT with reference to the histogram equalization LUT, generating a combined LUT by combining the histogram equalization LUT and the visual characteristics LUT, and correcting the image data.

Abstract: The invention relates to a method for segmentation of a digital image being represented by picture element data for the purposes of visualization, segmentation and quantification, such as determining the volume of a segment. The method comprises the steps of performing a watershed transformation of the digital image by applying a watershed transformation method on the picture element data to provide one or more basins and post-processing by processing the picture element data belonging to at least one of the basins, where post-processing is one or a combination of the following steps: (i) gray-scale based segmentation, (ii) visualization using a transfer function, or (iii) volumetry using histogram analysis.

Abstract: It is difficult properly to perform correction processing such as white balance adjustment and exposure compensation for all types of images. This invention provides a way in which white balance adjustment and exposure compensation are performed in accordance with image features by considering the arrangements of pixel values in the highlighted and shadow areas of an image. Proper correction processing can therefore be performed for any types of images.

Abstract: A reference image signal level curve V1 and a predetermined coefficient are provisionally stored in a ROM of a main controller. The predetermined coefficient provides a threshold level curve by multiplying by the curve V1. A white color image signal level curve V2 is formed upon reading a white reference surface by optical sensors. The white color image signal level curve V2 is compared with the reference image signal curve V1. If at least a part of the curve V2 is not coincident with at least a part of the curve V1, the curve V1 is multiplied by ?V percent, and this percentage is stored in a RAM. These are performed repeatedly until a part of the curve V2 is coincident with a part of the curve V1 as a result of increase in cumulative ?V percent. Thus, a correction coefficient K is determined based on the cumulative ?V percent to provide a corrected image signal level curve. The corrected image signal level curve is compared with the threshold level curve to obtain a binary image data.

Abstract: An apparatus for creating an ICC profile in a simple manner without using a specialized measuring instrument. A display control unit reads out a dot pattern image from a pattern image data holding unit and a grayscale pattern image containing a plurality of grayscale patches of gradually varying gray scale from a grayscale image data holding unit, and presents the thus readout images for display on a display device. A user selects the grayscale patch having brightness closest to the brightness of the dot pattern image by operating a selection unit. Based on the selection, a gamma coefficient value is calculated by a gamma coefficient value calculation unit, and based on this gamma coefficient value, a profile creation unit modifies the ICC profile held in a common information holding unit and thus creates a customized ICC profile.

Abstract: A method of processing a color digital image file provides a “metallic,” or a “sepia,” or an “antiqued” image file. The resulting image files may be viewed, for example, on a computer monitor, or may be printed out in hard copy form using a black-and-white or color printer. A color photocopy machine which has a digital image output may be used to produce the original image file, and such a color photocopier (if it will accept digital image files), may also be used to produce the output hard copy printouts of processed image files. Thus, such a digital photocopier may be configured internally to also process image files, and may be employed to selectively process images copied on the machine into the user's choice of a metallic, a sepia, or an antiqued image on the output hardcopy of the color photocopier.

Abstract: A system and method for generating a multi-tone representation of a digital image by applying a plurality of functions of luma to the digital image. The functions of luma comprise at least a first function and a second function, where each function has a value for each luma value in a range of luma values. Each function also has an associated display value. The digital image includes a plurality of pixels, where for each pixel, it is determined which of the first and second functions has a maximum value for a luma value of the pixel. Each pixel is represented using the display value associated with the determined function.

Abstract: A color conversion section converts R-, G- and B-image signals input by the reading of a color image on an original to C-, M- and Y-color signals. A histogram producing means of an image processing section produces density histograms of the respective color signals on the basis of the converted C-, M- and Y-color signals. An original type determination means determines a type of the original on the basis of the histogram data signals. A colored background determination means determines a colored background on the basis of the histogram data signals. A background process presence/absence determination means determines whether a background process is to be executed or not, on the basis of an original type determination result signal and a colored background determination result signal. A CPU produces, when it is determined that the background process is to be executed, a background process table using the density histogram values of the respective color signals.

Abstract: A method and associated apparatus for relating a test image with a reference image in an automated image processing system is disclosed. The test and reference images are aligned. A two-dimensional scatter plot is then created by plotting the gray level of a test image pixel against the gray level of a corresponding reference image pixel for each aligned pixel location.

Abstract: The present invention performs gradation conversion linearly on an image signal when the image signal is darker than a preset value. Consequently, the dark region of the image is not distorted nonlinearly, and the gradations of shadows and hair can be reproduced in full richness. On the other hand, gradation conversion is performed nonlinearly on image signals if the image signal is brighter than a preset value. The nonlinear conversion in this case: (1) has a slope that effectively equalizes an average noise amplitude of the image signal without being based on the output gradation value, and (2) is offset so as to be continuous with the gradation conversion characteristic of the dark area gradation conversion unit. Through condition (1), the level-dependent noise in the bright region is equalized. Furthermore, through condition (2), gradation differences and gradation reversals do not occur at the boundary between the dark region and the bright region.

Abstract: A method and system for performing automated biological identification. The system including a preprocessing module with a histogram transform for locally and globally enhancing biological data such as fingerprints. An enhancement module with a fast smoothing and enhancement function. A feature extraction module with a fingerprint oriented thinning function. A matching module with a resolution-enhanced Hough transform function for fingerprint registration and matching score function.

Abstract: A method for the automatic reproduction of the colors of an original scene from an original image present as a color negative or diapositive film includes scanning the original image electronically, and storing the RGB color values of the image points as scanned transmissions or scanned densities. In the RGB color space, a gray straight line is determined, which approximates the cloud of points formed by the scanned densities of the image points in an optimum way. The transmissions are corrected by minimum transmission values in each case being subtracted from the scanned transmissions. Then, reconstructed film exposures are determined, whereby, by the gray straight line, film exposure straight lines are constructed that describe the relationship between the logarithmic film exposures and the corrected densities. Following the normalization of the film exposures to a standard image range, the film exposures are transformed into the LAB color space.

Abstract: A method for evaluating the quality of an image, for extracting a luminance gradient displayed on a display device and for evaluating local luminance unevenness caused therein. The method includes the steps of: subdividing the image to be used as an evaluation object into a plurality of pixels; acquiring a first luminance information by calculating the difference between the sum of luminance values of predetermined pixels and the luminance value of a predetermined pixel, the predetermined pixels forming a first pixel group surrounding the predetermined pixel; acquiring a second luminance information by calculating the difference between the sum of luminance values of predetermined pixels and the luminance value of the predetermined pixel, the predetermined pixels constituting a second pixel group; acquiring a third luminance information by adding the first luminance information and the second luminance information; and evaluating the luminance of a screen photographed based on the third luminance information.

Abstract: This invention relates to an apparatus and method for providing calibration of photographic media. More particularly, the method and apparatus are based on measurements of areas of minimum optical density of a given photographic medium. Such measurements, when combined with reference optical density vs. exposure calibration data for related photographic media, provide an estimate of the optical density vs. exposure relationship of the given photographic medium. The method and apparatus of this invention are especially applicable for the calibration of photographic media used in hybrid imaging applications.

Abstract: A system and process for generating High Dynamic Range (HDR) video is presented which involves first capturing a video image sequence while varying the exposure so as to alternate between frames having a shorter and longer exposure. The exposure for each frame is set prior to it being captured as a function of the pixel brightness distribution in preceding frames. Next, for each frame of the video, the corresponding pixels between the frame under consideration and both preceding and subsequent frames are identified. For each corresponding pixel set, at least one pixel is identified as representing a trustworthy pixel. The pixel color information associated with the trustworthy pixels is then employed to compute a radiance value for each pixel set to form a radiance map. A tone mapping procedure can then be performed to convert the radiance map into an 8-bit representation of the HDR frame.

Abstract: The present invention provides a method for processing tone scale of a digital color image in which the histogram of tone scales (for example, of RGB, YCrCb, Lab or Luv) is considered for deciding the semi-S curve. The semi-S curve suits the digital color image and improves the brightness contrast and color saturation for the image output device. A weighting procedure can also be used for compensating those high occurrence colors in the image, and rearrange and analysis the histogram of tone scale, so as to decrease the influence of the high occurrence colors to the calculation and process of tone scale.

Abstract: An image reproducing apparatus, that outputs and reproduces an image having a greater number of gradation levels than that of input image data, is comprised of a buffer memory that accumulates input image data for a plurality of lines; an image data storing unit that extracts and stores image data of region of a predetermined size from the buffer memory; a specified portion detecting unit that detects a specified portion in which gradation of image data varies slowly from the predetermined region of stored image data; and an intermediate density data generating unit that generates, based on a result of detection by the specified portion detecting unit, intermediate density data composed with step smaller than the minimum value of a step between different gradation levels of image data. In the above apparatus, an image having a greater number of gradation levels than that of image data is output based on the intermediate density data.

Abstract: The method for evaluating a quality of an image on a display device displays a test pattern having different contrast intensities on a display screen of the display, then determines a contrast intensity at which the test pattern is visually discernible and uses the thus determined contrast intensity as a value for evaluation of granularity on the display device. The method is optimal for achieving quantitative and objective visual evaluation of image quality, particularly, its granularity.

Abstract: A compression and decompression system and process for optimally compressing and decompressing multibit per pixel image regions based on the type of data contained in the image region, e.g., whether the image region contains continuous tone data, including data to be halftoned, or non-continuous tone data, including antialiased text and lineart data. Segmented bytemap data blocks are processed to provide both low spatial resolution continuous tone data and high spatial resolution non-continuous tone data. However, the high spatial resolution non-continuous tone data is generated by quantizing and packing the high resolution bytes across an edge and discarding the high resolution bytes along the edge, i.e., the multibit data is discarded only in directions parallel to the edges of marks to be rendered in the image data. Additional information indicating the directions of the edges in the image data are stored to aid in decompression.

Abstract: An image processing method for image-processing digital image data acquired by a digital camera to enable reproduction of high-quality images includes the steps of computing first characteristic values characterizing colors of an image represented by digital image data, normalizing the digital image data based on the first characteristic values to produce normalized image data, computing from the normalized image data a second characteristic value characterizing density of the image represented by the digital image data, and correcting the normalized image data based on the second characteristic value to produce processed image data. Also provided is an image processing system for carrying out the method.

Abstract: Dynamic range equalization by histogram modification. A histogram is analyzed to determine locations of peaks. A mapping function is formed which relates to the locations of the peaks in a histogram. That mapping function may have areas of highest slope near the peaks. The mapping function is used to form a compressed histogram, which has the required number of levels to display on a display device.