Abstract: The sense of contrast perceived by a viewer of an image is quantified and adequate image processing is carried out on image data based on the sense of contrast. Contrast-sense quantification means generates unsharp image data of the image data and then generates a histogram of the unsharp image data. Since the histogram of the image data includes lightness information of details of the image, a distribution width thereof does not represent the contrast perceived by the viewer of the image as a whole. However, since the histogram of the unsharp image data excludes information of the details, a distribution width of the unsharp image data represents the contrast of the overall image. The distribution width of the histogram of the unsharp image data is found as the sense of contrast and input to processing means. In the processing means, tone conversion processing is carried out on the image data by changing a tone conversion LUT based on the sense of contrast, and processed image data are obtained.

Abstract: A scene adaptive power control device using a plurality of input images as consecutive input images and controlling a power level of a light source used in displaying the third input image. The scene adaptive power control device including a histogram analysis unit to analyze the second input image and detect a first maximum brightness value of the second input image, a determination unit to detect brightness values matching a first threshold as a predetermined frequency value in the generated histogram and determining a second maximum brightness value, a generation unit generating a power control signal to control the power level of the light source by a value obtained by dividing the second maximum brightness value by the first maximum brightness value, and a compensation unit increasing a brightness of the third input image inversely proportional to the power level of the light source reduced by the power control signal.

Abstract: The present invention discloses a method and a device for image contrast enhancement by taking the contribution of image chroma into account so as to define the luminance signal with the chroma weighted value. The new defined luminance signal can be applied towards expressing the image's parameters of original luminance signal and compensated chroma signal, through means of a statistic histogram extraction and the ratio relationship between before and after luminance curve process. Therefore, pictures can be provided with better saturation for satisfying the viewer's requirements, as observed from the process of the present invention.

Abstract: A driving method and apparatus for a liquid crystal display are disclosed that stabilizes the variation of the brightness of a back light in correspondence with data to be displayed. In the method, the data is converted into brightness components. The brightness components are divided into a plurality of brightness areas. The brightness components are arranged into a histogram for each frame and thereafter a control value of a most-frequent value or average value of the histogram is extracted. The extracted control value is stored along with other control values including the extracted control value of a frame prior to the control value of the current frame by at least two frames. The brightness of the back light is controlled using the extracted control value of the current frame and one or more of the other stored control values.

Abstract: The invention provides an apparatus for dynamically adjusting the saturation of an image signal consisting of a plurality of pixels. The apparatus includes a first transformation module, an operation module, a gain module, an adjustment module and a second transformation module. The first transformation module transforms the pixels of the image signal into a plurality of intermediate signals, where each of the intermediate signals has a respective saturation value. The intermediate signals are adjusted in accordance with a gain signal determined by a histogram relative to the saturation distribution of the intermediate signals. The adjusted intermediate signals are transformed back into the pixels of the image signal, thereby the saturation of the image signal is adjusted.

Abstract: A picture quality correction circuit is provided which performs contour correction by grasping features of an input video signal accurately. The correction circuit has a filter circuit for extracting contour components in an inputted video signal, a contour component nonlinear processor for changing amplitudes of the contour components extracted by the filter circuit, an adder for adding outputs of the contour component nonlinear processor and the input video signal, a histogram detection circuit for detecting a histogram of the contour components extracted by the filter circuit, and a control circuit for controlling contour emphasis quantities for the contour component nonlinear processor in accordance with the results of detection by the histogram detection circuit.

Abstract: A dynamic contrast enhancement circuit (DCE circuit) includes a grayscale statistical unit, an operation unit and a transformation unit. Wherein, the grayscale statistical unit receives a frame and divides the grayscale distribution of the frame into a plurality of statistical intervals to count the number of pixels of every statistical interval and obtains a plurality of statistical values. When one of the statistical values is greater than a threshold value, the operation unit would adjust every the statistical value according to the difference value between the statistical value exceeding the threshold value and the threshold value. In this way, the transformation unit is able to produce a transformation data according to the adjusted statistical values, so as to perform a DCE processing on the frame.

Abstract: A method, apparatus and system with a hierarchical histogram generator that generates sub-histograms of differing resolutions. These sub-histograms are used to adjust an image exposure setting.

Abstract: According to one embodiment, a video signal processing device includes a set-up level detecting unit that detects a set-up level of an input video signal, a set-up level correcting unit that corrects the set-up level of the input video signal, and a histogram detecting unit that detects a histogram corresponding to a brightness of a video signal output from the set-up level correcting unit.

Abstract: A video signal processing apparatus includes a characteristic detection circuit for detecting luminance distribution corresponding to one frame of a video signal, a contrast compensation circuit for compensating contrast of the video signal, an edge compensation circuit for compensating an edge portion of the video signal, and a control circuit for determining a luminance range to be controlled on the basis of the luminance distribution detected by the characteristic detection circuit, and controlling the contrast compensation circuit and edge compensation circuit to conduct predetermined compensation on the video signal belonging to the luminance range. The control circuit controls the contrast compensation circuit to increase contrast for the video signal in the luminance range as compared with the video signal in other regions, and controls the edge compensation circuit to make an edge compensation quantity for the video signal in the luminance range smaller as compared with other regions.

Abstract: The present invention provides a technique for performing gamma correction processing when there are a plurality of characteristic areas, each of which is characterized by the high frequency in a luminance histogram to improve the impression of contrast. According to the present invention, a luminance characteristic detector (4) detects the luminance of an input image signal and a microcomputer (5) calculates an APL and a luminance histogram of an input image signal. A gamma correction circuit (6) performs the gamma correction processing in response to the luminosity of the input image signal by use of the result of the calculation carried out by the microcomputer (5). Then, if there are a plurality of characteristic areas, each of which is characterized by the high frequency in the luminance histogram, a characteristic emphasis circuit (7) performs grayscale extension processing for the plurality of characteristic areas.

Abstract: In image processing apparatus and method for displaying and printing a person image photographed by a digital camera, it is possible to automatically correct image data and output the person image of an optimum characteristic. In this apparatus, an image obtaining processor obtains the image data from a recording medium, a face region extraction processor extracts a face region of a person from the obtained image data, an image feature amount calculator calculates an image feature amount of the extracted face region, a correction effect inference processor infers whether or not a correction effect can be obtained by correcting a characteristic of the image data, based on the calculated image feature amount, and an image correction processor corrects the characteristic of the image data based on the image feature amount and thus outputs post-correction image data when it is inferred that the correction effect can be obtained.

Abstract: The liquid crystal display device includes a histogram analyzer analyzing a histogram of an input image and determining the input image as being in one of a low brightness mode, a normal mode, and a high brightness mode based on the histogram analysis, a back light controller controlling a maximum brightness of a back light unit based on the mode determination, and a data modulator enlarging the histogram of the input image to modulate data of the input image. The histogram analyzer detects a most frequent value of gray scale occurring most frequently in the input image of one frame, compares the most frequent value with a predetermined low reference gray value and a predetermined high reference gray value, and determines the input image as in one of the low brightness mode, the normal mode, and the high brightness mode based on the compared result.

Abstract: Color saturation in chroma correction is reduced. Hence, a two-dimensional histogram is generated in association with the luminance and chroma levels of an image for one frame. An ease of saturation of the image is calculated from the two-dimensional histogram. A chroma gain is set according to the ease of saturation. Color-difference signals undergo chroma correction according to the chroma gain k.

Abstract: An analog-to-digital converter converts a video signal into a digital video signal consisting of N bits and outputs the converted signal. A correction value memory stores correction data consisting of M bits which is used to correct the difference in luminance between display pixels on a display. A multiplier multiplies the video signal consisting of N bits output from the analog-to-digital converter by the correction data consisting of M bits stored in the correction value memory, and outputs a video signal consisting of L bits with which the difference in luminance between display pixels on the display is corrected.

Abstract: An apparatus for controlling black stretch includes a black stretching unit, an offset adjusting unit and an output unit. The black stretching unit performs black stretch processing on a video signal less than or equal to the maximum value of a black stretch control range in response to a slope of black stretch. The slope of black stretch corresponds to a region between a minimum value and a maximum value of the black stretch control range. The offset adjusting unit adjusts an offset of the black-stretched video signal. The output unit outputs an output video signal corresponding to the offset-adjusted video signal when the offset-adjusted video signal has a positive value in a region less than or equal to the minimum value, and outputs the output video signal corresponding to 0 when the offset-adjusted video signal has a negative value in the region less than or equal to the minimum value.

Abstract: A technique for improving image quality using dynamic gray scale correction, in one example embodiment, includes dynamically computing non-linear gamma curves using histogram data extracted from a current video frame. A gray scale correction is then dynamically applied to each pixel in the current or next video frame as a function of the computed non-linear gamma curves.

Abstract: A method of driving a liquid crystal display includes arranging an externally provided first data into a histogram for each frame, producing a second data having an expanded contrast using the histogram, determining a control value by extracting a peak value at a position where brightness components are concentrated in a distribution, and controlling a brightness of a back light in accordance with a gray level of the control value.

Abstract: A system and methods for displaying data distribution information for time-series data is described. The methods include computing a condensed quantile function that may be used to generate approximate histograms for the time-series data, while decreasing the data storage requirements for generating a series of histograms for time-series data. The methods further include displaying the data distribution information using stack-bar histograms, many of which may be shown in a single display to permit a user to discern trends in the data distribution information. Methods for merging condensed quantile function tables are also described.

Abstract: Proper lightness correction is unavailable if a determination is unsuccessfully made whether or not an image to be retouched is a backlight image. A distribution ratio of luminance components is obtained from an image whose type is to be determined. The similarity is determined between the distribution ratio and a distribution ratio in the image of a specific type. When the similarity is acknowledged, it is determined that the image under inspection corresponds to the specific type. When a distribution ratio for backlight image is obtained in advance as the distribution ratio for the specific type of image, the above-mentioned determination process makes it possible to accurately determine whether or not the image under inspection is a backlight image.

Abstract: In gray-scale correction where extension to a dynamic range is performed based on a maximum value and a minimum value of a video luminance signal, sufficient correction effects cannot be obtained in some displayed images. Therefore, a histogram detecting circuit (2), a maximum value detecting circuit (3), and a minimum value detecting circuit (4) respectively detects, for each field, a maximum value (Kmax) and a minimum value (Kmin) in a detection WINDOW set in a screen, and distribution information in a gray-scale direction. The detected maximum value (Kmax) and minimum value (Kmin) are respectively corrected by a maximum value correcting circuit (5) and a minimum value correcting circuit (6) based on the output results of the histogram detecting circuit (2), and output as a corrected maximum value (Lmax) and a corrected minimum value (Lmin). Based on these corrected maximum value (Lmax) and a corrected minimum value (Lmin), an input video luminance signal is corrected.

Abstract: A signal processing unit in a liquid crystal display device, etc., includes a brightness component appearance frequency measuring unit that measures an appearance frequency of each brightness component in a video signal; a parameter outputting unit that outputs a distribution of each brightness component, as a parameter, based on the appearance frequency of each brightness component measured by the brightness component appearance frequency measuring unit; a changing signal outputting unit that alters an input signal recorded in a recording unit, by using the parameter, and that outputs the input signal as a changing signal; and a brightness component changing unit that changes a distribution of each brightness component, by using the changing signal, and that outputs the video signal in which the distribution of each brightness component is changed.

Abstract: In the present invention, image data from an image input device, including differences of tone levels of picture elements constituting these image data from surrounding picture elements, are figured out and the distribution of these differences of tone levels is prepared. Then, integrated processing, based on this distribution, makes it possible to determine whether each picture element is an edge picture element, a moiré picture element or an intermediate picture element. According to the determination, a sharpening filter is applied if the picture elements are edge picture elements, a smoothing filter is applied if they are moiré picture elements, or the tones of the original image are held if they are intermediate picture elements. This way of image data retouching makes it possible to carry out the whole execution from determination to retouching in a serial process.

Abstract: A method for dynamically adjusting video brightness performs histogram equalization on a video YUV brightness/color signal to generate an equalization brightness curve. The brightness of each pixel is compared with every pixel of the video frame before and after histogram equalization to generate a comparison difference value. The brightness of the pixel is adjusted so that the brightness difference after adjustment won't be larger than three times of the comparison difference value and won't be smaller than a fourth of the comparison difference value. The brightness of each pixel before and after histogram equalization is compared, one by one, to generate a brightness difference value. The brightness difference value is adjusted so that the brightness difference after adjustment won't be larger than a largest brightness value and won't be smaller than a smallest brightness value. The brightness of each video frame can be properly adjusted to accomplish clearer displaying effect.

Abstract: The sense of contrast perceived by a viewer of an image is quantified and adequate image processing is carried out on image data based on the sense of contrast. Contrast-sense quantification means generates unsharp image data of the image data and then generates a histogram of the unsharp image data. Since the histogram of the image data includes lightness information of details of the image, a distribution width thereof does not represent the contrast perceived by the viewer of the image as a whole. However, since the histogram of the unsharp image data excludes information of the details, a distribution width of the unsharp image data represents the contrast of the overall image. The distribution width of the histogram of the unsharp image data is found as the sense of contrast and input to processing means. In the processing means, tone conversion processing is carried out on the image data by changing a tone conversion LUT based on the sense of contrast, and processed image data are obtained.

Abstract: A method and apparatus that allows a display device to adaptively and automatically control display contrast and color is disclosed. The method and system in accordance with the present invention can be described by the following sequential process: 1. Separating an input image data value into its luma and chroma components. 2. Collecting the luma distribution data over the entire image or a specified window. 3. Analyzing the luma distribution. 4. Generating an appropriate contrast control response that modifies the input luma component to generate an output luma component, on a pixel by pixel basis. 5. Analyzing the input luma component and the output luma component, and an input chroma component, to generate an appropriate modification for the chroma component, on a pixel by pixel basis.

Abstract: A method is provided for automatically adjusting the color of a digital image. In one aspect, an strength offset is determined to automatically remove gray from a distorted image. In an other aspect applied independently or after gray removal, scaling factors are automatically determined to adjust the image to conform to empirically determined optimal brightening of the image. Using a determination of color dot maximums and a function which ensures constraint within the dynamic range, scaling factors are established which correspond to the strength values of each dot maximum and which are applied to each of the dot's R,G and B to maintain ratios therebetween and thus maintain the true color. The function for establishing the scaling factors is interpolated from a nominal function and a target average strength for the image.

Abstract: A luminance level compensating apparatus passes only the luminance signal of a pixel in a first detection range in the vertical direction of an image indicated by an input luminance signal, detects and stores a first frequency for each luminance level of the passed luminance signal for each predetermined period, passes only a luminance signal of a pixel in a second detection range including the first detection range in the vertical direction of the image, detects and stores a second frequency for each luminance level of the passed luminance signal for each predetermined period; generates a mixed frequency data based on the first and second frequencies stored.

Abstract: A process for detecting black bands in a video image within a luminance range corresponding to low luminance values comprises the steps of: calculating, for each line situated in a location in which a black band can be expected to be found if present in said video image, a value relating to a maximum number of occurrences of points having the same luminance value; averaging said value over said lines in said location; calculating a threshold dependent on said average; and, comparing said value relating to said maximum number of occurrences obtained for a new line with said threshold. Applications relate, for example, to the detection of the “letterbox” format.

Abstract: A method and system that allows a user to find images using a query by example is disclosed. Images similar to the selected image are retrieved based on color or shape. Each clip in a clip catalog is assigned a color metric and a wavelet, i.e., shape, metric. The selected clip is also assigned a color metric and a wavelet metric. Those clips that are most similar based on either the wavelet metric or the color metric are returned to the user.

Abstract: A video apparatus includes a histogram modification means circuit for matching at least luminance signals (Y) for separate pixels to prescribed values. The histogram modification circuit has a first memory (3) with a first look-up table for correcting the video luminance signals (Y), and a second memory (4) with a second look-up table (4) for correcting the color-difference signals (U and V). The values within the second look-up table (4) are derived from the values in the first look-up table (3). Preferably, in order to obtain a distribution of a rounding-off error over a pixel's neighbor, each of the channels for the luminance (Y) and color-difference signals (U and V) includes a closed lsb (least significant bit) correction loop (14, 14′) with a quantizer (15, 15′) and a pixel memory (16, 16′), the input of the lsb correction loop being formed by the corrected luminance and corrected color-difference signals, respectively.

Abstract: A television signal processor generates a wide dynamic range video signal on the basis of a first video signal matched to the brightness of a low-brightness region of an object image, and a second video signal matched to the brightness of a high-brightness region of the object image, and adjusting means for subjecting the first and second video signals individually to white balance process. The television signal processor further has means for detecting histogram values of particular signal level regions of the second video signal, means for detecting the peak value of the second video signal, means for determining a combining ratio of the first and second video signals according to the detected peak value and combining ratio, nonlinear processing means for nonlinear-processing the first video signal according to the detected histogram value, and combining means for combining the nonlinear-processed first and second video signals at a predetermined combining ratio.

Abstract: In a method of preventing doming phenomena, luminance histogram distribution values are obtained (10) from a luminance signal, the various luminance histogram distribution values are processed and normalized (12), the luminance histogram distribution values are processed (16) to correct for at least actual contrast and brightness settings to obtain corrected histogram data, a beam current is predicted (18) from the corrected histogram data, and a correction signal is derived (20) from the predicted beam current and making said correction signal effective in the processing and normalizing step (12).

Abstract: A device and method for controlling a brightness of an image signal in a moving picture transmission/reception system is disclosed. The present invention includes a control point detecting unit for receiving an image, calculating a Cumulative Density Function from two most significant bits of the image, dividing an axis into a required number of portions, and detecting a required number of control points. The present invention also includes an image signal brightness controlling unit for calculating and dividing six least significant bits of the image and a signal from the control point detecting unit for controlling a next frame of the image.

Abstract: In gray-scale correction where extension to a dynamic range is performed based on a maximum value and a minimum value of a video luminance signal, sufficient correction effects cannot be obtained in some displayed images. Therefore, a histogram detecting circuit (2), a maximum value detecting circuit (3), and a minimum value detecting circuit (4) respectively detects, for each field, a maximum value (Kmax) and a minimum value (Kmin) in a detection WINDOW set in a screen, and distribution information in a gray-scale direction. The detected maximum value (Kmax) and minimum value (Kmin) are respectively corrected by a maximum value correcting circuit (5) and a minimum value correcting circuit (6) based on the output results of the histogram detecting circuit (2), and output as a corrected maximum value (Lmax) and a corrected minimum value (Lmin). Based on these corrected maximum value (Lmax) and a corrected minimum value (Lmin), an input video luminance signal is corrected.

Abstract: A gradation correcting apparatus which is capable of preventing a luminance distribution from excessively extending over the dynamic range to accomplish an optimal gradation correction in accordance with the partiality of the luminance distribution of a particular video signal. A corrected luminance level is created for each of a plurality of luminance levels based on the frequency data in a luminance distribution such that the luminance distribution of the input luminance signal extends over a predetermined dynamic range, and is stored in an extension correcting table memory. A variance value is calculated for the luminance distribution in accordance with the frequency data to set a mixture ratio based on the variance value. Each of the plurality of luminance levels and the corrected luminance level in the extension correcting table memory corresponding thereto are mixed in the mixture ratio.

Abstract: A system and method for improving the uniformity in exposure and tone of a digital image using a locally adapted histogram equalization approach. This approach involves first segmenting the digital image into a plurality of image patches. For each of these patches, a pixel brightness level histogram is created. The histogram for each patch is then optionally averaged with the histograms associated with a prescribed number of neighboring image patches. A normalized cumulative distribution function is generated for each patch based on the associated averaged histogram. This normalized-cumulative distribution function identifies a respective new pixel brightness level for each of the original pixel brightness levels. For each of the original pixel brightness levels, the 1s associated new pixel brightness levels from one or more of the image patches are blended. Preferably, this blending is accomplished using either a bilinear or biquadratic interpolator function.

Abstract: In a video signal enhancement method, a video signal (Y) is histogram-based processed to obtain a histogram-processed video signal (Y′), and a sharpness of the histogram-processed video signal (Y′) is enhanced to obtain an output video signal (Y″) in dependence upon a sharpness enhancement control signal (CS) derived from at least the histogram-processed video signal (Y′). Advantageously, the sharpness enhancement control signal (CS) represents a derivative of the histogram-processed video signal (Y′).

Abstract: In an electronic endoscope, a flexible scope has an image sensor provided at a distal end thereof. A video-signal processing unit, to which a proximal end of the flexible scope is connected, processes image signals read from the sensor. A light source is provided in the unit, and light, emitted from the light source, is guided through the scope and radiates from the distal end. An aperture-stop is associated with the source that regulates the radiation of light from the distal end. An aperture-stop is controlled in accordance with the luminance-signal-histogram, such that an image having a constant luminance level is reproduced in accordance with the processed image signals. When a localized halation occurs on the reproduced image, the aperture-stop is controlled such that the radiation of light from the distal end is forcibly decreased, thereby avoiding the occurrence of the localized halation.

Abstract: In an image enhancement method and circuit, a luminance signal is extracted from input color signals. Histogram equalization is performed using a cumulative density function of the extracted luminance signal which is input in a screen unit. A transform function is controlled to map a mean level of the extracted luminance signal to itself, so that an adjusted luminance signal is output. The color signals are varied according to the variation of the luminance signals to output compensated color signals. Thus, image contrast is enhanced, and an undistorted color signal is provided at the same time. In order to reduce the hardware of the circuit, an interpolated cumulative density function is obtained by interpolating a quantized cumulative density function of an input luminance image and is used as a transform function. The transform function is controlled to map a mean level of the input luminance image to itself.

Abstract: Systems and methods that compute and apply a real-time transformation between digital input and output signals to achieve a specified output histogram. The systems and methods implement a predetermined (piecewise-linear) transfer function, coarse output histogram collection, and a closed-loop algorithm to produce a target (or specified) coarse histogram. Compact low-power systems contain a controller to implement the closed-loop algorithm, and a signal processor to implement the transfer function and coarse histogram collection. The use of a piecewise-linear transfer function in conjunction with coarse histogram collection, where the number of bins collected is equal to the number of piecewise-linear segments, results in a significant reduction in computational load and communication bandwidth required by the systems and methods.

Abstract: In a method of picture signal enhancement, a picture signal is subjected (3, 7) to a histogram-based picture signal modification based on a luminance level distribution over a whole picture or a first part of the picture, and the histogram-based picture signal modification is locally adjusted (5) in dependence on locally measured picture signal properties other than contrast and brightness, the locally measured picture signal relating to second parts of the picture that are each substantially smaller than the whole picture or the first part of the picture, the second parts being within the whole picture or the first part of the picture.

Abstract: Digital pictures are taken by a digital camera. The digital camera provides picture data with a large dynamic range of, for example, 10 bit. Data processing and display devices operate with 8 bit only, i.e do not take advantage of the high dynamic range of the camera This is important in traffic monitoring installations, where, on one hand, the driver in a relatively dark passenger compartment of a vehicle and, on the other hand, the bright license plate have to be recognized to provide evidence in court. For this reason, a dark picture and a bright picture are derived from the picture data provided by the camera. This is done by reading, on one hand, the eight least significant digits and, on the other hand, the eight most significant digits of the camera output to provide the dark and bright pictures, respectively. The dark and bright pictures thus obtained are balanced against color, gray, contrast or brightness values of histograms derived from previous pictures.

Abstract: The tone of video signals is corrected without degrading the tone of certain image features, such as a human face. A gain controller operates and outputs an adjustment value using a histogram output produced by a histogram generator. An average value of picture levels on a screen is detected by an average picture level detector. A histogram correction circuit calculates a look-up table, and a video signal correction circuit corrects the tone of the video signals using the look-up table.

Abstract: A luminance level compensating apparatus passes only the luminance signal of a pixel in a first detection range in the vertical direction of an image indicated by an input luminance signal, detects and stores a first frequency for each luminance level of the passed luminance signal for each predetermined period, passes only a luminance signal of a pixel in a second detection range including the first detection range in the vertical direction of the image, detects and stores a second frequency for each luminance level of the passed luminance signal for each predetermined period; generates a mixed frequency data based on the first and second frequencies stored.

Abstract: A video-apparatus comprises histogram modification means to match at least luminance signals (Y) for separate pixels to prescribed values. The histogram modification means comprises a first memory (3) with a first look-up table to correct the video luminance signals (Y), while a second memory (4) with a second look-up table is provided, the values within the second look-up table (4) being derived from the values in the first look-up table (3) and being applied to correct the color-difference signals (U and V). Preferably, in order to obtain a distribution of a rounding-off error over a pixel's neighbor, each of the channels for the luminance (Y) and color-difference signals (U and V) comprises a closed lsb (least significant bit) correction loop (14, 14′) with a quantizer (15, 15′) and a pixel memory (16, 16′), the input of the lsb correction loop being formed by the corrected luminance and corrected color-difference signals respectively.

Abstract: An image display method displays an image by different gradation conversion in every pixel, on the basis of gradation frequency distribution of luminance of pixels near an edge of the image, and counting of gradation frequency of luminance of pixels near the edge is weighted depending on the coordinate values of each pixel so as to eliminate relative contrast drop in the image central part from the image peripheral parts.

Abstract: A method for extracting a histogram and a cumulative distribution function (CDF) value for an image enhancement apparatus, and a circuit therefor are provided. The histogram extraction is performed during an active section of a video signal. The level of an input digital video signal is input as an address of a memory, and a data value stored at the address is increased. The processes are repeated during a one-screen period, thereby obtaining a histogram value indicating the number of samples distributed to each gray level. Also, a CDF value of each gray level is obtained by cumulatively integrating the number of samples from the lowest gray level on the basis of the histogram value obtained, during a vertical blanking period of the video signal. Therefore, the histogram/CDF extracting circuit can be built of simple hardware and an integrated structure, even though it performs both histogram and CDF extractions.

Abstract: The invention relates to adjusting contrast in television pictures and other natural picture sequences. In the method according to the invention, the pictures of the picture sequence are gathered into histograms which are processed in certain fashion in order to improve contrast in the pictures, whereafter there are formed mapping functions on the basis of the processed histograms, and the pixel values of the pictures in the picture sequence are then altered on the basis of said mapping functions. The histograms are processed so that from each class where the magnitude of values surpasses a given, predetermined limit, there are cut off all values surpassing said limit, which are then redistributed in the histogram, to classes nearest to the class under observation.

Abstract: A method and apparatus are provided to allow threshold values needed for the desired number of gradations to be set through a simple process when converting image data with numerous values into a low number of gradations. The desired number of gradations is achieved without shading being noticeable even for images having shading. The cumulative frequency distribution of the pixels for each brightness is determined from image data having a brightness range with designated gradations. The average brightness and standard deviation of the portion that is primarily background is determined from this cumulative frequency distribution. The first threshold value is determined on the basis of this average brightness and standard deviation, the second through n-1st threshold values corresponding to the meaningful information are determined on the basis of this first threshold value. An n value conversion process is accomplished using these threshold values.