Abstract: An image processing apparatus, method and computer-readable data storage medium to identify and process a negotiable instrument comprising a pre-processing unit 20 to select a binarization method to be used in a main processing unit 30 based on image data from only a scanned image of specific parts of the negotiable instrument for converting a full image of the entire negotiable instrument to binary image data.

Abstract: Methods of identifying the location and dimensions of a contaminant particle on a calibration strip comprise imaging a calibration strip comprising a plurality of channels and a plurality of pixel columns. The method also includes generating a normalized local average pixel intensity value and locating a contaminant particle in a pixel column by comparing the intensity of an individual pixel in the pixel column to the normalized local average pixel intensity value. An intensity value of an individual pixel less than a predefined limit set below the normalized local average pixel intensity value corresponds to a location of a contaminant particle. The method further includes identifying the number of adjacent pixels in a pixel column less than a predefined limit set below the normalized local average pixel intensity value.

Abstract: If an edge is detected between each pair of two mutually adjacent pixels among three serially adjacent pixels in a digital image, a candidate pixel selection unit in an intermediate value pixel judgment unit selects a pixel located at the middle among the three pixels as a candidate pixel. A pixel value comparison unit compares the pixel values of the three pixels, which are used for selecting the candidate pixel, with each other. Only if the pixel values of the three pixels monotonically increase or monotonically decrease along the arrangement direction of the pixels, a judgment unit judges that the candidate pixel is an intermediate value pixel.

Abstract: A method is used for analyzing scenes. The scene or objects in the scene and an optical sensor perform a relative movement and the scene information obtained is evaluated. Visual information of the scene is detected by the individual pixels of the optical sensor and pixel co-ordinates of established variations in intensity are determined. A temporization of the established variations in intensity is determined and a local accumulation of the variations in intensity is determined by statistical methods. The local accumulations are evaluated in terms of the number and/or position thereof by statistical methods and data area clearing methods. The determined values are used as parameters of a detected scene region. A parameter is compared with a pre-determined parameter considered characteristic of an object, and when the pre-determined comparison criteria are fulfilled, the evaluated local amassment associated with the respective scene region is seen as an image of the object.

Abstract: In an apparatus for performing printing using a color ink-jet head having a plurality of ink-discharge-port strings corresponding to ink materials having different color tones, a high-quality image having excellent gradation can be recorded, while reducing the cost of the apparatus and increasing the data processing speed by reducing the capacity of a memory for storing dot arrangement patterns.

Abstract: It is made possible that, in accordance with a plurality of radiographing modes such as the still image radiographing mode and the moving image radiographing mode, the outputs both in the irradiation period and in the non-irradiation period are made to fall within the dynamic range of the radiographing system, whereby an accurate, high-S/N-ratio X-ray radiographic image is obtained. For that purpose, in accordance with the plurality of radiographing modes, an arithmetic operation unit adjusts a power source to control voltage to be applied to a reading circuit unit or an Analogue-Digital conversion unit, such that, in each of the radiographing modes, both an electric signal in the X-ray irradiation period and an electric signal in the X-ray non-irradiation period fall within the dynamic ranges of the reading circuit unit and the Analogue-Digital conversion unit.

Abstract: A method for multi-level halftoning an input digital image to form an output digital image which includes a multi-level error diffusion halftoning process incorporating periodic dither signals whose amplitudes are adjusted as a function of the error-diffusion texture characteristics.

Abstract: An image processing device performs an error diffusion on multilevel input image data to generate multilevel output image data that has fewer levels than the multilevel input image data. The image processing device includes a plurality of setting devices, each of which sets a threshold value to be used at the error diffusion, a threshold value selecting device that randomly selects one of the plurality of setting devices with respect to each pixel to be processed and allows the selected setting device to set a threshold value with respect to the pixel to be processed when the image processing device performs the error diffusion, and a converting device that converts the pixel to be processed into multilevel output image data with fewer levels than multilevel input image data by the error diffusion, in accordance with the threshold value set by the setting device selected by the threshold value selecting device.

Abstract: By a program process, CPU 31 embeds a watermark data into a waveform data stored in wave memory 41a. The program includes a step for detecting a characterizing part (attack part and loop part) of a waveform data that represents a waveform of a musical tone where the characterizing part represents characteristics of the musical tone, and a step for embedding a watermark data into a part of the waveform data excluding the detected characterizing part. Further, CPU 31 can also extract the watermark data by a program process including a step for detecting the characterizing part and a step for extracting the watermark data embedded in a part excluding the detected characterizing part. Thus, from waveform data including a watermark data, natural musical tones can be reproduced without deteriorating the characteristics of the musical tones at the time of reproduction.

Abstract: The pseudo depth information of a subject is generated from multiple images of the subject captured with and without illumination or under various illumination intensities. A pseudo 3D image generating apparatus generates a pseudo 3D image. It includes an image storing unit that stores the images, and a depth computing unit that computes pseudo depth values of the subject based on operations between the pixel values of corresponding pixels in the images. A compact and handy 3D image generating apparatus is provided.

Abstract: A system that automatically adjusts a threshold value of cross color suppression and a method thereof are disclosed. The system includes a cross color suppression unit, a statistical unit and an adjustment unit. The cross color suppression unit is for receiving input video data and searching a plurality of cross color dots thereof. According to a threshold value, the cross color suppression unit determines whether the cross color dot is static or dynamic, suppresses the static cross color dot and then generates an output video data. The method used by the present invention is, the statistical unit calculates residual cross color amount of the output video data that has been suppressed. Then, the adjustment unit compares the cross color amount of the output video data with a reference value so as to send a corresponding adjustment signal to the cross color suppression unit to adjust the threshold value.

Abstract: A control unit selects a first labeling for a color image in a small number of colors so that the labeling is performed by clustering a color palette, and selects a second labeling for a color image in a large number of colors so that the labeling is performed by an adjacency expanding method.

Abstract: The present invention relates to an image processing device including pixel interpolation, such as a pixel interpolation device, a line interpolation device, an image size conversion device and an image interpolation device. The pixel interpolation device according to the present invention includes an interpolation pattern table, which outputs an interpolation direction data designating interpolation directions including directions joining intermediate points of pixels. The interpolation pixel data is calculated based on the pixel data located in the interpolation direction designated by the interpolation direction data. The image interpolation device, the pixel number conversion device and the line interpolation device according to the present invention includes the pixel interpolation device described above.

Abstract: It is an object of this invention to prevent a false edge phenomenon in quantization processing for a multilevel image. In order to achieve this object, according to the invention, (1) a reference threshold (Cthreshold) to be used for error diffusion for a cyan (C) component is obtained on the basis of a density value M of a magenta (M) component. (2) A threshold modulation amount table is referred to by using a combination of a density value C of the C component and the density value M of the M component. (3) A correction threshold modulation amount Cthreshold? is determined by adding the threshold modulation amount obtained in the second step to the reference threshold Cthreshold to be used for error diffusion for the C component. (4) A density Ct after error diffusion for the C component is compared with the correction threshold Cthreshold?. If the density Ct is higher, a quantization value binDataC of the target pixel is set to 255. If the density Ct is lower, the quantization value is set to 0.

Abstract: The amount of moiré in halftone printed images is reduced using unique moiré intensity functions and moiré vectors in a halftoner. In various embodiments, moiré phase angle zones are determined over the full field of an image and high addressability units in the full-field moiré phase angle zones of the image are adjusted, including in an iterative manner, until they significantly reduce the moiré. A useful relationship between halftoner memory locations and moiré phase angle zones in a full field image is determined. The moiré that occurs in a halftone image is quantified and moiré compensation values obtained are then used to generate an inverse moire amount which is used to compensate for the moiré.

Abstract: Certain embodiments of the invention may be found in a method and system for automatic aspect ratio detection and may comprise scanning lines in at least a selected portion of an image and locating a first reference pixel in one of the scanned lines. A corresponding sliding sum and a sliding number may be generated starting from the first reference pixel and a white edge determined based on the generated sliding sum and/or the generated sliding number. The first reference pixel may be a non-black pixel and a value which corresponds to and defines non-black may be variably defined. The sliding sum and the sliding number may utilize m bins, where m is greater than one (1). A luma sum threshold may be compared with the generated sliding sum to locate the white edge for aspect ratio detection.

Abstract: A color signal of a primary color or a color signal of a complementary color is converted from a CCD to signals in a color space having an intensity, a hue and a chroma. Tone conversion is performed on a luminance signal. A chroma correction coefficient is calculated to be used for performing correction on a chroma signal. A first maximum chroma value is calculated with respect to the luminance signal and a hue signal and a second maximum chroma value is calculated with respect to the hue signal and the converted luminance signal. And a correction coefficient is calculated based on the first and second maximum chroma values and the chroma signal is corrected based on the correction coefficient and the chroma correction coefficient.

Abstract: The present invention provides an improved integrated system for biological marker identification. The system uses Microvolume Laser Scanning Microscopy (MLSC) in order to measure patterns of expression of biological markers in biological fluids. The system includes improved instrumentation for performing MLSC, and also includes improved particle detection and analysis methods. The system further comprises an informatics architecture for the analysis of data obtained from the MLSC in tandem with other medical information.

Abstract: A method is provided for setting a dominant color using a spatial coherency in order to improve performance of an image search function. The method includes describing an image region based on several dominant colors, a frequency of each dominant color, and a spatial coherency (SC) of the dominant color. In the method, the spatial coherency is non-uniformly quantized based on a predetermined threshold. For example, the spatial coherency (SC) may be ranged from 0 to 1 and the threshold may be set to 0.70.

Abstract: An imaging device which assures high-quality image information free from a line noise by extracting line noise information from a taken image, detecting an existence of an extrinsic line noise in the image, and correcting the line noise if it exists. The imaging device comprises a memory circuit for storing image pick-up outputs at imaging of a two-dimensional area sensor comprising photosensors or radiation sensors, an extrinsic line noise detection unit for detecting an extrinsic line noise in the image pick-up outputs stored in the memory circuit, and an arithmetic processing circuit for calculating an output quantity of the detected extrinsic line noise. The line noise is eliminated by correcting the image pick-up outputs on the basis of the obtained output quantity of the extrinsic line noise.

Abstract: A method (1005) generates one or more linear blends. Initially, the method has a list of already received one or more fill-paths defining a current linear blend, and a newly received fill-path, where the fill-paths each comprise a single colored parallelogram (eg. 700). The method adds (1090) the new fill-path to the list to become the last fill-path in the list, if the difference (1230) in color between the new fill-path and the last fill-path in the list is no greater, in each color channel, than a predetermined threshold value multiplied by the difference in color between the last and second-last fill-paths in the list. The predetermined threshold value is preset to such a value so that the new fill-path will not be added to the list if the new fill-path does not visually form part of the current linear blend. The method repeats this step for each new fill-path received until the aforementioned condition is not satisfied.

Abstract: In a halftone module, it is judged whether or not the value “rate” for each pixel is greater than zero (0). In other words, it is judged whether or not the eight-bit input data Iin of each pixel is around a half of the relative density value for a small dot of a corresponding color. If the eight-bit input data Iin of the subject pixel is near to a half of the relative density value for a small dot, noise is added to the threshold values Ta, Tb, and Tc. The noise-added threshold values Ta?, Tb?, and Tc? are used in the comparing process.

Abstract: A technique for finding an optimal threshold for binarization of a gray scale image employs fuzzy reasoning. A triangular membership function is employed which is dependent on the degree to which the pixels in the image belong to either the foreground class or the background class. Use of a simplified linear fuzzy entropy factor function facilitates short execution times and use of membership values between 0.0 and 1.0 for improved accuracy. To improve accuracy further, the membership function employs lower and upper bound gray level limits that can vary from image to image and are selected to be equal to the minimum and the maximum gray levels, respectively, that are present in the image to be converted. To identify the optimal binarization threshold, an iterative process is employed in which different possible thresholds are tested and the one providing the minimum fuzzy entropy measure is selected.

Abstract: Diminished intensity defects occur in electrostatic printing between image regions having grey levels, i.e., different electrostatic potential and toner densities. Such defects occur when higher density regions “steal” toner from lower density regions. The system and methods according to this invention compensate for these defects by modifying the input image data. The input image data in lighter regions that precede or occur near a light-to-dark transition to a dark region are raised above the input image values. Thus, when printed, the printed image intensity values in such regions are higher than the corresponding image intensity values. As a result, when the higher density regions steal the extra toner provided due to the raised values, the gray level of the printed image corresponds to the desired gray level. The magnitude of these defects is periodically measured with a calibration pattern to generate and/or update compensation factors used in the compensation process.

Abstract: In a method for identifying objects in a digital image which is included in a sequence of images, luminance values of a current digital image are compared with at least one threshold value in order to create a current binarized image on the basis of the comparison. A quality measure for the current binarized image is also calculated, whereupon said at least one threshold value is updated on the basis of the quality measure for use in binarization of a subsequent image. The method can be realized in the form of a computer program, a computer program product, a device, and a hand-held apparatus for position determination.

Abstract: A method evaluating threshold of a data cell in a memory device including a programming locus coupled with the data cell for receiving a programming signal setting a stored signal level in the data cell and responding to a read signal to indicate the stored signal at a read locus; includes the steps of: (a) in no particular order: (1) selecting a test threshold signal; and (2) setting a read signal at a non-read level; (b) applying the test threshold signal to the programming locus; (c) cycling the read signal between a read level and a non-read level while applying the test threshold signal to the programming locus to present at least two test signals at the read locus when the read signal is at the read level; and (d) while cycling, observing whether the at least two test signals manifest a difference greater than a predetermined amount.

Abstract: The screened printing data are subjected to a filtering method, the raster information being maintained. Intermediate tonal values are produced by the filtering method, using the binary tonal values, the intermediate tonal values being configured in such a way that, by means of a color space transformation, transformed tonal values and/or intermediate tonal values can be formed which represent a true-to-color proof.

Abstract: An object of the present invention is to generate an image which is prevented from being influenced by a movement while suppressing increase in noise components. When a movement is detected during exposure of an image capturing device to light, an image capturing apparatus stops the exposure of the image capturing device and amplifies an image signal obtained with the exposure, thereby compensating exposure shortage. Luminance information is extracted from a captured image, and color information is extracted from a live view image obtained at a timing different from a timing at which the captured image is obtained. By synthesizing the luminance information of the captured image and the color information of the live view image, noise components included in color information are reduced.

Abstract: In order to render information contained in images more detectable in the presence of noise, the present invention discloses a system and method to binarize the images in the presence of noise. The method of this invention comprises the steps of applying a dynamic range reducing filter to the digitized image values, obtaining a range reduced image; applying an edge detecting filter to the range reduced image, obtaining a filtered image; and then, adaptively binarizing the digitized image utilizing the corresponding filtered image to obtain an adaptive threshold.

Abstract: An apparatus and a method for processing checks and other negotiable instruments efficiently captures MICR data required for electronic payment and an image of the check or negotiable instrument enabling the amount, payee, and other information printed or written on the check face to be clearly read. The image reading unit 11 of the check processing apparatus 110 scans and outputs a gray scale image of the check. A threshold value determination unit 12 sets a threshold value for digitizing the image data based on the density level frequency distribution of primary gray scale image data obtained by the image data reading unit scanning a first scanning area T. This first scanning area contains part of a printed text area 127 where text is printed on the negotiable instrument and part of the background 49 of the negotiable instrument.

Abstract: An image brightness level conversion method and apparatus which converts a multi-valued brightness level of an input pixel to a bi-valued brightness level using a threshold value. If the input pixel is determined to belong to an edge area, a predetermined reasonable distance by which dots should be isolated is reduced by a noise component and the threshold value is produced using the reduced distance. If the input pixel is determined not to belong to the edge area, the threshold value is produced without using the noise component. The method provides a uniform distribution of dots on the 2-dimensional space, a decrease in a generation of a void region where no dots appear around the edge area, a reduction of unpleasant appearing fixed patterns between dots, and a decrease in the generation of a typical pattern in which dots with a same color are diagonally arrayed.

Abstract: An image processing apparatus and method, which can appropriately extract an object even when the focus of a camera having an automatic focus adjustment function shifts from the background to the object. To this end, frame images which are sensed by an image sensing unit and are sequential in the time axis direction are input from an input unit. The input frame images are smoothed by a filter unit. A background image generation unit generates an average image of a predetermined number of smoothed frame images as a background image. An image differential unit generates a differential image between the predetermined smoothed frame image and the background image. An object extraction unit extracts an object region where a predetermined object is sensed, on the basis of the differential image.

Abstract: Halftone image data is generated according to a threshold array in which thresholds T up to a given gradation have been determined, and candidate pixels to be blackened are then determined. Then, a low-frequency component extractor extracts low-frequency component data from density image data which simulates the density of the halftone image data corresponding to an output image from an image output apparatus. A particular frequency component divider 70 divides the extracted low-frequency component data into particular frequency component data for intensifying the low-frequency components, and blackening candidate pixels for intensifying the particular frequency components are excluded, thus narrowing down candidate pixels. The positions of thus determined blackening candidate pixels are determined as the positions of thresholds for a next gradation.

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 cooperative camera network involving segmenting an image of an object and extracting a color signature from it. The color signature may be matched with the other signatures in an attempt to identify the object. There also can be combining and fusing the tracking of people and objects with image processing and the identification of the people and objects being tracked in an area or facility.

Abstract: In ink-jet printing apparatuses having a monochrome head which is longer than a color head, if a monochrome image is processed as a color image, the printing speed cannot be improved. Accordingly, the color attribute is determined by pixel based on a luminance signal indicating a color multivalue image, and the number of color attributes and the number of array attributes in a first line group are counted. Based on these count values, a parameter indicating an image characteristic of second line group including the first line group is calculated. The image attribute of the second line group is determined in correspondence with the respective count values and the parameter. Then, based on the results of determination about adjacent second line groups, the image attribute of third line group included in the second line groups is determined. Thus attribute determination can be appropriately performed in predetermined band units of image data.

Abstract: An image processing method of quantizing multi-tone image data by an error diffusion method, includes the steps of a) detecting change of the image data; and b) oscillating cyclically in image space a threshold for the quantization in an oscillation range controlled according to the detection result of the step a).

Abstract: A method of detecting both linear and non linear noise in video data. Linear noise is detected on a line-by-line basis, by blocks within each line. Non linear noise is detected during horizontal blanking periods. The method provides a noise floor value for linear noise and an impulse noise flag for non linear noise, both of which are delivered to a noise reduction filter.

Abstract: A device for generating fusion images by fusioning two images, in particular medical images, comprising an image-processing computation unit (2) for fusioning the images, as well as a monitor (3) connected thereto for image output, a gray-value histogram (7, I, II) being displayable on the monitor (3) for each image of the images to be fusioned, which device is designed in such a way that, in each gray-value histogram (7, I, II) of the images to be fusioned, one or more gray-value ranges can be selected by user-controlled highlighting of one or more markings (8) on the monitor (3), as well as for generating the fusion image with the aid of the selected gray-value ranges.

Abstract: A visual perception threshold unit for image processing identifies a plurality of visual perception threshold levels to be associated with the pixels of a video frame, wherein the threshold levels define contrast levels above which a human eye can distinguish a pixel from among its neighboring pixels of the video frame. The present invention also includes a method of generating visual perception thresholds by analysis of the details of the video frames, estimating the parameters of the details, and defining a visual perception threshold for each detail in accordance with the estimated detail parameters. The present invention further includes a method of describing images by determining which details in the image can be distinguished by the human eye and which ones can only be detected by it.

Abstract: The present invention provides a binarization device that realizes reproduction with a low error rate, even where optimum recording conditions such as recording power have not been set in the recording device, or where optimum recording has not been carried out for the reproducing device. The binarization device includes a binarization unit, a slice level setting unit, and a weight adding function. The binarization unit binarizes a reproduction signal obtained by reproducing information recorded by mark length recording on a recording medium to output high-level signals and low-level signals based on a slice level. The slice level setting unit calculates the average value of the high-level signals output from the binarization unit, and determines the slice level from the average value. The determined slice level is set to the binarization unit. Either the binarization unit or the slice level setting unit adds a predetermined weight to each signal having a short high-level time among the high-level signals.

Abstract: A memory stores an output value as a filter processing result. A first calculator calculates a difference between an input value of an image signal and the output value stored in the memory. The output value is the filter processing result of a previous input value. A lookup table stores a plurality of difference values and change values, and outputs the change value corresponding to the difference calculated by the first calculator. The change value is a product of the difference and a value which is above “0” and below “1” if an absolute value of the difference is below a threshold, and the change value is a product of the difference and a value which is above “?1” and below “0” if the absolute value is above the threshold. A second calculator outputs a difference between the input value and the change value.

Abstract: A method is provided for setting a dominant color using a spatial coherency in order to improve performance of an image search function. The method includes describing an image region based on several dominant colors, a frequency of each dominant color, and a spatial coherency (SC) of the dominant color. In the method, the spatial coherency is non-uniformly quantized based on a predetermined threshold. For example, the spatial coherency (SC) may be ranged from 0 to 1 and the threshold may be set to 0.70.

Abstract: An edge enhancement processing system and method for modifying image data at certain pixel locations to include gray scale image data so as to reduce jaggedness in the image. An adjustable threshold device establishes a binary pixel value for an incoming current gray level pixel in accordance with a thresholding criterion. An operator accessible input to the thresholding device is used by the operator to adjust the threshold value in the thresholding criterion. A current binary pixel formed in accordance with the thresholding criterion and neighboring pixels also so formed in accordance with the thresholding criterion are examined in accordance with predetermined criteria for determining adjustment of the current pixel to a gray scale value to reduce edge jaggedness of the image. Generally, adjustment of the thresholding value is made in instances where under color removal and/or gray component replacement is employed.

Abstract: The ability of the visual system to detect contrast in an image is a function of the frequency of the contrasting pattern and the distortion of the image. The visual system is more sensitive to contrasting patterns of lower frequency. When the image is significantly distorted, the visual system is even more sensitive to lower frequencies than higher frequencies. An image encoder employs lossy data compression processes producing a distorted reconstructed image. A method of quantizing image data including the step of varying the magnitude of a quantization step as a function of the distortion of an image is disclosed for further visually optimizing image quantization. Another method utilizes distortion adaptive weighting to vary the limit of code block truncation during embedded bitstream coding to visually optimize image compression by increasing relative lossiness of compression at higher frequencies.

Abstract: A monitoring method and apparatus for detecting an intruding object within a monitoring field of view by applying a subtraction method to an image obtained from an imaging device. A differential image of luminance values between an input image from the imaging device and a reference background image stored in a storage device is generated. The differential image is binarized using a predetermined binarization threshold value and the bianrization threshold value is changed until a noise level of a bianrized image becomes not greater than a predetermined value and based on a binarization threshold value at which the noise level becomes not greater than the predetermined value, an intruding object is detected.

Abstract: The gain difference between pixels is to be corrected for an image signal obtained by an image sensing element having a plurality of pixels. The first reference image is sensed without any object, and then an object is sensed. Gain correction is performed for the sensed object image by using the first reference image. To perform gain correction again, the second reference image is sensed without any object. Gain re-correction is performed for the object image having undergone gain correction by using the first and second reference images.

Abstract: A method for determining a number of balls in a projection space comprises determining a projection of a portion of a ball grid array, determining at least one local maximum of the projection space for a given threshold, and determining at least a distance between adjacent maximum. The method further comprises determining an inter-peak histogram of the distances, determining an inter-ball distance for each pair of adjacent balls that has the maximum value of the inter-peak distance histogram corresponding to the pair of adjacent balls, and determining a position of a first ball and a position of a last ball. The method comprises verifying the position of the first ball and the position of the last ball based on a general inter-ball distance, and determining the number of balls.

Abstract: An improved interpolation method in which a threshold value used for determining a pixel value of a pixel generated by interpolation according to a context which is a state value of adjacent pixels. In the interpolation method, the ambiguity between the interpolation value and the threshold value is removed by using the context, thereby reducing the blocking and smoothing phenomena in the restored binary image.

Abstract: A binarizing section generates binarized data from an image signal of a dot code on an information recording medium read by a code reading section. The binarizing section has a reference dot detection section, a dot area measuring section, a threshold value modifying section and a threshold value determining section. The reference dot detection section binarizes the image signal with a predetermined threshold value prior to generating binarized data to detect a reference dot from a binarized code image. The dot area measuring section measures the area of the reference dot detected by the reference dot detection section. The threshold value modifying section modifies the threshold value for binarization in such a manner that the area measured by the dot area measuring section approaches a predetermined target value. The threshold value determining section binarizes the image signal with the threshold value modified by the threshold value modifying section.