Abstract: A method of evaluating a silicon wafer includes obtaining first surface distribution information indicating an surface distribution of photoluminescence intensity on a surface of a silicon wafer; after obtaining the first surface distribution information, subjecting the silicon wafer to a thermal oxidation treatment, and then obtaining second surface distribution information indicating an surface distribution of photoluminescence intensity on the surface of the silicon wafer; obtaining difference information for the first surface distribution information and third surface distribution information, with the third surface distribution information having been obtained by correcting the second surface distribution information with a correction coefficient of less than 1; and based on the difference information obtained, evaluating an evaluation item selected from the group consisting of absence or presence of oxygen precipitates and surface distribution of oxygen precipitates in the silicon wafer being evaluated.

Abstract: A defect inspection apparatus is capable of inspecting an extremely small defect present on the top and edge surfaces of a sample such as a semiconductor substrate or a thin film substrate with high sensitivity and at high speed. The defect inspection apparatus has an illumination optical system, a plurality of detection optical units and a signal processor. One or more of the detection optical units receives either light diffracted from an edge portion of the sample or light diffracted from an edge grip holding the sample. The one or more of the detection optical units shields the diffracted light received by the detection optical unit based on a signal obtained by monitoring an intensity of the diffracted light received by the detection optical unit in order to inspect a sample portion located near the edge portion and a sample portion located near the edge grip.

Abstract: The a surface of an object is illuminated in sequence with a number of light beams, each of which is nearly tangential to the surface. Images of the surface are recorded for each light beam, and the images are analyzed to identify features such as depressions in the surface.

Abstract: A method is disclosed for in-situ monitoring of an EUV mirror to determine a degree of optical degradation. The method may comprise the steps/acts of irradiating at least a portion of the mirror with light having a wavelength outside the EUV spectrum, measuring at least a portion of the light after the light has reflected from the mirror, and using the measurement and a pre-determined relationship between mirror degradation and light reflectivity to estimate a degree of multi-layer mirror degradation. Also disclosed is a method for preparing a near-normal incidence, EUV mirror which may comprise the steps/acts of providing a metallic substrate, diamond turning a surface of the substrate, depositing at least one intermediate material overlying the surface using a physical vapor deposition technique, and depositing a multi-layer mirror coating overlying the intermediate material.

Abstract: The present invention provides a method and device for determining, in a non-destructive way, carrier concentration level and junction depth in a semiconductor substrate, independent from each other, during a single measurement.

Abstract: When size of a defect on an increasingly miniaturized pattern is obtained by defect inspection apparatus in the related art, a value is inconveniently given, which is different from a measured value of the same defect by SEM. Thus, a dimension value of a defect detected by defect inspection apparatus needs to be accurately calculated to be approximated to a value measured by SEM. To this end, size of the defect detected by the defect inspection apparatus is corrected depending on feature quantity or type of the defect, thereby defect size can be accurately calculated.

Abstract: A producing method of a wired circuit board includes the steps of applying light from above the wired circuit board toward the wired circuit board, and sensing pattern reflected light which is the light reflected by a conductive pattern, table reflected light which is the light reflected by a support table via an insulating layer exposed from the conductive pattern, and foreign-matter reflected light which is the light reflected by a foreign matter present on the insulating layer to inspect the conductive pattern and the foreign matter based on a contrast therebetween. A reflectance of the table reflected light is in a range of 30 to 70%, and a reflectance of the foreign-matter reflected light is in a range of not more than 10%.

Abstract: An oven wall three-dimensional profile data (701) representing concave and convex amounts on all over oven walls (14R, 14L) at a right side and left side of a coking chamber (11) is generated by using image signals obtained by a wall surface observation apparatus (200). A resistance index “k” in which a resistance received by pushed coke (15) resulting from a rising gradient existing on the oven wall (14) is indexed is asked by using the oven wall three-dimensional profile data (701). It can be verified that there is a correlation between this resistance index “k” and a pushing load. Accordingly, it is possible to quantitatively evaluate a state of the oven wall (14) affecting on the pushing load.

Abstract: An apparatus for optical inspection comprises a platform extending in a first direction, a transmitting unit for transporting at least one carrier in the first direction from an input port to an output port thereof, each of the at least one carrier to support one of at least one object to be inspected, a first detector disposed above the platform and extending in a second direction orthogonal to the first direction for inspecting the at least one object on the at least one carrier, the first detector including a first scanner extending in the second direction between the input port and the output port, and a first roller set between the first scanner and the input port to apply force onto a surface of each of the at least one object.

Abstract: Edge points are extracted by specifying a height (values indicating a distance from a substrate) on a pattern when edges of the pattern are extracted from a CD-SEM image. Further, LER values obtained by the extraction of a Fourier spectrum of the LER are obtained. When the same sample is previously observed with the AFM and the CD-SEM, a size of the LER obtained by specifying a height, an auto-correlation distance of the LER, or an index called the spectrum is obtained from results of the AFM observation. Further, theses indices obtained by specifying image processing conditions for detecting the edge points from the CD-SEM observation result are obtained. Also, it is determined that heights providing values when the values are matched correspond to the image processing conditions and then, the edge points are extracted from the CD-SEM IMAGE instead of the AFM observation by using the image processing conditions.

Abstract: The present invention provides an apparatus and method which enable detecting a microscopic defect sensitively by efficiently collecting and detecting scattering light from a defect in a wider region without enlarging the apparatus. In the apparatus for inspecting a defect on a surface of a sample, including illumination means which irradiates a surface of a sample with laser, reflected light detection means which detects reflected light from the sample, and signal processing means which processes a detected signal and detecting a defect on the sample, the reflected light detection means is configured to include a scattering light detection unit which collects scattering light components of the reflected light from the sample by excluding specularly reflected light components by using an aspheric flannel lens and detecting the scattering light components.

Abstract: An inspection system may include, but is not limited to: an illumination subsystem for directing light to an inspection specimen comprising: a power attenuator subsystem configured for altering the power level of a light beam emitted by the illumination subsystem; and a power attenuation control subsystem configured to provide control signals to the power attenuator subsystem according to a detected level of light scattering by the inspection specimen upon illumination by the illumination subsystem. A method for scatterometry inspection may include, but is not limited to: directing light having a power level to an inspection specimen from a light source; detecting light scattered from the specimen; and modifying a power level of one or more intermediate light beams within the light source according to a level of light scattering by the specimen upon illumination by the light source.

Abstract: A device that is capable of simultaneously inspecting both sides of surfaces of a magnetic disk to detect defects thereon includes a front-side defect detecting section and a back-side defect detecting section each of which optically detect a scratch and a defect that are present on the front and back surfaces of the magnetic disk, to improve a throughput for inspection. The back-side defect detecting section has an optical path changing section that reflects a laser beam emitted by a laser light source to change an optical path thereof and thereby to direct the laser beam toward the back surface of the magnetic disk and that reflects scattered light that has been collected by a Fresnel lens to change an optical path thereof and thereby to direct the scattered light toward a first photoelectric converter.

Abstract: A method for inspecting a nano-imprint template, includes irradiating light onto a template for nano-imprinting from a back surface side of the template, the template having a front surface where a pattern is formed, detecting near-field light which is generated near the front surface of the template by the irradiation of the light, and performing an inspection of the template on the basis of the detected near-field light.

Abstract: An inspecting apparatus and method including first and second illuminating units for illuminating a surface of a specimen to be inspected with different incident angles and first and second detecting optical units arranged at different elevation angle directions to the surface of the specimen for detecting images of the specimen illuminated by the first and second illuminating units.

Abstract: There is herein described an unmanned aerial vehicle capable of inspecting, identifying, and/or categorising defects on objects to be inspected using visible and/or non-visible wavelengths from infra-red to ultraviolet. More particularly, there is herein described a remotely controlled or autonomous unmanned aerial vehicle capable of inspecting, identifying, and/or categorising defects on objects to be inspected using visible and/or non-visible wavelengths from infra-red to ultraviolet and displaying information relating to said defects.

Abstract: A method of forming a device is disclosed. The method includes providing a substrate and processing a layer of the device on the substrate. The layer is inspected with an inspection tool for defects. The inspection tool is programmed with an inspection recipe determined from studying defects programmed into the layer at known locations.

Abstract: A method and apparatus of detecting a defect by inspecting a specimen in which a surface of a specimen on which plural patterns are formed is illuminated with an elongated shape light flux from one of plural directions which are different in elevation angle by switching an optical path of the light flux emitted from an illuminating light source in accordance with a kind of defect to be detected. Plural optical images of the specimen illuminated by the elongated shape light flux are captured with plural image sensors installed in different elevation angle directions by changing an enlarging magnification in accordance with a density of the pattern formed on the sample in an area irradiated with the illuminating elongated shape light flux. A defect on the specimen is detected by processing the images captured by the plural image sensors.

Abstract: A profilometer having a guide beam for providing translational movement of substrates in a Y axis relative to a stylus. A first stage receives a first substrate, where the first stage is slidably mounted to the guide beam. The first stage is associated with a first motor for providing independent translational movement for the first stage in an X axis relative to the stylus. A second stage receives a second substrate, where the second stage is slidably mounted to the guide beam. The second stage is associated with a second motor for providing independent translational movement for the second stage in the X axis relative to the stylus, where the first stage and the second stage move together in the Y axis as the guide beam moves in the Y axis, and move independently of one another in the X axis. A robot loads the substrates onto and unloads the substrates off of the first stage and the second stage.

Abstract: An apparatus and a method permit the 3D detection of specular objects which are transparent to visible light. The method operates on the basis of the principle of deflectometry with specific improvements.

Abstract: An improved method and apparatus for detecting problems with fit and finish of manufactured articles is presented which uses structured light. Two or more structured light images acquired from opposing directions is used to measure the fit of mating surfaces while avoiding false positives caused by small defects near the seam.

Abstract: Methods and systems for determining a characteristic of a wafer are provided. One method includes generating output responsive to light from the wafer using an inspection system. The output includes first output corresponding to defects on the wafer and second output that does not correspond to the defects. The method also includes determining the characteristic of the wafer using the second output. One system includes an inspection subsystem configured to illuminate the wafer and to generate output responsive to light from the wafer. The output includes first output corresponding to defects on the wafer and second output that does not correspond to the defects. The system also includes a processor configured to determine the characteristic of the wafer using the second output.

Abstract: In spectral detection for detecting the shape of repeating pattern structures uniformly formed on a surface of a test object, it is advantageous to use light having a wide wavelength range in a short wavelength region. However, it is not easy to realize a relatively simple optical system capable of spectral detection of light having a wide wavelength range in a short wavelength region, namely in ultraviolet region. The present invention provides an inspection apparatus for detecting pattern defects. The inspection apparatus includes a spectral detection optical system capable of spectral detection of light in a wavelength range from deep ultraviolet to near infrared. The spectral detection optical system includes a spatially partial mirror serving as a half mirror and a reflecting objective provided with an aperture stop for limiting the angle and direction of light to be applied to and reflected by a test object.

Abstract: An apparatus for optical inspection comprises a platform extending in a first direction, a transmitting unit for transporting at least one carrier in the first direction from an input port to an output port thereof, each of the at least one carrier to support one of at least one object to be inspected, a first detector disposed above the platform and extending in a second direction orthogonal to the first direction for inspecting the at least one object on the at least one carrier, the first detector including a first scanner extending in the second direction between the input port and the output port, and a first roller set between the first scanner and the input port to apply force onto a surface of each of the at least one object.

Abstract: A method and apparatus of inspecting a sample, in which the sample is inspected under a plurality of inspection conditions, and inspection data obtained by inspecting the sample under each of the plurality of inspection conditions and position information on the sample of the inspection date in correspondence with the respective inspection conditions, are stored. The inspection data for each of the plurality of inspection conditions is against each other by the use of the position information on the sample to determine a position to be inspected in detail, and an image of the sample at a position to be inspected in detail is obtained. The obtained image is classified, the inspection condition of the sample by the use of information of classification of the image is determined.

Abstract: In an inspection subject substrate, there is a problem that a defect signal is overlooked due to scattered light from a pattern and sensitivity decreases in an irregular circuit pattern part. The inventors propose a defect inspection method, characterized by comprising: an illumination step of guiding light emitted from a light source to a predetermined area on an inspection subject substrate under a plurality of predetermined optical conditions; a detection step of obtaining an electric signal by guiding scattered light components propagating in a predetermined range of azimuthal angle and in a predetermined range of elevation angle to a detector for each of a plurality of scattered light distributions occurred correspondingly to the plurality of optical conditions in the predetermined area; and a defect determination step of determining a defect based on the plurality of electric signals obtained in the detection step.

Abstract: To provide a defect inspection apparatus for inspecting defects of a specimen without lowering resolution of a lens, without depending on a polarization characteristic of a defect scattered light, and with high detection sensitivity that is realized by the following. A detection optical path is branched by at least one of spectral splitting and polarization splitting, a spatial filter in the form of a two-dimensional array is disposed after the branch, and only diffracted light is shielded by the spatial filter in the form of a two-dimensional array.

Abstract: A distinguishing size for distinguishing a pseudo defect from a defect caused by a process trouble is stored in a first storage area. Defect data are stored in a second storage area. A processing unit detects a defect on a wafer surface, and stores the defect data in the second storage area. Before a defect detection process is completed for all areas of the wafer surface, a size of a defect detected in a partial area is compared with the distinguishing size stored in the first storage area. If the detected defect has a size equal to or larger than the distinguishing size, an alarm is output through an output unit, whereas if a defect having a size equal to or larger than the distinguishing size is not detected, the defect detection process is executed for the area still not subjected to the defect detection process.

Abstract: Instruments and methods relating to surface plasmon imaging are described. An instrument comprises a semi-circular rail and a driving mechanism. The driving mechanism is attached to a light source mount and a detector mount, and both the light source mount and the detector mount are attached to the semi-circular rail with connectors. Each connector allows the light source mount and detector mount to slide along the rail. The synchronous movement of the light source mount and the detector mount changes the angle of incidence of a light beam from the light source with respect to the plane of the sample surface on the sample stage.

Abstract: An inspection apparatus and method for detecting defects and haze on a surface of a sample includes illumination optics which emit light to illuminate an inspection region on the surface of the sample from an oblique direction relative to the inspection region, first detection optics which detect first scattered light from the inspection region and having a beam analyzer through an optical path, second detection optics which detect second scattered light from the inspection region, the second scattered light being scattered from a direction different than a direction of the first scattered light, and a signal-processing unit which treats different processings for a first signal of the detected first scattered light and for a second signal of the detected second scattered light and detecting defects and haze on the surface of the sample on the basis of at least one of the first signal and the second signal.

Abstract: In the fabrication of a semiconductor integrated circuit device, a 2D-3D inspection technique for solder printed on a substrate is provided which permits easy preparation of data and easy visual confirmation of a defective portion. In a substrate inspecting step, first, a 3D inspection is performed, followed by execution of 2D inspection, whereby a 2D picked-up image of the portion of a pad determined to be defective can be displayed on a larger scale simultaneously with the end of inspection, thereby providing an environment for efficient visual confirmation of the defect. Further, by subjecting a raw substrate to measurement at the time of preparing inspection data, a relation between an original height measurement reference generated automatically by the inspection system and the height of a pad upper surface is checked, whereby it is possible to measure the height and volume of printed solder based on the pad upper surface.

Abstract: The present disclosure relates to a method for the quantitative determination of surface properties, wherein a spatially resolved image of a surface to be analysed, which contains a large number of measured values, is recorded. In a first method step, the measured values are analysed in order to determine those surface areas which have a specific physical property. A result value of this physical property is then determined, wherein this result value is characteristic of the values of the physical property of all those surface areas of the image determined by analyzing the image. According to the disclosure, the result value is displayed against the size of the determined surface areas.

Abstract: One embodiment relates to an oblique illuminator. The oblique illuminator includes a light source emitting a light beam, a first reflective surface, and a second reflective surface. The first reflective surface has a convex cylindrical shape with a projected parabolic profile along the non-powered direction which is configured to reflect the light beam from the light source and which defines a focal line. The second reflective surface has a concave cylindrical shape with a projected elliptical profile which is configured to reflect the light beam from the first reflective surface and which defines first and second focal lines. The focal line of the first reflective surface is coincident with the first focal line of the second reflective surface. The first and second focal lines of the second reflective surface may be a same line in which case the elliptical curvature is a projected spherical profile. Other embodiments, aspects and features are also disclosed.

Abstract: A pattern inspection method and apparatus in which a deep ultraviolet light or an ultraviolet light is irradiated onto a specimen on which a pattern is formed, an image of the specimen which is irradiated with the deep ultraviolet light or the ultraviolet light is formed and the formed image is detected with a rear-surface irradiation type image sensor, which is sensitive to wavelengths of no greater than 400 nmm. A signal outputted from the image sensor is processed so as to detect a defect of the specimen by converting an analog image signal outputted from the image sensor to a digital image signal with an A/D converter, and a display displays information of the defect detected.

Abstract: A system for monitoring foreign matter includes a manufacturing line having plural process processing apparatuses, a production management system which manages the processing of workpieces in the manufacturing line, plural optical heads which monitor foreign matter in relation to at least one of the workpieces, and which provide an output signal indicative thereof, and at least one image signal processing unit provided in a lesser number than a number of the plural optical heads for processing the output signal therefrom.

Abstract: The invention has a function of preparing a data base for a relation between a defect shape and an arrangement for the optical system capable of detecting the shape at high sensitivity and automatically adjusting the arrangement for the optical system. As the method of preparing the data base, a method of using optical simulation or an experimental method of using a sample having an optical shape is applied. A pinhole position and a beam size are adjusted automatically so as to attain the optimal arrangement for the optical system to an inputted defect shape based on the data base.

Abstract: A surface inspection method and a surface inspection apparatus in which a plurality of photodetectors are arranged in a plurality of directions so that light scattered, diffracted or reflected on a surface of an object to be inspected or in the vicinity of the surface is detected and a plurality of signals obtained by this are subjected to weighted addition processing or weighted averaging processing by linear combination.

Abstract: An interference measuring device comprises light sources lenses, an aperture, an optical multiplexer, an optical branching filter, a half mirror, an imaging unit, an analyzing unit, a light receiving unit, a displacement detecting unit, a piezoelectric actuator, a drive unit, a mirror, a stage, a drive unit, and a control unit. According to a result of optical path length difference detection by the displacement detecting unit, the control unit controls optical path length difference adjusting operations by the piezoelectric actuator and stage through the drive units such that the optical path length difference becomes a plurality of target values in sequence. The control unit subjects the moving operation by the piezoelectric actuator to a feedback control such that the optical path length difference becomes each of the target values upon the moving operation by the stage as well.

Abstract: A surface inspecting method including irradiating a laser light to a test object to generate an ultrasonic wave, irradiating a second laser light at a position apart by a known distance from a position where the laser light is irradiated and receiving a reflection light thereof, and correcting a generation surface wave of a received ultrasonic wave by using an ultrasonic wave other than the generation surface wave to thereby detect a flaw of the test object. A characterization of the generation surface wave is divided or integrated by the same characterization of the ultrasonic wave other than the generation surface wave included in an output signal to obtain a performance index value and obtain a depth of the flaw by applying the performance index value to a calibration curve in which a corresponding relation between the performance index value and the depth of the flaw is obtained preliminarily.

Abstract: In the conventional contaminant particle/defect inspection method, if the illuminance of the illumination beam is held at not more than a predetermined upper limit value not to give thermal damage to the sample, the detection sensitivity and the inspection speed being in the tradeoff relation with each other, it is very difficult to improve one of the detection sensitivity and the inspection speed without sacrificing the other or improve both at the same time. The invention provides an improved optical inspection method and an improved optical inspection apparatus, in which a pulse laser is used as a light source, and a laser beam flux is split into a plurality of laser beam fluxes which are given different time delay to form a plurality of illumination spots. The scattered light signal from each illumination spot is isolated and detected by using a light emission start timing signal for each illumination spot.

Abstract: In order to maximize the effect of signal addition during inspection of foreign substances in wafers, a device structure including line sensors arranged in plural directions is effective. Low-angle detection optical systems that detect light beams in plural azimuth directions, the light beams being scattered in low angle directions among those scattered from a linear area on a sample illuminated by illuminating means, each include a combination of a first imaging lens group (330) and a diffraction grating (340) and a combination of a second imaging lens group (333) and an image detector (350) having a plurality of light receiving surfaces. A signal processing unit processes signals from the image detectors of the low-angle detection optical systems by adding the signals from the light receiving surfaces corresponding between the image detectors.

Abstract: An appearance inspection apparatus analyzes a difference in detection characteristics of detection signals obtained by detectors to flexibly meet various inspection purposes without changing a circuit or software. The apparatus includes a signal synthesizing section that synthesizes detection signals from the detectors in accordance with a set condition. An input operating section sets a synthesizing condition of the detection signal by the signal synthesizing section, and an information display section displays a synthesizing map structured based on a synthesized signal which is synthesized by the signal synthesizing section in accordance with a condition set by the input operating section.

Abstract: An apparatus for optical inspection comprises a platform extending in a first direction, a transmitting unit for transporting at least one carrier in the first direction from an input port to an output port thereof, each of the at least one carrier to support one of at least one object to be inspected, a first detector disposed above the platform and extending in a second direction orthogonal to the first direction for inspecting the at least one object on the at least one carrier, the first detector including a first scanner extending in the second direction between the input port and the output port, and a first roller set between the first scanner and the input port to apply force onto a surface of each of the at least one object.

Abstract: A pattern defect inspection apparatus capable of detecting minute defects on a sample with high sensitivity without generating speckle noise in signals is realized. Substantially the same region on a surface of a wafer is detected by using two detectors at mutually different timings. Output signals from the two detectors are summed and averaged to eliminate noise. Since a large number of rays of illumination light are not simultaneously irradiated to the same region on the wafer, a pattern defect inspection apparatus capable of suppressing noise resulting from interference of a large number of rays, eliminating noise owing to other causes and detecting with high sensitivity minute defects on the sample without the occurrence of speckle noise in the signal can be accomplished.

Abstract: An inspecting apparatus and method including first and second illuminating units for illuminating a surface of a specimen to be inspected with different incident angles and first and second detecting optical units arranged at different elevation angle directions to the surface of the specimen for detecting images of the specimen illuminated by the first and second illuminating units.

Abstract: A defect inspection apparatus includes an illumination optical system, a detection optical system which includes a reflecting objective lens, and wavelength separation optics for conducting wavelength separation, and after the wavelength separation, branching the scattered light into at least a first detection optical path and a second detection optical path. The detection optical system further includes, on the first detection optical path, a first sensor, and on the second detection optical path, a second sensor. A signal processor is provided which, in accordance with at least one of a first signal obtained from the first sensor and a second signal obtained from the second sensor, discriminates defects or defect candidates present on a surface of a sample.

Abstract: A test object carrying device for use in an appearance inspection device for checking the appearance of the test objects, which includes a back/front reversal unit for turning over the test objects being conveyed by the forward conveying means and supplying them to the returning unit; the back/front reversal means is provided with a first drum for rotating and conveying the test objects unit while holding the test objects on the peripheral surface thereof, and a second drum for rotating and conveying the test objects being conveyed by the first drum while holding the test objects on the peripheral surface thereof; wherein at least one of the first drum and the second drum is structured so that the test objects are transferred in parallel to the forward conveying unit and returning unit by rotating and conveying the test objects while holding them on the peripheral surface thereof.

Abstract: Systems and methods for detecting defects on a wafer are provided. One method includes generating output for a wafer by scanning the wafer with an inspection system using first and second optical states of the inspection system. The first and second optical states are defined by different values for at least one optical parameter of the inspection system. The method also includes generating first image data for the wafer using the output generated using the first optical state and second image data for the wafer using the output generated using the second optical state. In addition, the method includes combining the first image data and the second image data corresponding to substantially the same locations on the wafer thereby creating additional image data for the wafer. The method further includes detecting defects on the wafer using the additional image data.

Abstract: A surface inspecting apparatus includes an illumination optical system irradiating linearly polarized light to a wafer surface under a plurality of inspection conditions; an imaging optical system capturing an image of the wafer formed by polarization components having an oscillation direction different from that of the linearly polarized light as part of reflected light from the wafer surface irradiated by the linearly polarized light under the plurality of inspection conditions; and an image-processing apparatus for extracting for individual pixels an image having the smallest signal intensity from among images of the wafer captured under the plurality of inspection conditions by the imaging optical system, and for inspecting for the presence of defects in a repeated pattern of the wafer based on an inspection image of the wafer generated by connecting each of the extracted pixels.

Abstract: An image processing method that differentiates image data using an image processing system that includes a processing unit and a storage unit includes: acquiring image data; sequentially picking up pixels one by one at a predetermined pitch from among the pixels that constitute the image data and setting the picked up pixels as reference pixels; setting a close region around each of the reference pixels; calculating an average value of densities of the picked up pixels for each of the close regions; setting a wide region larger than the close region around each of the reference pixels; calculating an average value of densities of the picked up pixels for each of the wide regions; and calculating a difference between the density of each of the reference pixels and a corresponding one of the average values of the densities of the pixels of the wide regions.