Abstract: This invention falls within the scope of steganography, i.e., encoding of information (such as a text) into other information, for example, an image. It is the object of this invention a computational method for generating at least one image with coded information comprising the steps of: i) associating an information to be coded to a plurality of graphic elements, each of the graphic elements consisting of a symbol out of a plurality of symbols, thus generating a pattern of graphic elements and ii) generating at least one image comprising at least one pattern obtained from step i). This method introduces a consistent and highly flexible way of encoding information into an image. Additionally, this invention has also as object a system associated to the said method, images obtained from the said method, as well as a reading method and system thereof.

Abstract: Provided are an information processing apparatus and program that are able to improve representable gradations in a pseudo manner while reducing flicker including a random number generator configured to generate a random number sequence; a comparator configured to make a comparison between a threshold and a random number value, the threshold being associated with any number of lower bits, the any number of lower bits forming input image data with any number of upper bits, the random number value forming the random number sequence.

Abstract: An image processing apparatus generates one image by using at least one frame each of a plurality of moving images obtained by taking moving images of a plurality of different regions of an eye at different times. The apparatus includes a deciding unit configured to decide the at least one frame in each of the plurality of moving images, so that regions which have actually been shot are included in the plurality of moving images in the plurality of regions; and an image generating unit configured to generate one image by using the at least one frames decided from each of the plurality of moving images.

Abstract: A reading unit reads a first side of a printed material having first image data printed on the first side and second image data printed on a second side, the second side being a back side of the first side, in order to obtain image data. A density determination unit determines whether a density of the second image data exceeds a predetermined density. A comparison unit compares a density of the image data obtained by the reading unit and a density of the first image data, and produces a comparison result. A determination unit, in a case when a density difference between the density of the image data and the density of the first image data exceeds a threshold as the comparison result of the comparison unit, determines that the printed material includes a defect portion.

Abstract: An image processing apparatus includes an extracting unit extracting custom color identification data that identifies each of one or more custom colors different from multiple predetermined basic colors from drawing data for every page; a separation data generating unit generating separation data that indicates an object to be drawn for each color in accordance with the drawing data for one page without waiting for the completion of the extraction of the custom color identification data for the pages other than the one page; a raster data generating unit generating raster data concerning each color in accordance with the separation data; an acquiring unit acquiring mixing ratio data; and a combining unit combining the raster data concerning the custom color with the respective pieces of raster data concerning the basic colors in accordance with the mixing ratio data.

Abstract: An image forming apparatus is described. Selecting a function desired by a user from among functions provided in the apparatus is provided to improve operability as well as eliminating erroneous copy. In the image forming apparatus, an operation unit includes a display panel for displaying a function selecting portion. An operation unit side control portion, as the function selecting portion, has a first function selecting portion in which selectable function items are displayed corresponding to an operation mode and a second function selecting portion in which other function items which are selectable at the same time. The first function selecting portion and the second function selecting portion are displayed at the same time on the display panel, so that functions of the first function selecting portion and functions of the second function selecting portion are selectable at the same time.

Abstract: A pulse width modulation technique is disclosed for use in an image forming device such as a laser printer or a photocopier. The technique implements a pacer to synthesize the frequency of a serializer circuit by stretching (or shrinking) pixel pulse train data. The pacer stretches the pixel pulse train data in accord with increment data that is based upon information about the image forming device, such as the number of bits in the pixel pulse train data, the number of bits in print engine pulse train, the target print engine frequency, and the serializer frequency. The technique can be implemented with digital circuits that provide digital test data.

Abstract: An image forming apparatus for forming images at a plurality of resolution levels including at least one low resolution level and one high resolution level includes a photoconductor, onto which a beam size is set for the low resolution level; and an adjustment unit to conduct an exposure time-based density adjustment using a plurality of half-tone patterns prepared by changing an exposure time per pixel at a timing when a resolution level shifts from the low resolution level to the high resolution level and before actually shifting to an image forming operation executed at the high resolution level.

Abstract: An image processing apparatus and an image processing method are provided, which are useful for faithfully reproducing luster even if a luminance reproduction range of an output apparatus is brighter than the luminance reproduction range of an input apparatus. The image processing apparatus includes a luster region determination unit configured to determine a luster region included in an input image based on a luminance value of the input image, a luminance correction value calculation unit configured to calculate a luminance correction value of the luster region, and a corrected image generation unit configured to generate an output image by adding the luminance correction value to the luminance value of the input image.

Abstract: A host computer groups a plurality of pixels to generate pseudo pixels, assigns representative values in an RGB format to the pseudo pixels, and transfers the representative values to a printer. Further, the host computer performs halftone processing and transfers generated dot data to the printer for pixels constituting the pseudo pixel which includes edges therein or of which boundary is the edge. The printer performs printing by using the transferred dot data and the representative values.

Abstract: Provided is an image processor and image processing method that are capable of suppressing both density unevenness and graininess that occur due to deviation of the printing position of dots that are printed by a plurality of relative movements (or a plurality of printing element groups). In order to accomplish this, the dot overlap rate of an image characteristic in which density unevenness stands out is made higher than the dot overlap rate of an image characteristic in which other defects stand out more than the density unevenness. By doing so, it is possible to suitably adjust the dot overlap rate according to an image characteristic, and to output an image having no density unevenness or graininess.

Abstract: A method and a printing system for gray balance correction of a printing process include determining first color values at on a gray axis of a color space of a reference printing process. These first color values determine tonal values describing a corrected gray balance of the target printing process. To avoid wastage and a further proof for gray balance calibration of the printing process, second color values of the printing process, describing the corrected gray balance, are derived from the first color values. The tonal values of the target printing process corresponding to the second color values are determined from first characterization data and the second color values of the printing process. A correction function created from these tonal values describes the corrected gray balance. Determining corrected characterization data is also possible. A printing form is produced and a printing material is imaged by using the corrected gray balance.

Abstract: Image forming apparatus (100) creates a toner pattern on intermediate transfer belt (11) as a preprocessing of gradation correction, and calculates a cycle at which density unevenness is largest. Then, a toner image for gradation correction is formed so as to cancel cyclic unevenness at a cycle at which the largest density unevenness occurs. As a result of this, it becomes possible to suppress the deterioration of density detection accuracy and perform a highly accurate gradation correction even if density unevenness of any cycle occurs.

Abstract: When dot data indicating whether or not a dot is formed on the basis of the gradation value for each pixel, dots belonging to a plurality of pixel groups having different printing conditions are printed in a common region in an overlapping manner, and the distribution of dots in the common region has a noise characteristic possessing a peak in the spatial frequency region on the high-frequency side. In a case where first and second pixels belonging to two pixel groups are proximal pixels in the common region in a predetermined gradation range in which probabilities k1 and k2 at which a dot is formed in the first and second pixels are such that k1<0.5 and k2<0.5, a probability K of a dot in both of the proximal pixels is set to be close to k1·k2.

Abstract: There is provided an image processing apparatus which can suppress degradation of an image quality in a recording material save mode processing and obtain an effect of consumption amount reduction of recording material desired by a user at low costs. A recording material consumption amount at the time of applying first color conversion processing unit is predicted corresponding to inputted image data. The setting of a second color conversion processing is changed from a prediction value and a target value of the recording material consumption amount.

Abstract: A method and system for generating a halftone image from an input image is disclosed. The method and system use error distribution and threshold perturbation that is based on the incoming tone value. A threshold bias table may be generated in real time for each incoming tone value. The values of the threshold bias tables are selected so that certain positions are forced to include a dot, in the case of light tone values, or not include a dot, in the case of dark tone values. A halftone process that uses threshold bias tables based on the incoming tone can reduce unnatural patterns in the image apparent to the casual observer, which results in a more pleasing image.

Abstract: An image forming apparatus is provided. The image forming apparatus includes a communication interface unit which receives print data, a rendering unit which converts the received print data into a bitmap image by rendering, a binarization unit which generates binary data by carrying out halftoning with respect to the bitmap image, a data combining unit which generates multi-bit data by combining a plurality of successive binary data of the generated binary data, and a print engine which forms an image on a print paper using the generated multi-bit data.

Abstract: A method and apparatus as provided for determining, for an ink to be deposited on a substrate by a halftone inkjet printing process, a nominal coverage value (the ‘ink restriction value’), that corresponds to an amount of ink sufficient to fully cover the area of the substrate to be printed. This determination is effected by measuring the reflectance of the printed substrate for a range of nominal coverage values, and then using an automatic processing arrangement to determine, from the change of measured reflectance with nominal coverage value, the nominal coverage value at which continuous tone behavior commences.

Abstract: An image processing apparatus is provided that includes a scanning unit for scanning a document to obtain scanning data and a control unit. The control unit is configured to specify a shadow region to be modified in the scanning data, execute a first adjusting operation for selecting a gray-scale level of a portion of the scanning data corresponding to the specified shadow region, and modify the scanning data according to the selected gray-scale level.

Abstract: A method of printing an image by a printer having an asymmetric printer resolution includes multi-level halftoning the image by assigning a level out of a number of levels to each pixel of the image. The method further includes determining the number of levels on the basis of the asymmetric printer resolution, selecting for each level a collection of at least one binary pattern, each binary pattern consisting of a plurality of sub-pixels the number of which is determined by the number of levels, selecting for each pixel of the halftoned image a binary pattern from the collection selected for the level assigned to the pixel, transforming each pixel of the halftoned image into the selected binary pattern, and printing the binary patterns of the transformed pixels using the asymmetric printer resolution. A printer is configured to perform the method.

Abstract: Inputted image data is converted to M number of multi-value data having a lower resolution than the inputted image data, and after quantization processing has been performed for each of the M number of multi-value data, an image is printed by M number of relative movements (M-pass printing) that corresponds to the M number of quantized data. By doing so, when compared with the case in which a resolution reduction process is not performed, it is possible to suppress the number of pixels that become the object of quantization processing, and it becomes possible to output an image with no fluctuation in image density or density unevenness without a decrease in the processing speed.

Abstract: An image processing apparatus which converts first image data having grayscale value of a predetermined color space for each pixel into second image data having grayscale values of recording material colors of a printing section and having pixels of which the number is reduced to 1/n, includes grayscale value difference determination section that determines whether or not grayscale value difference between a predetermined target pixel and each of other pixels in a pixel block exceeds a threshold value for each of the pixel blocks for the first image data, and color conversion section that performs color conversion process by referring to color conversion table, and color conversion section performs a second process such that grayscale value of the recording material color obtained through color conversion process for an average value of grayscale values of the predetermined color space of the respective pixels is used as the second image data.

Abstract: An image processing method generates a halftone image by forming a halftone dot represented by a set of one or plural output dots corresponding to an intensity of an input image signal while making a part of the dots constituting the halftone dot to be an actual non-output dot so as to reduce an amount of a coloring material of a halftone-dot portion. The image processing method includes holding in a predetermined storage medium halftone-dot profile data for forming the halftone dot corresponding to the intensity of the image signal and gap-size profile data representing a size of a set of the non-output dot; and generating the halftone dot comprising a gap having a size based on the gap-size profile data, a size of the halftone dot being based on the halftone-dot profile data.

Abstract: A color conversion device include a limit value setting unit that sets, in accordance with a color gamut, a limit value of a color material total amount that is used in an output device that uses color materials of M colors including black, where M is an integer equal to or larger than 4, and outputs an image; and a black amount determining unit that calculates a total amount limit value corresponding to the color gamut for each black amount on the basis of the limit value that has been set in accordance with the color gamut by the limit value setting unit and determines a black amount from a conversion target-independent color signal of a device-independent color space.

Abstract: An image processing apparatus is configured to process multivalued image data corresponding to a unit area of a recording medium so as to form an image on the unit area with a plurality of relative movements between a recording head and the recording medium. The apparatus has a selecting unit for selecting either a first processing mode to segment the multivalued image data into a plurality of multivalued image data corresponding to the plurality of relative movements, and then quantize each of the plurality of multivalued image data, or a second processing mode to quantize the multivalued image data into quantized image data, and then segment the quantized image data into a plurality of quantized image data corresponding to the plurality of relative movements. The selecting unit may select either the first processing mode or the second processing mode based on the number of relative movements to the unit area.

Abstract: A system and method of reducing noise in output image data is provided. Grayscale image data having a plurality of pixels is received and processed. During processing, pixels which may produce noise are identified, and a mask associated with the image data is generated. The mask provides information related to the pixels, such as opaque and transparent regions for overlaying the pixels. The image data and the mask are compressed and stored. The mask assists in preventing the identified pixels from being visible when the image data is output, thereby reducing the noise in the image.

Abstract: Display image data for displaying images on a screen, and when display image data that has undergone specified gradation conversion is received, the characteristics of the output brightness displayed on the screen is checked. In the area for which the output brightness of the display image data is convex at the bottom in relation to the image data gradation values, the display image data gradation values are corrected so as to have a roughly linear relationship between the gradation values and the output brightness. Printing image data is generated based on the post-correction image data and an image is printed. In the area for which the output brightness bottom is convex, by performing this kind of correction, it is possible to print an image with an impression closer to the display on the screen. As a result, it is possible to print images on the monitor screen easily and without losing the impression received from the image displayed on the monitor screen.

Abstract: A scan line profile characteristic representing the distortion of a scan line is detected. Dot image data undergoes the screen process using a dither matrix. At this time, the quantization process is done by shifting a dither matrix element in the sub-scanning direction opposite to the direction of the scan line changing process at a scan line changing point in the scan line changing process in accordance with the profile characteristic. The image data after the screen process undergoes the scan line changing process, and the interpolation process smooths the scan line changing point.

Abstract: A method for controlling a tone reproduction curve of an image printing system includes generating an actual printed image tone reproduction curve using printed image data from a printed image sensor; determining a set of adjusted contone values by comparing the actual printed image tone reproduction curve with a target printed image tone reproduction curve, where the adjusted contone values being representative of the print contone values at which target color density data of the printed image is achieved in the image printing system; and determining adjusted image transfer surface reflectance data to update a target image transfer surface tone reproduction curve, where the adjusted image transfer surface reflectance data being obtained by interpolating the target image transfer surface tone reproduction curve at the adjusted contone values; and controlling subsequent toner image data to achieve the updated target image transfer surface tone reproduction curve.

Abstract: An error diffusion processing method and apparatus quantizes an input grayscale value of a pixel (m, n) of an input image based on a determination of whether the input grayscale value belongs to one of ranges divided by a plurality of thresholds. The ranges include at least one shadow area which is darker than a median grayscale value, and the input grayscale value is quantized to a predetermined grayscale value which is brighter than the median grayscale value in a predetermined method and thereby a binary grayscale value of the pixel (m, n) is determined. The error diffusion processing method and apparatus obtains an error from the input grayscale value and the binary grayscale value of the pixel (m, n), and distributes the error to neighboring pixels of the pixel (m, n) according to a predetermined error diffusion coefficient and modifies input grayscale values of the neighboring pixels.

Abstract: An image processing apparatus 101 that generates output image data based on multi-level image data is provided with an error diffusion processing unit 104 that generates tone pixel data from the pixel-of-interest data according to an error diffusion method, a dither processing unit 103 that generates tone pixel data from the pixel-of-interest data according to a dither processing method, an allotment ratio determination unit 105 that increases the allotment ratio with respect to the error diffusion method as the difference between the maximum density and the minimum density increases, and a composition unit 109 that composites the tone pixel data for a pixel of interest that has been generated by the error diffusion processing unit 104 and the dither processing unit 103 according to the allotment ratios determined by the allotment ratio determination unit 105, and outputs the composited data as pixel data of the output image data.

Abstract: A method and system for controlling color output includes receiving a document containing a color image, producing a first output copy of the document using a first color processing path, receiving at least one natural language request to adjust the color output of the device, adjusting the color output of the device, and producing a second output copy of the document. The method and system further includes presenting natural language descriptions of the effects of color processing paths with or without sample palettes to the user either to solicit a suggestion from the user or present the user with choices based upon the natural language request received.

Abstract: Line width of images marked by an image marking device is adjusted by reading a calibration patch marked by the marking device, and then adjusting one or more settings of the marking device, such as exposure intensity or cleaning field intensity, independent of the digital control of the tone reproduction curve so that the line width of subsequently marked images becomes closer to a target value. A digital control may be implemented to compensate for the impact of the modification of the one or more settings on the tone reproduction curve.

Abstract: An image processing device includes an additional image formation unit configured to form an additional image having a first predetermined density. At least a part of the additional image is overlaid with a main image having a second predetermined density, the main image being formed on an image formation medium. A boundary image formation unit is configured to form a boundary image which is formed in an area defined in the vicinity of an overlaid area where the additional image is overlaid with the main image. A density of the boundary image is lower than both the first predetermined density and the second predetermined density. A synthesized image formation unit is configured to synthesize the main image, additional image and the boundary image to form a synthesized image.

Abstract: When multi-pass printing is performed, the dot overlap rate (ratio of the number of dots that overlap and are to be printed in the same pixel area by the plurality of relative movements with respect to the total number of dots to be printed in a pixel area by the plurality of relative movements) in pixel areas having medium-density where density unevenness caused by density fluctuation easily stands out is made higher than the dot overlap rate in pixel areas having low-density and pixel areas having high-density. By doing so density unevenness caused by density fluctuation is suppressed. In addition, the dot overlap rate in pixel areas having low-density and pixel areas having high-density is low, so it is possible to reduce graininess in low-density areas and suppress a decrease in density in high-density areas.

Abstract: An image forming apparatus includes a tone correction storage unit that stores a plurality of tone correction charts for correcting tone of image data; a determination unit that determines characteristics of the image data; a selection unit that selects a tone correction chart suitable for the image data from the plurality of tone correction charts stored in the tone correction storage unit; a chart print unit that prints the tone correction chart selected by the selection unit on a sheet; a receiving unit that receives an adjustment value inputted based on the tone correction chart printed by the chart print unit; a tone correction unit that corrects tone of the image data based the adjustment value; and a print unit that prints out the image data after correcting tone of the image data.

Abstract: An image processing device includes a multiplier 1 for multiplying a pixel signal P(x) by a weighting factor ?0 (0??0?1), a delay element 2 for delaying the pixel signal P(x) which has not been multiplied yet by the weighting factor ?0 by the multiplier 1 by one pixel, and a multiplier 3 for multiplying the pixel signal P(x?1) delayed by the delay element 2 by a weighting factor ?1 (0??1?1), the total sum of the weighting factors ?0 and ?1 being larger than 1 and smaller than an upper limit ?max. An adder 4 adds the multiplication result ?0·P(x) of the multiplier 1 and the multiplication result ?1·P(x?1) of the multiplier 3, and a limiter 5 limits the addition result P?(x) of the adder 4 in such a way that P?(x) falls within a maximum density value Pmax.

Abstract: An apparatus, system, and method for image processing are disclosed, each of which obtains a mark from image data, detects additional information in the mark, determines whether the mark is detected in the mark to generate a determination result, and controls processing performed by an image processing apparatus with respect to the image data based on the determination result.

Abstract: A method and apparatus are provided for compensating for spatial non-uniformities in a printer by deriving a true spatial non-uniformity tone response curve (TRC) that characterizes the printer in terms of color output variation for each addressable pixel location in a spatial range. The “true average” tone response curve is determined for a color channel. A prediction of the true response as a function of the spatial location is derived by printing and scanning a specially designed halftone-independent target of binary patterns. The predicted tone response curve for each color channel and halftone is predicted using a binary printer model, wherein the “predicted tone response curve” provides a model based approximation of the actual response for each addressable pixel location in the spatial range. Also stored is an “average predicted tone response” by averaging the “predicted tone response curve” over the spatial range of the printer.

Abstract: An image forming apparatus shifts dots of a recording dot pattern by half of a dot pitch in a main scanning direction to generate a shift dot pattern, corrects a jagged outline of the shift dot pattern caused by shifted dots using correction dots to generate a corrected shift dot pattern, and determines an increased number of ink droplets to be additionally ejected from one or more of a plurality of nozzles to form the shifted dot or the correction dot of the corrected shift dot pattern with an increased dot size, based on an estimated shift value indicating the displacement in landing position of ink droplets forming the dot of the recording dot pattern.

Abstract: Systems and methods are provided for processing at least one document comprising color data. Color data in the document in a first color space is inspected to determine if a color space conversion operation for a portion of the color data is specified using a color space dictionary or a transformation matrix, wherein the color space conversion operation converts the color data from the first color space to an intermediate standard color space. An input profile corresponding to the color conversion operation is generated, wherein the input profile comprises information to convert color data from the first color space to the intermediate standard color space; and color space conversion operations are performed on the color data using the generated input profile to convert the color data from the first color space to the intermediate standard color space.

Abstract: Print data is generated to form an image on a printing medium by superposing a plurality of types of printing materials in some or all pixels of an output image in an order complying with the intensities of the light scattering characteristics of the plurality of types of printing materials. The generated print data is transmitted to a printing apparatus.

Abstract: A method for performing a color based white balance of a digital image, the method includes: generating or receiving multiple chromaticity value pairs of multiple pixel areas of the digital image; finding selected candidates; wherein a selected candidate represents a pixel area and has a chromaticity value pair that falls within at least one color gamut out of a group of color gamut of different colors; wherein the different colors comprise at least one color that differs from gray; calculating at least one white balance compensation parameter in response to pixel information of pixels areas that have selected chromaticity values; and providing a compensated digital image by applying at least one white balance compensated image.

Abstract: A technique for performing high-quality cluster type FM halftone image output without “anisotropy” or “sweep out texture” phenomenon is provided. An error diffused to a current pixel position and a random number RND are added by an adder to multi-level pixel data as a subject of binarization, and supplied as pixel data Pxy to a selector. The selector compares the pixel data Pxy with thresholds, and supplies the pixel data Pxy to one of a highlight portion processor, a dark portion processor and an intermediate portion processor. The highlight and dark portion processors refer to already-binarized results within a range determined in accordance with the value of the input pixel data Pxy, and determine a binarization result Qxy. The intermediate portion processor compares a threshold, which monotonously increases in accordance with the value of the pixel data Pxy, with the pixel data Pxy, thereby determines the binarization result Qxy.

Abstract: An information processing apparatus processes, for each pixel, multivalued image data for a unit area of a recording medium, so as to form an image on the unit area with a plurality of relative movements between a recording head and the recording medium. The apparatus has a selector that selects a first processing mode for dividing the multivalued image data into a plurality of pieces of multivalued image data corresponding to the plurality of relative movements, and then quantizing each of the plurality of pieces of multivalued image data, or a second processing mode for quantizing the multivalued image data into quantized image data, and then dividing the quantized image data into a plurality of pieces of quantized image data corresponding to the plurality of relative movements. The selector selects the processing mode based on a content (attribute, grayscale, color, etc.) of the multivalued image data.

Abstract: Machine-enabled methods of, and system, and processor readable media, embodiments for, tone quantization error diffusion comprising a first stage process and a second stage process. where pre-calibrated index tables may be applied by which quantized pixels may be expressed according to halftones.

Abstract: Disclosed is a method for generating a basic template utilized to form a screening mask. The method includes adjusting lines per inch or minimum pattern (such as cluster size or density) of a testing template, printing the adjusted testing template by an outputting device, determining if the gray level of the printing result matches a specific gray level, and continuously adjusting the setting of the lines per inch or the minimum pattern when it does not match the specific gray level, otherwise selecting the adjusted testing template as a basic template. The basic template is optimized according to the printing ability of the outputting device, so the printing performance of the outputting device when using the screening mask formed from the basic template can also be optimized, and the minimum color points can be printed faithfully thereby avoiding dropping of the carbon powder.

Abstract: An image processor includes a color conversion unit that generates color converted image data by converting color data and an error diffusion process performing unit that generates print data by performing an error diffusion process on the color converted image data. The error diffusion process performs a first error diffusion process on remaining data and performing a second error diffusion process on edge data such that an amount of ink used in the edge region by performing the second error diffusion process on the edge data is less than an amount of ink used in the edge region by performing first error diffusion process on the edge data.

Abstract: The present invention aims to prevent a problem that an image on a document sheet is erased due to misdetection of a line-shaped noise. A copy machine 1 compares RGB values of a target pixel with averaged RGB values (Step S103). If only one of the RGB values has a difference that is greater than a prescribed value Ref2 (Step S103: YES), the copy machine 1 extracts the target pixel as a line-shaped noise pixel, and moves to a line-shaped noise correction (Step S108) while holding the address of the target pixel in a line-shaped noise address storing area 49b. If two of the RGB values have differences (Step S103: NO, Step S104: YES) and a difference between these two of the RGB values is no greater than a prescribed value Ref3 (Step S105: YES), the copy machine 1 extracts the target pixel as a line-shaped noise pixel, and moves to the line-shaped noise correction (Step S108) while holding the address of the target pixel in the line-shaped noise address storing area 49b.

Abstract: An image compensating method. First, multiple scanning lines are used to scan a document and a longitudinal black and white pattern, in order to produce the actual gray level value for multiple pixels with respect to each of the scanning lines and the document, as well as a correctional gray level value for complete black and a correctional gray level value for complete white with respect to the longitudinal black and white pattern. Then, the compensational gray level value with respect to the actual gray level value for each of the pixels is obtained according to the correctional gray level value for complete black, the correctional gray level value for complete white, the theoretical gray level value for complete black, the theoretical gray level value for complete white, and the actual gray level value for each of the pixels. Then, the procedure is complete.