Abstract: An image processing system having an input/output unit for inputting or outputting a video signal, and a scanner for reading an original image or a printer for printing the video signal, in which the aspect ratio of the image is converted at the input or output of the video signal between the input/output unit and the scanner or the printer.

Abstract: An image or other multi-dimensional data set may have its sampling rate changed by determining weighting factors for the values of points in the original (input) data set used to calculate the value of a point in the new (output) data set. The weighting factors are determined using a function, such as a Gaussian function, that takes as input the relative location of the point in the new data set with respect to the locations of surrounding (neighboring) points in the original data set. The values of the points in the original data set are multiplied by the weighting factors, and the resultant products are added (or combined by another function) to give a value of the point in the new data set. In particular, when the input and output data sets are regularly spaced, such as with pixels for computer displays, the locations of the surrounding points and thus their weights repeat periodically.

Abstract: An image processing device comprises an image reader section, an A/D converter section, a speed detection roller, an encoder, and an image information precision control section. The image reader section detects the intensity of one or more colors on a subject on which the image reader section moves, and outputs an electrical signal corresponding to the intensity. The A/D converter section quantizes the electric signal to a digital signal. The movement speed of the image reader section which is moving on the subject is detected by the speed detection roller and the encoder. The image information precision control section controls quantization precision of the digital signal according to the movement speed detected by the speed detection roller and the encoder.

Abstract: A method and apparatus for digital image reduction using an improved “extendible” perspective projection technique which allows for flexible control of the averaging cell or window size separately from the reduction ratio to improve moir{acute over (e)} suppression or sharpness as desired in the resulting reduced-size image. The extendible perspective projection technique can also be implemented together with ordinary perspective projection or together with a combined one-dimensional filter and linear interpolation technique to produce a reduced-size image of a quality comparable to those produced by the prior technique of using a two-dimensional pre-filter prior to interpolation at a much lesser cost due to the reduced number of required scanline buffers.

Abstract: There is disclosed a resolution conversion apparatus for converting an original digital image into a digital image having a different number of pixels in accordance with an instructed conversion magnification factor. In the apparatus, a determination circuit determines the number of pixels to be interpolated in each block of the original image and positions where they are interpolated in accordance with the conversion magnification factor. The block includes a predetermined number of pixels of the original image. A converted image generation circuit generates pixel data for the interpolation pixels at the positions where they are interpolated in accordance with a predetermined interpolation equation whose coefficients are determined with the positions and data values of the pixels in the block, and combines the pixel data for the digital original image and the generated pixel data to output a converted digital image. The interpolation equation includes spline functions and Bezier functions.

Abstract: A method and apparatus for processing an image by adding a border to the image, where said border has a width that is proportional to the extent of a filter used during image processing. Specifically, the processing reduces an image to produce an image pyramid and expands an image pyramid to produce an image. At each pass through the reduction or expansion process, the border is added to the image being processed, where the border has a width that is at least as large as an extent of a filter used in the reduction or expansion process.

Abstract: A facsimile section receives and decodes data transmitted through a communication line, converts the received data into dot image data line by line, and further performs resolution conversion of the data using a resolution converter. The data subjected to the resolution conversion is transferred to a printer section through a Centronics interface. When data of an entire line is all white, a white-skip command is transferred for that line. The printer section performs horizontal/vertical conversion of the transferred dot image data and data corresponding to the transferred white-skip command using a horizontal/-vertical converter, the converted data being stored in a scan buffer. When the scan buffer is full of the data for one scan, a recording head is driven to record an image.

Abstract: A control command indicating the end of a command is set in a remote command in file data to be transmitted, and the remote command is transmitted as packet data having a data length based on the control code to a receiving apparatus. When the receiving apparatus extracts the command from the received packet data, it informs, as a response signal, to the apparatus which transmitted the command that the command was extracted, and the transmitting apparatus restarts command transmission from a portion where the response signal cannot be received.

Abstract: An image data transmission apparatus reads image data from a document placed on a document tray via a line sensor or the like, and transmits the obtained image data to a receiving apparatus either after rotation of the image data or without rotation of the image data wherein whether rotation is performed or not is determined in accordance with the receiving capability of the receiving apparatus and also on the document setting position. If the rotation is required, the reading operation is performed in such a manner that the line density in the secondary scanning direction in the reading operation will become the line density in the principal direction after the rotation so that no degradation in the resolution and processing efficiency occurs.

Abstract: There is disclosed a resolution conversion apparatus for converting an original digital image into a digital image having a different number of pixels in accordance with an instructed conversion magnification factor. In the apparatus, a determination circuit determines the number of pixels to be interpolated in each block of the original image and positions where they are interpolated in accordance with the conversion magnification factor. The block includes a predetermined number of pixels of the original image. A converted image generation circuit generates pixel data for the interpolation pixels at the positions where they are interpolated in accordance with a predetermined interpolation equation whose coefficients are determined with the positions and data values of the pixels in the block, and combines the pixel data for the digital original image and the generated pixel data to output a converted digital image. The interpolation equation includes spline functions and Bezier functions.

Abstract: In an image processing device, a white level reference value is obtained by allowing an CCD sensor to scan a white level standard sheet. The white level reference value is stored in SRAM which is resident in a scan cartridge. The white level reference value in the SRAM is modified when an original document is read through a clear sheet, to obtain a high-quality image.

Abstract: A scan converting method of converting image data from a raster sequence scan to a block sequence scan to divide the image data into blocks each having predetermined vertical width and lateral width and converting the image data from the block sequence scan to the raster sequence scan. One block buffer having a size in which a vertical width is set to the vertical width of the block and a lateral width is set to the horizontal width of the raster is used. Raster data by the raster sequence scan is written into the block buffer. The block data by the block sequence scan is read out. The block data is written and the raster data is read out. Upon conversion from the raster sequence scan to the block sequence scan, the block buffer is read out by the block sequence scan, the raster data is written into empty addresses which are caused by the reading, and the read address by the next block sequence scan is obtained by a predetermined arithmetic operation on the basis of the order of writing.

Abstract: A facsimile printer (1) in which sets of one or two pels contiguous to longer lines of such pels are reduced or eliminated. When reduced the smaller pels are positioned continuous to the longer line and are extended one pel on each side where the longer line exists. This reduces scanner errors and significantly improves images. Gray effects from dithering are not significantly effected when the pels are reduced and spread. When the image is graphic or otherwise more random than text scanned in the line and column direction, the correction may be deactivated.

Abstract: A method and apparatus for converting a resolution of a document to be transmitted at a high rate is disclosed. Horizontal converting section reduces or magnifies an input signal in accordance with the horizontal resolution specified by both a conversion magnification signal and a reduction/magnification mode signal in response to reference clock signals, and provides a horizontal conversion signal horizontally converted and a horizontal dot signal. Vertical converting section reduces or magnifies the horizontal conversion signal from the horizontal converting section in accordance with the vertical resolution specified by the conversion magnification signal on the basis of a line start signal, the conversion magnification signal and the mode signal, and provides a vertical conversion signal. Address generating section provides an address signal on the basis of the line start signal.

Abstract: The invention concerns a method and device for binarization of pixel data in which a number of black-and-white binary images each having binarization characteristics of different degrees of sensitivity is formed from a set of grey scale value binary data. A dimension S is calculated for each of these binary images, according to the equation ##EQU1## where FS designates the number of black binary pixels and U designates the number of black-and-white transitions. A selection of the binary image for which the dimension S is at its maximum is optimally carried out.

Abstract: In an image reading device including an LED array, an image sensor, and an A/D converter, an initial digitizing condition is first set while determining whether or not the initial digitizing condition to be set meets a first criteria. Then, the initial digitizing condition is adjusted so as to meet the second a second criteria. An example of the digitizing condition is a high reference voltage applied to the A/D converter which converts an analog voltage ranging from a low reference voltage to the high reference voltage to a digital value. The second criteria is provided for, for example, reducing an S/N ratio when the image reading device reads half-tone images.

Abstract: An image forming apparatus and method produce, when 600 dpi image data is generated from 300 dpi image data, interpolated data of a pixel of interest by a two-value logical operation in a case where the image data about the periphery of the pixel of interest appertains to binary representation. When the image data is judged to appertain to an image of multivalued representation, the interpolated data of the pixel of interest is produced by a numerical operation. As a result, a 600 dpi picture of the same size can be printed and recorded in such a manner that outline sharpness and smoothness, which are characteristics possessed by a two-value image, are maintained at portions of the input 300 dpi image data that are two-value images while smoothness of the grayscale is maintained at portions of the input 300 dpi image data that are halftone images.

Abstract: A method and apparatus for implementing facsimile transmission over data networks is disclosed. In accordance with the preferred embodiment, the invention receives a modulated compressed facsimile message, which is then demodulated, decompressed and stored as a file. Thereafter, it is compressed for data transmission and sent to a server for transmission over a data network. At the receiving end, the file is decompressed and then re-compressed and modulated for transmission to a receiving facsimile machine.

Abstract: An apparatus for digital correction in an image system is disclosed. The present invention comprises pre-processing means for automatically adjusting dc gain of an image signal; an analogue-to-digital converter for converting the adjusted image signal to a digital signal; bit-enhancing means for generating a bit-enhanced signal; and post-processing means for generating an image code by processing the bit-enhanced signal through highlight, shadow, Gamma and shading correction. The present invention provides an improved apparatus for correcting the photo-response non-uniformity, avoiding image defect, without sacrificing the accuracy of the image system.

Abstract: A method and system eliminates visible quantizing artifacts in a digital image. The present invention eliminates visible artifacts by determining a function descriptive of a noise model for an input source of image data, utilizing a critical noise/quantizing factor in conjunction with the noise model function to determine a quantization function, and deriving optimum coding for the image data from the quantization function to produce digital image data lacking visible quantization artifacts. The critical noise/quantizing factor is a constant value found to be a value of 3/8. The present invention further includes deriving inverse coding for the optimum coding to allow processing of the digital image.

Abstract: An apparatus for coding an input analog video signal to a digital code. The apparatus comprises an A/D converter for converting the input analog video signal to a first quantization code having a first number of bits, a class sorting circuit supplied with the first quantization code from the A/D converter, for effecting a class sorting process on a plurality of pixels including a pixel to be marked, based on the first quantization code corresponding to the pixel and the first quantization code corresponding to each of the pixels provided near the periphery of the pixel, and a quantizing circuit supplied with the first quantization code produced from the A/D converter and the result of class sorting by the class sorting means, for adaptively converting the first quantization code into a second quantization code having a second number of bits smaller than the first number of bits, based on the result of class sorting by the class sorting circuit.

Abstract: An improved method for providing a more faithful and pleasing rendition of a pixel pattern is described herein. This method first places the original pixel pattern in a bit mapped memory. A small portion of this bit mapped pattern, called an input tile, acts as an address for a look-up table containing a corrected pixel pattern portion (an output tile) corresponding to the target pixels to be corrected in the input tile. To derive the output tiles stored in the look-up table, a high resolution bit map is created from an input tile by scaling the input tile. A triangular portion of each convex corner in the high resolution bit map is chopped off, and a triangular portion of each concave corner in the high resolution bit map is filled in. The resulting pattern is then smoothed using a low pass filter. The size of these triangular portions and the extent of low pass filtering are determined using a function based on the vulnerability of a pixel to being eliminated during the above smoothing process.

Abstract: A method and apparatus for cropping an image in digital form. The image to be cropped is represented as a first digital array which is operated on by an edge enhancement transformation to generate a second, binary digital array wherein edges of the image are emphasized. The second digital array is then partitioned into predetermined segments which are typically rows and columns of the array and the pixel values of each row and column are summed to generate brightness sums. The second digital array is then partitioned into a first, brighter, central group of rows and a second, less bright group consisting of upper and lower borders of rows; and a third, brighter, central group of column and left and right borders of columns in accordance with predetermined criteria relating to the brightness sums.

Abstract: In an image processing apparatus in which digital data of a certain number (m) of levels are converted into digital data of a larger number (n) of levels, then subjected to certain desired editing processing, and again digitized to data of the original number (m) of levels. The redigitization to m levels is conducted by determining the average density of a predetermined area, utilizing data of pixels already redigitized to m levels, and redigitizing the data of n levels into m levels, utilizing the average value. This process significantly reduces the amount of data processing required without formation of an unpleasant texture on the image resulting from errors in digitization.

Abstract: A system and method for processing image data converts a pixel of image data having a first resolution to a plurality of subpixels, the plurality of subpixels representing a second resolution, the second resolution being higher than the first resolution. The plurality of subpixels are thresholded to generate a group of subpixel values for each pixel and a threshold error value. It is then determined if the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel. If the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel, the group of subpixel vales is modified to produce a pattern without an isolated subpixel. The modification process produces a subpixel error value which is diffused in the slowscan direction to adjacent pixels.

Abstract: An image reading apparatus such as a color copying apparatus has a plurality of sensing CCD chips for converting an image of an object into an electrical signal, each sensing CCD chip having a plurality of sensing elements. The apparatus also has a circuit for converting the electrical signal into digital data. A first adjusting circuit is provided for conducting either an operation for obtaining level matching of the electrical signal converted by the sensing chips, or an operation for controlling the gain of the electrical signal converted by the sensing chips.

Abstract: An image communication apparatus and a method therefor are operable in an error correction communication mode so as to reduce the usage of a data bus. The apparatus receives image data and outputs it in byte units, and includes an image memory for storing at least one page of image data. The apparatus further includes a controller for inputting the image data from the receiver and for directly storing the input image data into the image memory without using a buffer memory.

Abstract: A system and process prints a high resolution image on a high addressable image output terminal by converting an image at one resolution to an image having a lower resolution in a fast-scan direction and a higher resolution in a pixel depth direction. The converted image is then processed and binarized prior to being printed on a high addressable printer. The system or process utilizes a conversion circuit which includes a two-bit per pixel packing circuit, a scanline buffer circuit, a logic circuit, and a look-up table. The conversion circuit initially converts the image into an image having a lower resolution in the fast-scan direction and a higher pixel depth resolution. Thereafter, the image is further converted to an image having a lower resolution in the slow-scan direction and a higher pixel depth resolution. This conversion of a high resolution image to a lower resolution is carried without any substantial lost to the image content data.

Abstract: The invention relates to pixel insertion on optical scanners. The invention increases the efficiency of video buffer in optical scanners and improves the speed of I/O device by locating the position of interpolation device in front of video buffer which is for temporarily storing image data and outputting the image data. Immediately after the video buffer is an input buffer which is for receiving the output of the video buffer. The input buffer provides an interface for video buffer and the interpolation device. The function of the interpolation device is for inserting pixels into the original pixels to increase the resolution of the image. When the host machine is requesting image data, an output buffer delivers the image data in the interpolation device to an I/O device for the host machine to read.

Abstract: In a digital image scanning system, dynamic testing of digital and analog channels is performed by injecting photosite-by-photosite variable test data to simulate imager signals. The test data is stored at photosite related addresses in random access memory means and are accessed by a pixel (photosite) counter for output to the channels under test.

Abstract: The tonal resolution of an image scanner is improved by adjusting the dynamic range of an analog-to-digital converter of the scanner. A preview scan of the image is made. The image data from the preview scan is then analyzed to determine a maximum intensity and a minimum intensity. The value of the maximum intensity is used to set a white intercept of the image scanner such that a maximum digital value of the analog-to-digital converter corresponds to the maximum intensity present in the image data from the preview scan. The minimum intensity is used to set a black intercept of the image scanner such that the minimum intensity in the image data from the preview scan corresponds to the minimum digital number output by the analog-to-digital converter. Tonal resolution of the image scanner is optimized then by performing a final scan of the image with the analog-to-digital converter programmed to reflect the new white intercept and black intercept values.

Abstract: The present invention is a method for automating the design of pattern matching templates used to implement a print quality enhancement filter. More particularly, the method is directed to the use of a representative set of page description language decomposed training documents, and statistical data derived therefrom, in an automated process which generates templates for resolution enhancement and/or conversion of bitmap images.

Abstract: An output circuit of a solid-state imaging device has been improved. The output circuit receives a plurality of pixel signals in a dummy bit portion, an optical black portion and an effective pixel portion from a charge transfer device of the solid-state imaging device.

Abstract: A resolution conversion system for real-time expansion and reduction of a first plurality of input pixels into a second plurality of output pixels. The resolution conversion system comprises a base-n counter for counting input pixels as each pixel is captured. The base-n counter has a plurality of carry out signals. Also, there is a control register for selectively enabling the carry out signals of the base-n counter based on a predetermined resolution ratio between the first plurality of input pixels and the second plurality of output pixels. The control register uses a mode bit to select either one of inserting and removing operations. An inserting logic unit is used for inserting, as indicated by the mode bit, a pixel into the plurality of input pixels upon a transition of one of the carry out signals if the carry out signals have been enabled by the control register.

Abstract: A low-cost A/D converting apparatus having a high precision includes a first A/D converter to which an analog input signal is applied as an input, a plurality of D/A converters to which an output from the first A/D converter is applied as an input, a subtractor for subtracting at least one output of outputs of the plurality of D/A converters from the analog input signal, and a second A/D converter, to which an output from the subtractor is applied as an input, having a resolution higher than a resolution of the first A/D converter.

Abstract: There is disclosed an image reading apparatus constructed by two line sensors, a reading circuit for reading out outputs of the two line sensors through different channels, memory units for storing image signals which were read out by the reading circuit, and a control unit for controlling so that the image signals stored in the memory units are read out at a speed higher than that upon storage, wherein the reading circuit reads the outputs of the two line sensors from the different channels while deviating the outputs by a predetermined time, respectively.

Abstract: A reader having a high-resolution mode and a high-speed mode is disclosed. The reader comprises a CCD sensor, a buffer, a first AD convertor, a second AD convertor, a data selector and a control circuit. The input of the buffer is connected to the CCD sensor through a capacitor and a 5 V power source through an analog switch, and an output of the buffer is connected to the first AD convertor for the high-resolution mode and the second AD convertor for the high-speed mode in parallel. The data selector for selecting an output from the first AD convertor or the second AD convertor and sending it out to the control circuit is connected to the outputs of the first AD convertor and the second AD convertor.

Abstract: The present invention is an apparatus for scanner system having an infrared ray source, and this scanner system can be utilized in a region where there is lack of visible light. The present invention includes an infrared ray source, a mirror, a lens set, a filter, a charge couple device (CCD), a pro-processing means, an analogue to digital converter, and a post-processing means.

Abstract: An apparatus for processing original image data to produce print image data used by a printer, wherein a data bus switching circuit provided between an original image data memory and a shift register is selectively placed in a 1X mode or an NX mode. In the 1X mode, each bit of the original image data is transferred as a bit of the print image data to the shift register without conversion. In the NX mode, each bit of the original image data is converted into N (.gtoreq.2) number of bits of the print image data which have the same logical value equal to that of the original image data bit. The addresses of the shift register at which the print image data are sequentially stored are designated by an address counter based on a mode select signal and a write command for reading a set of the original image data for one line from the original image data memory. A read signal is generated for reading out a next set of the original image.

Abstract: A method for increasing the speed of color conversion from a plurality of color spaces to a single color space by reducing the number of color pixels by a factor of two prior to the color conversion step. This pixel reduction constitutes a lossy data compression scheme which takes advantage of the advance knowledge that the pixels will later undergo anti-aliasing by averaging subsequent to the color conversion. First the pixels are grouped into pairs, and one pixel of each pair is eliminated to form a pseudo halfpixel. The eliminated pixel is replaced with a tag identifying either the previous, current or next pseudo halfpixel. Then each pseudo halfpixel is color converted. Finally the indicated previous, current or next pseudo halfpixel, now color converted, is averaged with the current pseudo halfpixel to form a halfpixel, which is then averaged with the halfpixel above or below it to form an anti-aliased full pixel which can be displayed.

Abstract: An improved error diffusion filter for a DMD display (10) includes both an inverse gamma LUT (Look-up Table) (51) and an Error LUT (Look-up Table) (82), both responsive to the raster scan red, green, or blue video data for when the video data calls for an intensity level different from the achievable level of a DMD device. The Error LUT (82) provides an error value for that difference. The error is distributed to neighboring DMD devices.

Abstract: An adaptive threshold for converting an analog video signal to a binary video signal. This video system employs two identical array sensors. These sensors are operated synchronously and each has its own lens. The lens of the primary array sensor is focused for a sharp image. The analog output of this primary array sensor is the primary video signal. A secondary array sensor is implemented with its lens intentionally set to some degree of defocus. This degree of defocus defines the adaptive threshold function, independent of the primary video. The analog output of this secondary array sensor is the adaptive threshold signal.

Abstract: An apparatus for coding an input analog video signal to a digital code. The apparatus comprises an A/D converter for converting the input analog video signal to a first quantization code having a first number of bits, a class sorting circuit supplied with the first quantization code from the A/D converter, for effecting a class sorting process on a plurality of pixels including a pixel to be marked, based on the first quantization code corresponding to the pixel and the first quantization code corresponding to each of the pixels provided near the periphery of the pixel, and a quantizing circuit supplied with the first quantization code produced from the A/D converter and the result of class sorting by the class sorting means, for adaptively converting the first quantization code into a second quantization code having a second number of bits smaller than the first number of bits, based on the result of class sorting by the class sorting circuit.

Abstract: A method and system implements a high addressability characteristic into an error diffusion process. A grey level value representing a pixel is received: The grey level value has a first resolution which corresponds to an original input resolution. The grey level value is interpolated to generate subpixel grey level values which correspond to a second resolution. The second resolution is higher than the first resolution and corresponds to the high addressability characteristic. A threshold circuit thresholds the interpolated grey level value and generates an error value as a result of the threshold. The error value has a resolution corresponding to the first resolution. A portion of the error value is diffused to adjacent pixels on a next scanline.

Abstract: An image processing apparatus obtains image data with a low resolution by processing a plurality of pixel values read in with a high resolution into one pixel value, for the low resolution mode. Thereby, the image processing apparatus is able to transmit unfailingly image data needed for reproduction of a narrow line in a document even during a low-resolution mode. Further, in accordance with a resolution mode that is currently selected, an image processing apparatus adjusts the ratio between the amount of edge enhancement with respect to the main scanning direction and the amount of edge enhancement with respect to the sub-scanning direction, thus unfailingly including the image data needed for reproduction of a narrow line extending in the main and/or sub-scanning direction.

Abstract: A method of improving the contrast in a natural scene image. A relevant histogram of the image is derived for from a selected subset of local histograms representing regions of the image. The signal describing the histogram is operated on with a filter having the characteristic of weakening strong peaks and valleys in the function, but not effecting flat portions of the signal. The filtered histogram signal is used for controlling the TRC mapping in a device at which the image is to be printed. To assure optimum selection of local histograms, regions including the black point and white point of an image are determined and added to the subset of local histograms representing regions of the image.

Abstract: A method of arbitrary image resolution conversion takes an original print ready image at a first resolution and orientation and simulates printing of that image by creating a representation of a page at a particular resolution and orientation using a suitable spot model for the reconstruction function. The image is then filtered with a low pass filter and sampled with an aperture that corresponds to the desired output. The image data, which may be definable at several bits per pixel, is then made print-ready by reducing the number of bits defining each pixel to a valid output state. The reduction step is accomplished through error diffusion methods that maintain the local area gray density level. The filtering step reduces moire in the converted image.

Abstract: In an image signal processing apparatus, an amplifier for amplifying the output signal of an image sensor and an A/D converter for performing an A/D conversion upon the output signal of the amplifier are provided. When the output signal of the image sensor indicates a white level reference signal, a gain G of the amplifier is controlled so that the output signal of the A/D converter is brought close to a predetermined value. When the gain G reaches its minimum or maximum value, an alarm signal is generated.

Abstract: A video-to-FAX conversion system includes a video camera (10) for generating video signals which are then captured by a frame grabber and stored in a frame buffer (14). The data in the frame buffer is comprised of digitized values from the video signal which are stored in pixels with a first aspect ratio. A conversion device (16) is operable to map information in the frame buffer to the binary output space of a Group III FAX protocol and perform contrast enhancement thereon. The contrast enhancement includes the steps of first generating a histogram of all of the pixel values in the frame buffer (14) after expansion thereof into the output space of the Group III FAX. The histogram values are then utilized to generate an adjusted value for each of the gray scale values available for the pixels in the frame buffer 14. Each pixel in the frame buffer (14) is then expanded and the contrast enhancement applied thereto to adjust the values therein.

Abstract: Disclosed are a printing method capable of high speed printing of a color video printer using a frame-sequential method, and a printing apparatus adapted thereto. The printing method comprises the steps of sampling a video signal by two times for a duration of one horizontal scanning line within one frame to generate digitally converted pixel data, alternately writing the digitally converted pixel data in two line memories by frame periods, and alternately reading the digital data which is stored in the two line memories to perform printing of the read digital data. Here, two vertical lines are written in a first line memory during one frame, and the written two vertical lines are printed for a subsequent frame while alternately writing in a second memory two more vertical lines which are sequential to the printed vertical lines. Accordingly, a doubled printing speed is obtained compared with the conventional method of alternately printing single lines.