Abstract: A light beam scanner unit includes a light beam generating unit for generating light beams at a fixed power, a polygon mirror for reflecting light beams generated from the light beam generating means toward a surface to be scanned, thereby scanning it, and a light beam power sensing unit for sensing light beam power for scanning a surface to be scanned with the polygon mirror. This light beam scanner unit further has a mirror contamination sensing unit for sensing contamination of the polygon mirror by comparing a sensing result obtained from the light beam power sensing unit when light beams are emitted by the light beam generating unit with a preset reference value.

Abstract: An optical scanning apparatus includes a light source, a deflector with a deflecting/reflecting surface which deflects an incident light beam from the light source, an imaging optical system including at least one scanning optical element for leading the light beam deflected by the deflector onto a surface to be scanned and forming an image as a spot on the surface to be scanned and, a synchronization detector for obtaining a scanning start position signal with respect to a main scanning direction on the surface to be scanned. The scanning optical element is provided with a light-beam passage for allowing a light beam traveling toward the synchronization detector to pass through. The light-beam passage is provided in an inner portion of the scanning optical element located outside an effective portion of the scanning optical element.

Abstract: A scanning sync-signal detecting circuit for a laser scanner is provided. The circuit prevents misdetections of a horizontal sync signal caused by stray beams and enables a precise detection of the sync signal, independent of the beam power. The scanner comprises a laser detector and a sync-detecting circuit. The sync-detecting circuit detects a proper beam for generating the sync signal in accordance with the duration of the signal from the detector for which the signal level is higher than a predetermined level. The sync-detecting circuit comprises a ramp generator, a comparator, and a sync signal generator. The level of the ramp signal corresponds to the signal duration from the detector. The signal level is compared with a predetermined boundary level, so that the output signal due to the proper beam is detected.

Abstract: An image forming apparatus includes: a writing device for writing an image on the basis of image data thereof; a controller for controlling a writing position in a primary scanning direction by the writing device; a conveying device for conveying a recording material; and a position detecting sensor for detecting an edge of the recording material, which is conveyed by the conveying device in the primary scanning direction as an absolute position. The controller determines the writing position in the primary scanning direction by the writing device on the basis of a position of the edge of the recording material in the primary scanning direction detected by the position detecting sensor, and controls the writing position of the writing device in the primary scanning direction.

Abstract: A multi-beam image recording apparatus changes a diameter of a laser beam using a beam diameter changing board, an order in which the line data is to be read from the memory unit, a rotational speed of a polygon mirror, and a clock frequency employed when the image data is read in units of pixels, in accordance with the specified resolution. Accordingly, the multi-beam image recording apparatus can switch between the resolutions without changing a distance between the centers of two laser beams emitted from an optical system. The resolution switching can be achieved with high accuracy at low costs.

Abstract: An electrophotographic apparatus includes a photosensitive body and electrostatic image forming device for forming an electrostatic image on the photosensitive body. The electrostatic image forming device includes an exposing device for exposing the photosensitive body by a digital light in accordance with image information. The exposing device exposes a portion that is a background for an image. A developing device develops the electrostatic image using a developer, wherein a rate throughout the developer of the contained particles have a diameter equal to or smaller than 1 &mgr;m is 5 to 40 number %, and wherein, when A denotes a one-pixel width and Wv denotes a width at half value of a peak in a potential distribution of the electrostatic image formed by exposing the photosensitive drum using the digital light of one pixel, 0.6≦Wv/A≦1.0 is satisfied.

Abstract: An image forming apparatus including a photoreceptor including a photosensitive layer on a surface of an electroconductive substrate and a light irradiator configured to irradiate the photoreceptor with a light beam having a wavelength &lgr; represented in units of micrometers and a diameter &phgr; represented in units of micrometers to form a dot latent image on the photoreceptor, wherein a maximum height in a part of a profile of the lower surface of the photosensitive layer in a sampling range of &phgr; is not less than &lgr;/(2n), where n is a refractive index of the photosensitive layer at the wavelength &lgr;.

Abstract: A xerographic printer includes a rotatable photoreceptor which is exposed, with each cycle, by a regular exposure device to create an image desired to be printed. Elsewhere along the photoreceptor is disposed a supplemental discharge device which discharges only those small areas on the photoreceptor which were not discharged by the regular exposure device within the cycle. In this way, every small area of the photoreceptor is evenly discharged within each cycle, and thus every small area of the photoreceptor experiences the same amount of aging. The system is particularly useful for full-color xerographic printers, in which the photoreceptor is repeatedly discharged by different exposure devices within each cycle.

Abstract: An image forming apparatus checks the paper size of input documents images one by one, and cancels the stapling process when the documents have different widths in the main scanning direction. When the documents have the same width in the main scanning direction, the maximum number of the documents that can be stapled is set to be the value which is set when the documents have different sizes. Therefore, even if it is not preliminary known whether the documents have the different sizes, the appropriate stapling operation can be executed, the received document images can be sequentially printed, and processing can be improved.

Abstract: A light beam scanner unit includes a light beam generating unit for generating light beams at a fixed power, a polygon mirror for reflecting light beams generated from the light beam generating means toward a surface to be scanned, thereby scanning it, and a light beam power sensing unit for sensing light beam power for scanning a surface to be scanned with the polygon mirror. This light beam scanner unit further has a mirror contamination sensing unit for sensing contamination of the polygon mirror by comparing a sensing result obtained from the light beam power sensing unit when light beams are emitted by the light beam generating unit with a preset reference value.

Abstract: A dot pattern is generated by using scalable font data on the basis of received print data, and then printed. One scalable font set corresponds to two kinds of dot pattern generating modes. One generates a dot pattern with quality being given precedence, and the other generates a dot pattern with speed being given precedence and for printing at high speed, though quality inferior. The two modes are switchable to perform printing to fit user's needs.

Abstract: There are provided a multi-beam scanning optical system which can obtain a high-quality image at high speed by effectively reducing an error between the imaging positions of light beams from a plurality of light sources without requiring any complicated adjustment, and an image forming apparatus using the same.

Abstract: An optical scanning apparatus includes a laser unit formed by integrating a semiconductor laser and collimator lens, an incident optical system for making a light beam emerging from the laser unit strike an optical deflector while keeping the light beam wider than the width of a deflecting surface of the optical deflector in the main scanning direction, and an imaging optical system for forming the light beam reflected/deflected by the optical deflector into an image on a scanned surface. The laser unit is shifted by a shift adjusting means in a predetermined direction with respect to the optical axis of the incident optical system so as to make an illuminance distribution of scanning lines on the scanned surface become substantially symmetrical about the scanning central axis.

Abstract: A lenticular imaging product comprising: a lenticular lens element having an array of lenticules; and means for encoding characteristics of the lenticular lens element for use in processing the lenticular lens element.

Abstract: A method for processing a job, including image data and a set of attributes, in a document processing system is provided. Each attribute is corresponded with either a default value or a user set value. The document processing system further includes a user interface at which a set of default values are settable, in response to user input, to create a set of user set values, and a memory for storing at least a part of the image data of the job wherein the at least part of the image data of the job is less than all of the image data of the job. The method includes: (a) storing the at least part of the image data in the memory; (b) in response to user input, respectively changing one or more values of the set of user set values to one or more values of the set of default values; and (c) in response to the changing in (b), deleting the at least part of the image data in the memory when a selected condition is met.

Abstract: In an optical printer which performs image recording by using plural laser beams, there is a case where abnormality can not be normally confirmed even if a test pattern is recorded. In order to prevent such a problem, an electrophotographic apparatus is provided to drive each of the plural laser beams according to inputted image data, and to perform scanning on scan paths mutually different on an identical recording medium with the plural laser beams. In this apparatus, any one of the plural laser beams is driven within a predetermined area to record the test pattern.

Abstract: In forming a multi-colored image by superimposing a plurality of plane images, positional offsets of the plane images are prevented, thereby obtaining high quality color images. The timing at which image data corresponding to each plane image is generated is controlled in accordance with the phase difference between the sub-scanning start signal indicating the rotational timing of an image carrier and the main-scanning start signal representing the rotational timing of a rotating polygonal mirror. Various controls are further performed.

Abstract: An image forming apparatus and method wherein a writing device writes information of an image on a photoconductive body traveling in the sub-scanning direction to form an electrostatic latent image of the image thereupon by driving a light source to emit luminous flux, in response to an image signal corresponding to the image information, using a write clock and scanning the luminous flux from the light source with a scanning device in the main scanning direction on the photoconductive drum. The electrostatic latent image on the photoconductive body is developed by a developing device to a toner image, a transfer sheet having a size in the main scanning direction is selected by a selecting device, and the toner image on the photoconductive body is transferred by a transfer device to the selected transfer paper.

Abstract: In an image forming apparatus in which an exposure is conducted by scanning of a laser beam, the apparatus includes a photoreceptor for forming a latent image thereon; an exposure device having a rotary polygonal mirror for exposing the photoreceptor, wherein the laser beam is deflected and scanned onto the photoreceptor by rotating the rotary polygonal mirror; a controller for controlling a linear speed of the photoreceptor; and a braking device for decreasing forcibly a speed of rotation of the polygonal mirror. When the controller decreases the linear speed of the photoreceptor according to an image formation mode, the braking device decreases the speed of rotation of the polygonal mirror.

Abstract: There is provided a method for use with a printing machine having a movable imaging member and a projecting system for modulating a beam and projecting an image into the movable imaging member. The printing machine further includes a developer for application of developer material to the image projected onto the movable imaging member for transfer of the image to a print media sheet.

Abstract: An image forming apparatus for effecting an image exposure on an electrophotographic photosensitive member by a digital optical system device, having a charging device for charging the photosensitive member, an electrostatic latent image forming device for forming a minute dot pattern corresponding to image data, a developing device for developing the latent image on the photosensitive member with a developer, a transfer device for transferring the developer image onto a transfer material, a fixing device for fixing the developed image on the transfer material, a photosensitive member surface cleaning device for cleaning residual developer remaining on the photosensitive member after transferring, a detector for detecting the fixing device's temperature, and a detector for detecting a water vapor amount in a surrounding environment, and wherein, when a power supply of the apparatus is powered ON and if a fact that the detected temperature of the fixing device is a predetermined temperature or lower and a

Abstract: The present invention checks the paper size of input document images one by one, and cancels the stapling process when the documents have different widths in the main scanning direction. When the documents have the same width in the main scanning direction, the maximum number of the documents that can be stapled is set to be the value which is set when the documents have different sizes. Therefore, even if it is not preliminarily known whether the documents have the different sizes, the appropriate stapling operation can be executed, the received document images can be sequentially printed, and thereby the processing ability can be improved.

Abstract: In conventional color digital copy machines, when copying in color mode, the polygon mirror of the laser beam scanner for black, which is driven at a higher speed than those of the other colors, is switched to a slower speed in conformity with the speed of the polygon mirrors for the other colors. However, a drawback of this structure is that, especially when switching from monochrome to color mode, the time required to obtain the first copy is lengthened, and the operating efficiency of copying is poor. In the present invention, when copying in color mode, the rotation speed of the polygon mirror of the laser scanner unit for black is not changed at all, but, by skipping certain mirror surfaces of the polygon mirror, and/or by skipping certain of a plurality of laser light sources, the scanning density of the laser scanner unit for black can be brought into conformity with that of the laser scanner units for the other colors.

Abstract: A method and system are disclosed for the modification of the timing of one of a plurality of PEL clocks included within an electrophotographic device. A first indicator is generated which is associated with a first position on a print receiving material. A second indicator is generated which is associated with a second position on the print receiving material. A first enable signal is generated for initiating a first scan. The first scan is executed utilizing a first laser beam synchronized by a first PEL clock. A second enable signal is generated for initiating a second scan. The second scan is executed utilizing a second laser beam synchronized by a second PEL clock. The first and second scans are executed approximately concurrently. An offset of the second position from the first position is determined. The timing of a second PEL clock is modified by adjusting the second enable signal utilizing the offset so that the first and second positions are approximately aligned.

Abstract: An electrophotographic apparatus and method are provided to reduce smearing on printed medium by reducing the toner pile height of printed lines and characters. Control is provided for establishing the amount of toner to be applied on a picture element (PEL) basis. This is accomplished by the creation of mask patterns that distinguish characters and lines from large patches to be printed, and by identifying PELs internal of characters boundary requiring exposure modulation during printing.

Abstract: A rotational shaft of a photosensitive drum is connected to a rotational shaft of a stepping motor by a coupling, so that the stepping motor directly drives the photosensitive drum. Here, &thgr; (°) indicating a step angle of the stepping motor, p (mm) indicating a distance between scanning lines on the photosensitive drum, &pgr; indicating the circular constant, and d (mm) indicating a diameter of the photosensitive drum are set so as to satisfy an equation n·&thgr;=(360·p)/(&pgr;·d) to make an optical unit scan the photosensitive drum by one scanning line every time the photosensitive drum is made to rotate n steps, n being a positive integer.

Abstract: A laser printing process using a rotary light sensitive roller electrically charged by points by a laser beam and intended for receiving onto the charged points particles of a toner powder and then transferring the same onto a band to be printed, includes a first step wherein the image to be printed is stored, by a first laser beam coming from a first laser source controlled by a computer, onto a rotary memory roller whose surface is covered with a layer of a material capable of assuming either an amorphous or a crystalline structure, this structure being convertible under the action of a laser beam, and this material showing a high difference in reflecting ability according to whether it assumes the one or the other of its structures, and includes a second step wherein the thus stored image is transferred, by the optical reflection of a second laser beam coming from a second laser source having in its whole a linear character, onto the light sensitive roller intended to receive the toner and to transfer the

Abstract: A raster output scanner assembly having a first laser source for producing first and second laser beams, and a second laser source for producing third a fourth laser beams. The first and second laser beams are directed to a first rotating, multifaceted polygon while the third and fourth laser beams are directed to a second rotating, multifaceted polygon. The first polygon reflects the first and second laser beams onto a moving photoreceptor while the second polygon reflects the third and fourth laser beams onto the photoreceptor. The spots produced by the various laser beams are interlaced such that the scan line produced by the third laser beam is between the scan lines produced by the first and second laser beams, while the scan line produced by the fourth laser beam is adjacent the scan line produced by the second laser beam.

Abstract: A recording head includes a recording element having a plurality of light-emitting elements, a first substrate on which the recording element is mounted, a driving unit for driving the recording element, a second substrate on which the driving unit is mounted, and bonding wires. The recording element has bonding pads, and the second substrate has through holes. The bonding wires connect the bonding pads and the inner surfaces of the through holes.

Abstract: Correcting motion quality induced color banding problems resulting from photoreceptor motion defects in a color imaging device having a laser based multifaceted polygon and a rotating cylindrical mirror whose rotation is set by a controlled rotation inducing element. A motion sensor senses the motion of the photoreceptor. Based upon motion errors a controller either advances or delays the production of a latent image. The controller further controls the rotation inducing element, beneficially a piezoelectric element, such that a latent image is produced in a predetermined location. When multiple latent images are produced, the controller beneficially causes the latent images to be properly registered.

Abstract: There is disclosed a color xerographic printing system which utilizes one full length developer to develop a first latent image and registration marks on the margins along the first latent image. The color printing system of this invention, also utilizes a second developer which only covers the second latent image created over the first latent image to prevent the developed registration marks from attracting more toner.

Abstract: An image forming apparatus includes an image bearing member; a scanning device for scanning the image bearing member in accordance with image data; driving source for driving the image bearing member; and a gear for transmitting power to the image bearing member from the driving source.The movement pitch of the image bearing member corresponding to a gear pitch of the gear, and a line pitch of a basic matrix for tone gradation printing are sufficiently different to prevent interference fringe of the image.

Abstract: The present invention relates to a laser diode driving circuit for supplying a drive current to a laser diode, a semiconductor integrated circuit for driving the laser diode, and an image recording apparatus in which a step of executing a scanning on a predetermined member to be scanned with a laser beam holding image information is included in an image recording step. The laser diode is certainly kept in a no light emitting state at a timing when the laser diode should be kept in the no light emitting state and is allowed to emit a laser beam of the light quantity faithfully corresponding to the drive current at a timing when the drive current is supplied to the laser diode. A bias current out of the bias current and a drive current which are supplied to a laser diode 1 is further divided into a first bias current and a second bias current. Normally, only the first bias current is supplied to the laser diode. The second bias current is supplied and stopped in a manner similar to the drive current.

Abstract: A system for reading and writing indicia on a medium including a light source for producing a light beam; a reading element for directing the light beam at the medium so as to scan indicia disposed on a first portion of said medium, detecting at least a portion of the light of variable intensity reflected off the indicia, and generating an electrical signal indicative of the detected light intensity; and a writing element for directing the light beam at the medium in a pattern on a second portion of the medium so as record information on the medium. The light beam is preferably a laser beam generated by a semiconductor laser, and a mirror is used to scan the beam both for reading and writing.

Abstract: A magnetically preloaded air bearing motion system for an imaging system motion system includes a carriage for moving a scanning means along a rigid spar for reflecting an optical feed beam onto media. The carriage includes a pair of orthogonal walls for engaging the orthogonal walls of the spar and an air bearing system disposed therein. The air bearing includes a plurality of permanent magnets secured in a prearranged pattern to the orthogonal walls of the carriage for providing an attractive force to couple the carriage to the spar. The carriage further includes a series of passageways terminating at a plurality of output orifices arranged in a predetermined pattern on the orthogonal walls of the carriage. Compressed air is system is electrically connected to the linear motor for controlling the movement of the carriage along the spar.

Abstract: An electrophotographic facsimile having a single integrated transmitting and receiving unit includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, a transfer unit, a heating roller, a pressure roller, a latent image erasing lamp, a cleaning blade, an automatic feeding convey roller, a rubber pad, a whiter roller, a contact image sensor, and a pickup roller, in which document transmission, reception and copying operations are implemented by the integrated transmitting and receiving unit.

Abstract: A first data rate detecting portion sends a first data transfer rate on a first interface, and a second data rate detecting portion sends a second data transfer rate on a second interface, respectively, to a CPU. The CPU compares the first and second data transfer rates and sets a connection state of a selector so that the image recording onto a photosensitive material is made at a high speed. The CPU also respectively determines the optimal rotation speeds of a polygon driving motor and a roller driving motor from the first or second data transfer rate, and rotates the polygon driving motor and the roller driving motor at the optimal rotation speeds. Then, when image data is inputted, an image is recorded on the photosensitive material.

Abstract: There is disclosed a color xerographic printing system which utilizes a full length developer to develop a first latent image and registration marks on the margins along the first latent image. The color printing system of this invention, also utilizes two margin chargers prior to a second developer. Each one of the margin chargers restores the charge under the developed registration marks to prevent the registration marks from attracting more toner.

Abstract: A digital positioning system has a carrier in the form of a belt with a work surface and arrays of first and second conductors extending under that surface generally parallel to one another, each second conductor being spaced close to a first conductor to define a narrow gap between them. A voltage source applies a potential difference between the conductors to produce electrostatic fields which can attract and hold a substrate to said carrier work surface. Monitoring means are provided to enabling the longitudinal and lateral positions of the belt to be monitored to produce control signals to shift work elements operating on selected locations of the substrate at successive work stations to compensate for unwanted movements of the belt.

Abstract: An electrophotography recording method is adapted to a recording apparatus having a carriage which includes processing means for forming a latent image on an image bearing member that is rotatable about an axis parallel to a transport direction of a recording sheet by charging the image bearing member and for developing the latent image, where the carriage is successively moved for each 1 line region having a width corresponding to a width of the image bearing member in a main scanning direction which is perpendicular to the transport direction of the recording sheet so that a developed image on the image bearing member is transferred and thermally fixed on the recording sheet.

Abstract: An image forming apparatus is provided with a photoreceptor, and an exposure device for exposing the photoreceptor based on image data so as to form an electrostatic latent image on the photoreceptor. The exposure device has a plurality of light emitting devices aligned along a main scanning direction of the photoreceptor, the respective light emitting devices having a plurality of luminescence portions, and a light emitting device driver for applying a voltage to the respective luminescence portions so that the luminescence area of the light emitting device increases step by step whenever the applied voltage increases by a predetermined voltage based on the image data. With the arrangement, tone expression is realized in the electrostatic latent image, according to the size of the luminescence area of the respective light emitting devices, which can be controlled by the voltage applied to the respective light emitting devices based on the image data.

Abstract: A non-impact printing apparatus and method for tri-level color xerographic recording. A binary printhead having M recording elements per inch is used to record each mainscan line (1/M lines per inch) of pixels using two sublines for recording each mainscan line. In a first embodiment, pixels to be developed in a first color are recorded during a first subline, and during a second subline of pixels to be developed in a second color are recorded using a different exposure duration from that used in recording the first subline of pixels. In a second embodiment, pixels of the first and second colors are recorded during a first subline and supplementary exposure is provided for completing the recording of pixels of the second color during a second subline of recording.

Abstract: An image forming apparatus arranged to synthesize a plurality of images having different numbers of steps of tone representation, and thereafter form an image at different degrees of resolution corresponding to the respective numbers of steps of tone representation. According to one representative embodiment, an image forming apparatus inputs first and second image information to be synthesized with each other, the number of tone-levels of the second image information being less than the number of such levels of the first information. An image synthesizer, which is capable of changing an image forming resolution, forms a synthesized image from the first and second image information, and a controller controls the image forming resolution of the image synthesizer such that the first image information is formed at a first resolution and the second information is formed at a second resolution higher than the first resolution.

Abstract: A method and apparatus for conserving a substance dispensed by a printer engine for forming print on a media. As an example, the method stores a plurality of bits in a memory, the plurality of bits representing a cumulative pattern to be printed by reproducing the bits on the media. Each bit is either in a first memory state or a second memory state. The method further selects a subset of the plurality of bits, wherein the subset forms a first pattern and has a center bit. If each of the plurality of bits of the subset is in the first memory state, the method outputs to the printer engine a print bit corresponding to the center bit and in a print state which is opposite the memory state of the center bit. If, however, at least one of the plurality of bits of the subset is in the second memory state, the method outputs to the printer engine a print bit corresponding to the center bit and in a print state the same as the memory state of the center bit.

Abstract: An image forming apparatus for performing a recording operation with respect to a recording medium, includes an image forming device for forming an image on a recording medium, a recording medium receiver for receiving the recording medium on which the image is formed, and a laser beam emitter, arranged below the recording medium receiver, for emitting a laser beam in accordance with image information so as to cause the image forming device to form an image. The laser beam emitter is arranged below the recording medium receiver to emit a laser beam obliquely upward.

Abstract: A raster scanning optical system and method for adjusting the pixel placement of light beams being scanned across an image receiving device. A spot velocity of a first laser beam is measured and then a spot velocity of a second laser beam is measured. From these measurements, the pixel positions of each of the beams can be determined. The firing rate of the second laser beam is then adjusted to adjust the pixel placement of the second beam. This helps avoid problems caused by tangentially offset laser diodes that scan with varying spot linearities.

Abstract: In the electrophotographic image recording apparatus, the optical path switching mechanism switches the optical path between an image reading mode and an image recording mode. In the image reading mode, the optical path switching mechanism directs light from a light scanning portion toward the original. Light reflected from the original is guided by a light guiding mechanism to a light receiving element where the light is converted into electrical signals.

Abstract: A laser printer can record high definition and high quality images without requiring any increase of electrical and mechanical design precision for increasing a scanning line density thereof. The laser beam is deflected in a primary scanning direction and a subsidiary scanning direction. With such scanning, an artificial scanning line along an edge of a recording image can be established for accurately recording an oblique line, a curved line, a barbel portion of a character, a half-tone image or so forth.

Abstract: This invention relates to an image forming apparatus based on the electrophotographic process, more particularly to the image forming apparatus having an exposure member inside of a photoreceptor member, which develops upon receiving light exposed with the exposure member. The image forming apparatus features to include the exposure member having a plurality of LED elements arrayed along a main scanning line of the photoreceptor member which is exposed with the LED elements in a time sharing manner by n bits unit, and the photoreceptor means having the photoconductive layer formed of amorphous silicon compounds for receiving the light. The photoreceptor member is electrified through brushing contact of the developer carried by the toner support member, and wherein the exposure portion of the exposure means is located in the developer brushing contact region.

Abstract: An electrophotographic image forming method including a toner image transfer step and eliminating an independent step for cleaning transfer residual toner is operated without causing ghost images and with good gradation and dot reproducibilities. In the method, the photosensitive member is exposed at an exposure intensity which is at least a minimum exposure intensity and below a maximum exposure intensity. The minimum exposure intensity is determined on a surface potential-exposure intensity characteristic curve of the photosensitive member by determining a first slope S1 of a straight line connecting a point giving a dark part potential Vd and a point giving a value of (Vd+ a residual potential Vr)/2, determining a contact point between a tangent line having a slope of S1/20 and the surface potential-exposure intensity characteristic curve and determining the minimum exposure intensity as an exposure intensity at the contact point.