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WO1995011565A1 - Procede et appareil de reglage de la densite d'une image electronique - Google Patents

Procede et appareil de reglage de la densite d'une image electronique Download PDF

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Publication number
WO1995011565A1
WO1995011565A1 PCT/US1994/011920 US9411920W WO9511565A1 WO 1995011565 A1 WO1995011565 A1 WO 1995011565A1 US 9411920 W US9411920 W US 9411920W WO 9511565 A1 WO9511565 A1 WO 9511565A1
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WO
WIPO (PCT)
Prior art keywords
image density
neutral
threshold
density setting
thresholds
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1994/011920
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English (en)
Inventor
Robert P. Robideau
James S. Laird
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Xerox Corp
Original Assignee
Xerox Corp
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Filing date
Publication date
Application filed by Xerox Corp filed Critical Xerox Corp
Publication of WO1995011565A1 publication Critical patent/WO1995011565A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
    • H04N1/1021—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components using a lead screw or worm
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
    • H04N1/1017—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components the main-scanning components remaining positionally invariant with respect to one another in the sub-scanning direction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
    • H04N1/1039—Movement of the main scanning components
    • H04N1/1043—Movement of the main scanning components of a sensor array
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
    • H04N1/1039—Movement of the main scanning components
    • H04N1/1048—Movement of the main scanning components of a lens or lens arrangement
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/10—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces
    • H04N1/1013—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using flat picture-bearing surfaces with sub-scanning by translatory movement of at least a part of the main-scanning components
    • H04N1/1039—Movement of the main scanning components
    • H04N1/1052—Movement of the main scanning components of a mirror
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/401—Compensating positionally unequal response of the pick-up or reproducing head
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/40—Picture signal circuits
    • H04N1/407—Control or modification of tonal gradation or of extreme levels, e.g. background level
    • H04N1/4076—Control or modification of tonal gradation or of extreme levels, e.g. background level dependent on references outside the picture
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
    • H04N1/19—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays
    • H04N1/191—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays the array comprising a one-dimensional array, or a combination of one-dimensional arrays, or a substantially one-dimensional array, e.g. an array of staggered elements
    • H04N1/192—Simultaneously or substantially simultaneously scanning picture elements on one main scanning line
    • H04N1/193—Simultaneously or substantially simultaneously scanning picture elements on one main scanning line using electrically scanned linear arrays, e.g. linear CCD arrays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/04—Scanning arrangements
    • H04N2201/0402—Arrangements not specific to a particular one of the scanning methods covered by groups H04N1/04 - H04N1/207
    • H04N2201/044—Moving a scanning element into cooperation with a calibration element, e.g. a grey-wedge mounted on the document support, or vice versa

Definitions

  • This invention relates generally to a scanner or copier having a scanner. More particularly, this inven- tion relates to a method and apparatus for adjusting the density of an image in a scanning system.
  • copies of document originals have been produced by a xerographic process wherein the docu- ment original to be copied is placed on a transparent platen, either by hand or automatically through the use of a document handler, and the document is illuminated by a relatively high intensity light.
  • Image rays reflected from the illuminated document are focused by a suitable optical system onto a previously charged photoconductor.
  • the image light rays function to discharge the photo ⁇ conductor in accordance with the image content of the document to produce a latent electrostatic image of the document on the photoconductor.
  • the latent electrostatic image so produced is thereafter developed by a suitable developer material.
  • the developed image is transferred to a sheet of copy paper brought forward by a suitable feeder.
  • the transfer image is thereafter fixed by fusing to provide a permanent copy.
  • various parameters such as exposure intensity, transfer voltage, and/or developer bias voltage are varied.
  • the image of the document is converted to electronic signals or pixels and these signals, which may be processed, transmitted over long distances, and/or stored, are used to produce copies.
  • the optical system focuses the image rays reflected from the document onto an image reading array that serves to convert the image rays into electronic signals.
  • These signals could be used to create an image by some means such as operating a laser beam to discharge a xerography photoreceptor, or by operating some direct marking system such as an ink jet or a thermal transfer printing system.
  • thermal transfer systems that use a thermal printhead and ink ribbon in a portable copier are disclosed, for example, in U.S. Patent No. 5,187,588 to Denis J. Stemmle, the disclo- sure of which is incorporated herein by reference, and in copending U.S. Patent Application No. 08/(Attorney Docket No. JAO 29010), entitled "PORTABLE COPIER AND METHOD OF USING A PORTABLE COPIER", filed October 22, 1993, to Denis J. Stemmle and Egon Babler, the disclosure of which is incorporated herein by reference.
  • the density of the output image can be corrected or changed by comparing the output of each reading element with a threshold to deter ⁇ mine whether the read pixel is lighter or darker than the threshold.
  • U.S. Patent No. 4,602,293 to Sekine discloses an apparatus having a shading correction reference surface that is scanned prior to scanning a manuscript.
  • the output of a photoelectric converter i.e., an image sensor array
  • the output of each cell of the photoelectric converter is applied to a comparator along with an analog version of the corresponding reference signal in memory to effect shading correction of the output.
  • U.S. Patent No. 4,383,275 to Sasaki et al. dis ⁇ closes a system for providing read-out level compensation in an optical reader system.
  • the system first reads a white background to obtain a reference output.
  • the reference output is reversed and stored in a memory.
  • the actual sensor output derived from an original is multiplied by the memorized, reversed reference output to get a compensated video signal.
  • U.S. Patent No. 4,520,395 to Abe discloses a system for correcting shading or non-uniformity in a photosensitive element array due to light source, lens, optical transmission, and sensor characteristics.
  • the system employs a memory having a number of cells corre ⁇ sponding to the number of photo elements positioned along a linear photosensitive array.
  • the sensor output of each respective element is successively compared with data value stored in a corresponding memory cell.
  • the data stored in the memory is updated by determining the larger data value signal and then storing that signal in the corresponding memory cell.
  • the stored data for each line is converted with a waiting factor and multiplied by the sensor output to produce a compensated output.
  • the scanner then scans a document in a normal fashion, comparing the sensor response for each pixel on the document to the previously recorded response to the gray patch.
  • Each document pixel is declared to be either white or black depending on whether the response is above or below the response for the gray scale reading for that - A - particular sensor.
  • the color density of the gray patch is changed prior to the calibration sequence. For a darker copy, the operator moves a lighter gray patch into position prior to the calibration sequence so that the threshold between printing black dots would be lowered.
  • the above described apparatus has a disadvantage in that only four different calibration patches are provided. While it is conceivable that more than four gray patches may be provided, it is limited to a small number of calibration settings. Therefore, the image density of the output print is limited to only a small number of color densities.
  • a method for varying an image density of a scanning system having a plurality of reading elements.
  • a calibration patch having a known image density is scanned.
  • a neutral threshold is determined for each reading element based on a signal response of each reading element from scanning the calibration patch.
  • the neutral threshold for each reading element is associated with a neutral image density setting for each reading element.
  • An operator then varies an image density setting device to set a desired image density setting. Based on the desired image density setting and the neutral image density setting of each reading element, a desired threshold is determined for each reading element. Subsequently, a document is scanned by the reading elements in normal fashion.
  • a calibra ⁇ tion patch is again scanned with the plural reading elements.
  • a plurality of neutral thresholds are determined based on a signal response of each reading element to the calibration patch scanning.
  • the total number of different neutral thresh ⁇ olds is less than the number of total reading elements, although each reading element is assigned a neutral threshold.
  • Each neutral threshold is associated with a neutral image density setting.
  • the neutral thresholds are stored in a first memory. An operator then varies an image density setting device to a desired image density setting.
  • a desired threshold of each reading element is determined based on the desired image density setting, the neutral image density setting, and the neutral thresholds in the first memory.
  • the document is then scanned with all of the reading elements in a normal manner. Subse ⁇ quently, it is determined whether to print a mark corre- sponding to each reading element based on a comparison between the scanning response of each reading element and the respective desired threshold corresponding to each reading element.
  • FIG. 1 is a schematic illustration of a machine incorporating a calibration control system in accordance with the present invention
  • Fig. 2 is a graph illustrating the response curves of reading elements of a scanner to 3 different gray patches
  • Fig. 3 is a block diagram of a first preferred embodiment of the present invention.
  • Fig. 4 is a flow chart of a method performed by the first preferred embodiment
  • Fig. 5 is a schematic illustration of the user operable controls of one type of image density setting device that can be used with the invention
  • Fig. 6 is a circuit diagram of the image density setting device of Fig 5;
  • Fig. 7 is a flow chart of a method performed by a second preferred embodiment.
  • Fig. 8 is a block diagram of the second preferred embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
  • FIG. 1 illustrates a combined input/output scanner 10, such as can be used in the portable copier disclosed in the above-incorporated U.S. Patent No. 5,187,588 and U.S. Patent Application No. 07/782,200.
  • the scanner 10 generally includes the carriage assembly 12 mounted on a lead screw 14 for reciprocal motion along the lead screw 14 in relation to the machine frame 16 as illustrated by the carriage motion arrows 15.
  • An array of light emitting diodes 18 are mounted on carriage 12 to project light upwardly.
  • the array 18 preferably comprises a number of light emitting diodes, other embodi ⁇ ments are similarly capable of using light sources such as a laser beam.
  • the array of reading elements 24 includes 3 sensor chips (not shown) with each sensor chip having 128 photosites. Accordingly, a total of 384 photosites are provided in the preferred embodiment. Each of the 384 photosites outputs a signal in response to the light it receives as is known in the art. The number of sensor chips and photosites in the scanner may vary depending on the type of scanner. Similarly, other types of reading elements may be used.
  • Machine frame 16 also includes a suitable printing device 28 such as, for example, a thermal printhead that is usable with an ink transfer ribbon, or an ink jet printhead.
  • Fig. 2 illustrates the responses of the photosites to 3 different calibration patches, each having a differ ⁇ ent level of gray.
  • three separate chips, each having 128 photosites are provided.
  • Lines A, B and C represent the responses of the 384 photosites to calibra ⁇ tion patches having gray level densities of 0.17, 0.37 and 0.57, respectively.
  • the photosites do not all respond equally to a constant input, and the response of photosites located at ends of the chips is reduced. Additionally, differences in response are less for darker inputs (i.e., Line C) .
  • Fig. 1 shows the carriage assembly 12 located at a home position where the scanner is aligned with a calibra- tion patch as detailed below.
  • the carriage assembly 12 moves to a start of scan position to suitably position the LEDs 18 and mirror 20 at the right edge 31 of the document 30.
  • the carriage assembly 12 then moves further to the left so that the LEDs 18 project light to the document 30.
  • the document 30 reflects the light to the mirror 20, the lens 22, and finally to the array of reading elements 24 that sense the amount of reflected light from the document 30.
  • the carriage 12 moves to a start of print position at the right edge of the copy paper 32.
  • the printing device 28 moves with the machine carriage 12 across the copy paper 32 to suitably form dots on the copy paper 32.
  • the decision whether to print a dot depends on whether the reflected document image exceeds a desired threshold calibrated for each reading element 24.
  • a single calibration patch 42 is mounted on the inside surface 34 of the machine frame 16.
  • the calibration patch 42 preferably is of a continu ⁇ ous gray color.
  • the color density of the gray color can be of any level, in a preferred embodiment, it has a density of about 0.37, and thus produces a response curve similar to Line B in Fig. 2.
  • the array of light emitting diodes 18 is suitably positioned under the calibration patch 42 in step 100.
  • the response of each reading element 24 to the calibration patch 42 is determined in step 104.
  • the response to the calibration patch 42 represents what will be referred to as a neutral threshold (C neutral ) for each respective reading element 24.
  • the neutral threshold ( c neutra l ) ° ⁇ each reading element 24 corresponds to the response of that reading element to an image having a predetermined, or neutral density, and is associated with a neutral image density setting (to be explained below).
  • the neutral threshold (c neutra l ) ° ⁇ each reading element 24 is stored in a memory of control circuit 50 during step 106.
  • each reading element 24 is capable of distinguishing up to 256 different densities of the color gray. Therefore, in order to store the response of each reading element 24, 8 bits of memory are required for each reading element 24.
  • 384 8-bit sequences corresponding to 384 neutral thresholds (C neutral ) are stored in a memory in control circuit 50.
  • the desired image density setting represents a desired image density.
  • the desired image density setting is varied using an image density setting device 52, as shown in Fig. 5.
  • the image density setting device 52 can be any of several types of devices capable of producing a variable output. Preferably, the device provides an infinite number of different outputs (set ⁇ tings) between two extreme (minimum and maximum) outputs (settings).
  • the image density setting device 52 includes a slidable button 54, as shown in Fig. 5. Devices other than a slidable button, such as, for example, a rotating knob or separate buttons for increas ⁇ ing and decreasing the setting may be provided.
  • the button 54 is suitably connected to a potentiometer in the preferred embodiment as is well known in the art in order to vary the output of the potentiometer when button 54 is moved.
  • the operation of the image density setting device 52 will now be described with respect to the preferred embodiment using the potentiometer P shown in Fig. 6.
  • the output of potentiometer P is determined, preferably when button 54 is located at a neutral, for example, central position, as shown in Fig. 5. For illustration purposes, assume that the output at such a position is 50. This value is referred to as S neutral>
  • This value, S neutra ⁇ is associated with the output of the reading elements 24 when scanning the calibration patch (this corresponds to a reading element output of C neutral , which can be a differ ⁇ ent value for each reading element 24).
  • step 112 the operator varies the output of the potentiometer P by moving button 54 to the left for a lighter image or to the right for a darker image.
  • This new output (S new ) corresponds to the desired image densi ⁇ ty. Accordingly, the output between points A and B (Fig. 6) varies with the potentiometer's resistance as button 54 is moved.
  • the selected output (S new ) falls between a maximum output value (darkest image) and a minimum output value (lightest image) of the potentiometer P.
  • the maximum output corresponds to a 100 value (S max ) while the minimum output corresponds to a zero value (S min ). Accordingly, the selected output (S new ) can be of any value between 0 and 100.
  • a de ⁇ sired threshold (C ⁇ y ) is computed for each reading ele ⁇ ment 24 in step 114 using a formula represented by either circuitry or as a program in a microprocessor.
  • the formula relates the neutral threshold (C neu t ra ⁇ ) of each reading element 24 with the selected output (S new ) of the image density setting device 52.
  • the formula can be the following equation (1 ) :
  • step 114 When used with 384 reading elements as described above, step 114 produces 384 desired thresholds (C new ).
  • the desired threshold (C new ) of each reading element 24 is stored in a memory of control circuit 50 in a 8-bit
  • the new or desired thresholds C new for each reading element 24 form a response curve that approximates the response curves of Fig. 2, except that it is possible to generate a large
  • each reading element 24 to the reflected light is compared to the desired threshold (C new ) of the same respective reading 30 element 24 in step 118.
  • the comparison between the desired threshold (C new ) and the response of each reading element 24 is described in pending U.S. Patent Application S.N. 07/782,200, the disclosure of which is incorporated herein by reference, and results in data representing either a mark or no mark to be stored and/or printed, depending on whether the response is greater than C new .
  • the document image signal of a respec ⁇ tive reading element 24 is greater than the desired threshold (C new ) of the same respective reading element 24, then it is determined that a dot is to be formed by printing device 28.
  • the document signal is less than the desired threshold (C new ) of the same respective read ⁇ ing element, then it is determined that no dot is to be printed.
  • the above described method defines a threshold between black (for example) and white on a scanner.
  • the operator is able to adjust the output density of the scanner 10 by modifying the recorded response based on the setting of the potentiometer P (or other operator adjustable/machine readable device) to achieve a wide choice of density settings in a copier or scanner.
  • a neutral threshold (C neutral ) is determined for each of the photosites (read- ing elements 24) based on a signal response to the cali ⁇ bration patch 42 as described above.
  • Each of the neutral thresholds (C neutral ) are stored in threshold memory 70 in an 8-bit sequence for each of the respective 384 photo ⁇ sites.
  • the desired image density is input with density input device 52, for example, a potentiometer P.
  • Block 74 represents circuitry that implements any one of the respective formula (1), (2) or (3) utilized to convert the neutral threshold (Cneutra l ) into the desired threshold (C new ) based on the operator input image density setting s new ° -he image density setting device 52, and the stored neutral density setting S neutral , which was estab ⁇ lished in advance.
  • the neutral threshold (C neutral ) for each of the 384 photosites also is used by circuitry 74 to determine the desired threshold (C new ) for each photosite.
  • the desired threshold for each of the 384 photosites are subsequently stored in the threshold memory 70, for example, in another memory location composed of 8 bits for each of the 384 photosites.
  • the values c neutra l can ⁇ e replaced with the values C new in memory 70 because each time C new is recalculated, the scanner can be positioned so that readings are taken from calibration patch 42 to obtain C neutral .
  • the 8-bit digital signal stored in the threshold memory 70 for each reading element 24 is converted by the digital to analog converter 78 and input into the negative input of comparator 80.
  • the response of each of the reading elements when the document 30 is scanned is determined in block 76.
  • the analog readings of each of the respective reading elements 24 are input from block 76 into the positive input of the comparator 80.
  • the output of the comparator 80 is determinative of whether the desired threshold (C new ) has been exceeded by the respec- tive reading element 24.
  • the results of comparator 80 can be used immediately for printing, or can be stored for later use.
  • FIG. 7 A second embodiment will now be described with reference to Figs. 7 and 8.
  • This second embodiment requires less memory and can determine the desired thresh ⁇ old values (C new ) faster than the first embodiment.
  • This is advantageous, especially when implemented in the portable copier disclosed, for example, in the above- incorporated U.S. Patent No. 5,187,588, which prints in bands on a copy sheet, because the output image density can be changed with each band, and without the scan carriage having to pause between bands to redetermine the threshold values C new .
  • a preliminary neutral threshold of each reading element 24 is obtained in a similar manner to that de ⁇ scribed above by positioning the array of light emitting diodes 18 over a calibration patch 42 in steps 120 and 122. However, rather than storing 384 8-bit sequences representing the response of each reading element as in the first preferred embodiment, only 16 8-bit sequences are ultimately stored and updated in the second preferred embodiment.
  • 16 neutral thresholds (C neutral ) are selected to represent the outputs of all 384 of the reading elements 24 in step 124. This is possible because, although 256 different outputs are possible, the outputs of the 384 reading elements usually span a relatively narrow portion of the entire possible range of response.
  • the highest and the lowest outputs of the 384 reading elements are obtained, and then this range is divided into 16 different possible C neutral values.
  • the C neutral values of the 384 reading elements are then assigned one of the 16 different C neutra ⁇ values, based on which one of the 16 c neutra l va l ues is closest to the actual output for that reading element when it scans the calibration patch 42. Accordingly, the selected neutral threshold (C neutral ) of each reading element 24 does not always correspond exactly with the preliminary neutral threshold actually measured for each reading element 24. Therefore, the calibration method of the second preferred embodiment may result in some small rounding errors. Other methods of selecting the 16 neutral thresholds (C new ) are also possible and are within the scope of this invention.
  • the 16 selected neutral thresholds (Cneutra l ) are stored in both a gray palette 64 and a new palette 66 in step 125.
  • Each of the 16 selected neutral thresholds ( ⁇ neutra l ) is represented by an 8-bit sequence.
  • a 4-bit pointer is stored in step 126 for each reading element 24.
  • the 4-bit pointers are stored in threshold memory 62. Each pointer corresponds to one of 16 locations in the new palette 66. Because only 16 neutral thresholds (C neutral ) are stored, only 4 bits are needed to represent the pointer for each reading element 24.
  • the desired image density setting is obtained from the image density setting device 52 in a manner similar to that of the first preferred embodiment.
  • the second embodiment only obtains 16 desired thresholds (C new ) in step 130 using the formula circuitry 74, which uses data relating to the desired image density setting (S new from device 52), the predetermined value S neutral , and the 16 neutral image density settings (C n eutra l ) stored in the gray palette 64.
  • the new 16 desired thresholds (C new ) are stored in the new palette 66 during step 132 in the same memory locations corresponding to the original 16 neutral thresholds.
  • the 16 desired thresholds (C new ) are written over the thresholds previously stored in the new palette 66. Therefore, in the second embodiment, when the operator desires to change the image density by varying the image density setting device 52, only the values in the new palette 66 are modified. Therefore, only 16 8-bit sequences are modified, rather than 384 8- bit sequences in the first embodiment. This results in a quicker update of the desired threshold.
  • the scanner 10 recalibrates the desired threshold after each scan line of the document. According to that embodiment, steps 128, 130, and 132 are performed after each scan line of the printer. Therefore, the operator is able to adjust the output density while the scanner is in operation.
  • each of the reading elements 24 is only referenced by a 4-bit pointer stored in memory 62, each one of the reading elements 24 corresponds to one of the 16 desired thresholds (C new ) .
  • step 134 the document 30 is scanned in a manner similar to that described above.
  • Comparator 80 compares the scanning response of each reading element 24 with the respective desired threshold (C new ) for each reading element in step 136.
  • each reading element 24 is represented by a pointer that points to one of the 16 desired thresholds (C new ) .
  • the scanning response of each respective reading element 24 is compared with one of the 16 desired thresh ⁇ olds (C new )in the new palette 66.
  • a print operation is determined based on whether the scanning response of each printing element 24 exceeds the respective desired thresh- old (C new ).
  • the embodiments described above vary the image density by increasing or decreasing the number of dots printed (and/or stored).
  • the image density also can be varied by increasing or decreasing the size of the dots that are printed (and/or stored) .

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  • Signal Processing (AREA)
  • Facsimile Image Signal Circuits (AREA)

Abstract

Procédé et appareil, permettant de faire varier la densité d'image d'un système de lecture à balayage (10) dans lesquels une pastille d'étalonnage (42) ainsi qu'un dispositif de réglage de densité d'image variable sont utilisés. Une pastille d'étalonnage (42) de densité connue est lue par balayage afin de déterminer un seuil neutre pour chaque élément de lecture (24) du dispositif de balayage (10). Un utilisateur fait varier ultérieurement un dispositif de réglage de densité d'image afin d'augmenter ou de réduire la densité de l'image. Au cours d'un tel étalonnage, un seuil requis pour chaque élément de lecture (24) est déterminé en fonction d'un réglage de densité d'image requis et d'un réglage de densité d'image neutre pour chaque élément de lecture (24). Lorsque le document (30) est ultérieurement lu par balayage, la réponse balayée est comparée au seuil requis pour chaque élément de lecture (24) afin de déterminer si un point doit être imprimé.
PCT/US1994/011920 1993-10-22 1994-10-19 Procede et appareil de reglage de la densite d'une image electronique Ceased WO1995011565A1 (fr)

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US13979293A 1993-10-22 1993-10-22
US08/139,792 1993-10-22

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EP1178664A1 (fr) * 2000-07-31 2002-02-06 Ricoh Company Procédé, appareil et produit de programme informatique pour initialiser un dispositif de traitement d'image et un dispositif de formation d'image

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