Patent Application
20090238587
1. Field of the Invention
The present invention relates to a gradation adjustment technique for a color image printer forming an image on a photosensitive material by laser scanning exposure, the invention relating more particularly to a dot adjustment technique.
2. Description of the Related Art
According to the type of color printer mainly employed in the photographic printing industry in recent years, a photographic image formed on a photographic film is digitized by a film scanner into photographic image data, or a photographic image is directly digitized by a digital photographic instrument, such as a digital camera, into photographic image data. Then, this photographic image data is subjected to such image processing as density adjustment, color adjustment, etc. The resultant adjusted image data is converted into print data, based on which an exposure engine is driven to print the photographic image on a photosensitive material (print paper). Such color image printer usually employs a laser exposure engine configured to effect an image forming operation by scanning laser beam on the photosensitive material in a main scanning direction while moving this photosensitive material in a sub scanning direction. With such laser exposure engine, the laser beam is irradiated onto a polygon mirror while this polygon mirror is being rotated, thereby to polarize the laser beam, thus realizing scanning along the main scanning direction.
The art has made various proposals for overcoming the problem of image quality deterioration which tends to occur when such laser exposure engine is employed in the color image printer. For instance, according to the technique disclosed in Japanese Patent Application “Kokai” No. 2006-58677 (paragraphs 0008-0012, FIG. 12), in a scanning exposure apparatus for exposing/forming an image with using a plurality of kinds of laser beam, in order to reduce color bleeding due to difference between color beam modulation methods used, arrangement is provided such that the spot size of the second laser beam subjected to direct modulation by driving current control is set larger than the spot size of the first laser beam subjected to intensity modulation by AOM (Acousto-Optic Modulation). The arrangement changes the integrated light amount of the second laser beam, thereby reducing color bleeding. According to a further technique disclosed in Japanese Patent Application “Kokai” No. 2-160563, a clock employed for one-dot exposure is frequency-divided into four clocks. Then, when effecting exposure of one black dot, the laser beam exposure is effected in correspondence with three of the frequency-divided four clocks, thereby to reduce the exposure period for this dot, thus reducing the area of the dot formed by the exposure. With this, through the reduction in the exposure period for the dot based on the determination result, undesired enlargement of the dot area is restricted, thereby to enable exposure with the theoretically determined dot size. As a result, an image with high quality is obtained.
However, in the case of the above-described dot adjustment techniques proposed by the Japanese Patent Application “Kokai” No. 2006-58677 and the Japanese Patent Application “Kokai” No. 2-160563, the techniques are based on controlling the laser exposure engine from the theoretical point of view, not on information fed back through measurement on an actually outputted test print. Hence, even when the dot adjustment is effected appropriately, this does not necessarily result in satisfactory quality of the image outputted. One cause of this is as follows. With the laser scanning exposure, when a horizontal line extending along the main scanning direction and a vertical line extending along the sub scanning direction are exposed, in the main scanning direction, a control error occurs due to such factors as delay in rising or falling, overshoot, ringing of the modulated laser; whereas, such control error does not occur in the sub scanning direction. Accordingly, between the vertical line greatly influenced by the control error and the horizontal line free from such control error, there occurs a difference between the density values thereof even if they are exposed with a same gradation value.
Notwithstanding the above, the art has so far been devoid of technical concept of first outputting a test print taking into consideration the occurrence of density difference between a horizontal line and a vertical line due to control error of modulated laser beam and subsequently adjusting the control of the exposure engine, based on information obtained through measurement effected on such test print.
The primary object of the present invention is to provide a test print that allows adjustment of correcting conditions for the exposure engine, so as to enable output of high quality image in consideration of occurrence of density value difference between a horizontal line and a vertical line, due to control error of modulated laser.
For accomplishing the above-noted object, in a test print for use in image adjustment for a color image printer configured for forming a color image on a photosensitive material by laser scanning exposure under predetermined exposure conditions, according to the present invention, the test print comprises:
a plurality of sets of horizontal stripe test patterns, each set including a plurality of horizontal lines formed by the laser scanning exposure to extend in a main scanning direction;
a plurality of sets of vertical stripe test patterns, each set including a plurality of vertical lines formed by the laser scanning exposure to extend in a sub scanning direction;
said horizontal lines being formed with a gradation value set in advance for said each horizontal stripe test pattern; and
said vertical lines being formed with a gradation value set in advance for said each vertical test pattern.
This test print includes two kinds of test patterns, namely, the horizontal stripe test patterns having a plurality of horizontal lines hardly affected by bleeding due to control error of modulated laser; and the vertical stripe test patterns having a plurality of vertical lines affected by the bleeding due to control error of modulated laser. And, both the horizontal stripe test patterns and the vertical stripe test patterns are formed with a gradation value preset for the horizontal lines or the vertical lines of corresponding test pattern. Therefore, it is possible to prepare the horizontal stripe test pattern and the vertical stripe test pattern for each certain particular density level. Then, when this test print having such horizontal stripe test patterns and vertical stripe test patterns prepared for such respective density levels is outputted, then, by comparing measured density of the horizontal stripe test patterns with measured density of the vertical stripe test patterns, it is possible to grasp any influence of bleeding due to control error of modulated laser, as a difference between these measured densities. Then, based on these two measured densities of the vertical stripe test patterns and the horizontal stripe test patterns, it is possible to control the exposure engine, with using a corrected value which is corrected so as to minimize the occurrence of a density difference between a horizontal line and a vertical line to be actually formed.
Incidentally, in the case of rising correction for reducing bleeding due to rising control error of modulated laser, the amount of resultant bleeding can be detected from a vertical line having one-dot width. Whereas, in the case of falling correction for reducing bleeding due to falling control error of modulated laser, in order to be able to distinguish this from the bleeding due to rising control error, the bleeding amount detection is possible only from a vertical line having two or more dots width. For this reason, it is convenient to form the horizontal line constituting the horizontal stripe test pattern and the vertical line constituting the vertical stripe test pattern respectively with a plurality of widths, one width being the minimum unit of one dot. Therefore, according to one preferred embodiment of the present invention, said horizontal stripe test patterns include a horizontal stripe test pattern having horizontal lines having a first width and a further horizontal stripe test pattern having horizontal lines having a second width different from said first width; and said vertical stripe test patterns include a vertical stripe test pattern having vertical lines having said first width and a further vertical stripe test pattern having vertical lines having said second width. More particularly, it is preferred that said first width be one-dot width and said second width be one of two-dot width, three-dot width and four-dot width or any desired combination thereof. For instance, the combination of two-dot width and three-dot width means forming a stripe pattern having two-dot width stripes and three-dot stripes in alternation, thereby to together form “apparently” a two-dot-and-a-half (2.5-dot) width stripe pattern. In actuality, the specific numeric values for these widths will be derived from experiments to be conducted for the purpose of outputting high quality photographic print, in consideration of the fact that smaller line widths are more advantageous for density measurement.
The horizontal stripe test pattern having the horizontal lines hardly affected by bleeding due to control error of modulated laser is used as a “reference pattern”. The vertical stripe test pattern having the vertical lines affected by the bleeding is used as a “comparison pattern” for use in obtaining optimal conditions. When the comparison pattern is to be laser-exposed, it is necessary to set a comparison correction condition offset from a base correction condition. Then, if the setting period for this comparison correction condition is to be taken into consideration, it is preferred that said horizontal stripe test patterns and said vertical stripe test patterns be arranged alternately with each other in the sub scanning direction. This is because with such alternate arrangement, it is possible to effect the setting of the comparison correction condition for scanning/exposing the next vertical stripe test pattern while the horizontal stripe test pattern is being formed (main scanning exposure) under the standard correction condition, i.e. without any special setting for the exposure engine.
The present invention is intended to encompass within its scope, not only the test print described above, but also a color image printer capable of outputting such test print and its correction technique. For example, in a method for adjusting a color image printer forming an image on a photosensitive material by laser scanning exposure, the method according to the present invention comprises the steps of:
outputting the inventive test print;
measuring densities of said horizontal stripe test pattern and said vertical stripe test pattern having either the horizontal lines or the vertical lines having a same width, thus obtaining measured density values; and
adjusting said color image printer such that the measured density value of said horizontal stripe test pattern and the measured density value of said vertical stripe test pattern be equal to each other.
With this method, the exposure engine can be corrected/adjusted to allow output of high quality image taking into consideration the occurrence of density difference between a horizontal line and a vertical line due to control error of modulated laser. In this, if consideration is to be made on the fact that the vertical line is significantly affected by and the horizontal line is hardly affected by the control error of modulated laser due to such causes as rising or falling delay, overshoot or ringing, it is preferred that the color image printer be adjusted such that the measured density value of the vertical stripe test pattern be caused to be equal to the measured density value of the horizontal stripe test pattern.
Further and other characterizing features and advantages of the present invention will become apparent upon reading the following detailed description of the preferred embodiments thereof with reference to the accompanying drawings.
Next, preferred embodiments of the present invention will be described.
At a loading section where the print paper magazine 11 is loaded, there is provided an ID code reader 11a for reading a print paper ID code attached to the print paper magazine 11. This print paper ID code is used for uniquely specifies the type of print paper P. With recognition of this print paper ID code, the type of the print paper P accommodated in the print paper magazine 11, that is, the type of the print paper P to be used for printing is recognized.
The print engine 13 effects irradiation of beams of three primary colors, i.e. R (red), G (green), B (blue), on the print paper P, based on print data sent from the control station 1A. In this exposure operation, the exposure is done linearly along the main scanning direction at a same conveying speed and in synchronism with conveying operation of the print paper A along the sub scanning direction.
The print engine 13, as shown in
This photographic print apparatus 1 is constructed of a main body frame 2 having its outer side covered with a plurality of sheet metal panels. Some of these sheet metal panels are configured as doors which can be opened for inside inspection. Especially, the sheet metal that covers the upper side of the developing section 14 is constructed as an upper cover 10 which can be opened by approximately 90 degrees so as to allow maintenance from above of the developing tanks 14a. The drying section 15 is disposed inside a protruding frame 2a which is disposed adjacent the developing section 14 and protrudes upwardly above this developing section 14. The transverse feeding conveyer 16 is arranged to extend in the horizontal direction from the protruding frame 2a and forms a space relative to the upper cover 10. In this space between the upper cover 10 and the transverse feeding conveyer 16, as may be clearly seen in
In the instant embodiment, the upper cover 10 is attached to the main body frame 2 to be pivotable about a horizontal axis extending in the right/left direction on the deeper side of the main body frame 2 in
As shown in
The calorimeter 20 is configured to measure densities of test patterns formed on the test print TP while advancing this test print TP conveyed therein, by frame-by-frame. This colorimeter 20 comprises a spectrometer, which is a standard commercially available device having an effective measurement density range of about 2.2 D. The colorimeter 20 includes a plurality of crimping type conveying roller pairs 23 driven by a stepping motor and a sensor section 22. The sensor section 22 incorporates therein sensor elements configured to irradiate white light onto the test print TP and receive its reflection light and obtains from this reflection light, density data for each one of the three primary colors of R (red), G (green), B (blue), or C (cyan), M (magenta) and Y (yellow). The obtained density data are transferred to the controller 4. A lid 21 for the colorimeter 20 is provided for rendering the temperature and brightness inside the colorimeter 20 constant, the lid 21 being formed of e.g. a synthetic resin member or the like. The conveying roller pairs 23 are configured to convey the test print TP in such a manner as to allow the sensor section 22 to measure the densities of test patterns in the test print TP. After the densities of all the test patterns are obtained by the sensor section 22, the test print TP is conveyed by the conveying roller pairs 23 to a discharging section 24.
The photographic print apparatus 1 effects measurement on the respective test patterns (density patterns) in the test print TP by using the sensor portion 22 mounted in the colorimeter 20. The test print TP is printed for setup at each time of startup of the apparatus which is effected daily. And, based on the result of this measurement, the controller 4 effects setup operation for adjusting output conditions of the print engine 13. Normally, e.g. the quality of print (density of print) outputted from the photographic print apparatus 1 undergoes some change due to the illumination condition of the print engine 13, the conditions of the respective developing tanks 14a (developing liquid temperature, oxidization condition, activation degree condition, etc.). For this reason, the respective densities of a plurality of test patterns having densities differing from each other and formed in the test print TP are measured by the sensor section 22, and based on the result of this measurement, the adjustment of the output condition of the print engine 13, so-called “setup”, is effected. By effecting such setup, photographic prints of high reproducibility can be outputted.
The control station 1A is constructed as a control table disposed adjacent the main body frame 2. In this embodiment, the control station 1A consists essentially of a film scanner 3 for obtaining image data from a photographic film, a monitor 5 for displaying various information, a general-purpose computer acting as the controller 4 for effecting processing of photographic image read from the photographic film by the film scanner 3, or image data directly read from a semiconductor memory, generation of print data, control of the print station 1B. To the controller 4, there are connected also such peripheral devices as a keyboard and a mouse functioning as control input sections, a media reader for obtaining photographic image from a semiconductor memory used as a photographic image memory for a digital camera.
The controller 4 is comprised of a computer as described above and its functional sections for effecting various operations of the photographic print apparatus are comprised of hardware and/or software. Referring to principal functional sections relating to the present invention, an image processing section 41 is provided for effecting various kinds of photo-retouch operations such as color correction or filtering (softening, sharpening, etc.), trimming. A gradation conversion LUT 42 is provided for storing a group of data (gradation conversion characteristics) used for covering gradation values (input gradation values) of image data to be printed/outputted to output gradation values for the print engine 13 for the respective color components, with the group of data being stored for respective types of print paper in the form of gradation conversion curves. A print data generating section 43 includes a gradation converting section 43a for converting final image data to output gradation values for the print engine 13 with using the gradation conversion LUT 42 and generates print data for driving the print engine 13 from the image data converted into appropriate gradation values. A print paper type recognizing section 44 is provided for specifying the type of print paper P held in a currently loaded print paper magazine 11, based on a print paper ID code read by an ID code reader 11a. Further, a correcting module 50 is provided for effecting dot adjustment, correction of the LUT 42, etc. Incidentally, in the instant embodiment, the gradation conversion curves representing the gradation conversion characteristics of the print papers P are stored in the form of a lookup table in the gradation conversion LUT 42, as described above.
The correcting module 50, as sections thereof relating to the present invention, a test print managing section 51, a density value relationship deriving section 52, a density value relationship analyzing section 53, an LUT managing section 54, an undershoot correcting section 55, a rising correcting section 56, and a falling correcting section 57.
The test print managing section 51 manages the output of the test print TP which includes horizontal stripe test patterns having horizontal lines extending in the main scanning direction and vertical stripe test patterns having vertical lines extending in the sub scanning direction. The density value relationship deriving section 52 obtains measured density values of the test patterns formed in the test print TP and processes these into a format which can be easily processed by the functional sections downstream.
The density value relationship analyzing section 53 functions for a black balance correction which will be detailed later. That is, this density value relationship analyzing section 53 receives, from the density value relationship deriving section 52, a test input gradation value-density value relationship derived based on the measured density values of a predetermined test pattern in the test print TP and test input gradation values corresponding to that particular test pattern; and then specifies, in the respective test input gradation values, a minimum measured density value of a color component which has the minimum measured density value of them all; and also calculates, for each color component, a correction input gradation value that has a substantially same density value as this minimum measured density value.
The LUT managing section 54 is provided for managing the gradation conversion LUT 42. Especially, as its functions provided for the black balance correction, the LUT managing section 54 includes a black area pseudo conversion relationship creating section 54a for creating a black area pseudo conversion curve from an output gradation value obtained based on a gradation conversion curve from a correction input gradation value calculated by the density value relationship analyzing section 53 for each color component and from the test input gradation value. The LUT managing section 54 further includes a combining adjusting section 54b for creating a black area correction gradation conversion curve by combining the black area pseudo conversion curve with a gradation conversion curve of a non-black area and a correction executing section 54c for correcting the gradation conversion curve based upon the black area correction gradation conversion curve created by the combining adjusting section 54b.
The undershoot correcting section 55 calculates an undershoot correction amount for a main scanning undershoot correction in which an undershoot component is added to one dot after a fall in order to reduce bleeding due to a delay in fall control of a modulated laser. The rising correcting section 56 calculates a rising correction amount based on a measured density value of the predetermined test pattern of the test print TP for a main scanning rising correction in which a rising correction component is added to one dot after a rise in order to reduce density difference between a horizontal line and a vertical line. The falling correcting section 57 calculates based on a measured density value of the predetermined test pattern of the test print TP for a main scanning falling correction in which a falling correction amount is added to one dot after a fall in order to reduce density difference between a horizontal line and a vertical line.
Before explaining the test print TP employed in the gradation correction according to the present invention, with reference to
Under the management by the test print managing section 51, two kinds of test prints TP are outputted. The first test print TP is shown in
This first test print TP contains 21 (twenty-one) kinds of test patterns from No. 1•1 to No. 1•21. The No. 1•21 pattern is a solid white pattern, and all the others are stripe patterns. Of the stripe patterns, the odd-numbered patterns (counted from the top) are horizontal stripe patterns and the even-numbered patterns are vertical stripe patterns, respectively. Also, the stripe patterns include those formed by repetition with lines 1-dot width, those formed by repetition with 2-dot width and those formed by repetition with 3-dot width. In
What is important for the layouts of the test patterns in these two test prints is that the base test patterns and the comparison test patterns with α% changes from the base are arranged in alternation. For laser-exposing a comparison test pattern, it is necessary to set, in a register, a correction value for changing α% from the base. The alternate layout allows this operation for setting, in a register, a correction value for changing α% from the base, to be effected while the preceding base test pattern is being laser-exposed.
However, with such control described above, bleeding will occur from the black dot immediately before the white dot, thus resulting in image quality deterioration. The undershoot correction is the correction for reducing this bleeding. Specifically, this is a process for adding a correction value calculated by the following method from an output gradation value immediately after a rise in the main scanning direction.
Namely, a correction value B for the undershoot correction is a product obtained by multiplying a falling amount A and an undershoot correction coefficient: X[i]≦0 which is set in advance for the falling amount A. That is, the correction value B for the undershoot correction can be obtained from: B=A×X[f(A)], where i is a register number, f( ) is a function for converting a falling amount to a register number. Incidentally, the undershoot correction coefficient is obtained by the predetermined method and then stored in the LUT 42.
The solid line in
In the above, rising correction values C and C′ are determined, based on rising amounts A and A′ and rising correction coefficients calculated by the above-described process and stored in the LUT 42. Supposing the rising correction coefficient stored in the LUT 42 is: −1≦Y[i]≦1, then, the rising correction value C can be obtained from: C=A×Y[f(A)], where i is a register number, f( ) is a function for covering an output gradation to a register number. Similarly, C′=A′×Y[f(A′)].
A rising correction value thus obtained is added to an output gradation value immediately after a rise, whereby a new output gradation value is obtained (dotted line portions in
In the above, like the rising correction values described above, falling correction values D and D′ are determined, based on falling amounts B and B′ and rising correction coefficients stored in the LUT 42. Supposing the falling correction coefficient stored in the LUT 42 is: −1≦Z[i]≦1, then, the falling correction values are D=A×Z[f(B)], D′=A′×Z[f(B′)]. Here, it should be noted, however that the falling correction is done only when such condition continues for 2 or more dots after the falling. Namely, no falling correction is done when a rise occurs immediately after that fall.
A falling correction value thus obtained is added to an output gradation value immediately before the fall, whereby a new output gradation value is obtained (dotted line portions in
Next, there will be explained a procedure for obtaining the rising correction coefficients or falling correction coefficients described above. As the procedures take place similarly in the two cases, here only the procedure for obtaining rising correction coefficients will be explained with reference to the flowchart in
The test print TP used here is the first test print shown in
First, from the base test pattern (No. 1•1) having gradation [0], the procedure obtains a measured density value as a base value (#01). Next, from the comparison patterns (No. 1•2 and No. 1•12) for the gradation [0], the procedure obtains measured density values as two comparison values (“first comparison value” and “second comparison value” hereinafter) (#02).
The rising correcting section 56 calculates a difference value (“first difference value d1” hereinafter) between the first comparison value and the second comparison value obtained from the density value relationship deriving section 52 and a difference value (“second difference value d2” hereinafter) between the second comparison value and the base value (#03).
Further, based on the first difference value d1 and the second difference value d2, an approximate straight line is calculated (#04). This operation will be specifically explained with reference to
Then, based on the approximate straight line thus calculated, a correction coefficient is calculated (#05). Specifically, the ordinate intercept of the calculated straight line will be obtained as the correction coefficient . In the case of the example shown in
With the above-described procedure, there is obtained a correction coefficient for the input gradation [0]. And, this procedure is repeated for all of the input gradations from gradation [0] to gradation [150] (NO branching at #06).
With the above-described procedure, correction coefficients V0, V25, V50, V100, V150 for input gradations [0], [25], [50], [100] and [150] are obtained. Then, correction curve calculating means 85 calculates and obtains a correction curve from these correction coefficients (#07).
Then, based on the points thus obtained, a correction curve is obtained by a well-known method. In the instant embodiment, there is effected approximation by a cubic curve, so the solid line shown in the lower section in
If a value on the approximate correction curve is employed as a correction coefficient for an output gradation outside the range employed for the approximation of the correction curve, there can occur image quality deterioration due to low reliability. For this reason, for obtaining a correction coefficient for a gradation lower than the output gradation corresponding to the input gradation [150], the correction coefficient V150 for the output gradation B will be employed. That is, the correction coefficient for the output gradation interval [0, B] will be V150. On the other hand, for correction coefficients greater than the output gradation A corresponding to the input gradation [0], the values of the correction curve will be employed as the correction coefficients, until the output gradation 1.1A. However, as correction coefficients for over the output gradation 1.1A, the correction coefficient V0′ corresponding to the output gradation 1.1A is employed. That is, the correction coefficient for the output gradation interval [1.1A, maximum gradation]: is V0′. In this way, correction coefficients for all the output gradations are obtained and stored in the LUT 42 (#08).
The undershoot correction, the rising correction and the falling correction described above are provided for eliminating density difference between a horizontal line and a vertical line due to control error for modulated laser. However, even if these corrections are done, a color development density difference can occur in the respective color components (C, M, Y in the case of print paper) in the black area, so there occurs color irregularity in this black area. The black balance correction is the correction for restricting such color irregularity in the black area. Through this correction, the black areas on the gradation conversion curves (group of gradation conversion data) stored in the LUT 42 are corrected. Incidentally, in this black balance correction, the second test print TP shown in
Next, the procedure of the black balance correction will be explained with reference to the flowchart in
The outputted test print TP is sent into the colorimeter 20 through a test print discharging/conveying passage for measurement of density values of the respective test patterns herein (#13). Upon completion of the density measurement on the test print TP, the result of the density measurement is transferred to the density value relationship deriving section 52. The measured densities used in the black balance correction are shown in
From the test input gradation value-density value relationship derived as above, the density value relationship deriving section 53 specifies the respective test input gradation values, namely, the minimum measured density vales: Min [1] through Min [11] in the eleven test patterns (#15). In the example shown in
Upon completion of the calculation of the correction input gradation values shown in R, G, B components, the black area pseudo conversion relationship creating section 54a calculates an output gradation value for each correction input gradation value, with reference to the currently set gradation conversion LUT 42 (#17) and links this output gradation value with the test input gradation value (input value), thereby to create the input gradation value-output gradation value relationship shown in
Next, the combining adjusting section 54b combines the black area pseudo conversion curve with the gradation conversion curve (the data contents of the LUT 42) for the non-black areas to create a black area correction gradation conversion curve as a black-area-corrected, i.e. black-balance-adjusted gradation conversion curve (#19). For the creation of this black area correction conversion curve, in this embodiment, first, as shown in
x3=(x1+x2)/2
y3=(2y1+3y2)/5
Then, by using the quadratic expression calculated from the respective coordinate values of the points P1, P2 and P3, the gap (blank) portion is interpolated (bridged). The resultant continuous black area correction gradation conversion curve is shown in
Upon obtaining the black-balance adjusted black area correction gradation conversion curve through the above-described process, the gradation conversion curve, that is, the LUT 42, is corrected by the gradation correction executing section 54c, based on the data of this black area correction gradation conversion curve (#20).
Next, the overall adjusting operation of the color image printer having the above-described construction will be explained with reference to the flowchart of
First, the laser bias adjustment of the laser source (R laser source 131, B laser source 132) is effected (#51). In this laser bias adjustment, a laser bias values is obtained from result of measurement of laser current monitor. Further, the process executes a setup operation, which per se is well-known, and comprises general correction of the gradation conversion curve, including shading correction and so on (#52). The values set by this stet-up operation are referred to as set-up values.
Next, the process initiates the plurality of corrections relating to the present invention. First, the process effects the undershoot correction in which an undershoot correction value is obtained by calculation from the laser bias value and the set-up values (#53). Further, the process reads the base correction value from the base correction curve lookup table in the LUT 42 and then calculates correction values offset by +α% and −α% from this base correction value (#54). First, the process creates image data for the first test print and outputs this first test print TP (#55). The process obtains measured density values for all of the test patterns included in the outputted first test print TP (#56). In this, first, the rising correcting section 56 obtains a rising correction value with using the measured density value of a predetermined test pattern and establishes a rising correction curve (rising correction table) (#57). That is, in this rising correction, there is set a correction value for matching the density of the 1ON1OFF vertical stripe test pattern with the density of the 1ON1OFF horizontal stripe test pattern. After setting of the rising correction, the process further creates image data for the second test print and outputs this second test print TP (#58). The process obtains measured density values for all of the test patterns included in the outputted second test print TP (#59).
Next, the falling correcting section 56 obtains a falling correction value, with using the measured density values of the base test pattern formed in the first test print TP and the comparison test pattern formed in the second test print TP and establishes a falling correction curve (falling correction table) (#60). That is, in this falling correction, there is set a correction value for matching the density of the 2ON2OFF &3ON3OFF vertical stripe test pattern with the density (corresponding to the 2.5 dots as a whole) of the 2ON2OFF & 3ON3OFF horizontal stripe test pattern. Then, the LUT managing section 54 executes a black balance adjustment for correcting black area in the base gradation curve, with using a measured density of a predetermined test pattern in the second test print TP (#61).
Through the above-described series of correction operations, in this color image printer, occurrence of density difference between a horizontal line and a vertical line due to control error of modulated laser is restricted and also color irregularity in a black area between the horizontal line and the vertical line is restricted also. Incidentally, if satisfactory result is not obtained with one time adjustment operation, the operation from step #53 through step #63 will be repeated
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-074666 | Mar 2008 | JP | national |
