JP2013154593A - Image processing device and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute highly precise calibration in a calibration using a density sensor.SOLUTION: An image processing device measures a density of a gradation pattern recorded on a recording medium by differentiating the amount of a recording material by an optical sensor using an optical source emitting light of a predetermined wavelength region, and uses a calibration function for correcting recording data by an output correction means so that an image of the gradation pattern becomes a target density, which is a recording density as a target based on a measuring density, which is a measured density. The image processing device has a switching means for switching the output correction means at a boundary gradation value, which is a predetermined gradation value. An output correction of gradation equal to or lower than the boundary gradation value includes a first correction means for calculating an output correction amount based on the target density and the measuring density in each gradation. An output correction of gradation larger than the boundary gradation value includes a second output correction means for predicting the output correction amount based on the output correction amount in the boundary gradation value and defining the predicted output correction amount as an output correction amount.

Description

  The present invention relates to an image processing apparatus and an image processing method, and more particularly, to an image processing apparatus and an image processing method for performing calibration on the density or color of an image to be recorded.

  In many recording apparatuses, the density and color of an output image may change due to factors such as individual differences between apparatuses, environmental changes, and changes over time due to long-term use. Calibration is performed as a measure for suppressing changes in image density and color due to such a phenomenon. In general, in calibration, a patch is recorded by a recording device, and the color is measured using a measuring instrument such as a spectrocolorimeter or a scanner. Then, an image processing parameter such as a table is created or updated in accordance with a difference from a target color or density that should be output from the color measurement result. By such calibration, an image to be recorded can be brought close to the target color and density regardless of individual differences of the recording apparatus that are the objects, environmental changes, and temporal changes.

  As a colorimeter built in the recording device for calibration, a method using a density sensor that uses an LED that emits light in a predetermined wavelength range as a light source, reads the reflection intensity as voltage information with a photodiode, and converts it to density information is known. (For example, refer to Patent Document 1). By using such a density sensor, it is relatively easy to reduce the size, and a low-cost colorimeter can be built in the recording apparatus.

JP 2009-39915 A

  By the way, depending on the recording material such as ink used for recording, when light of a specific wavelength is received, secondary light emission such as fluorescence may occur in a wavelength region different from the specific wavelength. This is considered to be because a by-product compound generated in the process of synthesizing the recording material may be contained in the recording material, and light is emitted from this by-product compound (fluorescence).

  This light emission may vary for each manufactured recording material. Since the above-mentioned by-product components of the recording material are slightly different from lot to lot, even when the same light is received in the recording materials of different lots, the amount of light emission is different. For such a recording material, calibration may not be performed normally because the density measured by the density sensor varies from lot to lot under the influence of fluorescence. As described above, the influence of light that is not a visible wavelength that does not affect the appearance in a recorded state is a concern for accurate calibration. When this effect is converted from the reflection intensity received by the photodiode to the density, it is considered that the measurement error becomes particularly large in a high density portion where the reflection intensity is small, and the calibration accuracy is lowered.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an image processing apparatus and an image processing method capable of executing high-precision calibration in calibration using a density sensor. .

  Therefore, in the present invention, the density of the gradation pattern recorded on the recording medium by varying the amount of the recording material is measured by an optical sensor using a light source that emits light in a predetermined wavelength range, and the measurement is performed. An image processing apparatus using a calibration function for correcting recording data by an output correction unit so that an image of the gradation pattern has a target density that is a target recording density based on a measured density that is a density, And reading means for reading the target density of the recording data stored in the section, and switching means for switching the output correction means at the boundary gradation value which is a predetermined gradation value, and having a value equal to or lower than the boundary gradation value The gradation output correction includes first output correction means for calculating an output correction amount based on the target density and the measured density in each gradation, and output of a gradation larger than the boundary gradation value. Correction, the predicted output correction amount based on the output correction amount in the boundary gradation value, and having a second output correction means for the output correction amount correction amount corresponding predicted.

  According to the above configuration, the output correction amount is obtained based on the density of the patch measured by the colorimeter at the gradation below the boundary gradation value. The output correction amount is determined on the basis of the output correction amount obtained with the gray scale. As a result, in calibration using a density sensor that reads the reflection intensity of the light source with a photodiode, high-precision calibration is performed that reduces the influence of measurement errors in the high-density area, regardless of secondary light emission variations. can do.

1 is a block diagram illustrating a configuration of a recording system according to a first embodiment. 1 is a perspective view illustrating an outline of a mechanical configuration of a recording apparatus according to a first embodiment. FIG. 3 is a block diagram illustrating a control configuration of the recording apparatus according to the first embodiment. It is a block diagram which shows the density | concentration sensor of 1st Embodiment. It is the schematic which shows the control circuit of the density | concentration sensor of 1st Embodiment. It is a block diagram which shows the structure of the image processing of 1st Embodiment. It is a flowchart which shows the procedure of the image processing of 1st Embodiment. It is the schematic which shows the patch for a calibration of 1st Embodiment. It is a graph which shows the target value and 1-dimensional LUT for correction | amendment of 1st Embodiment. It is a graph which shows the influence on the density | concentration of 2nd Embodiment.

Embodiments of the present invention will be described below in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing the configuration of the recording system of this embodiment. In FIG. 1, a host apparatus 100 as an information processing apparatus is an apparatus connected to a recording apparatus 200 such as a personal computer. The host device 100 includes a CPU 10, a memory 11, a storage unit 13, an input unit 12 such as a keyboard and a mouse, and an interface 14 for communication with the recording device 200. The CPU 10 executes various processes such as the processes described below in accordance with a program stored in the memory 11. The host 100 and the recording apparatus 200 are connected via an interface, and exchange of image data represented by R ′, G ′, and B ′, parameter information related to calibration, and the like in image processing to be described later. Done.

  FIG. 2 is a perspective view showing an outline of the mechanical configuration of the recording apparatus of the present embodiment. Based on the transmitted image processing information, the recording apparatus 200 according to the present embodiment executes image processing such as color processing and binarization processing described later, and recording characteristic correction processing according to the embodiment of the present invention. . Also, recording is performed based on recording data obtained by image processing.

  The ink tanks 208 to 214 for storing ink as recording materials contain seven inks (black, cyan, magenta, yellow, gray, photocyan, photomagenta: K, C, M, Y, GY, PC, PM). Each is housed. Each of the seven types of ink is supplied to the corresponding recording heads 201 to 207. The conveyance rollers 215 and 216 rotate while sandwiching the recording medium 219 together with the auxiliary rollers 217 and 218 to convey (sub-scan) in a direction crossing the scanning direction of the recording head, and also have a role of holding the recording medium 219. ing. The carriage 220 is mounted with ink tanks 208 to 214, recording heads 201 to 207, and a density sensor 221, and is configured to be able to reciprocate (main scan) along the X direction in the figure. During the reciprocating movement of the carriage 220, ink is ejected from the recording head onto the recording medium 219 to record an image. After the recording scan in the main scanning direction, the transport rollers 215 and 216 rotate to transport the recording medium in the sub scanning direction (Y direction) (sub scanning). By repeating the recording scan of the recording head and the conveyance of the recording medium, the recording of the image on the recording medium 219 is completed.

  Further, during the reciprocation of the carriage 220, the density sensor 221 can be used to measure the density of the gradation pattern recorded on the recording medium. The density measurement of the gradation pattern recorded on the recording medium can be performed by the density measurement scanning by the main scanning and the conveyance of the recording medium by the conveying roller.

  FIG. 3 is a block diagram illustrating a control configuration of the recording apparatus according to the present embodiment. The control unit 20 of the control system includes a CPU 20a such as a microprocessor, a ROM 20c, a RAM 20b, and the like as memories. The ROM 20c stores various data such as a control program for the CPU 20a and parameters necessary for the recording operation. The RAM 20b is used as a work area for the CPU 20a, and temporarily stores various data such as image data received from the host device and generated recording data. Further, the RAM 20b has gradations for recording processing programs related to image processing and calibration functions, which will be described later with reference to FIG. 5, parameters such as target values used for calibration, and gradation patterns (patches). Stores pattern data (patch data).

  The control unit 20 inputs / outputs data and parameters used for recording image data and the like with the host device 100 via the interface 21 and various information (for example, character pitch, character type, etc.) from the operation panel 22. Process to input. Further, the control unit 20 outputs ON and OFF signals for driving the motors 23 and 25 via the interface 21. Further, an ejection signal or the like is output to the driver 28 to control driving for ejecting ink in the recording head.

  The control system has an operation panel 22 and drivers 27, 28, and 29. The driver 27 drives the carriage driving motor 23 and the conveyance roller driving motor 25 in accordance with instructions from the CPU 20 a, and the driver 28 drives the recording head 5. The driver 29 drives the density sensor 221.

  Next, the density sensor 221 mounted on the carriage 220 will be described.

  FIG. 4 is a configuration diagram showing the density sensor (optical sensor) of the present embodiment. 4A shows a plan view of the density sensor 221, and FIG. 4B shows a cross-sectional view of the density sensor 221.

  The density sensor 221 of this embodiment is arranged so that the measurement region is located downstream of the recording surface of the recording head 5 and the lower surface is the same position as or higher than the lower surface of the recording head. The density sensor 221 includes two phototransistors, three visible LEDs, and one infrared LED as optical elements, and each element is driven by an external circuit (not shown). These elements are all shell-type elements having a maximum diameter of about 4 mm (general production type of φ3.0 to 3.1 mm size).

  The infrared LED 601 has an irradiation angle of 45 degrees with respect to the surface (measurement surface) of the recording medium parallel to the XY plane, and the center of the irradiation light (the optical axis of the irradiation light is referred to as the irradiation axis) is the measurement surface. The sensor center axis 602 parallel to the normal line (Z axis) is crossed at a predetermined position. A position on the Z-axis of the intersecting position (intersection point) is set as a reference position, and a distance from the sensor to the reference position is set as a reference distance. The irradiation light of the infrared LED 601 is optimized so that the width of the irradiation light is adjusted by the opening and an irradiation surface (irradiation region) having a diameter of about 4 to 5 mm is formed on the measurement surface at the reference position. In the present embodiment, a straight line connecting the center point of the irradiation range of the irradiation light irradiated from the light emitting element to the measurement surface and the center of the light emitting element is referred to as an optical axis (irradiation axis) of the light emitting element. This irradiation axis is also the center of the luminous flux of the irradiation light.

  The two phototransistors 603 and 604 are sensitive to light having wavelengths from visible light to infrared light. When the measurement surface is at the reference position, the phototransistors 603 and 604 are installed such that the light receiving axis thereof is parallel to the reflection axis of the infrared LED 601. That is, the light receiving axis of the phototransistor 603 is arranged so as to be moved by +2 mm in the X direction and +2 mm in the Z direction with respect to the reflection axis. Further, the light receiving axis of the phototransistor 604 is arranged to be moved to -2 mm in the X direction and -2 mm in the Z direction. When the measurement surface is at the reference position, the intersection of the measurement surface and the irradiation axes of the infrared LED 601 and the visible LED 605 coincide with each other, and the light receiving areas of the two phototransistors 603 and 604 at this position sandwich the intersection. Is done. A spacer having a thickness of about 1 mm is sandwiched between the two elements, and the light received from each other is prevented from entering. An opening is also provided on the phototransistor side in order to limit the light incident range, and the size is optimal so that only reflected light in the range of 3 to 4 mm in diameter on the measurement surface at the reference position can be received. It becomes. In this embodiment, on the measurement surface (measurement target surface), the line connecting the center point of the region (range) where the light receiving element can receive light and the center of the light receiving element is the optical axis (or light receiving axis) of the light receiving element. Called. This light receiving axis is also the center of the reflected light beam reflected by the measurement surface and received by the light receiving element.

  4A and 4B, an LED 605 is a monochromatic visible LED having a green emission wavelength (about 510 to 530 nm), and is installed so as to coincide with the sensor central axis 602. The LED 606 is a monochromatic visible LED having a blue emission wavelength (about 460 to 480 nm), and is moved to a position moved +2 mm in the X direction and −2 mm in the Y direction with respect to the visible LED 605 as shown in FIG. is there. When the measurement surface is at the reference position, it is arranged so as to intersect the light receiving axis of the phototransistor 603 at the intersection point between the irradiation axis of the visible LED 606 and the measurement surface.

  Further, the LED 607 is a monochromatic visible LED having a red light emission wavelength (about 620 to 640 nm), and is moved by −2 mm in the X direction and +2 mm in the Y direction with respect to the visible LED 605 as shown in FIG. It is in. When the measurement surface is at the reference position, it is arranged so as to intersect the light receiving axis of the phototransistor 604 at the intersection point between the irradiation axis of the visible LED 607 and the measurement surface.

  FIG. 5 is a schematic diagram showing a control circuit that processes input / output signals of each sensor of the density sensor of the present embodiment. The CPU 301 performs on / off control signal output of the infrared LEDs 601 and visible LEDs 605 to 607 and calculation of output signals obtained in accordance with the amounts of light received by the phototransistors 603 and 604. The drive circuit 302 receives an ON signal sent from the CPU 301, supplies a constant current to each light emitting element to emit light, or adjusts the light emitting amount of each light emitting element so that the light receiving amount of the light receiving element becomes a predetermined amount. Or The I / V conversion circuit 303 converts the output signal sent as a current value from the phototransistors 603 and 604 into a voltage value. The amplifying circuit 304 functions to amplify the output signal converted into a voltage value which is a minute signal to an optimum level in the A / D conversion. The A / D conversion circuit 305 converts the output signal amplified by the amplification circuit 304 into a 10-bit digital value and inputs it to the CPU 301. A memory 306 such as a nonvolatile memory is used for recording a reference table for deriving a desired measurement value from the calculation result of the CPU 301 and temporarily storing an output value. Note that the CPU 301 and the memory 306 may be the CPU 20a or RAM 20b of the recording apparatus.

  FIG. 6 is a block diagram showing a configuration of image processing for generating recording data in the recording system of the present embodiment described above with reference to FIGS. In the image processing according to the present embodiment, image data (luminance data) of 256 gradations is input for each of red (R), green (G), and blue (B) colors of 8 bits. Finally, a process of outputting 1-bit bit image data (recording data) ejected by the recording heads of K, C, M, Y, GY, PC, and PM is performed. Of course, the type of color and the gradation of the color are not limited to these values.

  First, in the host apparatus 100, image data represented by a luminance signal of 8 bits for each color of R, G, and B using a three-dimensional LUT 401 is converted into data of R ′, G ′, and B ′ of 8 bits or 10 bits for each color. Convert to This color space conversion process (also referred to as pre-stage color process) is for correcting the difference between the color space represented by the R, G, B image data on the recording target and the color space reproducible by the recording apparatus 200. Done.

  Data of each color R ′, G ′, and B ′ that has been subjected to the preceding color processing is transmitted to the recording apparatus 200. The recording apparatus 200 uses the three-dimensional LUT 402 to convert the data of each color R ′, G ′, B ′ subjected to the preceding color processing into data of 10 bits for each color of K, C, M, Y, GY, PC, and PM. Convert to In this color conversion process (also referred to as subsequent process), input RGB image data represented by a luminance signal is converted into color data for K, C, M, Y, GY, PC, and PM used in the recording apparatus 200. To convert.

  Next, output γ correction is performed on the 10-bit data of each color K, C, M, Y, GY, PC, and PM that has been subjected to the subsequent color processing using the one-dimensional LUT 403 of each color. Usually, the number of dots recorded per unit area of the recording medium and the recording characteristics such as reflection density obtained by measuring the recorded image do not have a linear relationship. Therefore, K, C, M, Y, GY, PC, and PM 10-bit input gradation levels and the density level of the image recorded thereby have a linear relationship so that K, C, M, Y, GY , PC, PM An output γ correction process for correcting the input gradation level of 10 bits each is performed.

  Next, in this embodiment, the color misregistration correction one-dimensional LUT 404 is used for 10-bit data of each color K, C, M, Y, GY, PC, and PM that has undergone output γ correction. Then, output γ correction (output correction) for color misregistration correction is performed. For example, there are individual differences in the ejection amount from each nozzle in the recording head that ejects ink used in the recording apparatus, that is, the size of the dots to be recorded. For this reason, even if the number of dots to be recorded is adjusted by output γ correction using the one-dimensional LUT 403, color misregistration may occur due to the difference in the obtained optical density. For this reason, in this embodiment, the color misregistration correction output γ correction is performed by the color misregistration correction one-dimensional LUT 404 for each color of K, C, M, Y, GY, PC, and PM. The one-dimensional LUT for color misregistration correction is an image processing parameter to be created or updated by a calibration function described later.

  In the present embodiment, the pre-processing is performed by the host 100 and the other image processing is performed by the recording apparatus 200. However, the present invention is not limited to this. That is, the entire image processing may be performed by the host 100, or the entire image processing may be performed by the recording apparatus 200. Alternatively, a part of image processing may be performed by the host 100 and other image processing may be performed by the recording apparatus 200.

  FIG. 7A is a flowchart illustrating a procedure of image processing according to the present embodiment. That is, the procedure of image processing by the recording system shown in FIG. 6 is shown.

  In the image processing at the time of image recording, the input image data undergoes color space conversion processing in the host device 100 (step S501). Then, color conversion processing is performed on the image data subjected to color space conversion transferred to the recording apparatus 200 (step S502), and then output γ processing (step S503) is performed. Then, a color misregistration correction process for performing calibration described with reference to the flowchart shown in FIG. 7B is performed (step S504). Thereafter, 10-bit data for each color of K, C, M, Y, GY, PC, and PM is converted into each color of K, C, M, Y, GY, PC, and PM by binarization processing (quantization processing) (step S505). Convert to 1-bit binary data.

  Next, calibration in the present embodiment will be described. Calibration is executed by inputting a calibration start command as part of user input via the input unit 12 of the host device 100 or processing by the CPU 10. Alternatively, calibration is executed by inputting a calibration start command as part of user input via the operation panel 22 of the recording apparatus 200 or processing by the CPU 20a.

  FIG. 7B is a flowchart showing the procedure of the calibration process of the present embodiment. First, a calibration patch is recorded on a recording medium (step S511).

  FIG. 8 is a schematic diagram showing a patch which is a gradation pattern for calibration according to the present embodiment. FIG. 8A shows a state of patches recorded with patches arranged side by side without a gap. FIG. 8B shows a patch state in which patches are recorded side-by-side. In FIG. 8B, the inks are arranged vertically for each ink color, and are arranged horizontally for each number for identifying the gradation of the patch. In the present embodiment, a patch in which patches are recorded side by side with a gap between them may be used, or a patch in which patches are recorded side by side without being spaced may be used.

  Patches K1 to K8 are recorded with black ink, patches C1 to C8 are recorded with cyan ink, patches M1 to M8 are recorded with magenta ink, and patches Y1 to Y8 are recorded with yellow ink. GY1 to GY8 are recorded with gray ink, PC1 to PC8 are recorded with photocyan ink, and PM1 to PM8 are recorded with photomagenta ink. In the figure, the numbers 1 to 8 for identifying patches correspond to the order of the density gradation (ink recording amount per unit area) of the patch to be recorded. , 153, 205, 307, 512, 767, 1023. In this embodiment, each color has 8 gradations, but the present invention is not limited to this. In the present embodiment, patches are arranged in the order of density gradation, but the present invention is not limited to this.

  Referring to FIG. 7B again, after the patch recording is completed, after waiting for a predetermined time to dry the patch (step S512), the reflection intensity measurement of the patch and the unrecorded portion of the recording medium is started. (Step S513). The measurement result of the unrecorded part is used as a reference when calculating the density of the patch. Therefore, the measurement of an unrecorded part is performed for every LED. The reflection intensity is measured by turning on an LED suitable for the ink color whose density is to be measured among the LEDs 605 to 607 mounted on the density sensor 221, and reflected light by phototransistors 603 and 604 serving as a measuring means for measuring the density of the patch. This is done by reading The green LED 605 is turned on when, for example, a patch recorded with M or PM ink or an unrecorded portion (white) of a recording medium is measured. The blue LED 606 is lit when measuring patches recorded with, for example, K, Y, and GY inks and an unrecorded portion (white) of the recording medium. Further, the red LED 607 is turned on when, for example, a patch recorded with C or PC ink and an unrecorded portion (white) of a recording medium are measured.

  Subsequently, based on the output values from both the patch and the unrecorded part (white), the density value of the patch is calculated from the following formula (step S514).

  Here, the influence when the ink has fluorescence will be described. In the ink containing the fluorescent component, when the emission wavelength of the irradiated LED matches the fluorescence excitation wavelength, the fluorescence spectrum is excited in addition to the reflection spectrum of the LED. In addition, when a fluorescent component is mixed unintentionally, the intensity of the fluorescence spectrum may change due to manufacturing variations. Since the phototransistor of the concentration sensor described in this embodiment has sensitivity to light having a wavelength from visible light to infrared light, it receives a fluorescence spectrum and reflects it in the output value.

  Next, the influence of the reflection spectrum and the fluorescence spectrum on the concentration value will be described. The intensity of the reflection spectrum (reflection intensity) decreases as the amount of ink recorded on the recording medium increases. On the other hand, the intensity of the fluorescence spectrum (fluorescence intensity) increases as the amount of ink recorded on the recording medium increases.

  FIG. 9A is a graph showing the recording density of patches recorded with inks having different fluorescent influences in the same recording head. The influence of the fluorescence on the density value is small at the low gradation, but increases as the gradation becomes high.

  As described above, the density value measured by the fluorescence effect varies greatly in the density sensor, but there is no great difference between the human vision or the density measurement value obtained by the spectrocolorimeter. In the case of observation with the human naked eye, it is normal to observe under a light source in a wide wavelength range, and the spectrophotometer uses a halogen light source in a wide wavelength range, so the influence of fluorescence is minimal. It is because it becomes.

  Referring to FIG. 7 (b) again, a predetermined target density value called a target value and stored in the storage unit is read, and the target density value and the density value of each patch are compared and recorded. The one-dimensional LUT for color misregistration correction is calibrated (color misregistration correction processing) so that the density of the current patch approaches the target value (step S515). This target value is determined for each color and for each patch (specific gradation value). For example, as described above, the reference of the ejection amount (dot size) of each nozzle of the recording head The density value for each gradation value is defined. The target value differs for each type of recording medium and is stored in the memory.

  FIG. 9A is a graph showing the target value of each patch. The target value of the present embodiment is created with fluorescence: small ink.

  Details of the color misregistration correction processing that is a feature of the present invention will be described below. The color misregistration correction process uses a different processing method depending on the gradation value. The processing method is switched at the boundary gradation value which is a predetermined gradation value. As the boundary gradation value, a gradation value in which variation in the density value measured by the density sensor due to the influence of fluorescence is previously experimentally set is small. In this embodiment, the boundary gradation value is set to 205.

(1) First output correction: Color misregistration correction processing method below boundary gradation value Target value corresponding to each gradation value lower than the boundary gradation value from gradation value 0 to boundary gradation value 205 The tone value indicating the same density value is calculated, and a one-dimensional correction LUT for color misregistration correction is created. In calculating the gradation value (output correction amount), the target value and the measured density value are expanded from the data of 8 gradations to the entire gradation area using the complementary process. For example, at the gradation value 102, the target value is 0.28. The gradation value having a measured density value of 0.28 is 86 for fluorescence: small ink and 86 for fluorescence: large ink. Therefore, the fluorescence: small ink is converted into the gradation value 90 with respect to the input gradation value 102 and output. Further, fluorescence: large ink is also converted into a gradation value 90 with respect to the input gradation value 102 and output.

(2) Second output correction: Color misregistration correction processing method when larger than the boundary tone value The density value measured by the density sensor due to the fluorescence effect is greater than the boundary tone value, and the density sensor based on the ink difference is used. There are large variations in measured density values. For this reason, when the correction processing method for low gradation values described in the first output correction is used, the one-dimensional LUT for color misregistration correction is largely deviated due to variation in the fluorescence influence of ink, and erroneous correction is performed. Therefore, when the gradation value is larger than the boundary gradation value 205, the ratio of the input gradation value to the output gradation value in the boundary gradation value 205, that is, the ratio of the ink recording amount before and after the execution of the color misregistration output correction. Based on this, an output correction amount is predicted, and a one-dimensional LUT for color misregistration correction is created. In other words, the difference in the discharge amount of the recording head is detected by the boundary gradation value and reflected in the correction of the gradation larger than the boundary gradation value, so that the discharge amount of the recording head can be controlled regardless of the variation in the fluorescence influence of the ink. Variations can be corrected.

  An output tone value for each input tone value is calculated based on the following formula to create a one-dimensional LUT for color misregistration correction.

  Since the output gradation value of the boundary gradation value 205 is 171 and the output gradation value of the fluorescence: large ink is 172, for example, the output gradation value of the gradation value 512 is fluorescence: small ink. 427, fluorescence: 430 for large ink.

  Next, the one-dimensional correction LUT for color misregistration correction created in (1) and (2) is synthesized to create a one-dimensional LUT for color misregistration correction of all gradations.

  FIG. 9B is a graph showing a correction one-dimensional LUT according to the present embodiment. In this figure, the fluorescence when the correction processing method is applied: a one-dimensional LUT for correcting color misregistration of large and small inks, and, as a comparative example, the color misregistration correction processing of (1) for all gradations as a conventional example Shows a one-dimensional LUT for correcting color misregistration of large and small inks. When these are compared, by applying the present invention, in the conventional example, a large difference has occurred in the correction LUT due to the difference in fluorescence influence, whereas by applying the correction processing method of the present embodiment, the fluorescence influence is increased. It can be seen that the difference in the correction LUT due to can be greatly reduced. Further, when the present invention of fluorescent: small ink is applied and the conventional example, although there is a slight difference near the input gradation value 900, the correction LUT is almost the same, and the correction of the difference in the ejection amount of the recording head is also possible. You can see that it is doing well.

  In this embodiment, the recording material affected by the fluorescence has been described. However, in the present invention, the normal correction is applied to the recording material not affected by the fluorescence, and the present embodiment is performed only on the recording material affected by the fluorescence. The color misregistration correction described in the embodiment may be applied. Further, when there are a plurality of recording materials having a fluorescent influence, it is preferable to investigate the influence of the fluorescence for each recording material and set the boundary gradation value individually.

  As described above, the color misregistration correction processing method is switched at the boundary tone value, and the ink recording amount before and after execution of the color misregistration correction processing at the boundary tone value is applied to a tone larger than the boundary tone value. Correction processing is performed based on the ratio. This makes it possible to create an optimal one-dimensional LUT for color misregistration correction regardless of variations in the fluorescence effect due to lots of recording materials. Further, by applying the created one-dimensional LUT for color misregistration at the time of image processing, it is possible to output a target color and realize high-precision calibration.

  Note that the boundary tone value may vary depending on the type of recording material, or may vary depending on the type of recording medium.

(Second Embodiment)
In the first embodiment, the influence of the measurement error in the high density portion due to the variation in the fluorescent influence due to the lot of the recording material is reduced. However, the present invention can also be applied to reduce the influence of measurement errors in the high density portion of the density sensor.

  FIG. 10 is a graph showing the influence on density when a certain measurement error is added to the reflection intensity of the density sensor of this embodiment. The density value is converted from the reflection intensity measured by the density sensor. Therefore, since measurement errors such as electric noise generated in the electric circuit are inherent in voltage information representing the reflection intensity, if converted to density from there, the influence increases as the density increases as shown in FIG. Therefore, the reliability of the density value measured by the density sensor decreases as the density increases. For this reason, the color misregistration correction processing method is switched for a reliable density value or a gradation larger than the gradation value corresponding to the density value (boundary gradation value), and the input gradation value and output gradation value in the boundary gradation value are switched. The color misregistration correction one-dimensional LUT is created based on the ratio of the ink recording amounts before and after the color misregistration correction process. In other words, by detecting the difference in the ejection amount of the recording head with the boundary gradation value and reflecting it in the correction of the gradation larger than the boundary gradation value, the influence of the measurement error of the density sensor in the high density portion is reduced, and the recording is performed. Variations in the ejection amount of the head can be corrected.

  Here, it is desirable to change the boundary tone value in accordance with the density characteristics of the ink type. For example, K, C, M, and Y with high density can set the boundary gradation value small, and GY, PC, and PM with low density can set the boundary gradation value high, or a normal correction method can be used. .

  As described above, the color misregistration correction processing method is switched with the boundary tone value described above as a boundary. For a tone larger than the boundary tone value, the ink recording amount before and after the execution of the color misregistration correction processing at the boundary tone value is changed. Correction processing is performed based on the ratio. By such processing, an optimal one-dimensional LUT for color misregistration correction can be created regardless of the measurement error of the high density portion of the density sensor. Furthermore, by applying the created one-dimensional LUT for color misregistration during image processing, it is possible to output a target color and perform highly accurate calibration.

(Other)
In the correction processing described in the first and second embodiments, for example, the image processing apparatus does not have information serving as a reference such as the type of the recording medium such as a new recording medium (unknown recording medium). Even if it can be done.

In order to meet the criteria of individual variations in the discharge amount of the print head and changes over time due to long-term use,
Calibration is performed using a known recording medium to meet the standard. Then, the patch described in FIG. 8 is recorded on a new recording medium by a recording head conforming to the standard, and the target value is obtained by measuring with the density sensor. Thus, calibration can be performed even if the image processing apparatus is a recording medium that does not have information serving as a reference for the recording medium.

20 control unit 100 host device 200 recording device 221 density sensor

Claims (4)

The density of the gradation pattern recorded on the recording medium by varying the amount of the recording material is measured by an optical sensor using a light source that emits light in a predetermined wavelength range, and the measured density is the measured density. An image processing apparatus using a calibration function for correcting recording data by an output correcting unit so that an image of the gradation pattern has a target density that is a target recording density based on the image,
Reading means for reading the target density of the recording data stored in the storage unit;
Switching means for switching the output correction means at the boundary gradation value which is a predetermined gradation value;
Have
The output correction of the gradation below the boundary gradation value is greater than the boundary gradation value by first output correction means for calculating an output correction amount based on the target density and the measured density in each gradation. The gradation output correction includes an output correction amount that is predicted based on the output correction amount at the boundary gradation value, and has second output correction means that uses the predicted correction amount as an output correction amount. Processing equipment.   The prediction of the output correction amount is calculated so that the ratio of the recording amount before and after the output correction by the second output correction unit becomes the ratio of the recording amount before and after the output correction of the boundary gradation value. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the boundary gradation value varies depending on a type of recording material. The density of the gradation pattern recorded on the recording medium by varying the amount of the recording material is measured by an optical sensor using a light source that emits light in a predetermined wavelength range, and the measured density is the measured density. An image processing method using a calibration function for correcting recording data by an output correction unit so that an image of the gradation pattern has a target density that is a target recording density based on the image,
A reading step of reading the target density of the recording data stored in the storage unit;
A switching step of switching the output correction means at the boundary gradation value which is a predetermined gradation value;
Have
The output correction of gradations equal to or lower than the boundary gradation value is greater than the boundary gradation value in a first output correction step for calculating an output correction amount based on the target density and the measured density in each gradation. The gradation output correction includes a second output correction step in which an output correction amount is predicted based on the output correction amount at the boundary gradation value, and the predicted correction amount is used as an output correction amount. Processing method.

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