JP2013213975A - Image processing apparatus and correction method for image forming condition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately correct concentration by estimating the concentration in an observation from an incident light quantity to a surface and a back side of a sample according to observation conditions and correcting image forming conditions.SOLUTION: An image processing apparatus measures a reflection light quantity of a patch for concentration correction by applying light from an irradiation section 92 to a sample on which the patch is formed on a recording medium and receiving the reflected light by a reflection light quantity measuring section 91. Then, a white backing 82 or a black backing 81 is disposed at a patch non-forming surface on the sample. The image processing apparatus calculates an estimate concentration value for every patch under prescribed observation conditions using a first measurement result by the white backing 82 and a second measurement result by the black backing 81, and corrects image forming conditions on the basis of the estimate concentration value.

Description

  The present invention relates to an image processing apparatus that corrects an image forming condition of an image forming apparatus by feeding back a color measurement result of a patch image formed on a recording medium, and an image forming condition correcting method.

  2. Description of the Related Art Conventionally, so-called electrophotographic image forming apparatuses such as a laser beam printer and a copying machine that form an image by scanning an image carrier with laser light are known. In general, an electrophotographic image forming apparatus forms an image through a plurality of processes such as charging, exposure, development, transfer, and fixing.

  Here, an electrophotographic process in a general electrophotographic image forming apparatus will be described. In the apparatus, the photosensitive member is uniformly charged by the charging process provided in the apparatus based on the input image data, and the photosensitive member is exposed in accordance with the image signal by an exposure unit including a laser light source. As a result, an electrostatic latent image is formed on the photoreceptor. Thereafter, the electrostatic latent image on the photoconductor is developed by a development process to become a toner image, and the toner image on the photoconductor is transferred to a recording medium by a transfer process. The toner image transferred to the recording medium is fixed by a fixing process to form an image.

  The density of an image output from an image forming apparatus is required to be highly stable regardless of the installation environment of the apparatus and changes with time. However, since an electrophotographic image forming apparatus performs an electrostatic phenomenon as described above, the apparatus may be affected by environmental conditions in which the apparatus is placed, such as temperature and humidity, or deterioration over time of a photoconductor or developer. The output state of itself changes. That is, there is a problem that the density reproducibility is low.

  Therefore, in an electrophotographic image forming apparatus, feedback control is performed to keep the image density optimal. In this feedback control, the intensity of the laser beam during the exposure process is controlled, and patch images with different potential differences are formed on the recording medium. Here, the potential difference is Vcont obtained from the difference between Vl and Vdc when the potential changed by the laser is Vl and the development bias component of the development process is Vdc in the later-described exposure process. Vl is controlled by changing the laser light intensity in the exposure process, and patch images with different potential differences Vcont are formed. Then, the color of the patch image formed on the recording medium is measured using a measuring instrument mounted on the image forming apparatus. With respect to the density obtained by the color measurement, an error from a target density predetermined for each medium is obtained, and a desired density is obtained by controlling the laser light intensity of the exposure process based on the error.

  Here, a general concentration measurement method will be described. First, an irradiation unit that irradiates light onto a sample image (hereinafter referred to as a sample) on a recording medium and a received light amount measurement unit that measures light reflected from the recording medium are arranged at positions based on a predetermined geometric condition. For example, as a geometric condition of the sample for colorimetry and the irradiation unit / received light amount measurement unit, light is irradiated from an angle of 45 ° with respect to the normal of the sample, and light is received at an angle of 0 ° with respect to the normal of the sample. Suppose that the so-called 45/0 geometric condition is used. The irradiating unit and the light receiving unit are arranged under a 45/0 geometric condition, and the amount of reflected light of the sample whose reflectance is known and the amount of reflected light of the image formed on the recording medium are measured. Then, the reflectance of the image formed on the recording medium is calculated based on the measured light quantity, and the density is obtained from the reflectance.

  Here, FIG. 1 shows a conceptual diagram of general sample measurement. This figure shows a state in which a sample composed of a recording medium 2006 and an image 2007 formed on the surface thereof is placed on a backing 2002 as a reflector background. The light measured by the light receiver 2005 includes not only the light 2008 irradiated from the light source 2001 and reflected from the sample, but also the light 2009 reflected from the backing 2002 located on the back surface (non-image forming surface) of the recording medium 2006. Therefore, when the reflectance of the backing 2002 changes, the reflectance of the sample measured by the light receiver 2005 also changes.

  In the conventional image forming apparatus, when the color of the sample on which the image is formed on the recording medium is measured, the type of backing located on the back surface (non-image forming surface) of the recording medium is not particularly considered. Therefore, even after density correction by feedback of the measured density value, when the user actually observes the printed matter, the target density cannot be reproduced depending on the backing used for the correction. For example, when the reflectance of the backing 2002 used for the sample measurement at the time of density correction is higher than the reflectance of the backing at the time of observation, the density actually observed of the printed matter formed after the density correction is It might be higher than the target concentration. On the contrary, when the reflectance of the backing at the time of observation is higher than the reflectance of the backing 2002 at the time of sample measurement, the density observed in the printed matter after density correction may be lower than the target density. there were.

  Therefore, a method has been proposed in which the backing part is detachable at the time of sample measurement and the target density is reproduced regardless of the observation conditions by changing the reflectance of the backing 2002 according to the user's application (e.g., patent document). 1).

JP 2008-275587

  However, even if the method described in Patent Document 1 is used, the observed density may be lower than the target density depending on the conditions under which the user observes the printed matter. For example, when the user observes only one printed material by hand, there is no reflecting material on the back surface of the printed material, and light from the back surface passes through the printed material. Under such observation conditions in which there is transmitted light from the back surface of the sample, the amount of light from the printed material is greater during the user's observation than during colorimetry of the printed material for density correction in the image forming apparatus. It will increase. As a result, the density of the printed matter actually observed by the user may be lower than the target density by correction.

  In view of the above problems, the present invention makes it possible to perform appropriate density correction by predicting the density at the time of observation from the amount of incident light on the front and back surfaces of the sample and correcting the image forming conditions according to the observation conditions.

  As a means for achieving the above object, an image forming apparatus of the present invention comprises the following arrangement.

  That is, a measuring unit that measures the amount of reflected light for each patch by irradiating the sample with the density correction patch formed on the recording medium and receiving the reflected light, and the non-patch of the sample in the sample. The sample in a state in which the first backing is disposed on the forming surface by the backing setting means for arranging the first backing or the second backing having a lower reflectance than the first backing, and the measuring means. Using the first measurement result obtained by measuring the second measurement result obtained by measuring the sample in a state where the second backing is disposed, and calculating a predicted density value of the patch under a predetermined observation condition, Correction means for correcting image forming conditions in the image forming apparatus on which the sample is formed based on the predicted density value.

  According to the present invention, appropriate density correction can be performed by predicting the density at the time of observation from the amount of incident light on the front and back surfaces of the sample and correcting the image forming conditions according to the observation conditions.

Conceptual diagram showing a general sample concentration measurement method, Sectional drawing which shows schematic structure of the image forming apparatus in this embodiment, Block diagram showing the functional configuration of the image forming apparatus, Figure showing an example of observation environment A flowchart showing data input processing; A diagram showing the structure of print data, A conceptual diagram showing the configuration of patch data, A flowchart showing image forming processing; A flowchart showing a concentration prediction process; The schematic diagram which shows a mode that a sample is measured in this embodiment, FIG. 6 is a schematic diagram showing the positional relationship between a sample and a light source / receiver when the observation environment is condition (1). Figure showing an example of color separation LUT, It is a schematic diagram which shows the example of a measurement of the sample by a multiple reflection model.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. The following embodiments do not limit the present invention related to the scope of claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not necessarily.

  In the present invention, when the image forming conditions are corrected by feeding back the color measurement result of the sample on which the patch is formed on the recording medium, the density at the time of observation is particularly determined according to the amount of incident light on the front and back surfaces of the sample. An example of prediction is shown.

  For this purpose, it has a measuring means for measuring the amount of reflected light for each patch by irradiating the sample with the density correction patch formed on the recording medium and receiving the reflected light. In addition, a backing setting unit is provided in which a first backing or a second backing having a lower reflectance than the first backing is disposed on a non-patch surface of the sample. Then, using the first measurement result obtained by measuring the sample with the first backing disposed and the second measurement result obtained by measuring the sample with the second backing disposed, predetermined observation conditions are used. Calculate the predicted density value of the patch below. Then, by correcting the image forming conditions based on the predicted density value, it is possible to perform appropriate density correction according to the observation conditions.

<First Embodiment>
Apparatus Configuration FIG. 2 is a cross-sectional view showing a schematic configuration of the image forming apparatus in the present embodiment. The image forming apparatus of the present embodiment includes a photosensitive drum 1 as an image carrier, a charging unit 2 for forming an electrostatic latent image, and an exposure unit 3. The charging unit 2 includes a charging roller (not shown) disposed in contact with the surface of the photosensitive drum 1 and a charging bias electric wire that applies a charging bias to the charging roller, and uniformly charges the surface of the photosensitive drum 1. Let The exposure unit 3 includes a laser oscillator 31, a polygon mirror 32, and an Fθ lens 33. The surface of the photosensitive drum 1 uniformly charged by the charging unit 2 is irradiated with a laser beam emitted from the laser oscillator 31 based on the input halftone image signal, so that an electrostatic latent image is formed on the surface of the photosensitive drum 1. Is formed. The formed electrostatic latent image is developed as a toner image when a bias voltage is applied by the developing unit 4 and toner adheres thereto. In the example of FIG. 2, the developing unit 4 is a four-cycle type, and includes developing devices 4Y, 4M, 4C, and 4K that contain developers (toners) of yellow, magenta, cyan, and black. Further, the image on the photosensitive drum 1 developed by the developing unit 4 is heated and applied to the transfer unit 5 for transferring to the recording medium S using the intermediate transfer member 51 and the transfer belt 52, and to the recording medium S that has been transferred. A fixing unit 71 for performing a fixing process with pressure is provided. The toner remaining on the photosensitive drum 1 after development is removed by the cleaner 6.

  The image forming apparatus of the present embodiment further includes an irradiation unit 92 that irradiates light on the surface side (image forming surface side) of the recording medium S after fixing, and a received light amount that measures the light that is irradiated and reflected from the recording medium S A measurement unit 91. The irradiating unit 92 and the received light amount measuring unit 91 are movable and move according to a user input so that the measurement position can be changed. Further, a black backing portion 81 and a white backing portion 82 are provided as fixed backgrounds at the time of measurement. It is assumed that the black backing portion 81 and the white backing portion 82 conform to the ISO standard black backing reflectance and the white backing reflectance, respectively. However, the black backing portion 81 and the white backing portion 82 do not necessarily conform to the ISO standard, and it is sufficient that the reflectance of the black backing portion 81 is lower than the reflectance of the white backing portion 82. Further, the configuration of the backing unit in the present embodiment is not limited to the example including the black backing unit 81 and the white backing unit 82 as described above, and a backing unit that reproduces the reflectance of the recording medium S may be added. .

  FIG. 3 is a block diagram illustrating a functional configuration of the image forming apparatus according to the present embodiment. In FIG. 3, reference numeral 300 denotes a printer driver, and 310 denotes an image forming unit. The printer driver 300 includes an observation condition input unit 301 and a data input unit 302, and executes creation of image data (print data) to be printed by the image forming unit 510 based on the observation conditions and the input data. Hereinafter, the processing in the printer driver 300 will be described in detail first.

  In the observation condition input unit 301, a user inputs conditions for observing an image (hereinafter, printed matter) formed on a recording medium using an input device (not shown) such as a touch panel or a keyboard. In this embodiment, as the observation condition of the printed matter, the light amount of the front side irradiation light irradiated on the surface of the printed matter is Y1 (first light amount), and the light amount of the rear side irradiation light irradiated from the back surface is Y2 (second light amount). The following three conditions are prepared.

Y1 ≒ Y2 ... Condition (1)
Y1> Y2 and Y2 ≠ 0… Condition (2)
Y2 = 0 ... Condition (3)
That is, the condition (1) indicates an observation condition (first condition) where Y1 and Y2 are substantially equal. The condition (2) indicates an observation condition (second condition) in which Y1 is larger than Y2 and Y2 is not 0 (zero). Condition (3) represents an observation condition (third condition) in which Y2 is 0 (zero).

  Among the above conditions (1) to (3), the one closest to the condition when the user actually observes the printed matter is selected. Here, an example of selecting observation conditions for an actual observation environment is shown. For example, in an environment where uniform light is radiated, such as in an office environment, when observing a printed material with a single sheet as shown in FIG. Condition (1) is selected considering that the amount of light is almost the same. In addition, when observing a plurality of printed materials as shown in FIG.4 (b), the amount of the back-illuminated light is less than the front-illuminated light for the printed material on the uppermost surface, and the condition ( Select 2). In addition, as shown in FIG. 4 (c), when the printed material is attached to an object surface with a low reflectance such as a mount or wall having a large basis weight, the amount of light irradiated on the back surface is almost equal to the printed material. Consider condition 0 and select condition (3).

  Note that the observation conditions are not limited to the three patterns of the above conditions (1) to (3), and the relationship between the front side irradiation light and the rear side irradiation light on the printed material may be defined. For example, a condition of Y1 <Y2 may be assumed as in the case where a printed material is attached to the light emitter. In addition, an observation condition that specifically indicates an observation state by the user may be prepared, such as when using a single printed material or when using multiple printed materials.

  The data input unit 302 creates and outputs print data to be printed by the image forming unit 310. At this time, it is determined whether or not density prediction described later is necessary according to the observation conditions set by the user using the observation condition input unit 301 or the current state of the apparatus, and the print data corresponding to the determination result Create That is, if it is determined that density prediction is necessary, first, print data based on the previously stored patch data 303 is generated and output. Then, after the image forming unit 310 finishes the density prediction process based on the printed matter of the patch data 303, print data based on the image data to be printed is created and output.

  Here, the density prediction process in this embodiment will be described. In the image forming unit 310 of the present embodiment, a value that is optimal for the user to observe an image is set in advance as a target density to be reproduced at the time of image formation. Here, the maximum density that can be formed for each recording medium is applied as the target density. Since the image forming conditions for reproducing the target density differ depending on the observation conditions designated by the user, it is necessary to specify the image forming conditions for reproducing the target density according to the observation conditions. In this embodiment, the image forming conditions for achieving the target density are estimated by predicting the density that will be obtained in the print output under the current image forming conditions. The process for predicting the density is the density prediction process. As will be described in detail later, the patch data 303 held in the printer driver 300 is printed out, and the transmittance of each patch is calculated by measuring the amount of reflected light using two types of backings. Predict the concentration according to the conditions. Then, based on the predicted density value, an image forming condition for realizing the target density is specified. Here, the image forming condition indicates the intensity of the laser beam used in the exposure processing unit 313.

  Since the image forming unit 310 forms an image using an electrostatic phenomenon, the output state changes depending on environmental conditions such as temperature and humidity, and deterioration with time of the photosensitive member and developer. For this reason, it is desirable that the density prediction process be performed periodically.

  FIG. 5 is a flowchart showing data input processing in the data input unit 302. First, in S501, it is determined whether or not the image forming condition holding unit 318 holds an image forming condition that is specified by a density predicting unit 317, which will be described later, according to the observation condition specified by the user. If it is not held, the process proceeds to S503, and the patch data is output as print data in order to perform density prediction. If it is held, the process proceeds to S502.

  In S502, for the image forming conditions determined to be held in the image forming condition holding unit 318 in S501, the number of image data formed in the image forming unit 310 since the creation of the image forming conditions is confirmed. If the number of formed sheets is 100 or less, the process proceeds to S505 to output image data. If the number of formed sheets is greater than 100, the process proceeds to S503, and patch data is output for density prediction.

  Note that the condition for determining whether or not to perform density prediction is not limited to the examples shown in S501 and S502. For example, whether or not the number of output sheets is 50 or less may be used as the determination condition, or the elapsed time after the image forming condition is created may be used as the determination condition. The determination condition may be whether or not the image forming condition has been created since the power supply to the image forming unit 310 is turned on.

  In step S503, print data with the patch data 303 as a print target is created and output to the image forming unit 310 in order to perform density prediction.

  FIG. 6 shows the configuration of print data in this embodiment. The print data is composed of an observation condition area 601 in which observation conditions are described and an image data area 602 in which image data to be printed is described. Although not shown, general print conditions such as a recording medium type (media information) to be printed and the number of copies are also added to the print data.

  When print data is generated based on patch data 303 held in advance in the printer driver 300, the patch data 303 is described in the image data area 602 to generate print data. In the patch data 303 used in the present embodiment, the relationship between the type of color material to be recorded and the intensity of the laser beam irradiated in the exposure processing unit 313 is shown for each patch. FIG. 7 shows the concept of patch data in this embodiment. As shown in the figure, the patch data is composed of a plurality of patches. The upper part of the text written in each patch indicates the type of color material, and the lower part indicates the laser light intensity. Lp0 to Lp4 shown in the lower stage indicate a plurality of laser beam intensities having different intensities. Of course, the patch data is not limited to the example shown in FIG. 7. For example, the number of patches may be increased. Further, FIG. 7 shows an example of a patch image when four colors of toner are used, but the number of patches may be increased when six colors of toner are used.

  In the image forming unit 310 to which print data based on the patch data 303 is input, as described later, this is printed on a recording medium to create a sample, and density prediction based on the sample is performed. In the present embodiment, the recording medium and the patch image formed on the surface thereof are collectively referred to as “sample”. The image forming condition specified according to the predicted density value and the target density value is held in the image forming condition holding unit 318. When the specification of the image forming conditions is completed, the printer driver 300 is notified that the density prediction process is completed and the image forming preparation is ready. In step S503, the data input unit 302 outputs print data based on the patch data 303. In step S504, the data input unit 302 waits for an end notification of density prediction processing from the image forming unit 320. When the notification is received, the process proceeds to step S505.

  In step S505, print data is created using image data input from an input unit (not shown) by the user as a print target, and is output to the image forming unit 310. Then, the image forming unit 310 prints out the image data on a recording medium. At this time, in the image forming unit 310, an optimum image forming condition reflecting the density prediction result is set as necessary, so that the target density is achieved in the printed matter to be output.

Image Forming Process Hereinafter, the image forming process including the density prediction process in the image forming unit 310 will be described in detail.

  FIG. 8 is a flowchart showing an image forming process in the image forming unit 310. First, in S201, it is determined whether or not the input print data is for density prediction, that is, whether or not the print data is based on the patch data 303. If the print data is based on the patch data 303, the process proceeds to S202, and a patch image forming process corresponding to the print data is performed. Details of the patch image forming process will be described later. The recording medium on which the patch image is formed in this way is sent to the density prediction unit 317 as a sample.

  As described above, when the sample is prepared in S202, the concentration prediction processing by the concentration prediction unit 317 is performed in S203. Although details will be described later, first, the reflectance of each patch in the sample is measured using two types of backing portions having different reflectances. Then, the transmittance of each patch is calculated based on the measurement result, and the density that will be observed under the observation conditions specified by the user is predicted. Then, based on the predicted density, the exposure processing unit 313 sets an image forming condition optimal for achieving a predetermined target density.

  When the density prediction process in S203 ends, the end of the density prediction process is notified to the printer driver 300 in S204, and the process ends.

  On the other hand, in step S201, if the input print data is based on general print image data instead of the patch data 303, the process proceeds to step S205 to perform image formation processing according to the print data. Details of the image forming process will be described later.

  In this embodiment, if the data input as the image formation target is patch data, after printing a sample based on the patch data, the sample is automatically measured in the machine to perform density prediction, and the optimum Set the image forming conditions. Therefore, when image data is input, it is possible to perform image formation under optimum image formation conditions, and a target density can be achieved.

Patch image formation processing (S202)
Here, the patch image forming process in S202 will be described in detail.

  When print data based on the patch data 303 is input to the image processing unit 311, the print data is input to the charging processing unit 312 without being processed by the image processing unit 311. In the charging processing unit 312 to which the print data has been input, the charging unit 2 is controlled to uniformly charge the surface of the photosensitive drum 1. Next, the exposure processing unit 313 controls the exposure unit 3 to emit a laser beam based on the laser beam intensity information recorded in the input print data. By irradiating the surface of the photosensitive drum 1 with the laser light, an electrostatic latent image is formed on the surface of the photosensitive drum 1. The intensity of the laser light emitted here corresponds to the value of the patch data 303 described in the image data area 602 of the input print data.

  Next, the development processing unit 314 develops the electrostatic latent image by applying each color toner stored in each color developing device 4Y, 4M, 4C, 4K by applying a bias voltage to obtain a toner image. . Then, in the transfer processing unit 315, first, the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer member 51, which is an image carrier formed in a cylindrical shape. Then, using the transfer belt 52 provided below the intermediate transfer member 51, the four-color toner images primarily transferred onto the intermediate transfer member 51 are collectively transferred to a recording medium. Then, the fixing processing unit 316 applies heat and pressure to the recording medium on which the toner image is secondarily transferred to fix the toner image on the recording medium. In this way, a patch image is formed on the recording medium.

Concentration prediction process (S203)
Hereinafter, details of the density prediction processing in S203 will be described with reference to the flowchart of FIG.

  As described above, before the sample prepared in S202 is transported to the measurement position by the received light amount measurement unit 91 or the like, first, the white backing unit 82 is measured in S801 to be irradiated from the irradiation unit 92. The amount of light is measured (irradiation light amount acquisition processing). Specifically, first, the reflectance Rw of the white backing portion 82 installed in the image forming apparatus is measured under the geometric condition 45/0. Here, the geometrical condition indicates the relative relationship (positional relationship) between the sample and the position of the irradiation unit / light receiving unit during colorimetry, and light is irradiated from an angle of 45 ° with respect to the normal of the sample. When the light is received at an angle of 0 °, it is expressed as 45/0. In the present embodiment, it is assumed that the reflectance Rw of the white backing portion 82 is known and stored in advance in the image forming apparatus. Then, the amount of light Ydst emitted from the irradiation unit 92 and reflected from the white backing unit 82 is measured by the received light amount measurement unit 91. From the reflectance Rw and the light amount Ydst measured as described above, the irradiation light amount Ysrc from the irradiation unit 92 is calculated using the following equation (1).

Ysrc = Ydst / Rw (1)
Here, an example in which the irradiation amount of the irradiation unit 92 is measured using the white backing unit 82 is shown, but if the reflectance of the sample to be measured is known, the irradiation of the irradiation unit 92 is measured by the measurement of the black backing unit 81. The amount of light may be calculated. In addition to the backing unit, a calibration sample may be mounted on the apparatus. Further, a measurement unit different from the received light amount measurement unit 91 may be prepared, and the amount of light emitted from the irradiation unit 92 may be directly measured.

  Next, in S802, among the plurality of patches in the sample formed in S202, a patch for which density prediction is not performed, that is, an unmeasured patch is selected.

  In S803, the recording medium (sample) is moved so that the patch selected in S802 is on the white backing portion 82, and the amount of light reflected from the patch is measured under the geometric condition 45/0 (first measurement). Result acquisition processing). In this way, the amount of reflected light from the patch measured using the white backing unit 82 is Ydst_w.

  Next, in S804, the recording medium (sample) is moved so that the patch selected in S802 is on the black backing unit 81, and the measurement position of the irradiation unit 92 and the received light amount measurement unit 91 is the same as that of the black backing unit 81. Move to come up. Then, the amount of reflected light from the patch is measured under the geometric condition 45/0 (second measurement result acquisition process). In this way, the amount of reflected light from the patch measured using the black backing portion 81 is Ydst_b.

  In the present embodiment, an example is shown in which measurement is performed in the order of the white backing portion 82 and the black backing portion 81. However, the measurement order is not limited to this example, and measurement values using two types of backing portions having different reflectivities are obtained. It only has to be acquired. That is, the measurement using the black backing unit 81 may be performed first and the measurement using the white backing unit 82 may be performed later, or these measurements may be performed simultaneously.

  Next, in S805, based on the reflected light amounts Ydst_w and Ydst_b from the patches measured in S803 and S804, the transmittance T of the patch is calculated (transmittance calculation processing). Here, the transmittance T of the patch is the transmittance of the sample including the recording medium. Here, the relationship between the reflected light amounts Ydst_w and Ydst_b from the patch and the transmittance T of the patch will be described with reference to FIG. FIG. 10 (a) shows the concept of measurement of Ydst_w in S803, and FIG. 10 (b) shows the concept of measurement of Ydst_b in S804. As shown in FIG. 10 (a), the amount of light Ydst_w received by the received light amount measuring unit 91 is the amount of light Ysample directly reflected from the patch, and the amount of light Yback_w of light transmitted through the sample and reflected from the white backing unit 82. And the total value. Therefore, the relationship between the light amount Ysrc of the light irradiated from the irradiation unit 92 calculated in S801, the reflectance Rw of the white backing unit 82 stored in the apparatus, and the transmittance T of the patch and the directly reflected light amount Ysample from the patch Is represented by the following equation (2).

Ydst_w = Ysample + Ysrc / Rw / T ² (2)
Similarly, the relationship between the irradiation light amount Ysrc calculated in S801, the reflectance Rb of the black backing unit 81 stored in the apparatus, the transmittance T of the patch, and the direct reflected light amount Ysample from the patch is expressed by the following equation (3): It is represented by

Ydst_b = Ysample + Ysrc / Rb / T ² (3)
Then, based on the reflectance Rw of the white backing portion 82 and the reflectance Rb of the black backing portion recorded in the apparatus, and the reflected light amounts Ydst_w and Ydst_b measured using the respective backing portions, Equations (2) and (3) ), The patch transmittance T is calculated from the equation (4).

  Here, since the directly reflected light amount Ysample by the patch depends on the light amount Ysrc of the light irradiated on the surface of the patch, if Ysrc does not change, Ysample also does not change. Therefore, the change in the amount of light irradiated from the back surface of the sample is equivalent to the change in the second term of the equations (2) and (3). Therefore, the present embodiment is characterized in that the second term of the expressions (2) and (3) is corrected according to the observation condition specified by the user.

  In S806, the transmittance T calculated in S805 is the density that would be obtained when observing the printed matter of the patch selected as the measurement target in S802 under the observation conditions set by the user in the observation condition input unit 301. To predict (concentration prediction processing).

  Here, the density prediction processing in S806 will be described in detail. In the present embodiment, the concentration prediction method differs depending on the set observation conditions.

  First, the case of condition (1) in which the amount of light irradiated on the surface of the sample is equal to the amount of light irradiated from the back surface will be described. FIG. 11 shows a schematic diagram of measurement under condition (1). The reflected light amount Ytarget that is a prediction target in this case is a total value of the light amount Ysample that is directly reflected from the patch and the light amount Yback_th that is transmitted from the light source 1101 located on the back surface of the sample through the sample. The amount of light Ysample directly reflected from the patch is predicted from the above equation (2) by the following equation (5). The light amount Yback_th of the light irradiated from the back surface of the sample is a value obtained by multiplying the light amount Ysrc irradiated on the front surface by the transmittance T of the patch because the light amount of the light source 1101 on the back surface is equivalent to that of the front surface irradiation unit 92. It becomes. Therefore, the light amount Ytarget under the condition (1) is predicted using the following formula (6).

Ysample = Ydst_w−Ysrc ・ Rw ・ T ² (5)
Ytarget = Ysample + Yback_th = Ysample + Ysrc · T (6)
Next, the case of condition (2) in which the amount of light irradiated from the back surface is smaller than the amount of light irradiated on the surface of the sample will be described. The reflected light amount Ytarget, which is a prediction target under the condition (2), is similar to FIGS. 10 (a) and 10 (b), the light amount Ysample reflected directly from the patch, and the sample is transmitted and reflected by the backing part It can be expressed as a total value with the amount of light. That is, in the case of the condition (2), the light amount Ytarget of the reflected light is predicted by replacing the reflectance Rw of the white backing portion in the above formula (2) with the reflectance Rx of the general backing. This prediction formula is shown in the following formula (7). The general backing reflectance Rx is determined by an input from the user. For example, the reflectance of a typical recording medium may be stored in the image forming unit 310 in advance.

Ytarget = Ysample + Ysrc / Rx / T ² (7)
As described above, when the observation environment is the condition (2), the value calculated by the equation (7) is set as Ytarget. When it is desired to simplify the calculation, it is possible to use Ydst_w measured in S803 as Ytarget as it is in this condition (2).

  Next, the case of condition (3) where the amount of light irradiated from the back surface of the sample is 0 will be described. The amount of reflected light Ytarget to be predicted under condition (3) is reflected only by the amount of direct reflected light Ysample from the patch because the amount of light from the back of the sample is 0. Therefore, when the observation environment is the condition (3), Ysample calculated by the equation (5) is used as Ytarget as it is.

  As described above, in S806, one of the above conditions (1) to (3) is selected as the observation condition closest to the observation environment set by the user, and the reflected light amount Ytarget is predicted based on the selected condition. To do. Then, using the predicted reflected light amount Ytarget, the density Dsam of the patch that will be observed under the environment set by the user is calculated from the following equation (8). In Equation (8), Rsam is a ratio (reflectance) between the predicted reflected light amount Ytarget and the irradiated light amount Ysrc of the irradiation unit 92 calculated in S801 in the patch to be measured.

Dsam = -log (Rsam) =-log (Ytarget / Ysrc) (8)
In this embodiment, an example is shown in which the density is calculated from the reflectance. However, the density calculation method is not limited to the equation (8), and it is sufficient that a value corresponding to the density can be calculated.

  The calculated density is held in a memory (not shown) in the image forming unit 310. For example, in the patch example shown in FIG. 7 in the present embodiment, the laser intensity at the time of exposure processing is 5 patterns, and the color material is 4 patterns of CMYK. Therefore, if the laser intensity is represented by i having a value of 0 to 4 and the color material is represented by j having a value of 0 to 3, all 20 patterns of Dij {i = 0 to 4, j = 0 to 3} A memory area for storing the density values of the patches is secured in the apparatus. Each time a sample corresponding to each patch is measured, the corresponding density value is updated.

  In S807, it is determined whether or not density prediction has been performed for all patches in the sample. If all are completed, the process proceeds to S808, but if there is an unmeasured patch, the process returns to S802, and the unmeasured patch is selected as a measurement target.

  In S808, an image forming condition for the exposure processing unit 313, that is, a laser beam intensity for reproducing the target density is specified (forming condition correcting process). First, the target density Dt previously stored in the image forming unit 310 is read. The target density Dt here is the maximum density that can be formed for each type of recording medium, but a plurality of patterns may be held for each type of recording medium as the target density Dt. Next, of the patch densities Dij predicted in S806, two patch densities sandwiching the target density Dt are specified. Then, from the two identified patch densities D1, D2 and the two laser light intensities Lp1, Lp2 when recording these two patches, the laser light intensity that achieves the target density Dt using a known linear interpolation method Calculate Lp. This calculation formula is shown in the following formula (9). In the equation (9), D1 and Lp1 are the density and laser light intensity of the patch showing a density higher than the target density Dt, and D2 and Lp2 are the density and laser light intensity of the patch showing a density lower than the target density Dt.

Lp = Lp2 + (Dt−D2) / (D1−D2) ・ (Lp1-Lp2)… (9)
The calculation of the laser light intensity corresponding to the target density Dt is not limited to linear interpolation, and a non-linear interpolation method such as spline interpolation may be used.

  The laser light intensity Lp calculated by Expression (9) is recorded in the image forming condition holding unit 318 as an image forming condition optimum for the observation condition selected by the user.

  In the present embodiment, as described above, the target density can be reproduced in the formed image by printing out the patch data and specifying the image forming condition according to the observation condition designated by the user.

Image formation processing (S205)
Hereinafter, the image forming process in S205 will be described in detail.

  In the image processing unit 311, based on the RGB information of each pixel recorded in the image data area of the input print data, color separation data indicating the amount of color material corresponding to the combination of toners that reproduce the color of each pixel Performs color conversion processing to obtain CMYK. In the present embodiment, the color conversion process is executed by using a color separation look-up table (LUT) describing the correspondence between RGB and CMYK, and performing an interpolation operation as necessary. By this color conversion processing, each pixel is output as an 8-bit value for each color corresponding to the amount of each color material of cyan (C), magenta (M), yellow (Y), and black (K). Here, FIG. 12 shows an example of the color separation LUT. As shown in the figure, a corresponding 8-bit CMYK value is determined for an 8-bit RGB value. Note that the number of CMYK bits is not limited to 8 bits, and may be, for example, 10 bits.

  After the color conversion process, a known halftone process is performed on the color material amount of each toner. That is, the 8-bit CMYK value is converted into, for example, a 1-bit halftone image signal expressing halftones by area gradation. The converted halftone signal is output to the charging processing unit 312.

  In the charging processing unit 312 to which the halftone image signal is input, the charging unit 2 is controlled to uniformly charge the surface potential of the photosensitive drum 1. Next, the exposure processing unit 313 forms an electrostatic latent image on the surface of the photosensitive drum 1 based on the input halftone image signal and the image forming conditions recorded in the image forming condition holding unit 318. That is, first, control is performed so that the intensity of the laser beam irradiated from the laser oscillator 31 satisfies the image forming condition created by the above-described density prediction, for example. Next, the laser oscillator 31 is turned on according to the halftone image signal. The laser light emitted from the laser oscillator 31 is reflected as the polygon mirror 32 rotates, and an electrostatic latent image is formed by scanning the surface of the photosensitive drum 1 by the Fθ lens 33. As described above, in S205, the target density is set under the observation conditions specified by the user by controlling the intensity of the laser light emitted from the laser oscillator 31 according to the image forming conditions created based on the patch data in S203. It can be reproduced.

  Since the processing by the development processing unit 314 to the fixing processing unit 316 after the exposure processing is the same as that in S203, description thereof is omitted. In S205, the density prediction unit 317 does not perform any particular processing, and the recording medium on which the image is fixed by the fixing processing unit 316 is output as it is.

  As described above, according to the present embodiment, the concentration that will be obtained under the observation conditions specified by the user is predicted based on the measurement results of the sample using two types of backing parts having different reflectances. Then, an image forming condition for reproducing the target density is specified based on the predicted density. Therefore, it is possible to reproduce the target density in the designated observation environment including the case where the amount of light irradiated from the back surface of the sample is equal to that on the front surface.

  In the present embodiment, an example in which the image forming condition is controlled using the maximum density in the recording medium as the target density is shown. In this way, when the target density is set to the maximum density, it is only necessary to prepare a high density area as a patch to be measured, and for example, the same effect can be obtained without using a patch in the low density area.

<Modification>
In the first embodiment, the example in which the transmittance T of the patch image is calculated using the equation (4) is shown. However, the calculation method is not limited to this example, and any method can be used as long as the transmittance T of the patch image can be obtained. Such a method may be used. For example, the transmittance of the patch image may be calculated using a multiple reflection model with the bottom surface of the recording medium as the interface. Here, an example of obtaining the transmittance T of the patch image using the multiple reflection model will be described with reference to FIG.

  FIG. 13 (a) is a schematic diagram when a multiple reflection model using the bottom surface of the recording medium as an interface is applied during the Ydst_w measurement in S803. FIG. 13B is a schematic diagram in the case where a multiple reflection model using the bottom surface of the recording medium as an interface is applied in the Ydst_b measurement in S803. For example, in FIG. 13A, the light reflected by the white backing unit 82 is separated into light Ydst_w1 that is transmitted to the recording medium side with the bottom surface of the recording medium as an interface, and light Y_ref1 that is reflected again by the white backing unit 82. The separated Y_ref1 is further reflected on the bottom surface of the white backing portion 82, and is separated into light Ydst_w2 that is transmitted to the recording medium side and light Y_ref2 that is reflected to the white backing portion 82 side. As described above, in the multiple reflection model in which the bottom surface of the recording medium is the interface, the ratio of the incident light to the light transmitted through the recording medium and the light reflected from the interface is determined by the refractive index n of the recording medium. When the ratio X of light transmitted to the recording medium side is calculated from the refractive index n using the well-known Fresnel law, Ydst_w measured in S803 can be expressed by the following equation (2) ′.

  Similarly, Ydst_b measured in S804 can be expressed by the following equation (3) ′.

  From the reflectance Rw of the white backing portion 82 and the reflectance Rb of the black backing portion 81, the measured values Ydst_w and Ydst_b using each backing portion, and the transmittance X calculated from the refractive index n of the recording medium, the transmittance of the patch image T is calculated by the following equation (4) ′.

  As described above, the transmittance of the patch image may be obtained based on the multiple reflection model using the bottom surface of the recording medium as an interface. When the bottom surface of the recording medium is the interface, the transmittance X of the light reflected from the backing portion to the recording medium side is calculated according to Fresnel's law according to the refractive index n of the recording medium input by the user. Also good. Further, the transmittance X for each type of recording medium may be recorded in advance in the image forming apparatus.

  Also in the present modification, as in the first embodiment, the reflected light amount Ysample from the patch image depends on the front surface irradiation light amount Ysrc of the patch image, so the change in the irradiation light amount from the back surface of the sample is expressed by the equation (2) ′. , (3) 'is equivalent to changing the second term. That is, as in the first embodiment, the same effects as in the first embodiment can be obtained by correcting the second term of the above formulas (2) ′ and (3) ′ according to the observation conditions specified by the user. It is done.

<Other embodiments>
In the first embodiment described above, an example in which formation of patch data for density prediction is performed independently of formation of image data has been described. However, density prediction is performed by recording patch data in a blank portion where image data is recorded. May be performed. Further, even when there is no designation of density prediction by the user, patch data may be automatically output periodically to perform density prediction.

  In the first embodiment, the example in which the laser light intensity of the exposure processing unit 313 is controlled using the maximum density for each type of recording medium as the target density has been described. However, patch data with different color material area ratios is used. Then, density gradation correction may be performed.

  It is also conceivable that the backing part used in the density predicting part 317 is soiled by a color material or the like. Therefore, it is also effective to have a function of making it possible to measure the reflectance of the backing portion and correcting the reflectance (Rw, Rb) of the backing portion recorded in advance in the apparatus.

  If there is no patch for interpolating the target density in the density prediction unit 317, the density closest to the target density is selected from Dij (i = 0 to 4, j = 0 to 3), and the Dij The image forming conditions may be specified based on the laser beam intensity corresponding to. Further, the laser light intensity may be calculated using a known extrapolation method.

  In the first embodiment, the example in which the transmittance T of the sample is predicted based on the measurement values obtained by two types of backing parts having different reflectances has been shown. May be. In addition, an example is shown in which the transmittance T is predicted based on the measurement values of the two types of backing parts, and the reflected light amount Ysample from the patch image is predicted based on the predicted transmittance T, but the prediction order is reversed. There may be. That is, the reflected light amount Ysample may be predicted based on the measurement values obtained by the two types of backing parts, and the transmittance T may be predicted based on the predicted Ysample. Further, the transmittance T of the sample is not limited to the above prediction, and the transmittance separately measured by the user may be directly input.

  In the first embodiment, the geometric condition for measuring the sample is 45/0. However, the geometric condition is not limited to this example, and may be 60/0, for example.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media. The processor or computer (or CPU, MPU, etc.) of the system or apparatus reads out and executes the program.

Claims (10)

Measuring means for measuring the amount of reflected light for each patch by irradiating the sample with the density correction patch formed on the recording medium and receiving the reflected light;
A backing setting means for disposing a first backing or a second backing having a lower reflectance than the first backing on a non-patch surface of the sample;
A first measurement result obtained by measuring the sample with the first backing disposed and a second measurement result obtained by measuring the sample with the second backing disposed by the measuring means. A correction unit that calculates a predicted density value of the patch under a predetermined observation condition, and corrects the image forming condition in the image forming apparatus that formed the sample based on the predicted density value;
An image processing apparatus comprising: Further, when observing the image formed on the recording medium, the first light amount irradiated on the surface on which the image of the recording medium is formed and the surface on which the image of the recording medium is not formed are irradiated. Observation condition input means for inputting an observation condition indicating a relationship with the second light quantity to be
The image processing apparatus according to claim 1, wherein the correction unit calculates the predicted density value according to the observation condition. The correction means includes
An irradiation light amount acquisition means for acquiring an irradiation light amount irradiated on the sample in the measurement means;
First measurement result acquisition means for acquiring the first measurement result for each patch in the sample;
Second measurement result acquisition means for acquiring the second measurement result for each patch in the sample;
A transmittance calculating means for calculating a transmittance for each patch in the sample from the first and second measurement results and the irradiation light amount;
Concentration predicting means for calculating the predicted density value for each patch obtained when observing the sample under the observation conditions input by the observation condition input means from the transmittance;
The image processing apparatus according to claim 2, wherein the image forming condition is corrected based on the predicted density value for each patch. The observation condition input means, as the observation condition,
A first condition in which the first light quantity and the second light quantity are equivalent;
A second condition in which the first light amount is larger than the second light amount and the second light amount is not zero;
Any one of the third conditions in which the second light quantity is zero;
4. The image according to claim 3, wherein the density predicting unit is different in a method of calculating the predicted density value depending on whether the observation condition is the first, second, or third condition. 5. Processing equipment.   The transmittance calculating means calculates the transmittance for each patch from the first and second measurement results, the irradiation light amount, and the reflectance of the first and second backings. The image processing apparatus according to claim 3.   The image according to any one of claims 1 to 5, wherein the first backing is a white backing that conforms to an ISO standard, and the second backing is a black backing that conforms to an ISO standard. Processing equipment.   7. The measurement unit according to claim 1, wherein the positional relationship between an irradiation unit that irradiates the sample with light and a light receiving unit that receives the reflected light satisfies a geometrical condition of 45/0. The image processing apparatus according to item. The image forming apparatus irradiates a recording medium with laser light to form an image,
The image processing apparatus according to claim 1, wherein the image forming condition is a laser beam intensity in the image forming apparatus. A measuring means for measuring the amount of reflected light for each patch by irradiating the sample with the density correction patch formed on the recording medium and receiving the reflected light, and the patch non-formation surface of the sample A method for correcting an image forming condition in an image forming apparatus having a backing setting means for arranging a first backing or a second backing having a reflectance lower than that of the first backing, and a correcting means,
The correction means includes a first measurement result obtained by measuring the sample with the first backing disposed, and a second measurement result obtained by measuring the sample with the second backing disposed. A method for correcting an image forming condition, comprising: calculating a predicted density value of a patch under a predetermined observation condition, and correcting the image forming condition based on the predicted density value.   A program for causing a processor of the image forming apparatus to function as each unit of the image processing apparatus according to any one of claims 1 to 8 when executed by the processor of the image forming apparatus.

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