Patent Description:
There is known a technique of performing, with a color chart, quality adjustment, particularly color reproduction density adjustment, on an image forming apparatus. Such a color chart includes patches in colors reproducible by the image forming apparatus. The image forming apparatus forms an image of the color chart on a recording medium and outputs the recording medium bearing the color chart. The color chart on the recording medium thus output is measured by, e.g., a colorimeter. A color conversion profile is generated based on data of the color chart thus measured.

Specifically, a plurality of color patches is located such that the rate of the color reproduction density changes at a constant rate. In other words, the color patches in close tones are located adj acent to each other. For example, <CIT> discloses a technique of locating, in a color chart, a plurality of color patches as a whole in a density distribution indicating gradually changing color reproduction densities.

However, such a typical technique may cause a relatively large difference in gradation or luminance between the color patches and the background (e.g., a color of a recording medium). Such a relatively large difference may hamper a sufficient reduction of the influence of flare and degrade the image quality.

<CIT> discloses a density calibration chart. <CIT> discloses an image forming apparatus.

In light of the above-described problems, it is a general object of the present invention to provide a color chart that enhances the image quality.

In order to achieve the above-mentioned object, there is provided a color chart according to claim <NUM>. Advantageous embodiments are defined by the dependent claims. Advantageously, the color chart includes a first portion and a second portion. The first portion includes no patch. The second portion includes a plurality of patches having different densities or luminances. The plurality of patches includes a reference patch indicating a color having a reference density or luminance. The reference patch is adjacent to the first portion. The plurality of patches is located in order of increasing density from the density of the color indicated by the reference patch, decreasing density from the density of the color indicated by the reference patch, increasing luminance from the luminance of the color indicated by the reference patch, or decreasing luminance from the luminance of the color indicated by the reference patch.

Accordingly, the image quality is enhanced.

In a later-described comparative example, embodiment, and exemplary variation, for the sake of simplicity, like reference numerals are given to identical or corresponding constituent elements such as parts and materials having the same functions, and redundant descriptions thereof are omitted unless otherwise required.

It is to be noted that, in the following description, suffixes Y, M, C, and K (or Bk) denote colors of yellow, magenta, cyan, and black, respectively. To simplify the description, these suffixes are omitted unless necessary.

Referring to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, embodiments of the present disclosure are described below.

Initially, a description is given of a first embodiment of the present disclosure.

A color chart is used for, e.g., calibration for adjusting the color reproduction density of image formation performed by an image forming apparatus. Accordingly, the color chart may be referred to as a calibration chart. The color chart has a configuration as described below, for example.

<FIG> is a diagram illustrating an example of a color chart <NUM>.

For example, an image including a plurality of patches is formed on a sheet <NUM> serving as a recording medium. Thus, the color chart <NUM> is created. Note that such an image including a plurality of patches may be referred to as a pattern image in the following description.

The patch is an image in preset color, density, and shape. The image serving as the patch is set according to calibration. In other words, the image serving as the patch is not limited to an image in specific color, density, and shape. Similarly, e.g., the combination, number, and size of the patches constructing the color chart <NUM> are set in advance according to calibration.

In the present example illustrated in <FIG>, the color chart <NUM> includes a first portion <NUM> and a second portion <NUM>. The first portion <NUM> indicates an area in which no pattern image is formed. By contrast, the second portion <NUM> indicates an area in which a pattern image is formed. In other words, the first portion <NUM> includes no patch; whereas the second portions <NUM> includes a plurality of patches.

In the present example, the sheet <NUM> is white. <FIG> illustrates boundaries with dotted lines. Alternatively, the boundaries may be indicated by no line.

As in the example illustrated in <FIG>, the first portion <NUM> is, e.g., a so-called margin without a pattern image. The first portion <NUM> has a color of the sheet <NUM>. In other words, the first portion <NUM> has a background color.

As in the example illustrated in <FIG>, the second portion <NUM> is a portion in which patches are located such that the density increases in order from a reference patch <NUM> that is located at a portion adjacent to the first portion <NUM>. In short, the reference patch <NUM> is adjacent to the first portion <NUM>. The reference patch <NUM> is one of the outermost patches in the second portion <NUM>.

In the present example, the reference patch <NUM> is the lowest density patch in the second portion <NUM>. In the present example, the highest density patch in the second portion <NUM> is a last patch <NUM> located at a central portion of the second portion <NUM>.

For example, the patches are located such that the density increases from the reference patch <NUM> toward the last patch <NUM> (in the order indicated by arrow in <FIG>). In the present example, the density decreases outward and increases inward to the central portion of the second portion <NUM>. In a case in which the sheet <NUM> is white as in the present example, the reference patch <NUM> is preferably white or in a color having a density close to the color of the sheet <NUM>.

As indicated by arrow in <FIG>, for example, the patches are located in a spiral shape toward the central portion of the second portion <NUM>. Specifically, the patches are located in the order described below.

<FIG> is a diagram illustrating an example of location of patches.

Now, a description is given of an example in which the color chart <NUM> includes <NUM> patches. <FIG> illustrates the order in which the patches are located by numbers. <FIG> also illustrates the order of increasing density by a dotted arrow.

Specifically, the patches are located such that the density increases in order from the portion indicated by "<NUM>" to the portion indicated by "<NUM>. " In short, the highest density patch (e.g., the last patch <NUM>) is located at the portion indicated by "<NUM>"; whereas the lowest density patch (e.g., the reference patch <NUM>) is located at the portion indicated by "<NUM>. " In the color chart <NUM> of the present example, the density of the patches increases as the number increases, from the lightest patch located at the portion indicated by "<NUM>" to the darkest patch located at the portion indicated by "<NUM>.

The number of patches is not limited to <NUM>. The number of patches may be increased to finely change the density of the patches. By contrast, the number of patches may be less than <NUM>.

As described above, preferably, patches in a color having a density close to the color of the sheet <NUM> are located at portions adjacent to the first portion <NUM>, such as the portions indicated by "<NUM>" to "<NUM>. " In addition, preferably, the patches are located such that the density increases toward an inner portion such as a portion indicated by "<NUM>" or "<NUM>.

Such a location of the patches reduces the difference in gradation between adjacent patches such as patches "<NUM>" and "<NUM>" (i.e., the patches located at the portions indicated by "<NUM>" and "<NUM>").

Alternatively, the patches may be located as described below, for example.

<FIG> is a diagram illustrating a modification of the location of the patches of <FIG>.

The location illustrated in <FIG> is different from the location illustrated in <FIG> in that the order of patches "<NUM>" and "<NUM>" (i.e., the patches located at the portions indicated by "<NUM>" and "<NUM>") are reversed. In other words, the patches may not be located in order of completely increasing density.

Specifically, provided that the difference in gradation between adjacent patches is relatively small, such as a combination of patches "<NUM>" and "<NUM>", a combination of patches "<NUM>" and "<NUM>" (i.e., the patches located at the portions indicated by "<NUM>" and "<NUM>"), and a combination of patches "<NUM>" and "<NUM>" (i.e., the patches located at the portions indicated by "<NUM>" and "<NUM>"), the patches may not be located in the order of completely increasing density.

Whether the difference in gradation is relatively small is determined by, e.g., whether the difference in gradation is equal to or greater than a preset value. In short, the color chart <NUM> includes patches located such that patches having a relatively small difference in gradation less than the preset value are adjacent to each other.

The color chart <NUM> including the patched located as described above reduces the difference in gradation between the color of the sheet <NUM> and the color of outer circumferential patches of the second portion <NUM> such as the reference patch <NUM>. In short, such a color chart reduces the influence of flare in calibration. Reducing the influence of flare enhances the color reproducibility and the image quality in image formation. With the configuration described above, the number of patches is not to be reduced.

When a reading device reads a color chart in calibration, the reading device may capture reflected light entering from the periphery of target patches, thus causing the flare. As the difference in gradation between the color of patches and the color of the sheet <NUM> is larger, the detected data is more likely to deviate from the true value due to the influence of the flare. To prevent such a situation, preferably, the reference patch <NUM> as a patch located at a portion adjacent to the portion in the color of the sheet <NUM> has the same density as the color of the sheet <NUM> or a density close to the color of the sheet <NUM>. When the patches are located such that the density increases in order starting from the reference patch <NUM>, a patch having a relatively low density in the entire color chart <NUM> may be located at a portion in the color of the sheet <NUM> or having a density close to the color of the sheet <NUM>. In short, the difference in the density between e.g., the reference patch <NUM> and the color of the recording medium is preferably equal to or less than a given value.

A description is now given of a second embodiment of the present disclosure.

The second embodiment is different from the first embodiment in that the color of the sheet <NUM> is black, for example. In other words, in the second embodiment, the color of the first portion <NUM> in which no pattern image exists is black.

The reference patch <NUM> is preferably changed according to the color of the recording medium. Specifically, when the color of the sheet <NUM> is black as in the second embodiment, the reference patch <NUM> is preferably changed as follows.

<FIG> is a diagram illustrating an example of the color chart <NUM> on a black recording medium.

In the present example, the patches are located such that the density of the patches increases outward and decreases inward. In a case in which the sheet <NUM> is black as in the present example, the reference patch <NUM> is preferably black or in a color having a density close to the color of the sheet <NUM>. As described above, preferably, the reference patch <NUM> is changed according to the color of the sheet <NUM>, to a color having the same density as the color of the sheet <NUM> or a color having a density close to the color of the sheet <NUM>. The patches are located such that the density decreases in order from the reference patch <NUM> toward the last patch <NUM>.

Although the color of the sheet <NUM> is white in the first embodiment, the color of the sheet <NUM> is not limited to white. As in the second embodiment, the color of the sheet <NUM> may be black. Alternatively, the color of the sheet <NUM> may be an intermediate color. The intermediate color is, e.g., red.

In a case in which the sheet <NUM> is in an intermediate color, the color chart <NUM> may include a plurality of second portions <NUM>, for example. Now, a description is given of an example in which the color chart <NUM> includes two second portions (each corresponding to the second portion <NUM>).

<FIG> is a diagram illustrating an example of the color chart <NUM> including two second portions (each corresponding to the second portion <NUM>).

In the present example, the color of the sheet <NUM> is red. In <FIG>, the hatched portion is the first portion <NUM> as a portion in a background color.

For example, the two second portions are vertically located, one by one, in the Y direction in <FIG>. In the present example, the two second portions are referred to as an upper portion <NUM> and a lower portion <NUM>. The upper portion <NUM> is a second portion disposed above; whereas the lower portion <NUM> is a second portion disposed below.

The upper portion <NUM> includes patches located in a spiral shape such that the density decreases inward in order from a first reference patch <NUM>, which is located at the upper left in the upper portion <NUM>, to a first last patch <NUM>, which is the lightest patch located at the center of the upper portion <NUM>. On the other hand, the lower portion <NUM> includes patches located in a spiral shape such that the density increases inward in order from a second reference patch <NUM>, which is located at the upper left in the lower portion <NUM>, to a second last patch <NUM>, which is the darkest patch located at the center of the lower portion <NUM>.

<FIG> illustrates the first reference patch <NUM>, the second reference patch <NUM>, and the first portion <NUM> in different colors for the sake of description. Preferably, the first reference patch <NUM>, the second reference patch <NUM>, and the first portion <NUM> are in a color having densities close to each other.

As in the present example, the color chart <NUM> may include two second portions: a second portion in which patches are located such that the density decreases from the first reference patch <NUM> to the first last patch <NUM> as in the upper portion <NUM>, and a second portion in which patches are located such that the density increases from the second reference patch <NUM> to the second last patch <NUM> as in the lower portion <NUM>.

In particular, in a case in which an intermediate color is used, both the location of patches in which the density sequentially increases and the location of patches in which the density sequentially decreases may be used for calibration. In a case in which the recording medium is in an intermediate color, the density of the reference patch is an intermediate value. In other words, either the location of patches in which the density increases or the location of patches in which the density decreases may be insufficient to acquire all the densities, resulting in generation of insufficient calibration data. By contrast, as in the above-described example in which the color chart <NUM> includes a plurality of second portions, the color reproduction is enhanced by calibration with calibration data acquired, even in a case in which the recording medium is in an intermediate color.

The example described above is an example in which the two second portions (i.e., the upper portion <NUM> and the lower portion <NUM>) are equal to each other. Alternatively, the upper portion <NUM> and the lower portion <NUM> may not be equal to each other. Specifically, the ratio in number between the patches located in the upper portion <NUM> and the patches located in the lower portion <NUM> in the example described above is preferably adjusted depending on the intermediate color. For example, in a case in which the sheet <NUM> is in an intermediate and dark color, the patches located in the lower portion <NUM> is less in number or ratio than the patches located in the upper portion <NUM>. Thus, e.g., the number of patches in the plurality of second portions is preferably adjusted according to the density of the intermediate color.

Now, a detailed description is given of the reference patch <NUM>.

The reference patch <NUM> is located as described below.

<FIG> is a diagram illustrating an example of location of the reference patch <NUM>.

In the present example, the sheet <NUM> is white. For example, the reference patch <NUM> is located anywhere in an outer circumferential portion (e.g., an outermost circumferential portion <NUM> in <FIG>) of the second portion <NUM>. As illustrated in <FIG>, the outermost circumferential portion <NUM> may be a pattern image. On the other hand, patches may be or may not be located in an inner portion <NUM>, which is a portion inside the outermost circumferential portion <NUM> and illustrated as a hatched portion in <FIG>. In other words, the inner portion <NUM> may be blank without a pattern image or may include any image. For the sake of description, the inner portion <NUM> is hatched in <FIG>. However, the inner portion <NUM> is not hatched in actuality.

As described above, locating the reference patch <NUM> in the outermost circumferential portion <NUM> reduces the difference in gradation between the color of the patches and the color of the sheet <NUM>. Specifically, such a location attains a difference in gradation of about <NUM>% or less. Accordingly, the influence of flare is reduced.

As in the second embodiment, the color of the sheet <NUM> may be, e.g., black or an intermediate color as described below.

<FIG> is a diagram illustrating an example of location of the reference patch <NUM> on a black recording medium.

In a case in which the sheet <NUM> is black as illustrated in <FIG>, the reference patch <NUM> is set to a color close to black. As described above with reference to <FIG>, patches may be or may not be located in the inner portion <NUM>.

<FIG> is a diagram illustrating an example of location of the reference patch <NUM> on a recording medium in an intermediate color.

In a case in which the sheet <NUM> is an intermediate color such as red as illustrated in <FIG>, the color of the reference patch <NUM> is set to a color having a density, which is luminance in a modification described later, close to the color of the background. As described above with reference to <FIG>, patches may be or may not be located in the inner portion <NUM>.

Now, a description is given of an example of location of patches.

For example, the patches are located in gradation described below.

<FIG> is a diagram illustrating a gradation range.

As illustrated in <FIG>, in the present example, the second portion <NUM> is segmented into <NUM> areas inward: a first area <NUM>, a second area <NUM>, a third area <NUM>, a fourth area <NUM>, and a fifth area <NUM>.

The gradation has <NUM> tones from <NUM> to <NUM> in the present example. For each of the first to fifth areas <NUM> to <NUM>, the gradation range, which is a range of tones of patches, is set in advance. In the present example, a higher tone indicates a lighter color close to white. For example, the gradation range is set as presented in Table <NUM> for each of the first to fifth areas <NUM> to <NUM>.

As presented in Table <NUM> above, patches in tones from <NUM> to <NUM> are located in the first area <NUM>, which is adjacent to the first portion <NUM>. Also as presented in Table <NUM> above, patches in tones smaller than tones of the patches located in the first area <NUM> and greater than tones of patches located in the third area <NUM> are located in the second area <NUM>.

Similarly, the patches in tones smaller than the tones of the patches located in the second area <NUM> and greater than tones of patches located in the fourth area <NUM> are located in the third area <NUM>. The patches in tones smaller than the tones of the patches located in the third area <NUM> and greater than tones of patches located in the fifth area <NUM> are located in the fourth area <NUM>. Lastly, the patches in tones smaller than the tones of the patches located in the fourth area <NUM> are located in the fifth area <NUM>. As described above, the patches are preferably located such that the density increases (in other words, the tones indicated in the column of "gradation range" in Table <NUM> decreases) inward in the first to fifth areas <NUM> to <NUM>.

More preferably, such a location reduces a difference in gradation between the patches and the background and a difference in gradation between adjacent patches.

The location of the patches is not limited to the example presented in Table <NUM>, provided that the difference in gradation between the patches and the background and the difference in gradation between the adjacent patches are within a certain range. For example, the following combination of "gradation range" and "area" may be used.

<FIG> is a diagram illustrating a modification of the gradation range described above.

In the present example, as presented in Table <NUM> above, the gradation range of from <NUM> to <NUM> is classified into a gradation range class "A. " The two gradation ranges of from <NUM> to <NUM> and from <NUM> to <NUM> are collectively classified into a gradation range class "B. " Further, the two gradation ranges of from <NUM> to <NUM> and from <NUM> to <NUM> are collectively classified into a gradation range class "C.

The present example illustrated in <FIG> is different from the example illustrated in <FIG> in the gradation ranges for the areas in the gradation range class "B. " Specifically, the gradation range for the second area in <FIG> is for the third area in <FIG>. Similarly, the gradation range for the third area in <FIG> is for the second area in <FIG>. In other words, as illustrated in <FIG>, the second area <NUM> having a higher density than the density of the third area <NUM> is located outside the third area <NUM>. Specifically, the patches are located as presented in Table <NUM> below.

Table <NUM> above is different from Table <NUM> above in that the gradation range for the second area (presented in the second row from the top in Table <NUM>) and the gradation range for the third area (presented in the third row from the top in the Table <NUM>) are replaced with each other. As described above, the gradation ranges may be replaced with each other in the same gradation range class.

The gradation range class is not limited to the setting as presented in Table <NUM>. For example, three or more areas may belong to one gradation range class.

Setting the gradation range and setting the areas are not limited to the examples described above with reference to Table <NUM>. For example, the second portion <NUM> may be segmented into <NUM> or more areas. Alternatively, the second portion <NUM> may be segmented into less than five areas. Optionally, the "gradation area class" may not be set. In a case in which the "gradation area class" is set, the gradation ranges in different gradation range classes may be replaced with each other.

Now, a description is given of a modification.

The location of patches is not limited to the location according to the CMYK-based density, which is a value determined on a cyan, magenta, yellow, and black (CMYK) basis. For example, the order of the reference patch <NUM> and other patches may be determined according to a color space of L*a*b*, which may be referred to as Lab in the following description. In other words, the order of the reference patch <NUM> and other patches may be determined according to the Lab-based luminance, which is a value determined on an L*a*b* (Lab) basis.

The "Lab" is a color space defined by the Commission internationale de l'eclairage (CIE) standard.

The order of the reference patch <NUM> and other patches may be determined according to the luminance in the Lab color space.

The shape of patches (including the reference patch <NUM> and may be referred to collectively as a patch in the following description) is not limited to square. For example, the patch may be shaped as described below.

<FIG> is a diagram illustrating a modification of the patch.

For comparison, part (a) of <FIG> illustrates an example in which all patches have a square shape.

By contrast, part (b) of <FIG> illustrates an example including a patch having a rectangular shape. Specifically, the patches may include, e.g., a vertically long patch <NUM> (i.e., a patch elongated in the Y-axis direction in <FIG>) or a laterally long patch <NUM> (i.e., a patch elongated in the X-axis direction in <FIG>).

The patch that is used for calibration may have any shape provided that the patch has a certain area. In other words, the shape of the patch is not limited to square and may be other shapes such as rectangle. The patches may have a common shape or different shapes. Preferably, however, the patches have identical areas as much as possible.

In a case in which one or more patches are shaped as, e.g., rectangle, the patches are more freely located. For example, locating an elongated patch reduces the number of patches located at the outer circumferential positions of the second portion <NUM>. In short, the reference patch <NUM> and other patches preferably have identical areas and have different shapes.

Now, a description is given of an image forming apparatus according to an embodiment of the present disclosure.

The image forming apparatus has a hardware configuration described below, for example.

<FIG> is a block diagram illustrating a hardware configuration of an image forming apparatus <NUM>.

For example, the image forming apparatus <NUM> includes a control device <NUM>, a writing device <NUM>, an image forming device <NUM>, an intermediate transfer belt <NUM>, a secondary transfer device <NUM>, a fixing device <NUM>, and a reading device <NUM>.

The control device <NUM> is, e.g., an arithmetic device provided with a storage device. The control device <NUM> controls, e.g., the writing device <NUM> to control image formation.

The writing device <NUM>, the image forming device <NUM>, the intermediate transfer belt <NUM>, the secondary transfer device <NUM>, and the fixing device <NUM> perform the image formation according to, e.g., input image data. Specifically, in a case in which an image represented by image data is formed on the sheet <NUM>, a latent image generated according to the image data is developed into a visible toner image, which is transferred onto the intermediate transfer belt <NUM>. The secondary transfer device <NUM> transfers the toner image from the intermediate transfer belt <NUM> onto the sheet <NUM>. The fixing device <NUM> heats the sheet <NUM> bearing the toner image to fix the toner image onto the sheet <NUM>. In the case of duplex printing on the sheet <NUM>, such a series of image forming operations is performed on both sides of the sheet <NUM>.

The reading device <NUM> is, e.g., an optical sensor. Specifically, the reading device <NUM> reads, e.g., a pattern image for calibration formed on the sheet <NUM> and generates, e.g., image data. Calibration is performed based on, e.g., the image data thus generated.

Alternatively, the image forming apparatus <NUM> may have a configuration as described below, for example.

<FIG> is a block diagram illustrating a first modification of the hardware configuration of the image forming apparatus <NUM> described above.

The hardware configuration illustrated in <FIG> is different from the hardware configuration illustrated in <FIG> in that two reading devices <NUM> are disposed. Alternatively, three or more reading devices <NUM> may be disposed.

In other words, the reading devices <NUM> may be constructed of the reading device <NUM> that reads a front side of the sheet <NUM> and the reading device <NUM> that reads a back side of the sheet <NUM>.

<FIG> is a block diagram illustrating a second modification of the hardware configuration of the image forming apparatus <NUM> described above.

The reading devices <NUM> may be located as illustrated in <FIG>.

In particular, in printing such as production printing, high image quality is often required. In order to satisfy such a requirement, a user performs calibration depending on a change over time, an environmental change, usage conditions, or a combination thereof, thus enhancing the image quality of image formation. In such a case, performing calibration on an image forming apparatus with the color chart <NUM> according to the present embodiment adjusts the characteristics of the image forming apparatus.

In calibration, a gradation characteristic (e.g., a characteristic indicated by a γ correction curve) is adjusted based on data of the color chart <NUM> optically read.

One or more embodiments of the present disclosure may be applied to an image forming system that includes an apparatus or device in addition to the image forming apparatus <NUM>. For example, the image forming apparatus <NUM> and the reading device <NUM> may be separated from each other as described below.

<FIG> is a diagram illustrating a configuration of an image forming system <NUM>.

For example, the image forming system <NUM> is a system that includes a combination of the image forming apparatus <NUM> and the reading device <NUM>, which is an external device independent of and separate from the image forming apparatus <NUM>.

The image forming apparatus <NUM> illustrated in <FIG> is different from the image forming apparatuses <NUM> illustrated in <FIG> in that the image forming apparatus <NUM> illustrated in <FIG> does not include the reading device <NUM>. In the present example, the reading device <NUM> is, e.g., a so-called colorimeter. The reading devices <NUM> includes, e.g., a sensor <NUM> and a sensor control device <NUM>. The sensor <NUM> serves as a reading unit that reads the color chart <NUM>. The sensor control device <NUM> serves as an output unit that outputs data of the color chart <NUM> read by the sensor <NUM> to the image forming apparatus <NUM> that forms an image on a recording medium.

In the image forming system <NUM>, first, the image forming apparatus <NUM> forms a test chart on the sheet <NUM>. Thereafter, the reading device <NUM> reads the test chart. Specifically, the sheet <NUM> ejected from the image forming apparatus <NUM> is manually inserted into the reading device <NUM>, for example. Then, the reading device <NUM> reads the test chart on the sheet <NUM> and inputs the read data to the image forming apparatus <NUM>. The calibration may be performed with a plurality of devices, as in the present example in which an external device reads the test chart. In other words, the number and types of apparatuses or devices are not limited provided that the calibration is performed in a configuration as described below, for example.

<FIG> is a diagram illustrating a configuration for performing calibration.

For example, as illustrated in <FIG>, first, the image forming apparatus <NUM> forms an image of, e.g., the color chart <NUM> on the sheet <NUM> for calibration. Then, the reading device <NUM> such as a colorimeter reads the color chart <NUM>. With the read data output from the reading device <NUM>, an information processing apparatus <NUM> such as a personal computer (PC) calculates a characteristic value. The calibration may be performed with the settings of the image forming apparatus <NUM> updated to conform to the characteristic value thus obtained.

According to one or more embodiments of the present disclosure, the image forming apparatus may be an image forming apparatus other than an electrophotographic image forming apparatus. For example, the image forming apparatus may be an inkjet image forming apparatus. The image forming apparatus may have a hardware configuration including hardware components other than the hardware components described above.

Now, a description is given of an overall process.

The calibration is performed in a procedure described below, for example.

<FIG> is a flowchart of an overall process.

In the present example, the overall process is performed by the image forming apparatus <NUM> described above with reference to <FIG>. In other words, the following will describe an example in which the image forming apparatus <NUM> including the reading device <NUM> together with the other devices performs the overall process.

In step S1701, the image forming apparatus <NUM> sets a recording medium. Specifically, a user inputs information of the sheet <NUM> that is used for calibration, to the image forming apparatus <NUM>.

In step S <NUM>, the image forming apparatus <NUM> sets a patch. For example, the image forming apparatus <NUM> determines, e.g., the color of the reference patch <NUM>, the location of patches, and the number of patches, according to the color of the recording medium. Thus, the configuration of the color chart <NUM> is determined. Note that the image forming apparatus <NUM> may set, e.g., the location of the reference patch <NUM> to identify data based on the reference patch <NUM> from the read data.

In step S <NUM>, the image forming apparatus <NUM> generates a pattern image.

In step S <NUM>, the image forming apparatus <NUM> forms a pattern image. Specifically, the image forming apparatus <NUM> forms a pattern image on the recording medium, thus creating the color chart <NUM> including the pattern image.

In step S <NUM>, the image forming apparatus <NUM> performs reading.

In step S <NUM>, the image forming apparatus <NUM> generates read data. In other words, the image forming apparatus <NUM> generates read data indicating, e.g., patch information as data for calibration.

In step S1707, the image forming apparatus <NUM> updates, e.g., the characteristic value according to the read data, thus performing adjustment.

Note that the overall process is not limited to the subject, content, and order described above. For example, an apparatus or a device other than the image forming apparatus <NUM> described above may perform the process. An operation other than the operations described above may be performed.

Now, a description is given of a functional configuration of an image forming apparatus according to an embodiment of the present disclosure.

<FIG> is a block diagram illustrating a functional configuration of the image forming apparatus <NUM>.

For example, the image forming apparatus <NUM> includes, as functional units, a reading unit 10F1, a control unit 10F2, an image forming unit 10F3, and a setting unit 10F4.

The reading unit 10F1 performs a reading procedure to read the color chart <NUM>. For example, the reading unit 10F1 is implemented by the reading device <NUM>.

The control unit 10F2 performs a control procedure to perform calibration, based on data of the color chart <NUM> read by the reading unit 10F1. For example, the control unit 10F2 is implemented by the control device <NUM>.

The image forming unit 10F3 performs an image forming procedure to form an image in a state adjusted according to a result of the calibration performed by the control unit 10F2. For example, the image forming unit 10F3 is implemented by the writing device <NUM>, the image forming device <NUM>, the intermediate transfer belt <NUM>, the secondary transfer device <NUM>, and the fixing device <NUM>.

The setting unit 10F4 performs a setting procedure to set a position of, e.g., the reference patch <NUM> in the color chart <NUM>. For example, the setting unit 10F4 is implemented by the reading device <NUM> or an input device.

Now, a description is given of some comparative examples.

Specifically, a description is now given of three color charts as comparative examples of the color chart <NUM> according to the present embodiment.

<FIG> is a diagram illustrating a first comparative example.

Although the patches are located such that adjacent patches are in close tones, the color chart illustrated in <FIG> has a relatively large difference in gradation between the patches and the background color.

<FIG> is a diagram illustrating a second comparative example.

Although the outer circumferential patches have an area greater than the area of inside patches, the color chart illustrated in <FIG> has a relatively large difference in gradation between the patches and the background color.

<FIG> is a diagram illustrating a third comparative example.

<FIG> illustrates an image of a color chart formed in gradation from dark to light of various colors such as yellow, magenta, cyan, black, green, and brown.

When calibration is performed with the color charts described above as the first to third comparative examples, the flare affects reading of the color charts.

Now, a description is given of other embodiments of the present disclosure.

For example, the color, location, size, and shape of patches constructing the color chart <NUM> and the ratio between the patches and the margin are not limited to the examples described above.

The intermediate color may be other than red. In other words, the intermediate color is a color having a density between a color having the highest density (e.g., black) and a color having the lowest density (e.g., white).

The recording medium is, e.g., a sheet such as a sheet of plain paper. In addition to plain paper, examples of the recording medium include, but are not limited to, coated paper, label paper, an overhead projector sheet, a film, and a flexible thin plate. In other words, the recording medium (or a recording medium that is used for an inkjet image forming apparatus) is made of a material to which ink droplets are at least temporarily adherable, a material to which ink droplets adheres and fixes, or a material to which ink droplets adheres and permeate. In short, the recording medium is made of any material to which liquid is adherable, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramic, or a combination thereof.

Specific examples of a recording material or formation made of such a material include, but are not limited to, a recording medium such as a sheet, a film, or cloth, an electronic component such as an electronic substrate or a piezoelectric element (which may be referred to as a piezoelectric component), layered powder, an organ model, and a testing cell.

According to the embodiments of the present disclosure, the image quality is enhanced.

The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present claims.

Claim 1:
A color chart (<NUM>) provided on a recording medium (<NUM>), comprising:
a first portion (<NUM>) including no patch; and
a second portion (<NUM>) including a plurality of patches having different densities or luminances,
the plurality of patches, including a reference patch (<NUM>) indicating a color having a reference density or luminance closest to the color of the recording medium,
the reference patch (<NUM>) being adjacent to the first portion (<NUM>),
the plurality of patches being located in order of increasing tones corresponding to any one of:
increasing density from the density of the color indicated by the reference patch (<NUM>);
decreasing density from the density of the color indicated by the reference patch (<NUM>);
increasing luminance from the luminance of the color indicated by the reference patch (<NUM>); and
decreasing luminance from the luminance of the color indicated by the reference patch (<NUM>);
characterized in that:
the second portion (<NUM>) is segmented into a plurality of areas inward, including a first area (<NUM>) adjacent to the first portion, and a second area (<NUM>) inward of the first area; and
the tones of the patches located in the second area are greater than the tones of the patches located in the first area.