KR101176848B1 - Scanning apparatus and white calibration method thereof - Google Patents

Abstract

Disclosed is a scanning device for white correction. The scanning device is composed of a plurality of three-dimensional blocks to generate a three-dimensional lookup table for converting an input RGB signal into a standard RGB signal, a lookup table generator, scans white paper (R) for each of R, G, B A minimum value calculator for calculating a minimum value, and a correction area detector for detecting a block area having a minimum size including a BG (Background) point and a white point, which are points at which the calculated R, G, and B minimum values meet on a three-dimensional lookup table. And a correction unit for correcting the data value of the detected block area to a white value. Accordingly, only the white region can be detected and corrected without affecting other color regions, thereby realizing an optimal color.

Scanning device, 3D lookup table, white correction

Description

Scanning apparatus and its white calibration method

The present invention relates to a scanning device and a white correction method thereof, and more particularly, to classify a 3D lookup table into a plurality of blocks, and to perform white correction on a block area including a minimum value and a white point of an input signal. A device and its white correction method.

A scanning device is a device that scans an original image such as a document, a picture, or a film and converts it into digital data. The digital data may be displayed on a monitor of a computer or printed by a printer to generate an output image. The scanning device can be used not only in a scanner for generating digital data, but also in a facsimile that provides a fax function, a copier and a multifunction device that provide a copy function, and the like.

On the other hand, when scanning the color image, since the color image may be changed by the factors causing the color change, it is necessary to convert the input signal in order to maintain the accuracy and homeostasis of the color. Accordingly, the scanning apparatus has a lookup table for calibrating the input RGB signal to a standard RGB signal.

However, even if scanning is performed using the lookup table, the color difference should be generated due to the conditioner color of the scanning device while the original image passes through the scanning device, or should be expressed in white color due to the foreign matter of the image sensor. The color is expressed in the part.

The conventional scanning device corrects white by the following method. White paper was scanned to detect the minimum value among the distributions of the R, G, and B values, and the data value above the minimum value was corrected to the white area on the one-dimensional lookup table.

According to FIG. 1A, a three-dimensional lookup table in which a white region is corrected on each one-dimensional lookup table can be confirmed. FIG. 1B is a view showing output results for each sample color R, G, B, K, C, M, and Y when the correction is performed as shown in FIG. 1A. FIG. 1C is a graph representing FIG. 1B. In FIG. 1C, when scanning without performing the white correction of the lookup table, conversion is performed according to the data of the lookup table, and thus color reproduction according to the characteristics of the scanning apparatus may not be solved. That is, the color is expressed in the white area.

1A to 1C, when the white region of the lookup table is corrected using the conventional white correction method, the saturation of the input image is increased to brighten the output image as a whole. Accordingly, there is a problem that the color reproduction is not good as the color is high (Lightness).

In addition, this problem can be confirmed through FIGS. 1D and 1E. FIG. 1D is a result of scanning without performing white correction, and FIG. 1E is a result of scanning according to the white correction method of the prior art. For a specific color gamut, values such as Hue, Saturation, Value, and Lightness can be shown as Table 1 and Table 2 below.

Here, Table 1 shows values for specific color gamuts 10, 20 and 30 in FIG. 1D, and Table 2 shows values for specific color gamuts 10, 20 and 30 in FIG. 1E.

[Table 1]

First area Second area Third area Hue 308 9 55 saturation 18 85 18 Value 98 75 99 Lightness 87 45 97

[Table 2]

First area Second area Third area Hue 279 10 67 saturation 9 85 7 Value 100 81 100 Lightness 94 48 99

Comparing Table 1 and Table 2, it can be seen that the saturation of the input image is increased and the output image is overall brightened. Also, it can be seen that the higher the color, the lower the reproducibility. That is, it can be seen that the color gamut of the first area 10 and the third area 30 is not as good as the color gamut of the second area 20. Accordingly, there is a need for a scanning device that can improve color reproducibility and perform white correction.

Accordingly, an object of the present invention is to solve the above problems, and an object of the present invention is to classify a three-dimensional lookup table into a plurality of blocks, and to white a block area including a minimum value and a white point of an input signal. The present invention provides a scanning device for performing correction and a white correction method thereof.

Another object of the present invention is to provide a scanning apparatus and a white correction method thereof, which improves color reproducibility by performing correction for each color region in a minimum block region detected as a white correction region.

The scanning device according to the present invention for achieving the above object is a lookup table generator for generating a three-dimensional lookup table for converting an input signal into a standard signal, the minimum value for each of R, G, B by scanning a white paper (white paper) A minimum value calculating unit for calculating a value, an area having a minimum size including a BG (Background) point, which is a point where each of the calculated R, G, and B minimum values meet on the 3D lookup table, and a white point of the 3D lookup table And a correction area detector for detecting a value, and a correction part for correcting a data value of the detected area with a white value.

Preferably, the correction area detector may detect a region having the smallest size among the regions where the gray axis of the three-dimensional lookup table is matched when a difference value of each of the R, G, and B minimum values is equal to or less than a reference value.

Preferably, the detected region may be a cube block.

Preferably, the correction region detector may detect a region of the minimum size in the color region having the smallest value among the minimum values if the difference value of each of the R, G, B minimum values is greater than or equal to the reference value.

Preferably, the detected area may be a rectangular block including the BG point as the vertex of the white point.

Preferably, the three-dimensional lookup table includes (2 ⁿ +1) × (2 ⁿ +1) × (2 ⁿ +1) color representative values and 2 ⁿ × 2 ⁿ × 2 ⁿ three-dimensional blocks. The reference value may be 256/2 ⁿ .

On the other hand, the scanning device according to another embodiment of the present invention, the storage unit for storing the three-dimensional lookup table for converting the input signal into a standard signal, and the minimum value for each of the R, G, B by scanning a white paper (White paper) Calculating an area of a minimum size including a BG point and a white point of the 3D lookup table, wherein the calculated R, G, and B minimum values meet each other; It includes a central processing unit.

Preferably, the central processing unit may perform a first correction on each color axis with respect to the white point in the detected area.

Preferably, the central processing unit substitutes the n th point on each color axis corresponding to the BG point, the difference value between the n th point and the minimum value calculated by the minimum value calculator, and the reference value into the following equation. First correction may be performed on the n th point.

Where Pn is the nth point, Pn 'is the correction point of Pn, Pw is the white point, a is the difference between the nth point and the minimum value, b is the reference value, c is the sum of a and b, and n is a natural number.

Preferably, the central processing unit may correct a value equal to or greater than the corrected n 'point to a white value.

Preferably, the central processing unit may correct the n + 1 point having a value smaller than the n th point by the reference value through the following equation.

Where P (n + 1) is the n + 1 point, and P (n + 1) 'is the correction point of P (n + 1).

Preferably, the central processing unit may perform a second correction according to the color distribution ratio based on each color axis in the detected area after the first correction is performed.

Preferably, the central processing unit may perform the second correction by substituting the correction point and the color distribution ratio in the following equation.

Weight_Ri = (Pi ') / 255

Weight_Gi = (Pi ') / 255

Weight_Bi = (Pi ') / 255

Composite_Ri = Ri * Weight_Gi * Weight_Bi

Composite_Gi = Gi * Weight_Ri * Weight_Bi

Composite_Bi = Bi * Weight_Ri * Weight_Gi (where i = {n, n + 1})

Where Weight_Ri is the R color distribution ratio of Pn ', P (n + 1)',

Weight_Gi is the G color distribution ratio of Pn ', P (n + 1)',

Weight_Bi is the B color distribution ratio of Pn ', P (n + 1)',

Ri is the nth point of the R axis, Gi is the nth point of the G axis, Bi is the nth point of the B axis,

Composite_Ri is an internal point corrected according to the color distribution ratio based on the R axis.

Composite_Gi is an internal point corrected according to the color distribution ratio based on the G axis.

Composite_Bi is an internal point corrected according to the color distribution ratio based on the B axis.

In the meantime, the white correction method of the scanning apparatus according to an embodiment of the present invention comprises the steps of: (a) scanning a white paper to calculate a minimum value for each of R, G, and B; and (b) input signals as standard signals. Detecting a region having a minimum size including a background point and a white point of the three-dimensional lookup table, wherein the calculated R, G, and B minimum values meet each other on the three-dimensional lookup table which is converted into the first and second values; And (c) correcting the data value of the detected region to a white value.

Preferably, in the step (b), if the difference value of each of the R, G, and B minimum values is equal to or less than a reference value, the area having the smallest size among the areas of which the gray axis of the three-dimensional lookup table is aligned is detected. .

Preferably, the detected region may be a cube block.

Preferably, in the step (b), if the difference between each of the R, G, and B minimum values is greater than or equal to the reference value, the area having the smallest size may be detected in the color area having the smallest value among the minimum values.

Preferably, the detected area may be a rectangular block including the BG point as the vertex of the white point.

Preferably, the three-dimensional lookup table includes (2 ⁿ +1) × (2 ⁿ +1) × (2 ⁿ +1) color representative values and 2 ⁿ × 2 ⁿ × 2 ⁿ three-dimensional blocks. The reference value may be 256/2 ⁿ .

Preferably, in the step (c), in the detected region, the first correction may be performed on each color axis from the white point.

Preferably, in the step (c), an n th point on each color axis corresponding to the BG point, a difference value between the n th point and the minimum value calculated by the minimum value calculator, and a reference value are expressed by the following equation. Substituting for, the first correction may be performed on the n th point.

Where Pn is the nth point, Pn 'is the correction point of Pn, Pw is the white point, a is the difference between the nth point and the minimum value, b is the reference value, c is the sum of a and b, and n is a natural number.

Preferably, in the step (c), the value above the corrected n 'point may be corrected to a white value.

Preferably, the step (c) may further include correcting the n + 1 point having a value smaller than the n th point by the reference value through the following equation.

Where P (n + 1) is the n + 1 point, and P (n + 1) 'is the correction point of P (n + 1).

Preferably, the step (c) may further include performing a second correction according to the color distribution ratio on the basis of each color axis in the detected region.

Preferably, in the step (c), the second correction may be performed by substituting the correction point and the color distribution ratio into the following equation.

Weight_Ri = (Pi ') / 255

Weight_Gi = (Pi ') / 255

Weight_Bi = (Pi ') / 255

Composite_Ri = Ri * Weight_Gi * Weight_Bi

Composite_Gi = Gi * Weight_Ri * Weight_Bi

Composite_Bi = Bi * Weight_Ri * Weight_Gi (where i = {n, n + 1})

Where Weight_Ri is the R color distribution ratio of Pn ', P (n + 1)',

Weight_Gi is the G color distribution ratio of Pn ', P (n + 1)',

Weight_Bi is the B color distribution ratio of Pn ', P (n + 1)',

Ri is the nth point of the R axis, Gi is the nth point of the G axis, Bi is the nth point of the B axis,

Composite_Ri is an internal point corrected according to the color distribution ratio based on the R axis.

Composite_Gi is an internal point corrected according to the color distribution ratio based on the G axis.

Composite_Bi is an internal point corrected according to the color distribution ratio based on the B axis.

As described above, according to the present invention, the 3D lookup table may be classified into a plurality of blocks, and white correction may be performed on a block area including a minimum value and a white point of an input signal.

In addition, it is possible to prevent the tone jumping from occurring by linearly correcting the brightness change for each color axis. In addition, finer correction may be performed by differently applying the white correction region for each color according to each color distribution ratio.

Accordingly, only the white region can be detected and corrected without affecting other color regions, thereby realizing an optimal color.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the present invention.

2 is a block diagram illustrating a configuration of a scanning apparatus according to an embodiment of the present invention. According to FIG. 2, the scanning apparatus 200 includes a lookup table generator 210, a minimum value calculator 220, a correction region detector 230, and a correction unit 240.

The lookup table generator 210 is configured of a plurality of three-dimensional blocks to generate a lookup table for converting an input signal into a standard signal. The lookup table generator 210 prints a test color chart for generating a lookup table, and then uses a measurement device such as a spectrophotometer and a colorimeter to measure the color provided from the printed color chart. Color.

Next, a color conversion lookup table (LUT) is formed in accordance with the International Color Consortium (ICC) standard using color signals input to the scanning apparatus 200 and colorimetric values measured using the measurement apparatus.

In this case, the look-up table if the respective colors in the n steps (n is a natural ^{number), (2 n +1) ×} (2 n +1) will have a × (2 ⁿ +1) of the representative color values. That is, the 9x9x9 lookup table has 729 representative values, and has digital values of 0, 32, 64, 96, 128, 224, and 256 for each step. In addition, 17 × 17 × 17 has 4913 representative values, and 0, 16, 32, 48, 64, 80 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256 for each step. Has a digital value of.

Here, the three-dimensional lookup table is divided into a plurality of blocks using eight neighboring representative values as vertices. ^{(2 n +1) × (2} n +1) × (2 n +1) If the size of the look-up table, 2 ⁿ × 2 ⁿ × 2 ⁿ is divided into three-dimensional blocks, unit blocks 256/2 ⁿ It has size x256 / 2 ⁿ x 256/2 ⁿ .

The minimum value calculator 220 scans a white paper to calculate a minimum value for each of R, G, and B. In this case, the scanned values of R, G, and B are output signals converted into standard RGB signals according to the three-dimensional lookup table generated by the lookup table generator 210.

The minimum value calculator 220 detects each distribution of the output RGB signal and detects a minimum value for each color.

The correction area detector 230 detects a block area having a minimum size including a background point and a white point, which is a point where each of the R, G, and B minimum values meet on the 3D lookup table.

Here, the detection of the correction region may be determined according to the size of each of R, G, and B minimum values. When the calculated distributions of the minimum values of R, G, and B each exist within the reference value, it is determined that they exist in the vicinity of the gray axis to detect the isotropic block region.

Here, the gray axis is an axis composed of representative values of the same values of R, G, and B.

Meanwhile, when the calculated distributions of the minimum values of R, G, and B deviate from the reference value, it may be determined that the color, which is the lowest value among the minimum values, is reproduced in the white region due to the characteristic of the specific color sensor. Accordingly, the correction region detector 230 detects the anisotropic block region in the color region that is the lowest value.

Here, when the size of the lookup table is ( ²ⁿ + 1) × ( ²ⁿ + 1) × ( ²ⁿ + 1), the reference value is 256 / ²ⁿ .

Meanwhile, a detection method of the correction region detector 230 will be described in detail with reference to FIGS. 4 and 5.

3 and 4 are schematic diagrams illustrating a method for detecting a white correction region using a 3D lookup table according to an exemplary embodiment. 4 is a schematic diagram for explaining the detection of the isotropic block region, and FIG. 5 is a schematic diagram for detecting the anisotropic block region. Here, a three-dimensional lookup table of 17x17x17 will be described as an example.

Referring to FIG. 3, when the R, G, and B minimum values calculated by the minimum value calculator 220 are 245, 224, and 242, the difference values between the minimum values may be equal to or less than the reference value. As a result, the isotropic block region is detected along the gray axis.

Here, the reference value is calculated as 256/2 ⁿ , it can be seen that the reference value is 16 because n is 4.

At this time, the isotropic block region has a gray axis as a gray segment, which is a line segment connecting one vertex of a unit block including a white point and a BG point whose R, G, and B minimum values are coordinate values. Here, the block area having the smallest size among the isotropic block areas including the BG points is detected as the region to be corrected, and the (R, G, B) values of the vertices P are (240, 240) as long as they form a coincidence with the white point. , 240). Therefore, the detected block area becomes a cube.

According to FIG. 4, when the R, G, and B minimum values calculated by the minimum value calculator 220 are 245, 224, and 242, the difference between the minimum values may be greater than or equal to the reference value. Here, the reference value is calculated as 256/2 ⁿ , it can be seen that the reference value is 16 because n is 4.

Accordingly, the anisotropic block region may be detected along the color gamut of G, which is the smallest value among the minimum values of R, G, and B. Specifically, the detected anisotropic block region is a rectangular body having a white point and a line segment connecting the (R, G, B) values 240, 224, and 240 of the point P as a pair. Here, the point P is one vertex of the unit block including the minimum values of R, G, and B, respectively.

The correction unit 240 corrects the data value of the block area detected by the correction area detector 230 to a white value. That is, the data value of the detected block area is converted into a (255, 255, 255) value to correct the three-dimensional lookup table.

5A is a graph showing an output value according to the white correction of the present invention. FIG. 5A is a graph illustrating output values for each color scanned using the 3D lookup table according to the correction of the isotropic block region of FIG. 3. According to FIG. 6A, it can be seen that the output value of K is converted without affecting other color gamuts.

5B is a diagram illustrating an output image output according to the white correction of the present invention. FIG. 5B is an output image output by scanning a color patch having the input value of FIG. 5A, and is an image reproduced with the output value of FIG. 5A. Referring to FIG. 5B, it can be seen that the white region is corrected without affecting other color regions.

Meanwhile, the correction unit 240 may perform finer correction by detecting only the white region based on the color distribution ratios of R, G, and B, among the smallest block regions detected by the correction region detector 230. .

In this case, the correction unit 240 performs the first correction along the respective axes of R, G, and B on the three-dimensional lookup table, and performs the second correction on the inside of the block area of the minimum size detected by the correction area detector 230. Do this.

The correction unit 240 corresponds to R, G, and B corresponding to the BG points RPn, GPn, and BPn of the block area including the minimum value and the minimum value of each of the R, G, and B values calculated by the minimum value calculation unit 220. The difference between the point and the minimum value of each axis, and the point having a value smaller than the BG point by the reference value and the point of each of the R, G, and B axes corresponding to the BG point P using the reference value 1 Perform calibration. Meanwhile, the points of the R, G, and B axes corresponding to the BG points P may be corrected through Equation 1.

Where Pn is a point on each of the R, G, and B axes corresponding to the BG point P, Pn 'is a correction point for correcting Pn, Pw is a white point, a is the difference between the Pn point and the minimum value, and b is Can be a reference value. Here, the white point is 255, and n is a natural number.

Meanwhile, a point having a value smaller than Pn by a reference value may be corrected through Equation 2.

Here, P (n + 1) is a point having a value smaller than Pn by a reference value, and P (n + 1) 'may be a corrected correction point of P (n + 1). Meanwhile, Equations 1 and 2 will be described in detail with reference to FIG. 7.

6 is a schematic diagram illustrating a white correction method according to another exemplary embodiment of the present invention. FIG. 6 may be an R axis, a G axis, and a B axis on a three-dimensional lookup table, and coordinates of each color representative value are represented by a first point P1, a second point P2,. This may be the m th point Pm. For example, a three-dimensional lookup table of 17 × 17 × 17 will be described as an example. The interval between each point, that is, the reference value is 16, the value of the first point P1 is 240, and the value of the second point P2 is 224. ,… The value of the sixteenth point P16 may be zero.

Herein, a scanning apparatus using a three-dimensional lookup table having minimum values R, G, and B of (245, 240, 228) and 17 × 17 × 17 will be described.

In this case, the BG points RPn, GPn, and BPn become (240, 240, 224). Therefore, RPn may be P1, that is, 240. In addition, P (n + 1) may be P2, that is, 224. Here, the coordinates of RPn on the 3D lookup table may be (240, 255, 255).

In this embodiment, the value a may be 5, the value b may be 16, and the value c may be 21. These values can be substituted into Equations 1 and 2 to compensate for the R axis.

From Equation 1, 251 is obtained as the correction value P1 'of P1. In addition, through Equation 2, 237 is obtained as the correction value P2 'of P (2). That is, with respect to the R axis, a value of 251 or more is corrected to a white value, that is, 255, and a color value existing between the corrected P2 to P1 has a value of 251 to 237.

Here, the color values present between the corrected P2 to P1 have a color distribution by the linear interpolation method according to Equation (2). Meanwhile, in Equation 2, only the correction value P (n + 1) 'of P (n + 1) by the linear interpolation method is performed, but a correction method by gamma correction or the like may be used.

In addition to the correction for the R axis, the correction is also performed for the G and B axes in the same manner as described above. Accordingly, it is possible to reduce a sudden change in brightness at each point, thereby preventing ton jumping, in which contours occur in the image.

The correction unit 240 is based on the R, G, and B axes corrected through Equations 1 and 2, and weights according to the color distribution ratio to each point existing in the area of the minimum size detected by the correction area detector 230. By applying, second finer correction can be performed. This second correction is hereinafter referred to as internal point correction.

On the other hand, the internal point correction can be calculated through the following equation (3).

Weight_Ri = (Pi ') / 255

Weight_Gi = (Pi ') / 255

Weight_Bi = (Pi ') / 255

Composite_Ri = Ri * Weight_Gi * Weight_Bi

Composite_Gi = Gi * Weight_Ri * Weight_Bi

Composite_Bi = Bi * Weight_Ri * Weight_Gi (where i = {n, n + 1})

Here, Weight_Ri is the R color distribution ratio of Pn 'and P (n + 1)' corrected in Equations 1 and 2, and Weight_Gi is Pn 'and P (n + corrected in Equations 1 and 2, respectively. 1) 'is the G color distribution ratio, and Weight_Bi is the B color distribution ratio of Pn' and P (n + 1) 'corrected in equations (1) and (2). In addition, Composite_Ri becomes an internal point corrected by applying each color distribution ratio as a weight.

Here, Pi 'is a correction point of Pi obtained by using the equations (1) and (2). Ri may be Pi of the R axis, Gi may be Pi of the G axis, and B may be Pi of the B axis. Here, Pi is an nth point and n + 1 point, which is Pn of Equation 1 and P (n + 1) of Equation 2.

In the present embodiment, only the point correction for the color representative values has been described, but it is preferable to apply the same to the numerous points between the color representative values. Accordingly, by precisely performing white correction for each color, color reproducibility may be improved by minimizing changes in color, saturation, and brightness.

7 is a block diagram illustrating a configuration of a scanning apparatus according to another embodiment of the present invention. According to FIG. 7, the scanning apparatus 300 includes a storage 310 and a central processor 320.

The storage unit 110 stores a 3D lookup table that converts an input signal into a standard signal. Here, the lookup table has (2 ⁿ +1) x (2 ⁿ +1) x (2 ⁿ +1) color representative values when each color is n steps (n is a natural number). That is, the 9x9x9 lookup table has 729 representative values, and has digital values of 0, 32, 64, 96, 128, 224, and 256 for each step. In addition, 17 × 17 × 17 has 4913 representative values, and 0, 16, 32, 48, 64, 80 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256 for each step. Has a digital value of.

Here, the three-dimensional lookup table is divided into a plurality of blocks using eight neighboring representative values as vertices. In the case of a lookup table of size (2 ⁿ +1) x (2 ⁿ +1) x (2 ⁿ +1), it is divided into 2 ⁿ × 2 ⁿ × 2 ⁿ three-dimensional blocks, and the unit block is 256/2. ⁿ x 256/2 ⁿ x 256/2 ⁿ .

The central processing unit 320 scans a white paper to calculate a minimum value for each of R, G, and B, and in the three-dimensional lookup table, BG, which is a point where each of the calculated minimums of R, G, and B meets. A minimum size area including a background point and a white point of the 3D lookup table is detected and corrected to a white value. The central processor 320 may be a component that performs the functions of the minimum value calculator 220, the correction region detector 230, and the correction unit 240 of FIG. 2.

Therefore, the central processing unit 320 performs the first correction on each color axis with the white point as the viewpoint in the minimum size region. In addition, after the first correction is performed, the second correction according to the color distribution ratio is performed based on each color axis in the region of the minimum size. Meanwhile, the first correction may be performed through Equations 1 and 2, and the second correction may be performed through Equation 3.

On the other hand, according to the correction of the central processing unit 320, the storage unit 310 is to store the three-dimensional lookup table that performed the white correction. That is, the storage unit 310 stores the 3D lookup table to which the white correction region is applied differently according to the color distribution ratio. Here, the white correction region of the 3D lookup table has a dynamic correction region pattern instead of a constant correction region pattern.

8 is a schematic diagram showing a result of performing white correction according to Equations 1 to 3; In the case of scanning the color chart under the same conditions as in FIGS. 1D and 1E, the result according to an exemplary embodiment of the present invention may be confirmed through the following table.

[Table 3]

First area Second area Third area Hue 308 9 57 saturation 18 85 17 Value 98 75 99 Lightness 87 45 98

Compared with Table 1 and Table 2, it can be seen that the color reproduction is improved while performing the white correction.

9 is a flowchart illustrating a white correction method of a scanning apparatus according to an embodiment of the present invention. According to FIG. 7, a three-dimensional lookup table composed of a plurality of three-dimensional blocks to convert an input signal into a standard signal is generated (S910). At this time, the three-dimensional lookup table colorizes the test color chart with a measuring device, and generates a color signal input to the scanning device 200 and colorimetric values measured by the measuring device. Here, the 3D lookup table may be generated with a size of (2 ⁿ +1) × (2 ⁿ +1) × (2 ⁿ +1).

Next, in order to detect the white correction region, a white paper is scanned to calculate a minimum value for each of R, G, and B (S920).

Specifically, each distribution of the RGB signal output by scanning white paper is detected, and a minimum value is detected for each color. In this case, the scanned values of R, G, and B are output signals converted into standard RGB signals according to the 3D lookup table.

Next, on the three-dimensional lookup table, a block area having a minimum size including a BG (Background) point and a white point, which is a point where each R, G, and B minimum value meets, is detected (S930).

Here, the detection of the correction region may be determined according to the size of each of R, G, and B minimum values. If the calculated distributions of the minimum values of each of R, G, and B are within the reference value, it is determined that they exist in the vicinity of the gray axis to detect the isotropic block region. Here, the gray axis represents a representative of the same values of R, G, and B. An axis consisting of values.

Meanwhile, when the calculated distributions of the minimum values of R, G, and B deviate from the reference value, it may be determined that the color, which is the lowest value among the minimum values, is reproduced in the white region due to the characteristic of the specific color sensor. Accordingly, the anisotropic block region is detected in the color region that is the lowest value. Here, the reference value may be 256/2 ⁿ .

Next, the data value of the detected block area is corrected to a white value (S940). Accordingly, only the white correction region can be detected and corrected without affecting other color regions.

10 is a flowchart illustrating a white correction method according to another exemplary embodiment of the present invention. Referring to FIG. 10, a three-dimensional lookup table composed of a plurality of three-dimensional blocks to convert an input signal into a standard signal is generated (S1100). Meanwhile, since the method of generating the 3D lookup table has been described with reference to FIG. 9, it will be omitted below.

Next, in order to detect the white correction region, a white paper is scanned to calculate a minimum value for each of R, G, and B (S1120).

Next, a block area of the minimum size including the minimum value point and the white point where each of the R, G, and B minimum values meet is detected (S1130). Here, the block area of the minimum size may be an isotropic block or anisotropic block including at least one unit block. Here, the vertex forming the tangent with the white point among the detected minimum block areas may be a BG point.

Next, by correcting the color representative value corresponding to each point included in the detected block size of the minimum size, it is possible to improve color reproduction and perform white correction. The first correction is performed along the axes of R, G, and B on the three-dimensional lookup table (S1300), and the second correction is performed on the inside of the block area of the smallest size (S1400).

Specifically, the minimum value of each of R, G, and B, the difference value between the point and the minimum value of each of the R, G, and B axes corresponding to the BG points (RPn, GPn, BPn) of the block area including the minimum value, and The first correction is performed by using points of each of the R, G, and B axes corresponding to the BG points Pn and points having a value smaller than the BG points by the reference value using the reference values.

Here, the points of each of the R, G, and B axes corresponding to the BG points Pn may be corrected through Equation 1. Here, a point having a value greater than or equal to the corrected point is corrected to a white value.

Meanwhile, a point having a value smaller than the BG point Pn by a reference value may be corrected through Equation 2. Accordingly, it is possible to reduce a sudden change in brightness at each point, thereby preventing ton jumping, in which contours occur in the image.

In addition, the second finer correction may be performed by applying a weight according to the color distribution ratio to each point existing in the region of the minimum size based on the R, G, and B axes corrected through Equations 1 and 2. . On the other hand, the internal point correction can be calculated through the following equation (3). Accordingly, by precisely performing white correction for each color, color reproducibility may be improved by minimizing changes in color, saturation, and brightness.

Next, the 3D lookup table is converted by applying the corrected value (S1500).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention.

1A to 1E are schematic views for explaining a conventional white correction method;

2 is a block diagram showing a configuration of a scanning apparatus according to an embodiment of the present invention;

3 and 4 are schematic diagrams for explaining a method for detecting a white correction region using a 3D lookup table according to an embodiment of the present invention;

5A is a graph showing level values according to white correction of the present invention;

5B is a view showing an output image output according to the white correction of the present invention;

6 is a schematic view for explaining a white correction method according to another embodiment of the present invention;

7 is a block diagram showing a configuration of a scanning apparatus according to another embodiment of the present invention;

8 is a schematic diagram showing an output image output by the white correction method according to another embodiment of the present invention;

9 is a flowchart illustrating a white correction method of a scanning apparatus according to an embodiment of the present invention;

10 is a flowchart illustrating a white correction method of a scanning apparatus according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawing

200: scanner 210: lookup table generation unit

220: minimum value calculation unit 230: correction area detection unit

240: correction unit

Claims (25)

A lookup table generating unit generating a 3D lookup table for converting an input signal into a standard signal; A minimum value calculator configured to scan a white paper and calculate a minimum value for each of R, G, and B; A correction area detector for detecting a minimum size area on the three-dimensional lookup table including a BG point and a white point of the three-dimensional lookup table; And a corrector configured to correct data values of the detected area to white values. The method of claim 1, The correction region detector, And if the difference between the minimum R, G, and B minimum values is less than or equal to a reference value, a region having the smallest size among regions for which the gray axis of the three-dimensional lookup table is aligned. 3. The method of claim 2, And the detected region is a cube block. The method of claim 1, The correction region detector, And if the difference between the minimum R, G, and B minimum values is greater than or equal to a reference value, detecting a minimum size area in a color area having the smallest value among the minimum values. 5. The method of claim 4, And the detected region is a rectangular block having the white point as a vertex and including the BG point. The method according to claim 2 or 4, The three-dimensional lookup table includes (2 ⁿ +1) x (2 ⁿ +1) x (2 ⁿ +1) color representative values and 2 ⁿ x 2 ⁿ x 2 ⁿ three-dimensional blocks. Scanning device, characterized in that 256/2 ⁿ . A storage unit for storing a three-dimensional lookup table for converting an input signal into a standard signal; White paper is scanned to calculate a minimum value for each of R, G, and B, and in the three-dimensional lookup table, a point BG (Background) point and the point where each of the calculated R, G, and B minimum values meet And a central processing unit which detects an area of a minimum size including a white point of the 3D lookup table. The method of claim 7, wherein The central processing unit, And in the detected area, perform a first correction on each color axis using the white point as a viewpoint. 9. The method of claim 8, The central processing unit, An nth point on each color axis corresponding to the BG point, a difference value between the nth point and a minimum value calculated by the minimum value calculator, and a reference value by substituting the following equation into a first point for the nth point. A scanning device, characterized in that to perform a calibration:

Where Pn is the nth point, Pn 'is the correction point of Pn, Pw is the white point, a is the difference between the nth point and the minimum value, b is the reference value, c is the sum of a and b, and n is a natural number. 10. The method of claim 9, The central processing unit, And a white value corrected above the corrected n 'point. The method of claim 10, The central processing unit, A scanning device, characterized in that for correcting the n + 1 point having a value smaller than the n-th point by the reference value through the following equation:

Where P (n + 1) is the n + 1 point, and P (n + 1) 'is the correction point of P (n + 1). 12. The method of claim 11, The central processing unit, And after the first correction is performed, performing a second correction according to a color distribution ratio on the basis of each color axis in the detected region. The method of claim 12, The central processing unit, The scanning device, characterized in that for performing the second correction by substituting the correction point and the color distribution ratio in the following equation: Weight_Ri = (Pi ') / 255 Weight_Gi = (Pi ') / 255 Weight_Bi = (Pi ') / 255 Composite_Ri = Ri * Weight_Gi * Weight_Bi Composite_Gi = Gi * Weight_Ri * Weight_Bi Composite_Bi = Bi * Weight_Ri * Weight_Gi (where i = {n, n + 1}) Where Weight_Ri is the R color distribution ratio of Pn ', P (n + 1)', Weight_Gi is the G color distribution ratio of Pn ', P (n + 1)', Weight_Bi is the B color distribution ratio of Pn ', P (n + 1)', Ri is the nth point of the R axis, Gi is the nth point of the G axis, Bi is the nth point of the B axis, Composite_Ri is an internal point corrected according to the color distribution ratio based on the R axis. Composite_Gi is an internal point corrected according to the color distribution ratio based on the G axis. Composite_Bi is an internal point corrected according to the color distribution ratio based on the B axis. (a) scanning a white paper to calculate a minimum value for each of R, G, and B; (b) On a three-dimensional lookup table for converting an input signal into a standard signal, a BG (Background) point, which is a point where each of the calculated R, G, and B minimum values meet, and a white point of the three-dimensional lookup table are included. Detecting an area of minimum size; And (c) correcting the data value of the detected area to a white value. The method of claim 14, In step (b), And if the difference between the minimum R, G, and B minimum values is equal to or less than a reference value, detecting a region having a minimum size among the regions having the gray axis of the three-dimensional lookup table aligned. 16. The method of claim 15, And said detected region is a cube block. The method of claim 14, In step (b), And detecting a region having a minimum size in a color region having the smallest value among the minimum values when the difference between the minimum values of R, G, and B is equal to or greater than a reference value. 18. The method of claim 17, And the detected region is a rectangular block having the white point as a vertex and including the BG point. The method according to claim 15 or 17, The three-dimensional lookup table includes (2 ⁿ +1) x (2 ⁿ +1) x (2 ⁿ +1) color representative values and 2 ⁿ x 2 ⁿ x 2 ⁿ three-dimensional blocks. White correction method, characterized in that 256/2 ⁿ . The method of claim 14, In the step (c), in the detected region, the first correction is performed on each color axis based on the white point. 21. The method of claim 20, Step (c) is, An nth point on each color axis corresponding to the BG point, a difference value between the nth point and a minimum value calculated by the minimum value calculator, and a reference value by substituting the following equation into a first point for the nth point. A white correction method characterized by performing a correction:

Where Pn is the nth point, Pn 'is the correction point of Pn, Pw is the white point, a is the difference between the nth point and the minimum value, b is the reference value, c is the sum of a and b, and n is a natural number. 22. The method of claim 21, Step (c), the white correction method characterized in that for correcting the value of the corrected n 'point or more to a white value. 23. The method of claim 22, Step (c) is, And correcting the n + 1 point having a value smaller than the n th point by the reference value through the following equation.

Where P (n + 1) is the n + 1 point, and P (n + 1) 'is the correction point of P (n + 1). 24. The method of claim 23, Step (c) is, And performing a second correction according to a color distribution ratio on the basis of each color axis in the detected area. 25. The method of claim 24, In the step (c), the second correction is performed by substituting the correction point and the color distribution ratio in the following equation: Weight_Ri = (Pi ') / 255 Weight_Gi = (Pi ') / 255 Weight_Bi = (Pi ') / 255 Composite_Ri = Ri * Weight_Gi * Weight_Bi Composite_Gi = Gi * Weight_Ri * Weight_Bi Composite_Bi = Bi * Weight_Ri * Weight_Gi (where i = {n, n + 1}) Where Weight_Ri is the R color distribution ratio of Pn ', P (n + 1)', Weight_Gi is the G color distribution ratio of Pn ', P (n + 1)', Weight_Bi is the B color distribution ratio of Pn ', P (n + 1)', Ri is the nth point of the R axis, Gi is the nth point of the G axis, Bi is the nth point of the B axis, Composite_Ri is an internal point corrected according to the color distribution ratio based on the R axis. Composite_Gi is an internal point corrected according to the color distribution ratio based on the G axis. Composite_Bi is an internal point corrected according to the color distribution ratio based on the B axis.

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