TW202024585A - Color calibration method using a visible light source and an invisible light source to irradiate a color block respectively - Google Patents

Abstract

The present invention relates to a color calibration method which uses a visible light source and an invisible light source to irradiate a color block respectively, and captures and analyzes a first image and a second image through an image capturing device to obtain a first chromaticity value and a second chromaticity value. In addition, the visible light source and the invisible light source are used to respectively calculate and obtain a first illuminance ratio and a second illuminance ratio, and then a corrected chromaticity value of the color block is obtained by weighted computation to achieve the purpose of color calibration.

Description

How to verify color

The present invention relates to a verification method, particularly a method for verifying color.

Inkjet printing refers to a printing method that uses a computer to attach ink from nozzles to the substrate to obtain graphics and text. Traditional inkjet printing technology is based on the principle of inkjet printing and is developed on the basis of inkjet printer technology. Got up. The predecessor of the large-format color inkjet printer was a pen plotter. In 1991, its inkjet printing technology was applied to a large-format printer for the first time, and the inkjet technology was first introduced into the field of engineering graphics. After 1994, large format inkjet printers have been widely used in the inkjet industry. In recent years, many printing equipment manufacturers have applied the new technology of ordinary color inkjet printers to large-format inkjet printers, such as tiny ink droplets, split ink cartridges, color layering and multicolor inks, micro-pressure Electric technology, etc. At the same time, large-format color inkjet printers have been favored by users in various industries for their fast, flexible and exquisite output, which has strongly promoted the development of inkjet printing technology and inkjet printers.

Inkjet printing technology is a technology that uses inkjet output and thermal transfer to copy color images to fabrics. It has the advantages of a small amount of diversified production and reduced waste water discharge. It has gradually become a new generation of mainstream textile printing technology.

In order to make the printing color more vivid, the inkjet printing technology adds fluorescent pink and fluorescent yellow to the general four-color inks of cyan, magenta, yellow and black (usually abbreviated as CMYK, which is a non-fluorescent color). (Abbreviated as Fp and Fy) fluorescent color printing, make the color after inkjet printing more vivid and bright. CMYKFpFy six primary colors can use multi-color inkjet output machine. In this way, the color gamut can be expanded, and a variety of special color printing patterns can be output.

However, one of the purposes of inkjet printing is "multi-color mixing" printing, which includes the above-mentioned mixture of fluorescent colors and non-fluorescent colors. In order to accurately predict the color performance of different ink colors under various dot mixing ratios, the color guide table used must also have dot combination guide color blocks of multiple color inks. In fact, printing multi-color inks in one area at the same time can easily make the color turbid and black, and the color adhesion of this area may also deteriorate. Therefore, it is not advisable to use too much ink to print.

Moreover, when the color guide meter uses the measuring instrument to measure the color data, it usually only measures the color data of the non-fluorescent color system, because the general contact measuring instrument does not have sufficient ultraviolet light source, so it cannot be used. Get the color data of fluorescent ink under invisible light environment by contact measuring instrument.

Therefore, through the design of the guide table, the present invention restricts that only four color ink dot combinations can be used for printing a block, such as CMYK, CMFpK, CYFyK, or FpFyCK. Although there are other four-color combinations (such as FpFyYK, etc.), because the color gamuts of some combinations overlap, it is not necessary to use a color combination with a high color repetition rate in the present invention. A guide table composed of a combination of these four-color ink dots is used to capture the color guide table images under different light sources through an image capture device, and the chromaticity values of the guide table under visible light and ultraviolet light (UV) can be obtained through calculation.

Based on the above content, in order to accurately estimate the color performance, the present invention provides a method for testing color, which transmits the invisible light (UV light) and visible light (VIS) light source to irradiate the color guide block obtained by inkjet printing. , Capture the chromaticity images of the color guides under the two light sources, and use the visible light meter and the invisible light meter to measure the illuminance ratio between the target use environment and the image capture environment. A weighted formula can be used to calculate Guide the color value of the color block in the target environment. Through this chromaticity value, the effect of color reproduction can be predicted, and the color performance of the combined color system of fluorescent and non-fluorescent colors under different ultraviolet light sources can be clearly analyzed.

An object of the present invention is to provide a method of inspecting color. Using an image capturing device that can convert images into chromaticity values, the color guide blocks output by the inkjet printer are irradiated under a visible light source and an invisible light source to obtain the guide color blocks under a visible light source and an invisible light source. image. In addition, a visible illuminance meter and an invisible light (ultraviolet light) illuminance meter are used to measure the illuminance ratio between the target use environment and the image capturing environment, and a weighting formula is used to calculate the chromaticity value of the guide meter under the target use environment. Calculating the chromaticity values under visible light and invisible light separately can more accurately predict the color performance of fluorescent colors under different ultraviolet light intensities. Make the color of the print with fluorescent ink mixed color from the original unpredictable color performance to the predictable color performance.

In view of the above-mentioned object, the present invention provides a method for verifying color. The steps include: using an image capturing device under a visible light source and an invisible light source to capture a first image and a first image of the color block respectively Two images, where the color block has a chromaticity data. Then, the first image and the second image are converted into a first chromaticity value and a second chromaticity value, respectively. According to a first illuminance ratio of the visible light source and a second illuminance ratio under the invisible light source, the first chromaticity value and the second chromaticity value are respectively weighted and summed to obtain a correction Chroma value. Finally, adjust the chromaticity data of the color block with the corrected chromaticity value.

The present invention provides an embodiment, wherein the color block obtains the first illuminance ratio and the second illuminance ratio according to the visible light source and the invisible light source in the target use environment and the image capturing environment.

The present invention provides an embodiment in which the color block is taken from one of the colors of a color guide output by a color output device.

The present invention provides an embodiment, wherein after the step of capturing a first image and a second image of a color patch under the illumination of a visible light source and an invisible light source using an image capturing device, the method further includes the step of: The color block performs a brightness uniformity correction procedure and a color gradation linearization correction procedure.

The present invention provides an embodiment, wherein the brightness uniformity correction program uses the inner difference operation and sums up a plurality of color block rows and the brightness parameters of the color block, wherein the color block rows are composed of black, gray, The white three-color blocks are arranged and combined in order.

The present invention provides an embodiment, wherein the color gradation linearization correction program calculates the color gradation curve contained in a first region of the color guide, and the calibration result of the brightness uniformity correction program is used as a reference basis Adjust the color level.

The present invention provides an embodiment, wherein the illuminance value of the visible light source is 10 to 2000 Lux, and the illuminance value of the invisible light (ultraviolet light) is 0 to 1000 mW/cm ² .

In order to enable your reviewer to have a better understanding and understanding of the features of the present invention and the effects achieved, the preferred embodiments and detailed descriptions are provided. The description is as follows:

Hereinafter, various embodiments of the present invention will be described in detail by using drawings. However, the concept of the present invention may be embodied in many different forms and should not be construed as being limited to the exemplary embodiments described herein.

The advantage of the present invention is to clarify the influence of visible light and invisible light on the ink color. The fluorescent and non-fluorescent effects of fluorescent inks can be quantified and described separately. In the target environment where visible light and invisible light are mixed, the chromaticity value of the mixed ink can be accurately estimated.

Therefore, the present invention improves a color inspection method, which combines the image capturing device to obtain the image of the guide meter color block of the visible light source and the invisible light source. Through a weighting formula calculation, the color guide meter can be obtained in different colors. Chromaticity value under lighting environment. If you want to present a specific chromaticity value under a specific lighting environment, you can use the difference in the guide color block to substitute different ink dot combinations to find the dot combination with the smallest color difference to print the guide color block.

First of all, please refer to Fig. 1, which is a schematic flow chart of a method for color verification according to a preferred embodiment of the present invention. The method steps are: Step S10: Use an image capturing device under visible light source and invisible light source, Capture the first image and the second image of the color block respectively, wherein the color block has chromaticity data; Step S20: separately analyze the first image and the second image to obtain the first chromaticity value and the second chromaticity Step S30: According to the target use environment and the image capturing environment, the first illuminance ratio of the visible light source and the second illuminance ratio under the invisible light source are respectively weighted with the first chromaticity value and the second chromaticity value Calculate and add up to obtain the corrected chromaticity value in the target use environment; and step S40: adjust the chromaticity data of the color block with the corrected chromaticity value.

Continuing the above, please refer to Figure 2 together, which is a schematic flow diagram of the steps of checking color in a preferred embodiment of the present invention. In step S10, a color block 126 is used to pass through the image capturing device 14 capable of converting images into chromaticity values, and a visible light source 132 and an invisible light source 134 are used for capturing, and a first image 122 and a second image are obtained. Two images 124.

Wherein, the color patch 126 is taken from a guide color patch 12 output by a color output device 11. The color block 126 has a chromaticity data 128, which represents color data perceived by the human eye, such as CIE XYZ tristimulus values.

Then, as described in step S20, the first image 122 and the second image 124 are separately analyzed to obtain a first chromaticity value XYZ _vis and a second chromaticity value XYZ _uv , wherein the first chromaticity value The value XYZ _vis is obtained under the visible light source 132, and the invisible light source 134 used when the image capturing device 14 captures the second image 124 generates more noise. Therefore, in order to reduce the noise Influence, the second chromaticity value XYZ _uv obtained by the invisible light source 134 needs to be simultaneously turned on the visible light source 132 and the ultraviolet light source 134 for measurement, and then simultaneously subtract the first measured value under the visible light source 132 The chromaticity value XYZ _vis can obtain the second chromaticity value XYZ _uv .

，與影像擷取環境的照度

，利用公式(1)獲得目標使用環境與影像擷取環境下的可見光照度比值S_vis 。此外，用可見光照度儀量測目標使用環境的照度

，與影像擷取環境的照度

，利用公式(2)獲得目標使用環境與影像擷取環境下的該可見光光源132之一第一照度比值S_vis 。與不可見光(紫外光)照度儀量測目標使用環境與影像擷取環境下之一第二照度比值。依據目標使用環境與影像擷取環境下，該可見光光源132的該第一照度比值S_vis ，以及該不可見光源134下的該第二照度比值S_uv ，透過公式(3)進行加權運算，獲得該目標使用環境下的校正色度值XYZ_mix 。。

(1)

(2)

(3)Use a visible light meter to measure the illuminance of the target environment

, And the illuminance of the image capture environment

, Using formula (1) to obtain the ratio of visible illuminance S _{vis between the} target use environment and the image capturing environment. In addition, use a visible light meter to measure the illuminance of the target environment

, And the illuminance of the image capture environment

, Using formula (2) to obtain the first illuminance ratio S _vis of one of the visible light sources 132 in the target use environment and the image capturing environment. The ratio of the second illuminance to the invisible light (ultraviolet light) illuminance meter to measure the target use environment and the image capturing environment. According to the target use environment and the image capturing environment, the first illuminance ratio S _{vis of} the visible light source 132 and the second illuminance ratio S _uv under the invisible light source 134 are weighted by formula (3) to obtain The corrected chromaticity value XYZ _mix under the target use environment. .

(1)

(2)

(3)

The above description is the method of using the color block 126 to verify the color. From the above description, it can be seen that the present invention can not only be used to verify the chromaticity data 128 of a single color block, but also can use the complete color guide block 12 for calibration. Check color. A practical example is listed below. The inventor uses the color output device 11 to output the color guide block 12, and puts the color guide block 12 into the light box 13, which contains the visible light source 132 and the non The visible light source 134 uses the visible light source 132 and the invisible light source 134 to illuminate the color guide block 12, and then uses the image capturing device 14 to individually capture the color guide block 12 to illuminate the visible light source 132 and the invisible light source The first image 122 and the second image 124 generated by 134. And analyze the first chromaticity value XYZ _{vis of} the first image 122 and the second chromaticity value XYZ _{uv of the} second image 124. A visible light meter is used to measure the first illuminance ratio S _vis between the target use environment and the image capturing environment, and the second illuminance ratio S _uv under the ultraviolet light under the ultraviolet light source. After the weighting operation is performed by formula (3), the estimated chromaticity value XYZ _mix under the target use environment can be obtained. Then, the calibration chromaticity value XYZ _{mix is used} to verify the chromaticity data 128 on the standard color card 12, and a calibration guide color block 18 is obtained after the verification is completed.

After the verification is completed, the calibration guide color block 18 can be used for comparison with an image 15. After the comparison, an image chromaticity value 17 is obtained and can be used to output the image. The present invention can be applied to large image output equipment or Ink dot printing equipment, etc.

In addition, if it is necessary to measure multiple color guide meters at a time, it is traditionally necessary to place and measure the color guide meters 12 separately. The traditional method takes a long time, and the present invention designs the color guide block 12 as a small square of about 1 cm ^2. The color guide block 12 has 396 color blocks, and there are 18 and 22 colors in the vertical and horizontal directions. Piece. These color blocks can use the aforementioned color calibration method to estimate the chromaticity value XYZ _mix under the target use environment. These 396 color blocks can be used to infer the effect of four primary colors overprinting. The following will take CMYK as an example. It can also be used in CMFpK, CYFyK or FpFyCK and other ink dot combinations. In the method of checking colors of the present invention, at least one color block 126 can be detected.

As shown in Figure 4, it is a schematic diagram of a color uniformity calibration procedure for checking color according to a preferred embodiment of the present invention. When performing the calibration of the guide color block 12 (396 color blocks), in order to avoid using light sources The resulting uneven illumination results in the error of the chromaticity data 128. Therefore, the present invention arranges the standard color card 12 in the first, eighth, fifteenth, and 22nd columns in order of black, gray, and white. The multiple color block rows 129 calculate the brightness value of the white image through the linear inner difference of the above four rows, divide the XYZ chromaticity image point-to-point by the white inner difference image, and multiply it by the average value of the central area of the white image. The uniformity of the XYZ chromaticity image is corrected, and the three XYZ channels are respectively calculated according to the brightness uniformity correction procedure described above to obtain an XYZ chromaticity image with uniform illumination.

色差與網點值繪製成一條曲線，根據這個曲線將網點值換算成跟色差線性相關的「線性設備訊號值」，由於接下來要在CIELAB色空間做線性內差，因此對計算色差的CIELAB空間作線性化校正，可提高接下來4D對照表線性內差的準確度。本發明係採用照明均勻化後的白色色塊XYZ做為參考白值。Then perform a color gradation linearization correction program on the guide color block 12, as shown in Figure 4, the first zone contains 36 color blocks, which are the 12-level color of the three-color ink in the standard color card. Order (change in dot size). The purpose of these gradations is to do "gradation linearization" correction, that is, to adjust the CIE ∆ between the monochrome ink of the inkjet device and the white color.

The color difference and the dot value are drawn as a curve. According to this curve, the dot value is converted into a "linear device signal value" linearly related to the color difference. Since the linear internal difference is to be done in the CIELAB color space next, the CIELAB space for calculating the color difference is calculated Linearization correction can improve the accuracy of the linear internal error of the next 4D comparison table. In the present invention, the white color block XYZ after uniform illumination is used as the reference white value.

After using the above-mentioned brightness uniformity calibration procedure and color scale linearization calibration procedure, the corresponding chromaticity data is obtained through the difference in the 4D comparison table, and the high-resolution comparison table is used in the high brightness area (more color samples), Use low-resolution low-level comparison tables in low-brightness areas.

As shown in Fig. 5A to Fig. 5C, it is a schematic diagram of the 4D calibration procedure for checking color of a preferred embodiment of the present invention. Since black directly affects the brightness of the color, the three primary colors of 0% black dots are superimposed, as shown in One of the first color C, the second color M, and the third color Y shown in Figure 5A use a higher-resolution 6´6´6 three primary color standard color card (the second area shown in Figure 5A) Zone 2); Overprint the three primary colors of medium brightness with 20% black dots, use the 4´4´4 three primary color standard color card with medium resolution (the third zone shown in Figure 5B); Overprint the low of 70% black dots For the three primary colors of brightness, only use the 2´2´2 standard color card of the three primary colors (the fourth zone as shown in Figure 5C). Taking the four primary colors of CMYK as an example, first calculate the CMY linearization signal value and K value (black is recommended) through the 3D comparison table inner difference method, and the inner difference operation is used to overprint the CIELAB colors of 0%, 20%, and 70% black ink. Calculate the CIELAB chromaticity value under the designated black dot value through the linear inner difference of these several CIELAB chromaticity values.

The above process can calculate the chromaticity value of a four-color dot combination through the information in the image capturing environment and the individual illuminance ratios of visible light and ultraviolet light in the environment and the target use environment. If you want to make the printed color meet the corrected chromaticity value under the target use environment, you can use iterative convergence method to test the chromaticity value estimated by the above process for countless four-color dot combinations, and take the smallest error from the corrected chromaticity value The combined output of dots can meet the requirements of color correction.

Fluorescence has its particularity. The invisible light intensity ratio can only predict the performance of fluorescent color within a certain range. The fluorescent effect has an upper limit for the luminous intensity. The use of ultra-high illuminance invisible light sources may not increase the brightness proportionally. In addition, temperature will also affect the fluorescent intensity, and the increase in temperature will cause the intensity to decrease. Therefore, the color verification method of the present invention is only applicable to the visible light source 132 (10 to 2000 Lux) and the invisible light source 134 (, 0 to 1000 mW/cm ² ) of medium and low brightness and room temperature environments.

為波長(nm)，

為標準光度函數，J(λ)為光譜分步的功率強度(W/nm)，由於標準光度函數分布在380nm到780nm間，故僅有此區段的光譜能夠被轉換為亮度，這亦表示僅此區段的光譜為該可見光光源132之光譜，而不可見光光源134則因發光波段為380nm以下，屬於人眼無法辨識之光源，因此無標準光度函數分佈，僅可以光源功率來計算該不可見光光源強度，所以本發明之該可見光光源132以Lux做為光源單位，該不可見光光源134以mW/cm² 為不可見光之光源單位。

(4)The above-mentioned luminous flux calculation method of the visible light source 132 and the invisible light source 134 is calculated by formula (4), where F is the luminous lumens and K is the human eye’s ability to perceive colors.

Is the wavelength (nm),

Is the standard luminosity function, J(λ) is the power intensity (W/nm) of the spectral step. Since the standard luminosity function is distributed between 380nm and 780nm, only this section of the spectrum can be converted into brightness, which also means Only the spectrum of this section is the spectrum of the visible light source 132, while the invisible light source 134 is a light source that cannot be recognized by the human eye because the emission band is below 380nm. Therefore, there is no standard luminosity function distribution. Only the power of the light source can be used to calculate the difference. The intensity of the visible light source, so the visible light source 132 of the present invention uses Lux as the light source unit, and the invisible light source 134 uses mW/cm ² as the invisible light source unit.

(4)

The above-mentioned embodiment, the method of the present invention, provides a method of color inspection, which combines the image capturing device to obtain the image of the visible light source and the invisible light source respectively, and through a weighting formula calculation, the color image clearly has The combination of fluorescent colors and non-fluorescent colors enables inkjet printers to print objects with bright colors without making the colors cloudy or black.

However, the above are only the preferred embodiments of the present invention, and are not used to limit the scope of implementation of the present invention. For example, the shapes, structures, features and spirits described in the scope of the patent application of the present invention are equally changed and modified. , Should be included in the scope of patent application of the present invention.

11: Color output device 12: Guide color block 122: First image 124: Second image 126: Color block 128: Chromaticity data 129: Color block row 13: Light box 132: Visible light source 134: Invisible light source 14: Image Capture device 15: image 17: image chromaticity value 18: correction guide color block S _vis : first illuminance ratio XYZ _vis : first chromaticity value _Suv : second illuminance ratio XYZ _uv : second chromaticity value XYZ _mix : calibrated chromaticity value Zone1: first zone Zone2: second zone Zone3: third zone Zone4: fourth zone C: first color M: second color Y: third color S10: use image capture device in visible light Under the illumination of the light source and the invisible light source, respectively capture the first image and the second image of the color block, where the color block has chromaticity data S20: separately analyze the first image and the second image to obtain the first chromaticity value And the second chromaticity value S30: according to the first illuminance ratio of the visible light source under the target use environment and the image capturing environment, and the second illuminance ratio under the invisible light source, respectively, the first chromaticity value and the second chromaticity value Perform weighting operations and add them together to obtain the corrected chromaticity value S40: Adjust the chromaticity data of the color block with the corrected chromaticity value

Figure 1: It is a schematic flow diagram of the color verification method of a preferred embodiment of the present invention; Figure 2: It is a schematic flow diagram of the steps of verifying color according to a preferred embodiment of the present invention; Figure 3: It It is a schematic diagram of the output step flow diagram of the inspection color in a preferred embodiment of the present invention; Figure 4: It is a schematic diagram of the brightness uniformity correction procedure of the inspection color in a preferred embodiment of the present invention; and Figures 5A-5C: it It is a schematic diagram of the 4D calibration procedure of color rendering in a preferred embodiment of the present invention.

S10: Use an image capturing device to capture the first image and the second image of the color block under the illumination of a visible light source and an invisible light source, where the color block has chromaticity data

S20: Analyze the first image and the second image individually to obtain the first chromaticity value and the second chromaticity value

S30: According to the first illuminance ratio of the visible light source under the target use environment and the image capturing environment, and the second illuminance ratio under the invisible light source, perform a weighted calculation with the first chromaticity value and the second chromaticity value and add them In total, get the corrected chromaticity value

S40: Adjust the chromaticity data of the color block with the corrected chromaticity value

Claims (7)

A method for color verification, the steps of which are: Use an image capture device under a visible light source and an invisible light source, and capture a first image and a second image of a color block respectively, wherein the color The block has a chromaticity data; analyze the first image and the second image individually to obtain a first chromaticity value and a second chromaticity value; according to a first illuminance ratio of the visible light source, and the invisible light source A second illuminance ratio is respectively weighted with the first chromaticity value and the second chromaticity value and added together to obtain a corrected chromaticity value; and adjust the chromaticity of the color block with the corrected chromaticity value data. Such as the method for verifying color as described in item 1 of the scope of application, wherein the color block is based on the visible light source and the invisible light source in the target use environment and the image capturing environment to obtain the first illuminance ratio and the second Illuminance ratio. The method for verifying color as described in item 1 of the scope of application, wherein the color block is taken from one of the colors of a guide color block output by a color output device. The method for color verification as described in item 1 of the scope of application, wherein an image capturing device is used to capture a first image and a second image of a color block under the illumination of a visible light source and an invisible light source. After the steps, it further includes the steps of: performing a brightness uniformity correction procedure and a color scale linearization correction procedure on the color block. The method for verifying color as described in item 4 of the scope of application, wherein the brightness uniformity correction program uses the inner difference operation and sums up a plurality of color block rows and the brightness parameter of the color block, wherein the colors The block row is composed of black, gray, and white color blocks in sequence. For the method of color verification described in item 4 of the scope of application, the color gradation linearization correction program is to calculate the color gradation curve contained in the first area of the color guide block, and through the brightness uniformity correction program The calibration result is used as a reference to adjust the color level. For the method of color verification described in item 1 of the scope of application, the illuminance value of the visible light source is 10 to 2000 Lux, and the illuminance value of the invisible light (ultraviolet light) is 0 to 1000 mW/cm ² .

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