Density measurement has always been the most common measurement method in the printing industry, but density meters do not provide psychophysical quantities related to human eye sensitivity, so their analytical measurement capabilities are limited. Therefore, color measurement plays an increasingly important role in the detection and evaluation of printed matter. In the color measurement, in order to obtain measurement data that can accurately reflect the quality of the print, the following points must be noted. Whiteboard correction Since the densitometer and the spectrophotometer are very sophisticated instruments, the calibration of the measuring instrument is performed before the measurement to ensure the accuracy of the measurement results. In general, each device is equipped with a standard whiteboard, such as the DensiEye750 density meter and the X-Rite500 series spectrophotometer. According to the purpose of measuring the data, we choose to perform zero adjustment on the whiteboard or on white paper, set the correction warning, and if the calibration time is exceeded, the whiteboard should be corrected. 2. Substrate The color measurement values ​​will have different chromaticity values ​​depending on the substrate selected for the measurement. The effect of the black and white substrates on the color measurement will vary depending on the transparency of the substrate, and the greater the transparency, the greater the substrate will be affected by the substrate. Therefore, in the high-quality printing production and color matching inspection process, it should be noted that the correct substrate is placed and used on the inspection table. It is generally recommended to use the following standards: When the opacity of the substrate is greater than or equal to 99, the measurement results will not be affected by the substrate. When the opacity is between 95 and 99, the color should be measured with a black substrate and the opacity is less than A white substrate was used at 95 hours. In actual production, a white substrate is usually used as a substrate for color measurement. For example, when color measurement and inspection of packaging materials such as plastic film with greater transparency, a white substrate conforming to ISO standards should be placed under the tested printed matter to avoid unnecessary errors. At the same time, when measuring the color information on the same substrate, it is necessary to pay attention to the same substrate, that is, pay attention to the consistency of the substrate. 3. Measuring light source A, B, and C are simulated incandescent lamps, daylight at noon, cloudy daylight, or cloudy noon daylight, while the radiation distribution of the D65 source is measured after many measurements of daylight spectra at different times, in different climates, and at different locations. , after a complicated averaging process. The results of A light source and other light source measurements are very different and are now rarely used. The F series light source is generally used to measure fluorescent products. We can say that C light source and D65 light source are most useful for the printing industry. The D series light source has a good display performance because its color temperature is 5000K-7500K, which is close to white. In the printing industry, it is recommended to use D50 light source when observing transmission samples, and D65 light source is recommended when observing reflective samples. Therefore, when measuring the data, it must be noted under what light source. 4. Measuring the angle of view The resolution of the human eye to color is affected by the size of the field of view. Experiments have shown that the ability of the human eye to discern color differences is low when viewing colors with a small field of view (<4°). The accuracy of color matching and the ability to discriminate chromatic aberrations are observed when the field of view is increased from 2° to 10°. There is an increase; but when the field of view is further increased, the accuracy of color matching is not much improved. In the 2° field of view and the 10° field of view, the colors presented by the same color are also different. Therefore, in the color measurement, the angle of view selected for the measurement must also be marked. 5. Color space The standard colorimetric system has a variety of color spaces, that is, there are many different forms of expression to choose from. The choice of color space is actually the expression of the choice of measurement results. 6. Measurement of color difference Chromatic aberration is an important parameter indicator for the quality inspection and evaluation of printed matter. The size of the color difference directly affects the quality and grade of the product. The color difference formula based on CIE1976LAB uniform color space is commonly used in the printing industry, but the data expression of the color difference formula cannot match the visual perception of the human eye. Therefore, the color research experts have successively introduced the CMC (l:c) color difference formula, CIE94. The color difference formula and the latest CIEDE2000 color difference formula, in which the CMC (l:c) color difference formula is listed as an international and national standard in the textile industry. The results measured using different color difference formulas vary widely. Some people have measured the tristimulus values ​​of 10 pairs of color samples by experiment. By comparing the color difference calculated by the three color difference formulas respectively, it is found that there is △ELAB>△ECMC(2:1)>△E2000(1:1:1). the trend of. Therefore, it is necessary to indicate which color difference formula is selected in the measured color difference data. [next] 7. Aperture size When performing color measurement, the aperture of the color measurement instrument may be larger than the side length of the measurement color block. In this case, other color blocks should be selected for measurement or other color measurement instruments should be selected. The user specified aperture size should be no more than 5mm, and the standard 3 ~ 8mm and small 1 ~ 7mm aperture is generally used. The 3 to 8 mm aperture is used to measure the color scale (control strip) used in standard sheetfed printing, and the 1 to 7 mm aperture is used to measure the color scale used in web printing. 8. Response method The response state has states of T, E, A, and I, and state T and state E are the two most commonly used states. The commonly used wide band response is T state (American ANSI standard, widely used in the North American printing industry), the commonly used narrow band response is E state (European DIN standard), when the E state is selected, the density meter is on the print density value. Minor changes are more sensitive. In the case of print measurement, when the state T or the state E is used, for yellow, the value measured in the E state is larger than the value measured in the T state. Therefore, when comparing and evaluating the measured values, it is necessary to adjust the response state to be consistent. 9. Observation conditions The 0/d condition means that the light source illuminates the sample substantially vertically, and the diffuse light of the sample is received by the integrating sphere. In the case of regular reflection, the reflected energy of the sample is completely received, which is a true "reflectance ratio" in the physical sense. . The d/0 condition means that the light illuminates the sample after being diffused by the integrating sphere, and receives the reflected light substantially perpendicular to the surface of the sample. This condition is closer to the observation of the object by the human eye under normal circumstances, that is, the sample is white light from all sides. Illumination, the human eye is observed substantially perpendicular to the sample. Samples have different chromaticity values ​​under different illumination/observation conditions. Samples with good diffuse reflectivity are rarely affected by geometric conditions. Specimens with poor diffuse reflectance have high gloss. Different geometric conditions will bring about differences in the received luminous flux of the detector. The reflection factor is greatly affected by geometric conditions. The sample is measured under different geometric conditions and does not change the proportion of the tristimulus values. That is, different geometric conditions have little effect on the chromaticity coordinates, but the spectral reflectance factors are different, resulting in different tristimulus values. Therefore, as long as it is not the ideal Lambertian body, the difference in geometric conditions will affect the spectral reflectance and total reflectance of the sample to be tested, and the degree of influence is related to the gloss of the sample surface. The diffuseness of the white paper surface is better, the gloss is weaker, and the reflection factor is also higher. It is inferred from the above that the chromaticity values ​​under different geometric conditions should be relatively close. The data shows that this is not the case. The reason for this is that the fluorescent whitening material is added to the white paper, so its test is special. The fluorescent material has a fluorescent excitation property. When the fluorescent material is irradiated with light of a certain wavelength or a certain wavelength, the fluorescent material is excited to emit light longer than the irradiation wavelength, and the emitted light is both excited by the irradiated light and excited by the irradiated light. The portion of the fluorescent emission that is simultaneously received or separately received will affect its measurement. Therefore, the position of the monochromator in the measuring device has a large influence on the measurement result. When measuring the chromaticity value of a fluorescent sample, a post-spectrophotometer should be used, ie the monochromator is placed after the sample and before the detector. Non-fluorescent samples have no fluorescence excitation characteristics, and the light incident on them follows the law of reflection, only the reflection flux and no radiation flux. Whether the monochromatic illumination or monochromatic light is received, the detector receives the sample-to-irradiation wavelength. The reflected flux, how the position of the monochromator has no effect on the measurement. In principle, colorimetric instruments with different lighting/observation conditions cannot be substituted for each other, especially for high-gloss samples and fluorescent materials. Therefore, when performing the colorimetric test, it should be clear what lighting/observation conditions should be taken. When purchasing a color measuring instrument, it should be investigated whether the lighting/observation conditions of the instrument are consistent with the standards of the corresponding product. 10. Summary In the process of colorimetric measurement, we must pay attention to the choice of substrate, light source, color space, etc., and indicate in the measurement results, otherwise the measurement result is likely to be inconsistent with the customer's parameter requirements, so that it should be Qualified products become non-conforming products, which is not conducive to the implementation of data processing and standardization of production processes. Density measurement has always been the most common measurement method in the printing industry, but density meters do not provide psychophysical quantities related to human eye sensitivity, so their analytical measurement capabilities are limited. Therefore, color measurement plays an increasingly important role in the detection and evaluation of printed matter. In the color measurement, in order to obtain measurement data that can accurately reflect the quality of the print, the following points must be noted. Whiteboard correction Since the densitometer and the spectrophotometer are very sophisticated instruments, the calibration of the measuring instrument is performed before the measurement to ensure the accuracy of the measurement results. In general, each device is equipped with a standard whiteboard, such as the DensiEye750 density meter and the X-Rite500 series spectrophotometer. According to the purpose of measuring the data, we choose to perform zero adjustment on the whiteboard or on white paper, set the correction warning, and if the calibration time is exceeded, the whiteboard should be corrected. 2. Substrate The color measurement values ​​will have different chromaticity values ​​depending on the substrate selected for the measurement. The effect of the black and white substrates on the color measurement will vary depending on the transparency of the substrate, and the greater the transparency, the greater the substrate will be affected by the substrate. Therefore, in the high-quality printing production and color matching inspection process, it should be noted that the correct substrate is placed and used on the inspection table. It is generally recommended to use the following standards: When the opacity of the substrate is greater than or equal to 99, the measurement results will not be affected by the substrate. When the opacity is between 95 and 99, the color should be measured with a black substrate and the opacity is less than A white substrate was used at 95 hours. In actual production, a white substrate is usually used as a substrate for color measurement. For example, when color measurement and inspection of packaging materials such as plastic film with greater transparency, a white substrate conforming to ISO standards should be placed under the tested printed matter to avoid unnecessary errors. At the same time, when measuring the color information on the same substrate, it is necessary to pay attention to the same substrate, that is, pay attention to the consistency of the substrate. 3. Measuring light source A, B, and C are simulated incandescent lamps, daylight at noon, cloudy daylight, or cloudy noon daylight, while the radiation distribution of the D65 source is measured after many measurements of daylight spectra at different times, in different climates, and at different locations. , after a complicated averaging process. The results of A light source and other light source measurements are very different and are now rarely used. The F series light source is generally used to measure fluorescent products. We can say that C light source and D65 light source are most useful for the printing industry. The D series light source has a good display performance because its color temperature is 5000K-7500K, which is close to white. In the printing industry, it is recommended to use D50 light source when observing transmission samples, and D65 light source is recommended when observing reflective samples. Therefore, when measuring the data, it must be noted under what light source. 4. Measuring the angle of view The resolution of the human eye to color is affected by the size of the field of view. Experiments have shown that the ability of the human eye to discern color differences is low when viewing colors with a small field of view (<4°). The accuracy of color matching and the ability to discriminate chromatic aberrations are observed when the field of view is increased from 2° to 10°. There is an increase; but when the field of view is further increased, the accuracy of color matching is not much improved. In the 2° field of view and the 10° field of view, the colors presented by the same color are also different. Therefore, in the color measurement, the angle of view selected for the measurement must also be marked. 5. Color space The standard colorimetric system has a variety of color spaces, that is, there are many different forms of expression to choose from. The choice of color space is actually the expression of the choice of measurement results. 6. Measurement of color difference Chromatic aberration is an important parameter indicator for the quality inspection and evaluation of printed matter. The size of the color difference directly affects the quality and grade of the product. The color difference formula based on CIE1976LAB uniform color space is commonly used in the printing industry, but the data expression of the color difference formula cannot match the visual perception of the human eye. Therefore, the color research experts have successively introduced the CMC (l:c) color difference formula, CIE94. The color difference formula and the latest CIEDE2000 color difference formula, in which the CMC (l:c) color difference formula is listed as an international and national standard in the textile industry. The results measured using different color difference formulas vary widely. Some people have measured the tristimulus values ​​of 10 pairs of color samples by experiment. By comparing the color difference calculated by the three color difference formulas respectively, it is found that there is △ELAB>△ECMC(2:1)>△E2000(1:1:1). the trend of. Therefore, it is necessary to indicate which color difference formula is selected in the measured color difference data. [next] 7. Aperture size When performing color measurement, the aperture of the color measurement instrument may be larger than the side length of the measurement color block. In this case, other color blocks should be selected for measurement or other color measurement instruments should be selected. The user specified aperture size should be no more than 5mm, and the standard 3 ~ 8mm and small 1 ~ 7mm aperture is generally used. The 3 to 8 mm aperture is used to measure the color scale (control strip) used in standard sheetfed printing, and the 1 to 7 mm aperture is used to measure the color scale used in web printing. 8. Response method The response state has states of T, E, A, and I, and state T and state E are the two most commonly used states. The commonly used wide band response is T state (American ANSI standard, widely used in the North American printing industry), the commonly used narrow band response is E state (European DIN standard), when the E state is selected, the density meter is on the print density value. Minor changes are more sensitive. In the case of print measurement, when the state T or the state E is used, for yellow, the value measured in the E state is larger than the value measured in the T state. Therefore, when comparing and evaluating the measured values, it is necessary to adjust the response state to be consistent. 9. Observation conditions The 0/d condition means that the light source illuminates the sample substantially vertically, and the diffuse light of the sample is received by the integrating sphere. In the case of regular reflection, the reflected energy of the sample is completely received, which is a true "reflectance ratio" in the physical sense. . The d/0 condition means that the light illuminates the sample after being diffused by the integrating sphere, and receives the reflected light substantially perpendicular to the surface of the sample. This condition is closer to the observation of the object by the human eye under normal circumstances, that is, the sample is white light from all sides. Illumination, the human eye is observed substantially perpendicular to the sample. Samples have different chromaticity values ​​under different illumination/observation conditions. Samples with good diffuse reflectivity are rarely affected by geometric conditions. Specimens with poor diffuse reflectance have high gloss. Different geometric conditions will bring about differences in the received luminous flux of the detector. The reflection factor is greatly affected by geometric conditions. The sample is measured under different geometric conditions and does not change the proportion of the tristimulus values. That is, different geometric conditions have little effect on the chromaticity coordinates, but the spectral reflectance factors are different, resulting in different tristimulus values. Therefore, as long as it is not the ideal Lambertian body, the difference in geometric conditions will affect the spectral reflectance and total reflectance of the sample to be tested, and the degree of influence is related to the gloss of the sample surface. The diffuseness of the white paper surface is better, the gloss is weaker, and the reflection factor is also higher. It is inferred from the above that the chromaticity values ​​under different geometric conditions should be relatively close. The data shows that this is not the case. The reason for this is that the fluorescent whitening material is added to the white paper, so its test is special. The fluorescent material has a fluorescent excitation property. When the fluorescent material is irradiated with light of a certain wavelength or a certain wavelength, the fluorescent material is excited to emit light longer than the irradiation wavelength, and the emitted light is both excited by the irradiated light and excited by the irradiated light. The portion of the fluorescent emission that is simultaneously received or separately received will affect its measurement. Therefore, the position of the monochromator in the measuring device has a large influence on the measurement result. When measuring the chromaticity value of a fluorescent sample, a post-spectrophotometer should be used, ie the monochromator is placed after the sample and before the detector. Non-fluorescent samples have no fluorescence excitation characteristics, and the light incident on them follows the law of reflection, only the reflection flux and no radiation flux. Whether the monochromatic illumination or monochromatic light is received, the detector receives the sample-to-irradiation wavelength. The reflected flux, how the position of the monochromator has no effect on the measurement. In principle, colorimetric instruments with different lighting/observation conditions cannot be substituted for each other, especially for high-gloss samples and fluorescent materials. Therefore, when performing the colorimetric test, it should be clear what lighting/observation conditions should be taken. When purchasing a color measuring instrument, it should be investigated whether the lighting/observation conditions of the instrument are consistent with the standards of the corresponding product. 10. Summary In the process of colorimetric measurement, we must pay attention to the choice of substrate, light source, color space, etc., and indicate in the measurement results, otherwise the measurement result is likely to be inconsistent with the customer's parameter requirements, so that it should be Qualified products become non-conforming products, which is not conducive to the implementation of data processing and standardization of production processes. Article source address: http:// Barber Scissors Set,Pet Scissors Set,Small Pet Scissors,Fishbone Teeth Pet Scissors Zhangjiagang Mister Tools Co., Ltd , https://www.mingshitools.com