CN102307273A - Digital proofing quality evaluation method based on visual inspection, International color consortium (ICC) standard and custom standard - Google Patents

Abstract

The invention relates to a digital proofing quality evaluation method, in particular to a digital proofing quality evaluation method based on visual inspection, an International color consortium (ICC) standard and a custom standard. In the method, parameters, namely the average chromatic aberration of all color lumps, the maximum chromatic aberration of all the color lumps, the onsite chromatic aberration of a cyan lump, the onsite chromatic aberration of a pinkish red lump, the onsite chromatic aberration of a yellow lump, the onsite chromatic aberration of a black lump, the white chromatic aberration of paper, the average chromatic aberration of gray scale, the maximum chromatic aberration of the gray scale and the chromatic aberration peak value of 95 percent of color lumps, are taken as chromatic aberration evaluation standards; therefore, the digital proofing quality evaluation method has the advantages that: by synthesizing a subjective evaluation method and an objective evaluation method and supplying the ICC standard and the custom standard and adding custom color lumps into a standard control strip, the digital proofing quality can be evaluated more quickly, precisely and comprehensively.

Description

A digital proofing quality evaluation method based on visual inspection, ICC standard and self-defined standard

technical field

The invention relates to a method for evaluating the quality of digital proofing, in particular to a method for evaluating the quality of digital proofing based on comprehensive visual inspection, ICC standards and self-defined standards.

Background technique

With the wide application of digital workflow and the popularization of CTP, digital proofing has increasingly become an important part of printing production, and how to evaluate whether the quality of proofing is qualified has become particularly important.

Traditional digital proofing quality evaluation methods include subjective and objective evaluation methods.

1) Subjective evaluation method. This method is based on the quality requirements of the printed original and reproduction, and directly visually inspects and compares the proofs, and the evaluation observers make qualitative evaluations on the proofs, such as good or bad, excellent, good, general, or poor, based on experience. The evaluation results of the subjective evaluation method are relative, focusing on the subjective feeling of the appearance, easily affected by the observer's knowledge, experience, hobbies, mood and other psychological factors and objective conditions, poor preparation, low stability, so subjective evaluation There are many deficiencies in the method;

2) Objective evaluation method. Based on the authoritative quality standards in the printing and reproduction industry, the method uses relevant measuring instruments to analyze and evaluate the physical properties of the proof sheet, such as color, to verify the parameters of the proofing process, and finally to quantitatively evaluate the quality of the proof sheet. These authoritative quality standards are saved in the form of ICC characteristic files, which are referred to as ICC standards in this specification. The method has good stability, specific analysis content and relatively high accuracy. The disadvantage is that the measurement data is complicated, various instruments are used, and the measurement time is long, which is not conducive to improving production efficiency. In addition, printing factories may use printing standards suitable for their own characteristics instead of using ICC standards, so the traditional objective evaluation method has limitations in actual production applications.

Since ICC (International Color Consortium, International Color Consortium) established a series of color management standards in 1993, digital proofing has been popularized and applied rapidly as a new, high-quality, and efficient way of working. Ugra/FOGRA and IDEAlliance, etc. Organizations have successively engaged in research on digital proofing color quality evaluation, and a series of digital proofing color quality monitoring tools have been developed. At present, the digital proofing quality evaluation measurement and control strips used in actual production include Ugra/FOGRA Media Wedge measurement and control strip and IDEAlliance ISO 12647-7 Digital Control Strip measurement and control strip, which are mainly used to check the chroma readiness of digital proofing proofs and check the printing proofs and The color conversion accuracy of the proof sheet. These measurement and control strip color patches are composed of yellow, magenta, cyan, red, green, blue, black, three-color gray balance color patches and three-color overprint color patches, but these measurement and control strips cannot cover all colors. In actual production There are also certain limitations, because there may be situations where the proofing effect of the color block of the measurement and control strip meets the requirements, but some other color cannot be accurately simulated.

Generally speaking, judging whether the proofing sheet is qualified requires an accuracy rate of about 95%, a color difference of less than 6.0, and an average color difference of less than 3.5. However, there are limitations in the actual production and application process. First of all, the number of color blocks of the measurement and control strip is limited, generally only 20 to 60 color blocks. At this time, the guarantee of 95% restoration accuracy does not guarantee that the colors other than the measurement and control strip can also be used. Accurate restoration; Secondly, only ensuring that the average color difference is less than 3.5 does not guarantee the quality of proofs, because the quality of proofs will also be affected by other factors, such as neutral gray balance and some memory colors, so other settings such as neutral Standards such as gray blocks and other solid color block color differences are used to judge whether the quality of the proofing sheet is qualified.

Contents of the invention

The present invention mainly solves the limited number of color blocks of the measurement and control strips in the prior art, generally only 20 to 60 color blocks, and at this time, the 95% restoration accuracy cannot guarantee that the colors other than the measurement and control strips can also be accurately restored; In addition, only ensuring that the average color difference is less than 3.5 does not guarantee the quality of proofs, because the quality of proofs will also be affected by other factors, such as technical problems such as neutral gray balance and some memory colors; a comprehensive subjective evaluation method is provided And objective evaluation method, and provide a comprehensive visual inspection, ICC standard and custom standard for selecting ICC standard and custom standard and adding custom color blocks to the standard measurement and control bar, which can evaluate the quality of digital proofing more quickly, accurately and comprehensively Digital proofing quality assessment method.

Above-mentioned technical problem of the present invention is mainly solved by following technical scheme:

A digital proofing quality evaluation method that integrates visual inspection, ICC standards and self-defined standards, is characterized in that it includes the following steps:

Step 1, making digital proofing measurement and control strips;

Step 2, set the digital proofing quality evaluation standard parameters, including the average color difference of color blocks, the maximum color difference of all color blocks

Color difference, cyan solid color difference, magenta solid color difference, yellow solid color difference, black solid color difference, paper white color difference, gray level average color difference, gray level maximum color difference, 95% color block color difference peak value;

Step 3, carry out digital proofing in the form of adding measurement and control strips;

Step 4, visually inspect the digital proofing sheet, if it meets the evaluation standard parameters in step 2, perform color difference evaluation, otherwise check for errors and repeat step 3;

Step 5: Carry out color difference evaluation on the digital proof sheet that has completed step 4, use the data and output the evaluation data.

In the above-mentioned digital proofing quality evaluation method of comprehensive visual inspection, ICC standards and self-defined standards, in the step 1, the specific operation method of making a digital proofing measurement and control strip is to add a self-defined color block on the digital proofing measurement and control strip, and use When controlling digital proofing, the color of the proof is often inaccurate; if there is a spot color in the proof, add a spot color block on the measurement and control bar.

In the above-mentioned digital proofing quality evaluation method of comprehensive visual inspection, ICC standard and self-defined standard, in the step 5, the color difference evaluation method randomly selects to perform spectrophotometer measurement based on ICC standard or self-defined standard, and then performs color difference calculate.

In the aforementioned comprehensive visual inspection, ICC standard and self-defined standard digital proofing quality evaluation method, if the color difference evaluation method adopts the ICC standard, the standard of the color block can be obtained directly from the ICC file of the printing machine through the CMYK value of the color block Chromaticity value; if a custom standard is used, the standard chromaticity value of the color block of the control bar is obtained directly from the selected custom standard.

In the above-mentioned comprehensive visual inspection, ICC standard and self-defined standard digital proofing quality evaluation method, if the color difference evaluation method uses a spectrophotometer based on ICC standard to measure the chromaticity value of the sample sheet measurement and control strip color block, the operation steps are as follows:

A. Setting of the light source and viewing angle conditions of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees;

B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed.

In the aforementioned comprehensive visual inspection, ICC standard and self-defined standard digital proofing quality evaluation method, if the color difference evaluation method uses a spectrophotometer based on a self-defined standard to measure the chromaticity value of the color block of the sample measurement and control strip, the operation steps are as follows:

A. Setting of the light source/viewing angle condition of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees;

B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed.

In the aforementioned comprehensive visual inspection, ICC standard and self-defined standard digital proofing quality evaluation method, the specific operations for calculating the color difference are: calculating the average color difference of all color blocks, the maximum color difference of all color blocks, the cyan solid color difference, the magenta solid color difference Color difference, yellow solid color difference, black solid color difference, paper white color difference, gray level average color difference, gray level maximum color difference, 95% color patch color difference peak, and compare these color difference values with the set evaluation standards, only when all parameters are The proof sheet is judged to be qualified only when the requirements of the evaluation criteria are met, otherwise the sample sheet is considered unqualified.

Therefore, the present invention has the following advantages: comprehensive subjective evaluation method and objective evaluation method, and provides selection of ICC standards and self-defined standards and adding self-defined color blocks to standard measurement and control bars, which can evaluate the quality of digital proofing more quickly, accurately and comprehensively .

Description of drawings

Fig. 1 is a kind of work flowchart of the present invention.

Detailed ways

The technical solutions of the present invention will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Example:

First, introduce the theoretical basis of the present invention:

1. Visual observation conditions

Visual inspection starts with determining the lighting conditions. Generally, it should be carried out under a color comparison box or a standard light source. The inner wall of the color comparison box should be black; the standard light source is generally D50 or D65; in addition, it should be noted that the surrounding light is affected by the surrounding light, and the surrounding should be dull or neutral. Color; when observing, other lighting sources should be turned off, and the neutral color should be seen first to adapt our visual system, after 60 seconds of adaptation, then look at the sample. In addition, the boundary contact between the printing sample and the proofing sheet should be placed together for observation.

2. Measurement and control strip

The proofing measurement and control strip is composed of solid color blocks, different dot color blocks and signal elements for visual inspection, and there are many types. At present, the digital proofing quality evaluation measurement and control strips used in actual production include Ugra/FOGRA Media Wedge measurement and control strips and IDEAlliance ISO 12647-7 Digital Control Strip measurement and control strips.

The elements contained in the general measurement and control strip are: C, M, Y, K solid color blocks (to detect the proofing effect of the solid color block); R, G, B solid overprint color blocks (to detect the overprint color proofing effect); neutral gray blocks ( Detect proofing color cast).

In order to be more suitable for actual proofing requirements, the present invention proposes to add custom color blocks on the traditional proofing measurement and control strip. If there is a spot color in the sample sheet, you can also add spot color color blocks to the measurement and control strip.

3. Chromatic difference formula

In this specification, the CIE 1976 L*a*b* color difference formula is used to calculate the color difference of the color block, but it should be clear to those skilled in the art that the present invention is not limited thereto, and other color block formulas are also applicable, such as the ANLAB color difference formula , CIE DE 2000 color difference formula, etc.

CIE 1976 L*a*b* color difference formula:

，表示样张与标准的深浅差，

、

，

和

表示样品和标准在a*b*平面上位置的改变。 in,

, indicating the depth difference between the sample sheet and the standard,

,

,

and

Indicates the position change of the sample and standard on the a*b* plane.

、

、

可以视实际生产需要从印刷机的ICC特性文件中获取，也可以从印刷厂自定义标准中获取。 In the present invention,

,

,

It can be obtained from the ICC characteristic file of the printing machine according to the actual production needs, or from the custom standard of the printing factory.

4. Objective Evaluation Criteria

The objective evaluation standard is generally measured by color difference, which cannot represent absolute visual difference, but has been tested by practice for a long time as an industrial standard.

The relationship between color difference and visual experience is as follows:

<1

<1 almost no chromatic aberration

<2 Little sense of color difference

<3.5 Moderate perception of chromatic aberration

<6.0 The feeling of color difference is obvious

<12.0 Strong sense of color difference

>12.0 The two color blocks are completely different

The evaluation criteria proposed by the present invention include: the average color difference of all color patches, the maximum color difference of all color patches, the solid color difference of cyan, the solid color difference of magenta, the solid color difference of yellow, the solid color difference of black, the white color difference of paper, the average color difference of gray scale, the maximum color difference of gray scale , 95% color block color difference peak value. Only when all parameters meet the requirements can it be judged that the quality of the proof sheet is qualified.

The present invention refers to ISO12647-7 and IDEAlliance's color difference range for color quality control, and combines the actual printing production needs to give color difference control standards, as shown in the following table:

serial number control color block ISO12647-7 requirements IDEAllianceRequirements Reference standard of the present invention 1 Average color difference of all color patches ≤3 ≤3 ≤3 2 The maximum color difference of all color blocks ≤6 ≤6 ≤6 3 Cyan solid color block color difference ≤5 ≤5 ≤5 4 Magenta solid color patch color difference ≤5 ≤5 ≤5 5 Yellow solid color patch color difference ≤5 ≤5 ≤5 6 Black solid color block color difference ≤5 ≤5 ≤5 7 Paper white color difference ≤3 ≤6 ≤5 8 Gray average color difference none none ≤3 9 Gray scale maximum color difference none none ≤6 10 95% color block color difference peak value none none ≤5

Through the control of the above table, the proofs that meet the requirements are qualified proofs. It should be noted that the above standards are flexible and variable, and can be adjusted according to the printing environment and customer requirements during actual application.

Below is the specific embodiment of the present invention:

A digital proofing quality evaluation method that integrates visual inspection, ICC standards and self-defined standards, including the following steps:

Step 1, make a digital proofing measurement and control strip; the specific operation method for making a digital proofing measurement and control strip is to add a custom color block on the digital proofing measurement and control strip, which is used to control the color that is often inaccurate during digital proofing; if there is a spot color on the proof, then Add spot color patches on the control strip. On the basis of the traditional digital proofing measurement and control strip, add custom color blocks to control the often inaccurate color of proofing during digital proofing. If there are spot colors in the proofs, you can also add spot color color blocks on the measurement and control strip. For example, based on the Ugra/FOGRA Media Wedge measurement control strip and the IDEAlliance ISO 12647-7 Digital Control Strip measurement control strip, add the color blocks that need to be detected.

Step 2. Set the standard parameters for digital proofing quality evaluation, including the average color difference of color patches, the maximum color difference of all color patches, the solid color difference of cyan, the solid color difference of magenta, the solid color difference of yellow, the solid color difference of black, the white color difference of paper, the average color difference of gray scale, the gray Maximum color difference, 95% color block color difference peak value;

Step 3, carry out digital proofing in the form of adding measurement and control strips;

Step 4. Visually inspect the digital proofing sheet. If the evaluation standard parameters in step 2 are met, perform color difference evaluation. Otherwise, check for errors and repeat step 3. When performing visual inspection, attention should be paid to light source conditions and observation conditions.

Visual inspection is mainly to observe the color reproduction ability of digital proofing through eyes, including the tone range of images, lines, and text, the density or chroma of solid or saturated colors, gray balance, and the restoration of level curves (including bright tone, middle tone, Dark tone layer reproduction and dot gain reproduction) and delicate texture, etc.

The color difference evaluation method randomly selects to perform spectrophotometer measurement based on ICC standards or custom standards, and then calculates the color difference; if the color difference evaluation method adopts the ICC standard, the color is directly obtained from the ICC file of the printing machine through the CMYK value of the color block The standard chromaticity value of the block; if a custom standard is used, the standard chromaticity value of the color block of the measurement control bar is obtained directly from the selected custom standard.

If the color difference evaluation method uses a spectrophotometer based on the ICC standard to measure the chromaticity value of the color block of the sample measurement and control strip, the operation steps are as follows:

A. Setting of the light source and viewing angle conditions of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees;

B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed.

If the color difference evaluation method uses a spectrophotometer based on a self-defined standard to measure the chromaticity value of the color block of the sample measurement and control strip, the operation steps are as follows:

A. Setting of the light source/viewing angle condition of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees;

B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed.

Pay attention to the following issues when measuring the chromaticity value of a color patch:

a) Setting of the light source/view angle conditions of the spectrophotometer. Because the same spectrophotometer uses different light sources or different viewing angle conditions, the obtained chromaticity values are not the same. The light source of the standard chromaticity value of the color block taken from the ICC standard is D50, and the viewing angle is 2 degrees; while for the custom standard, you need to specify the standard light source and viewing angle conditions.

b) Maintenance of the spectrophotometer. As the number of times the instrument is used increases, the performance of the spectrophotometer may decrease or even be completely unusable, so the instrument must be checked during use to ensure that the instrument can be used normally.

The problem of the difference between the stations. Due to the different spectroscopic principles of different types of measuring instruments, the chromaticity value of the same color may vary greatly.

The specific operation of calculating the color difference is: calculating the average color difference of all color patches, the maximum color difference of all color patches, the solid color difference of cyan, the solid color difference of magenta, the solid color difference of yellow, the solid color difference of black, the white color difference of paper, the average color difference of gray scale, and the maximum color difference of gray scale , 95% of the peak value of the color block color difference, and compare these color difference values with the set evaluation standards, only when all parameters meet the requirements of the evaluation standard, the proof proof is judged to be qualified, otherwise the proof is considered unqualified.

Step 5: Carry out color difference evaluation on the digital proof sheet that has completed step 4, use the data and output the evaluation data.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (7)

1. A digital proofing quality evaluation method of comprehensive visual inspection, ICC standards and self-defined standards, is characterized in that, comprises the following steps: Step 1, making digital proofing measurement and control strips; Step 2, set the digital proofing quality evaluation standard parameters, including the average color difference of color blocks, the maximum color difference of all color blocks Color difference, cyan solid color difference, magenta solid color difference, yellow solid color difference, black solid color difference, paper white color difference, gray level average color difference, gray level maximum color difference, 95% color block color difference peak value; Step 3, carry out digital proofing in the form of adding measurement and control strips; Step 4, visually inspect the digital proofing sheet, if it meets the evaluation standard parameters in step 2, perform color difference evaluation, otherwise check for errors and repeat step 3; Step 5: Carry out color difference evaluation on the digital proof sheet that has completed step 4, use the data and output the evaluation data. 2. a kind of comprehensive visual inspection according to claim 1, the digital proofing quality evaluation method of ICC standard and self-defined standard, it is characterized in that, in described step 1, the specific operation method of making digital proofing measurement and control bar is in digital proofing measurement and control Add a custom color block on the control bar to control the inaccurate color of the proof during digital proofing; if there is a spot color in the proof, add a spot color block on the measurement and control bar. 3. a kind of comprehensive visual inspection according to claim 1, the digital proofing quality evaluation method of ICC standard and self-defined standard, it is characterized in that, in described step 5, color difference evaluation method randomly selects and executes based on ICC standard or self-defined Standards are measured with a spectrophotometer followed by color difference calculations. 4. a kind of digital proofing quality assessment method of comprehensive visual inspection, ICC standard and self-defined standard according to claim 3, it is characterized in that, if the color difference evaluation method adopts ICC standard, then pass the CMYK value of color piece directly from printing machine The standard chromaticity value of the color block is obtained from the ICC file of the . If a custom standard is used, the standard chromaticity value of the color block of the measurement control bar is obtained directly from the selected custom standard. 5. a kind of comprehensive visual inspection according to claim 3, the digital proofing quality evaluation method of ICC standard and self-defined standard, it is characterized in that, if the color difference evaluation method adopts the spectrophotometer based on ICC standard to measure the sample sheet measurement and control strip color block Chromaticity value, the operation steps are as follows: A. Setting of the light source and viewing angle conditions of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees; B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed. 6. a kind of comprehensive visual inspection, ICC standard and self-defined standard digital proofing quality evaluation method according to claim 3, it is characterized in that, if the color difference evaluation method adopts the spectrophotometer based on self-defined standard to measure sample sheet measurement and control strip color block The chromaticity value, the operation steps are as follows: A. Setting of the light source/viewing angle condition of the spectrophotometer: set the light source of the spectrophotometer to D50, and set the viewing angle to 2 degrees; B. Use a spectrophotometer to measure the color block of the sample sheet measurement and control strip, and save the data after the measurement is completed. 7. The digital proofing quality evaluation method of a kind of comprehensive visual inspection, ICC standard and self-defined standard according to claim 3, it is characterized in that, the concrete operation of described calculating color difference is: calculate the average color difference of all color blocks, all color blocks Maximum color difference, cyan solid color difference, magenta solid color difference, yellow solid color difference, black solid color difference, paper white color difference, grayscale average color difference, grayscale maximum color difference, 95% color patch color difference peak, and compare these color difference values with the set Only when all the parameters meet the requirements of the evaluation standard can the proof proof be judged to be qualified, otherwise the proof is considered unqualified.

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