GATF color reproduction test method for the hottes

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GATF color reproduction test method of offset press

briefly introduce the GATF color reproduction test chart, which is divided into six detection areas

1. Simple color wheel chart: it consists of yellow, magenta and cyan ink dots. Each color version has six levels, which are 5%, 15%, 25%, 50%, 75% and 90% respectively. 216 color blocks are obtained by overlapping, which are used to distinguish colors and detect the restoration of colors

2. There are six contents in the contact copy control standard section: ① development and exposure time check chart. Place a density ladder with a density range of 0.05~2.00 in a blank bar to detect the change of development conditions and calculate the new exposure time. ② Point area dividing standard is used to detect the expansion and change of line image in the process of contact copy. ③ The point ladder is divided into two sections from 1% to 99%. Each segment has 23 levels. The upper segment is from 1% to 56% points, which is called positive, and the lower segment is from 44% to 99% points, which is called negative. 56% of the points in the upper segment correspond to 44% of the points in the lower segment. The graph can show the gradual transition from positive point to negative point, so as to check the change of copy point. ④ Male and female crosshairs are used to check whether the crosshairs become thicker during the copy process. The signal of image quality change is given by the thickening of the positive line or the pasting of the negative line. ⑤ The black-and-white intersection marks can be embedded with each other because the ink area is just equal to the blank area under normal circumstances. ⑥ The mixed sign is composed of three square figures, in which two corners of one part intersect and two corners of the other part are separated, and the image quality is detected by the change of intersection or separation

3. Point line number comparison chart. The matching reference used to select the number of screen lines and paper suitability can also reflect whether the reproduction of tone of each color plate is normal while considering its compatibility and toughening. There are seven kinds of screen lines from 150l/in to 65 l/in from top to bottom, and from left to right, there are 10 levels of points with a total of 5% - 90%

4. The neutral gray balance control chart of three primary colors is a color bar composed of 26 connected blocks, which is composed of 22 color blocks and four star marks, 1~7 blocks form a group of primary colors and intermediate colors, 8~13 blocks form gray to black fading, 14~19 blocks calculate the printing relative contrast coefficient, 20~22 form intermediate color system, and finally four four color star marks

5. Grey balance map, find out the proportion of yellow, grade and green of grey balance from the map

6. Proofing control bar

from the test function of the GATF test chart, we can use a colorimeter to measure the tristimulus value XYZ of real yellow (y), magenta (m), cyan (c), red (y+m), green (y+c), blue (c+m), synthetic black (y+m+c), black (k) and the paper used from the color wheel chart by copying the chart (using the brand ink commonly used in the factory and a certain amount of paper), Then use the formulas x=x/(x+y+z) and y=y/(x+y+z) to calculate the brilliance coordinates x and Y respectively, where y is the brightness coordinate, the value range is 0~100, and the value range of X and Y is 0~1; From the point ladder, we can measure the expansion rate of 50% points and other points, as well as the ability to restore the tone; The gray balance of the ink used can be seen from the gray balance card. The test results of these data can further explain whether the printing performance of our printing machine is excellent, and these data can be transmitted to the prepress department as a reference for design and production

if there is no GATF test, when the maximum load exceeds 3% ~ 5%, we can make real plot yellow (y), product (m), green (c), red (y+m), green (y+c), blue (c+m), synthetic black (y+m+c), black (k) and yellow, product, green, black four colors 1% to save energy. After the trial printing is completed, we can put into printing, The basic data of color synthesis and the reduction ability of yellow, magenta, cyan and black tones can also be measured. At the same time, the expansion rate of 2%, 4%, 6%, 8%, 10% - 100% step points can be measured and calculated (such high-tech data of instrument products is required in the curve mode in Photoshop). Of course, the final full version still needs to be trial printed, although the raw materials need to be wasted and the test needs to be cumbersome, But for a device with tens of millions of investment, it is worth spending some money and energy to do such a test

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