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Color printing image color detection method
Jan 30, 2018

Color printing image color is yellow, magenta, cyan three primary colors in different proportions formed by the ink composition. Instead of measuring the color on the screen when measuring the color of a printed image, the quality control bar measures the color of the printed image at the same time. Control bar is generally placed in the printed sheet drag tip. The measuring instrument detects the corresponding color bars of the control bar to obtain the printing quality information, such as the solid density, overprint rate, dot gain, dot density, neutrality gray reduction and contrast of each primary color ink to judge the image tone and color reproduction.


There are three ways to measure the color of a printed image: density meter, colorimeter, and spectrophotometer.


Densitometer measurement


Densitometer is the main instrument in color separation, plate making and printing. This kind of measurement has been the most commonly used form of objective evaluation quality in the printing industry. The density meter is cheap and widely used. When a densitometer measures a color surface, it can only get the relative amount of ink of one of the primary colors printed on it. It does not indicate the hue of the color under test. Densitometer measurements are not associated with various color systems and therefore can not be described in color language. In color measurement and evaluation, the density meter has some limitations, it is not a standard color measurement instrument.


2. Colorimeter color measurement


Colorimeter by measuring the surface of the color measured directly with the color stimuli three stimulus value X, Y, Z proportional to the visual response, obtained by conversion of the measured color X, Y, Z value, these values Convert color parameters into other uniform color spaces. The colorimeter is a special densitometer with three broadband filters. Due to the thickness of the device itself and the principle of a certain error, the absolute accuracy of the color measurement is not good. However, due to its low price, it is still a widely used color measurement instrument.


3. Spectrophotometer (spectrophotometer) color measurement


Spectrophotometers measure the reflectance of the color surface to light of various wavelengths in the visible spectrum. The visible spectrum of the light at a certain step (5nm, 10nm, 20nm) illuminate the color surface, and then measure the reflectivity point by point. The relationship between the reflectance of each wavelength of light wavelength and the relationship between the spots can be measured on the surface of the color spectrophotometry curve. Each spectrophotometer curve uniquely conveys a color. Measured values can also be converted to other color system values. Spectrophotometer is a flexible, ideal color measurement instrument. At present, some foreign printing presses equipped with color quality testing of the color measurement instrument is the use of spectrophotometer.


Method of controlling the color quality of printing


Printing production, paper, ink and printing plate and other printing image quality constraints. When these factors have been set, how to control the color quality of the printed image when the image is reproduced on a printing press?


1. According to the upper body production, adjust the printing pressure


According to the printing image quality requirements of copy, paper thickness, printing plate and other conditions to adjust the printing pressure, the image dot to be the best reproduction.


2. Reasonable arrangement of color sequence


Currently, multicolor printing generally uses ink, cyan, magenta and yellow sequences or cyan, magenta, yellow, and black sequences. This color sequence makes color reproduction easier and more accurate. Ink layer thickness from small to large arrangement, such as offset printing using black, blue, magenta and yellow sequence, the ink layer thickness is: black ink is 0.8μm, green ink is 0.9μm, magenta ink is 1.0μm, yellow Ink is 1.1μm; ink viscosity from big to small arrangement, such as black ink 1188Pa, green ink 488Pa, magenta ink is 477Pa, yellow ink is 147Pa. Ink viscosity can not meet the arrangement requirements, the ink viscosity can be adjusted in advance.


3. Align the printing press


Adjust the press according to the proofing sheet and the established printing conditions to make the printed image consistent with the printed sheet.

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