Printing color images of control and detection methods

Printing and reproduction, the color printing step the number of images have a fairly large proportion. Color printing images through the cyan, magenta, yellow ink RGB composite print and present a variety of colors, so color original images to be reproduced. At reproduction, due to a variety of processes and production factors, so that the image colors do not print very well restore the original color. In order to obtain a satisfactory print image quality, in the printing production of color images must be tested, and by adjusting the variables to control some of the printing quality of color reproduction.

One, affecting a major factor in the quality of color reproduction

Graphics in the press on the replication and affect the image color copying many factors, such as: dot gain, print color sequence and overprint, ink hue and field density, ink temperature and viscosity, water volume (offset printing), paper properties, India version of the depth of layout, printing pressure.
1. Dot gain
In printing, dot gain and will occur, but the expansion of more than a certain range will have a lot of quality problems. This network expansion will reduce the image contrast and make the whole image become darker shadows outlets paste die, so that dramatic changes in hue reproduction, when printing colored images when the networks while expanding the image as a whole dark. When only one of a color dot gain, the copied image will have a color cast, for example: magenta version of network coverage of the expansion occurred in the notes, 50% of the network becomes 55%, print the image color reddish, flesh into a partial red, neutral color becomes pale red, green, dirty. The printing pressure and ink density of the ground affect dot gain. Printing small changes in pressure would produce significant change in the entire print image; ground ink density increases, the dot gain increases, the dark tone color images to reconcile a significant impact.

2. Printing color sequence and the overprint

Color image printing, ink is the same color the same color overlay, overprint bad will produce color bias, color mixing and levels of disturbance. Color printing color sequence arrangement on the trapping effect of a significant influence. For the multi-color printing machine, colored ink is printed a short time interval, after printing color ink is printed wet ink overprint earlier surface, are "stacked wet-wet" printing state. In the trapping color in the printed ink on paper, the wet ink over printed ink surface of an advantage. Two colors of ink as long as the reverse the color order, overprint color hue, brightness and saturation may be different. Such as cyan and magenta ink trapping, first printing after the printing blue magenta, cyan overprint Hue; first printing after printing magenta blue, red overprint Hue.

In order to achieve good trapping effects, color sequence but also a reasonable arrangement, after the scheduled colored ink viscosity.

3. Ink hue and field density

The printing ink used in production are varying degrees of color cast, so that printed images generated color cast, should maximize the use of too few colors for color printing ink. Printing ink density of the size of the image surface of the ground decided to print the image-order harmonic color reproduction range. The higher the density field, the more order to reconcile a wide range of color reproduction. Field density, so that the image color saturation reduction process color weakening.

4. Ink temperature and viscosity of

Printing the image reproduction, the ink viscosity is a very important parameter. General Gravure using liquid ink, the input device does not absorb ink ink ink and the channeling agency, ink viscosity by adding some solvent to the ink tank control. Offset and letterpress generally use the sticky ink, the ink viscosity greatly. In order to ink evenly on the surface of paper from the printing plate to transfer, offset and letterpress machines have a uniform ink ink, and channeling devices. Ink rollers in these devices have been hit between the transmission and absorption in the process of squeezing, shearing and separation. Ink roller to overcome friction and to do work inside, leaving ink roller surface temperature has been passed and beaten absorbed in the process of squeezing, shearing and separation. Ink rollers in order to overcome friction and to do work inside, leaving ink roller surface temperature, the ink viscosity is passed drop. Printing ink thinning, the ink roller surface is contained reduced, the surface of ink delivered to the paper reduced to print the image-order harmonic tone changed and destroyed the printing image consistency. Some studies have shown: the printing presses start, the printed image to produce colors are the reasons for deviation of 60% of the ink roller temperature caused by the change.

5. Offset ink-water balance

Offset ink-water balance produced a direct impact on the quality of the image reproduction. Small amount of water will play dirty plate, paste version; water ink emulsion Ambassador to print the image color saturation reduction.

2, printing, color image detection

Color printing color images by the yellow, magenta, ink blue primary colors in different proportions according to composite formation. General measure color printing images on the screen when the color is not measured, but measuring and printing images at the same time the quality control of printing. Control bar generally placed in the copies of the drag shoot at. Detection and control of measuring instruments available to the corresponding blocks of color print quality information, such as the field of color ink density, trapping rates, dot gain, dot density, neutral gray reduction, contrast and other parameters to determine the replication of the image-order harmonic tones.

Measurement of printing color images have three measurement methods, namely, the density measurements, the colorimeter measurements and spectrophotometer measurements.

1. Density meter measurements

Density meter is a color separation, plate making and printing of the main instruments, such measurement has been the printing industry the most commonly used form of objective evaluation of the quality, density meter cheap and widely used. Measuring the color density meter surface, can only get a color ink printing, the relative volume, it can not direct the measured color hue. Density meter measurements with a variety of surface color systems are not linked and therefore can not describe the measured colors with colorful language. In color measurement and evaluation, the density meter has certain limitations, it is not the standard color measuring instruments.

2. Colorimeter color measurement

Colorimeter was tested by direct measurements of the surface color and color 3 to stimulate the value of access to X, Y, Z is proportional to the visual response to the measured colors obtained through the conversion X, Y, Z values, these values can also be uniform color space converted into other color parameters. Colorimeter is a broadband filter with three special densitometer. Owing to equipment and principle of its own devices in a certain margin of error in thickness, so that the absolute accuracy of color measurement well. However, because of its cheap, is still widely used color measurement instruments.

3. Spectrophotometer (spectral spectrophotometer) color measurement

Spectrophotometer measuring the surface color of the visible spectrum at all wavelengths of light reflectivity. The visible spectrum of light in a certain step distance (5nm, 10nm, 20nm) irradiation color surface, and then point by point measurement of reflectivity. Will each wavelength of light reflectance value and describe the relationship between the wavelength of the color point of access to the tested surface of the spectrophotometric curve. Spectrophotometric curve of each one unique expression of a different color. Measured values can also be converted into other table color system values. Spectrophotometer is a flexible, ideal for color measuring instruments. At present, some foreign press is equipped with color printing products quality inspection of the color measurement instrument is the use of spectrophotometer.