Matters needing attention in the application of high-end screening technology in CTP

The advent of the CTP era has not only changed the efficiency and cost in printing production, but also has more and more flexible means of quality control than traditional CTF printing processes, such as: standardization of tone levels and data control are more accurate and color More stable restoration, more accurate gray balance control, more convenient sharpness control, easier to achieve the same appearance of colors in different printing conditions, easier dot reproduction, more popularized application of high-end screening technology, etc. It can be said that revolution in process technology has occurred Change.

With the popularization of the CTP printing process, hybrid screening and secondary FM screening techniques are widely used, however, they all have high-definition characteristics, so there are specific requirements for pre-press, plate-making and printing processes, otherwise the final printing The effect of the product is difficult to achieve the expected value, and even if it is not done well, some aspects are not as good as the quality of the traditional 200lpi amplitude modulation screen. Therefore, if users use high-end screen printing, they must pay attention to the following items in production:

1. Image quality

In terms of quality, the tone transition of the image is normal, the color saturation and clarity are high, and it is necessary to avoid the use of low-resolution images with insufficient information, the loss of tone levels and poor quality images with serious gradation, abnormal color and clarity, etc. . Because if there are defects in the image quality, the hybrid screening and the second FM screening will not only enlarge these defects of the 8-bit continuous tone image when it is half-toned, but also add the influence of the variable factors in the post-production and printing process, so As a result of the accumulated error, the print quality is even worse.

2. The accuracy of the image

In terms of accuracy, the amount of image information is sufficient. If the resolution is above 300dpi, the printing accuracy can be guaranteed. The early screening technology requires “image resolution = screening factor × screening line number, screening factor = 1.5 ~ 2, and the current Founder ’s new screening technology optimizes the layer uniquely, so it does not need to be limited to this formula , That is, 300 lpi screen does not require image resolution must be 450dpi ~ 600dpi.

3. Types of images

The biggest feature of the hybrid screening and secondary FM screening technology is to highlight the subtle layers of the image, which means that the dot technology is good at exerting the delicateness, texture and clarity of the image! For the image color, the color gamut space of the mixed screen printing is not much different from the traditional 200dpi printing. The color gamut space of the second frequency modulation screen printing is larger than the traditional 200dpi color gamut space, but from the visual observation of the printed product and the evaluation of psychological impression From the above point of view, the performance of secondary FM screening in terms of color cannot detonate the observer ’s eye, and the impact is not very obvious. The author speculates that this advantage may only be shown under specific conditions with a very narrow range. Hope that in the future Can be found in practice. As for the image contrast and appearance, as long as the color management in the CTP printing process can completely achieve the traditional 200lpi and hybrid screen printing remain consistent.

Therefore, in order to give full play to the characteristics of hybrid screening and secondary FM screening, the selection of the type of pre-press image in printing production needs to be accurately positioned, that is, not all jobs can be used for high-end screening. The precautions are as follows:

(1) Generally, the images with rich levels of dark tones and uniform distribution of highlights and bright tones are best. Such as: strong texture objects such as clothes, leather shoes and wooden doors; manuscripts with rich highlights, large flat screens and mostly gradients need to be used carefully, because mixed screening and secondary FM screening can be used Reproduce the complete tone level of these images, but due to the influence of post-plate making and printing factors, the restoration of small dots is not as easy as the traditional 200dpi. Microscopically, some dots are restored well, some dots are reproduced poorly, some dots are full of ink, and some dots The ink color is not true, and the final macroscopic reflection on the printed product is that the flat screen vision is uneven and rough;

(2) Character images (especially facial close-ups) require high quality original images, especially smooth gradation transitions, otherwise the transition of gradation transitions may be caused due to the effects of manuscript, plate-making and printing processes, and the face is not soft;

(3) Landscape images (especially the close-up of the sky) also require smooth transition of the original image gradation, otherwise the transition of the gradation transition may be caused by the influence of the original and plate-making printing process, and the graininess is heavy;

(4) For traditional Chinese paintings, oil paintings, gouaches and watercolors, because the general authors paint on rough-textured paper with outstanding texture, although the mixed screening and the second FM screening screen have small dots, there is a disadvantage of incomplete dot restoration in plate making and printing. , But it is not harmful to these manuscripts, and sometimes even becomes an advantage, so it is relatively ideal to print such manuscripts using hybrid screening and secondary FM screening technology;

(5) For newspaper printing, hybrid screening and secondary FM screening can be used in the CTP printing process. These screening methods will make the image more delicate, texture and sharper, which is in line with the characteristics of newspaper printing. And requirements. Perhaps some users worry that the high-definition screen printing will have the problems of dark tone gradation and gradation and blurring during printing compared with the traditional newspaper printing 100dpi ~ 120dpi amplitude modulation screen printing. This is understandable, and it does exist in the CTF printing process. The problem, but it can be solved by color management in the CTP printing process.

4. Plate-making process

Hybrid screening and secondary frequency modulation screening technology are high-precision screening, small dots are more sensitive to the working state of CTP, so the process control in the publishing process needs to be more strict than ordinary amplitude modulation. If the publication is not good, streaks may sometimes occur, and the uniformity and stability of the dots fluctuate greatly. Therefore, for such hanging nets, the publishing status needs to be strictly regulated, otherwise the printed products will have screens, lines and roughness. Quality issues.

5. Printing process

The hybrid screening and secondary frequency modulation screening technologies belong to high-definition screening, and small dots are also sensitive to the printing work status, so the process control in the printing process needs to be more strict than ordinary amplitude modulation. If the dot ink color and the edge smoothness in printing, the ink and ink balance, the rubber surface and the printing pressure are all in a good and stable state, then the reproducibility and stability of such dot printing can be guaranteed, otherwise it will The quality problems such as uneven gradient transition, uneven flat screen clothing and large color fluctuations have caused the effect of high-end screen printing to be inferior to traditional AM screen printing.

With the large-scale introduction of CTP, the application of high-end screening technology to improve printing quality has become the goal and desire of users. The author believes that as long as you understand the characteristics of these special screening processes in depth, make preparations to exert their advantages and avoid their shortcomings, strict Implementation of the "high quality and precision images", "appropriate image types" and "good publishing, printing status" specifications, I believe that the printing effect can be distanced from traditional printing, thereby generating good market feedback!

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