Trap process
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
In the process of color printing and copying, the overlapping of text and figure often occurs. When these objects (text, graphics and images) overlap each other, the front side will cover the back, and the printing will usually be in front. The object is called the foreground, and the object behind it is called the background. If the colors of the upper and lower "layers" are different, then we need to be precisely aligned in the subsequent imposition and printing process, otherwise it will appear white in the overprinting part. Or color overlap, which ultimately affects the effect of the output image.
However, due to equipment and process, people can't do absolute registration in the true sense, even in the digital printing era. Because when the paper is transferred at high speed on the printing press, it will generally produce slight shifting and stretching. In addition, the paper will have some deformation after absorbing the dampening solution and ink, which will bring a set of color products. Quasi-problem.
In order to avoid the influence of the deformation of the printing material or the relative displacement of the material on the printing quality, people apply trapping control (also called trapping) at the overlap of various objects to solve the problem, that is, before the printing. At the time of production, the computer software is used for proper processing, and the overprinting range of each color block is adjusted, thereby avoiding the phenomenon of white edge leakage, and this process is called a trapping process on printing.
1 trapping principle
The simplest understanding of the trapping principle is to create a mutual overlap between the foreground and background colors by means of indentation and expansion, thus ensuring that no white edges are produced between the two different colors. The outer expansion corresponds to the enlargement of the foreground color object, and the background color block size remains unchanged, so that the outer foreground block is overprinted on the hollow background. The indentation corresponds to the front view block keeping the size unchanged, so that the hollow portion of the background color is reduced, so that the foreground color block is overprinted on the reduced edge of the hollow portion of the background color block. Usually in the trapping process, whether to use internal contraction or external expansion mainly depends on the contrast between the foreground color and the background color. Generally speaking, the following principles are followed in the expansion: the background color is not expanded, the foreground color is not expanded, and the light color is not expanded. Color, there is also a flattened net without expanding the ground. The reason is that the background color, light color, and flat screen have less visual impact on people than on the foreground and dark colors. Otherwise, people will easily notice changes in the shape of the object.
What is the external pixel value? This mainly depends on the performance of the printing material, the registration accuracy of the printing equipment, and the printing method. Due to the improvement of the machining technology, the precision of the general printing machine is very high, so it is not very difficult to ensure the registration of the printing, but The factors of printed materials are not controlled by the printer, and the trapping values, such as newsprint and plastic substrates, can be appropriately increased for easily deformable substrates. For the coated paper with a small expansion ratio, the trapping value can be appropriately reduced. The trapping value can also be appropriately increased in the case where the old device is degraded due to other reasons such as machine wear. In addition, the trapping value can be appropriately increased for the rotating device.
In fact, in the pre-press production process, it is not necessary to set the trapping value. In many cases, there is no need to set the trapping value. The trapping function has a good effect only when there is a clear two-color intersection connection in the file, and the contrast is very strong, but trapping in a low contrast area tends to cause blurring of the image edge, so it has continuous Transition-tone images or gradient graphics generally do not require trapping.
2 trapping method
Usually trapping can be achieved in two ways. One is related prepress software in the field of desktop publishing, such as image processing software Adobe Photoshop, graphics software Adobe Illustrator, Macromedia Freehand and group software Adobe Pagemaker and Indesign, QuarkXpress With trapping function. One can use the "Trap" function to apply trapping effects at various object overlaps. The second is the use of professional trapping software. At present, quite a number of printing process providers and some output equipment providers provide professional trapping software. Previously, such professional trapping software generally processed PostScript files, such as Adobe Trapwise launched by Adobe. Process PostScript files on the application workstation (as RIP in the imagesetter), convert some of the image information into pixels and dots in the file, and then make trap settings on all adjacent objects. The current digital processes generally support the PDF file format, so there are a large number of PDF trapping tools on the market, such as Agfa's In-Rip Trapping and Heidelberg's Supertrap and Supertrap Plus trapping tools.
No matter which software is used to process the trapping, in principle, it is mainly realized in two ways, that is, expanding the object by external expansion or indentation or calculating a color ribbon from the edge pixel values intersected by the color blocks. Color value and position. Specifically, the first method includes a layering method in which trapping is performed on the different layers by indenting or expanding the elements, and the shifting method is performed by moving the inflection point position in the color block. Indentation or expansion, used in trapping related to the gradient.