Digital printing and traditional (analog printing)
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In the field of printing, the common traditional printing has the following methods:
● Lithography Printing: such as lithographic printing, keban printing, also known as direct printing.
Such as offset printing, also known as indirect printing. It transfers the graphic information on the printing plate (such as the PS plate) onto the blanket, and then transfers it to the paper through the blanket and the impression cylinder.
● Letterpress Printing: such as type printing and flexographic printing.
● Gravure Printing: such as photographic etching and electronic engraving.
● Silk-screen printing: such as screen printing or metal screen printing.
The above four traditional printing processes are as follows:
In the above four printing processes, the collection, processing (such as color separation, revision, plate making) and printing (text information recording) of the original information are performed in an analog mode or an analog-digital hybrid manner.
What is analog? What is digital? This is the boundary between analog printing and digital printing.
Let's talk about what is analog? What is a digital quantity?
There are two mathematical features of the analog:
● Continuous in space.
● The values are continuous.
Specifically, the values on the coordinate axes of the two-dimensional space or the three-dimensional space are continuous.
For example, an image (whether flat or stereo) has its optical signal (light or dark) or electronic signal (strong or weak), its value is arbitrary, and the value on the signal axis can be infinite.
Usually referred to as spatially continuous, the continuous value of the image is an analog image (Analog Image).
The simulated image can be taken by a conventional camera, or it can be a drawing, written text, etc.
If the densitometer is used to measure the density value of a photo (or negative film), the value is arbitrary, the area with low density is called the highlight area, and the area with high density is called the dark area, which is called the middle adjustment between the two. Area.
If the original density is the abscissa and the dot area ratio (%) of the printed matter is plotted on the ordinate, a continuous continuous curve, also called a Tone Carve, can be drawn.
What is digital? The characteristics of the digital quantity are:
● Discrete in space.
● The value is limited.
An image encoded in binary numbers is shown in Figure 1.
This image is composed of discrete pixels (Pixel). The spatial pixels of the image are arranged by equidistant rows/columns to form a rectangular array of pixels. The value of each pixel is discontinuous, only a limited number.
In practical applications, a black and white image has only two values, namely “0” or “1”, where “0” stands for white and “1” stands for black, as shown in Figure 2.
Figure 2 is also known as a Bit map or a Raster Image Processor. It is also the most common way to express digital images to date. Bitmap file formats are various, the most commonly used formats such as JPEG format, TIFF format, bitmap format, etc.
In common eight-digit images, the signal (or light and dark) has a total of 2 8 = 256 values, which means that a gray image on a computer screen can only have a maximum of 256 gray levels (ie, light and dark levels).
If a color image on the display consists of three components R (red) G (green) B (blue), each component takes eight bits, then the number of information after the three components are superimposed (ie, the number of colors) It is 28 (R) × 28 (G) × 28 (B) = 224 = 16.7 mega-color.
When we know what digital and analog are; what is the basic concept of analog and digital images, it is not difficult to judge what is the traditional printing method, what is the digital printing method, and what is the analog and digital printing method.
Analog images such as painting originals, negatives and photographs taken with conventional optical cameras are in the category of analog images.
Digital images such as optical discs, magnetic disks, or images downloaded from the Internet can also be images taken with a digital camera, or images obtained by scanning an analog image through a scanner.
Either way, the process of converting an analog image into a digital image is: firstly, the simulated image is divided into equidistant rows/columns, that is, divided into several small squares, which are also called gratings, each of which is called a grating. A pixel in a grid is also called a pixel. The eigenvalue of each pixel is discrete and the value is limited. For example, a black and white image of 1 bit may only have two values, namely "0" or "1". "If the 2 digits only have four values (00, 01, 10, 11), the corresponding shading gray is 2 2 = 4. Similarly, the gray level of the 8-bit image is 2 8 = 256, 16 The gray level of the bit is 2 16 = 65536. (See Figure 3)
Second, computer direct plate making and printing technology
Since computers only accept numbers, computer platemaking and printing technologies are also known as digital plate making and digital printing technologies. Since digital printing (such as inkjet, laser, thermal sublimation, thermal transfer, static electricity, etc.) does not require pressure, it is also called Non-impact Printing.
Computer-to-plate and printing technology systems:
Combined with the current situation in China, computer direct printing technology has the following three ways:
1. Computer to Film.
2. Computer to Plate.
3. Computer to Press.
Whether it is production, plate making or printing, originals including images, graphics, and text must be digitized before printing, and then grouped and impositioned. As shown in Figure 4.
In Figure 4, the image (such as color photos, drawings) is scanned to obtain a digital image, processed by the software Photoshop with image processing and color separation function, and then passed to the group software (such as Pagemaker) group software can be entered. Text, designed graphics and color-separated images are compiled into large versions by the group software, and the most commonly used PS (PostScript) format is used to generate digital files. At this time, the digital files can be sent to the computer for direct production. , plate making and printing.
The RIP (Raster Image Processor) in Figure 5 is also called raster processing (which can be a software or a hardware). Its function is to convert (or translate) the entire page imposition PS file into a control tablet. The platesetter and printer can output film, plates and prints close to the original.
1. Computer to Film
The computer direct production system can produce C, M, Y, K four full-page imposition film (also known as film), which is passed through a laser beam by a computer-controlled internal drum (or external drum) laser imagesetter. Scanning enables the film to be imaged (including text, graphics), and then developed and fixed to obtain a set of photographic film for printing. With the computerized version, there is no need to manually cut, trim, assemble, collage and other complex processes, which will greatly improve production efficiency and ensure the quality of the workpiece, and can be stored for reuse next time.
2. Computer to Plate
The use of computer-to-plate equipment will eliminate the computer directly from the film equipment, so the process of using the film to print the film will be abolished, and the film will be abolished. The biggest advantage of computer direct plate making is that the process is simplified and the efficiency is improved, but the main improvement is the quality. It can produce 1% to 99% tone value and can print fine products of 200 lines/inch to 300 lines/inch. These are unmatched in the PS version made with film.
The process of directly imaging a computer on a printing plate must also be developed and then printed by a conventional printing machine, either in single or web printing.
3. Computer to Press (Computer to Press)
Although the computer direct filming and computer direct plate making mentioned above adopt digital technology, the printing still uses the traditional simulation technology, so the whole process from the original to the printed matter is called the digital-analog mixing process.
After the original data file is combined into a large version, it is directly transferred to the printing machine to produce a printed matter called digital printing.
This is a new technology. It abolishes film, plates, and manual operations (such as printing collars, etc.). Computer direct printing technology can change the printed content at any time, from the beginning to the cost of printing thousands of copies, which is different from the traditional printing method, because traditional printing must produce film, plate, print and print thousands of sheets. The difference is huge. Therefore, digital printing is most suitable for short-lived and personalized work.
There are many kinds of equipment for direct computer printing, such as inkjet, laser, sublimation, static electricity, etc., no need for printing plates.
Figure 7 is a computer direct printing system based on the electrostatic principle, which uses liquid electronic ink for multicolor printing.
Its printing principle is: the computer scans the graphic information through the laser to the organic photoconductor roller PIP. According to the principle of electrostatic photography, the graphic part generates a positive charge, so the development of the negatively charged electronic ink, that is, the absorption by the opposite sex charge The principle is to transfer the toner ink to the image part of the organic photoconductor, at this time the roller PIP with the toner, transfer the image to the intermediate drum 1, (the drum 1 is similar to the offset blanket cylinder), the paper passes through the drum 1 and the roller 2 (similar to the offset printing cylinder), then the first color is printed on the paper, at which time the original graphic information on the roller PIP is completely erased, the laser scans the second color plate, and the paper is on the roller 1 and roller 2 again and again, at this time the paper is a two-color overlay. Therefore, the 4-color printing must be scanned 4 times, and the paper can be printed 4 times between the drum 1 and the drum 2 to complete the 4-color printing. This method is similar to the principle of printing color on a monochrome offset printing machine. It needs to be changed and replaced with ink, and 4 times of overprinting can obtain color.
The computer direct printing system E-Print 1000 exemplified above is a product of 1995. The current digital press has been greatly improved.
There are many types of computer direct printing systems, which are not discussed one by one. Their common features are simplified process, simple operation, and strong individuality. They are suitable for short-lived and short-lived personalization.
Commercial computer direct printing systems typically require millions of dollars in investment, while office computer printing systems require investments ranging from tens of thousands to hundreds of thousands of dollars. Home computer printing systems (such as inkjet, laser, sublimation) require an investment of several thousand dollars.
Therefore, the investment required for different uses, different grades, different qualities, and different production efficiencies varies. Users should choose the products that suit them according to the production target, activity and efficiency.