Introduction | Digital Presses | Digital Desktop Printers | Digital Copiers | Direct Imaging Presses | Output Considerations

Introduction

The method of outputting a digitally prepared print application depends on a number of considerations. The quality required, the delivery date, and the budget are all factors that may determine the best means of outputting the job.

Many digital presses, digital desktop printers, and digital copiers use dry toner technology. Although dry toner technology provides excellent results and is continually improving, it is a completely different process than, for example, traditional offset printing. For some applications, images printed with digital equipment may look as good or even better than the same images printed with traditional methods. However, for most applications, when the quality is the most important consideration, traditional printing methods such as offset lithography are still the preferred choice. It is difficult for digital print technology to achieve the fine print resolution that can be accomplished with traditional methods.

Although the output rate is faster, the overall process of producing print applications with traditional printing methods is usually much slower because of all the manual preparation involved with prepress, press make-ready, and finishing. A job may take several weeks depending on the quantity and degree of difficulty. It is usually best to use conventional methods for producing the largest print applications such as magazines, newspapers, and business forms.

When the budget is the main consideration and the quantity is small (under 500), then copying may be the best choice. Larger quantities can be output economically on desktop printers and digital presses, and the largest jobs are more cost effective on direct imaging equipment or traditional presses.

In most cases the print provider decides the method for outputting a print job. There may also be occasions when the customer is given a choice with the guidance of the print provider. In either case, it is best to have a basic knowledge of the various digital output methods.

Digital Presses

In some ways, digital presses are similar to digital desktop printers, but they are physically larger and can produce larger volumes of documents and at a higher rate than printers. The smaller desktop printers could also be considered small digital presses because some of the same technologies are used for both. Many digital presses use electrophotography to produce printed images and some use ink-jet technology. Many of them can print on both sides of the paper in one pass through the press (duplex printing).

Digital presses are part of the totally electronic workflow, also known as computer-to-paper technology. They utilize an image carrier that can be reimaged with every revolution of the press, which makes it possible to print a different page of content on every sheet of paper that passes through the press. This type of printing is known as "variable data printing" and is a unique feature of digital printing systems.

Like digital desktop printers, digital presses produce documents from electronic files. The processing time through the RIP doesn't allow digital equipment to print as fast as conventional printing equipment. Digital equipment usually cannot exceed a speed of 300 feet per minute.

The price per copy of an application printed on a digital press is usually the same regardless if one document is printed or 1000. The cost per copy may be higher than the same job printed with conventional processes, but the time spent producing the job is less than what it would be if printed with conventional means. This allows for more jobs to be printed within the same amount of time that is required to produce one job with conventional methods. The use of digital presses for various print applications is a good choice, especially if the application contains continuous tone images and the quality must be good.

Digital Desktop Printers

Digital desktop printers are the name given to most of the desktop digital printing equipment in use. Documents that are suitable for output on a digital desktop printer are designed on a computer and stored as digital information. When it is time for an application to be output, the documents are printed directly from the digital files.

A digital desktop printer differs from a copier in that it has the ability to print a new image for each sheet that passes through the printer. Like copiers, digital desktop printers produce documents in which the price per piece is the same regardless of the quantity. Most desktop printers use either electrophotography or ink-jet technology as the method of printing.

There is a wide range of output speeds available based on the type of printer, the manufacturer, the price, and the output resolution. Many digital desktop printers offer a choice of output resolutions such as "best", "normal", and "fast". The normal setting is the default setting for most desktop printers. The fast mode will increase the output speed but lower the resolution. The best mode will decrease the output while providing the best resolution. With a higher end desktop printer, the fast mode may provide as good or better quality as the normal setting on a less expensive printer. The actual print speed of most desktop printers may not be any faster than copiers and in many cases the speed is less, but the print quality is generally superior.

Most digital desktop printers are capable of printing on a wider variety of substrates than copiers. Many types of paper such as bond, glossy, cover, index, and tag can be used as well as label stock, envelopes, and transparencies.

The use of digital desktop printers for small quantities is an economical choice, especially if the application contains continuous tone images and the quality must be even better than what can be achieved with digital copiers.

Digital Copiers

A digital copier can be described as a scanner and printer contained in the same device. An original document is placed on the scanning bed and is recorded as digital information. With the use of electrophotography, the digital information is used to produce copies of the original. The content of the print output cannot change until the digital file is edited or a different item is placed in the scanning portion of the device. Most digital copiers are known as multifunctional units because they are scanners, copiers, and printers rolled into one and some models even include fax capabilities.

Copying is one of the best methods for outputting the smallest quantities (500 or less). If, for example, an application requiring a quantity of one hundred must be produced immediately, the only step necessary would be to place the original document in the scanning portion of the copier and push the start button. The cost per copy is the same regardless of the quantity because there is usually no preparation involved before the copies can be produced.

Although digital copiers have improved significantly, there is still a difference in the quality that they can achieve compared with traditional or digital presses. The toner used with most copiers is not as durable as inks used with traditional printing methods. An analog copier can produce good copies of simple applications with text and line art. Digital copiers are much better at producing accurate copies of more complicated documents, such as those containing continuous tone images (photographs).

A digital copier is more limited than traditional or digital presses with the types of substrates that can be used to produce documents. Copiers are restricted to paper stocks which have a smooth finish. Textured papers provide poor results and substrates other than paper do not work well or cannot be used at all.

The copying rates of various copiers usually depends upon the cost of the device. The more expensive high-end digital copiers are able to produce 50 or more pages per minute, while the lower priced models may produce fewer than 10. Your organization may require a large monthly volume (over 100,000) in which case the expense of a higher end digital copier is justified, but it would not make sense if your monthly volume is low (1,000 or less).

Copying can be an effective output method for a few hundred documents at a time, but is not a good choice for larger quantities because the process becomes less cost effective. Organizations offering quick print capabilities can be a good source for obtaining copies because of the speed and convenience.

Direct Imaging Presses

Direct imaging presses are a good choice for those who want the quality of offset printing with the advantages of a digital workflow. A direct imaging press is basically the same as a conventional offset press except that the image carrier (plate) is imaged directly on the press with digital information. When a new plate is ready to be imaged, the plate is automatically fed onto the plate cylinder from a spool.

Compared to offset presses without direct imaging capabilities, the preparation time per job is greatly decreased when using direct imaging presses. Many of the manual analog steps of conventional prepress and presswork are eliminated, such as producing films, preparing the films for platemaking, creating plates, and mounting and registering plates on the press.

Direct imaging presses are not as economical as digital copiers, digital desktop printers, and digital presses for producing the smallest print runs. They are, however, more economical than digital presses or desktop printers for producing large press runs of static documents due to the higher printing speed they are able to attain. They also provide similar quality as conventional offset presses. Most direct imaging presses produce printed documents that have a minimum resolution of 1270 dpi which is suitable for producing nearly 90% of all print jobs.

Some DI presses are able to print different versions of a document during a single press run, even though they cannot accomplish true variable information printing like a digital press. For example, a five-color press can use four print units for printing the full color static portions of a document and use the fifth unit to print the different versions of text that are needed. The plate on the fifth unit is reimaged at the appropriate intervals for each version that is required. After the plate is imaged, the printing proceeds until it is time for the plate for the next version to be imaged, and so on. The result is a document that has the same layout and color elements, but differences in the text for each version. This is a much better process compared to conventional printing in which a separate base run is printed and then the sheets are run back through the press at a later time to print the different versions of text (sheet-fed press), or when using a roll-fed press, having to print the static portions along with the text for every version.

Output Considerations

The "V" in the outlined box has been enlarged to show the concept of aliasing. The enlarged bitmap letter shows how the pixels produce a jagged appearance.	When anti-aliasing is applied to the enlarged letter, a smoother appearance is achieved.