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The Fundamentals of Digital Printing

(December 1999) posted on Tue Dec 14, 1999

Consider these ideas and options before going digital


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Are you ready to jump on the digital-printing bandwagon? Does your competition already own a wide-format inkjet or thermal-transfer printer? If you answered yes to any one of these questions, you're probably serious about making the "digital" leap. Before you jump, however, consider the mistakes we've made - and try to avoid them. Our digital-printing experience dates back to 1989 when "dinosaurs" ruled the digital world (we're referring to electrostatic printers, not a Gutenburg press). We'll discuss the equipment and components you need and the decisions you should make for quality printed results and successful installation. After reading this article, you'll know more about such things as printer technology, computer-system requirements, software issues and peripheral needs.

Digital considerations

First, consider how you're going to use a digital printing system: indoor/ outdoor usage, vehicle/tradeshow graphics, decals, photo enlargements, etc. Consider all your options because they'll dictate your equipment and software needs. Also, keep in mind, each technology used in this environment has pros and cons. You also have different options regarding technology types; however, we'll concentrate on wide-format inkjet and thermal-transfer printers. The prices (for these printer types) range from less than $2,000 to more than $50,000.

Inkjet pros and cons

Now, let's look at the pros and cons of wide-format inkjet printing. The pros of this technology include the capability of printing short-run, full-color posters and indoor point-of-purchase signage; low-cost of printers; an array of media types; 50-in. print widths; flexible print length; and stand-alone driver support. The cons include short-term outdoor durability, an absence of vehicle-graphics media, the use of laminates for longer outdoor durability, and difficult liquid-ink handling.

Thermal-transfer pros and cons

Like wide-format inkjet printing, thermal-transfer printing has its advantages and disadvantages. The pros of this technology include the capability of printing outdoor graphics and decals, vehicle graphics, and full-color logos, as well as the ease of handling dry ink. The cons include high-cost of ownership and limited print widths and areas.

Inkjet specifics

If you are expanding your business to include short-run posters or indoor point-of-purchase signage, you should look into purchasing an inkjet printer. For starters, inkjets can print on a variety of media including adhesive-backed vinyl, canvas, photopaper, and various film types. Also, the output quality is good - if you're marketing your digital printing well, don't be surprised if you begin using all the media types. There is, however, a drawback regarding the adhesive-backed vinyl: Its outdoor print life (without lamination) is 6 months-2 years. Because of this, inkjet-media manufacturers are looking to extend the outdoor durability. Of course, using UV-resistant laminates does increase the sign's longevity, but it also inflates the output cost.

Generally, inkjet printers cost less than thermal-transfer machines. And, the new low-cost units offer the same image quality as their big brothers. However, there are some factors to consider. For about $2,000, you can purchase a printer with a 24-in. print width. Keep in mind that the low-cost inkjets use replaceable cartridges - you'll probably get 4-10 fully saturated, D-size (24 x 36-in.) prints from a set. And more than likely, you'll run out of ink (and ruin your print) in the middle of a big printing job. Now, the more expensive inkjet machines solve this problem by incorporating bulk-ink systems. The bulk-ink system allows you to refill (at will) the ink levels, without interrupting the printing process.

Inkjets come in a range of sizes, and generally, a wider width indicates a higher cost. Because many sign-makers commonly use smaller widths, the 24-in. width is commonly sufficient for most. When choosing your printer size, consider the sizes your clients are requesting - conduct a survey if possible. Remember, investing your time from the start will keep you from making the wrong choice. Inkjets also have smaller print widths (as small as 12 in.). The only length limitation you will encounter is the length of media purchased - you'll have to purchase 100 ft. or more.

Thermal-transfer specifics

Now, if your goal is to produce vehicle graphics, long-term outdoor signage and decals, or full-color logos, then a thermal-transfer printer is your best option. A great benefit of thermal-transfer printers is that they print directly onto the vinyl commonly used for outdoor signage. You'll stock the same vinyl whether it's for cutting or digital printing. This is an important matter to consider when making your final buying decision.

Generally, thermals operate faster than inkjets. The speed used to complete the drawing does include the processing time on the computer. This is called the throughput speed. Both thermals and inkjets take up an equal amount of computer time when comparing a same-size print. It's actually the print time that's faster with thermal-transfer printers. If speed is an issue for your shop, then you need to benchmark the system. Ask your sales personnel for general throughput times. Remember, digital-printing files are hogs.

Dry ink is also an excellent selling point. Thermal-transfer machines use a multicolored ribbon or ribbons to designate a three- or four-color output. Many manufacturers offer spot colors (other than CMYK) and even metallics. If you plan on moving the machine around, you might consider the dry-ink alternative &emdash; you can easily remove the ribbons.

The low-cost thermal-transfer printers are restricted in size and media variety. For example, some thermal machines only print on cut sheets; others are restricted by the ink-ribbon size. The higher-priced printers will print on 15-in. media at lengths up to 50 ft. These machines are precise and allow you to tile large images &emdash; as is possible with a vinyl cutter. Of course, the smaller printers are still great for producing decal work, and their images can be tiled together as well.

Computer systems and processors

At this point, let's look at what type of computer system you'll need. Today, bigger and faster certainly means better; therefore, a fast Pentium is the best choice if you're a PC user. For Macintosh users, a 680040-based system is a minimum requirement. The PowerPC-based Macs are generally preferred. With a vinyl cutter, you can easily run an older, slower system like a 486 PC, but this isn't sufficient for a digital printer. You must have the horsepower needed for large-format printing. If you don't have it, the prints will not process.

Computer memory

Just having a fast processor doesn't prepare the system for digital printing. The most important addition to any computer is memory. The more memory your computer has, the better it will run. It should have a minimum of 16 Mb; however, a minimum of 32 Mb is more likely. Trust us, you can never have too much memory. In addition, your computer will need an abundance of free disk space - a minimum of 200 Mb. This actually means 200 Mb of free space, not total disk space. Remember, digital images are very large and tend to be memory hogs. Nothing is more frustrating than getting an "out of memory" or "out of disk space" message after an hour of file processing. Memory and hard drives are cheap, so don't cost-cut in this area.

If your system is not up-to-date, you will have to invest in a new system or at least upgrade your existing system. Considering today's computer prices, it makes more sense to buy a new system. Remember, you can always use another system, and hopefully, you have this covered.

Scanning devices

If you don't already have one, owning a scanner is essential. Primarily, digital printing is photo-based, and the best way to produce the input files is through a quality scanner. A 600 x 600-in. optical scanner is an economical choice, and flatbeds are better than inexpensive page scanners. When you make your scanner choice, make sure it's at least a 24-bit color scanner.

Software types

Now that you have a printer and a powerful system, you'll need software to run them. Here is the area where the most amount of confusion and difficulty occurs. In fact, you could spend as much for the software as you did for the printer. In this case, your software can be a professional sign package, and the good news is that you might already own one. It's possible that you'll only have to add the plug-in module for digital printing. Be sure to consult your sign-package salesperson before making any buying decisions.

There are many "buzz" words to further confuse the situation - RIP and DRIVER are the most common. These two items are classified as software. What's most important is how good a job the software does in producing a desired print.

Raster image processors (RIPs)

The RIP has come to mean PostScript RIP. Now, is it important for you to own one of these? Not necessarily. PostScript is a fairly standard method of describing a printed page. Many of the desktop laser printers already have a PostScript RIP built into them. Either a computer application (such as Adobe PageMaker or Illustrator) or a specific printer driver will convert your drawing or page into PostScript language. The RIP understands PostScript and converts the file into the printer's native language. You have experienced or produced PostScript files if you've ever used or saved an encapsulated PostScript (EPS) or Adobe Illustrator (AI) file.

Printer drivers

A driver is a component of your operating system (Windows 95 or Mac OS). It connects the application to the printer. The applications could be Adobe PhotoShop or PageMaker, QuarkXPress, CorelDRAW!, etc. When you purchase the printer, you'll usually receive a driver diskette with it. Keep in mind, you must install this driver to print to the device (unless you have a RIP). The driver takes the system's native graphic-description information and converts it into the printer's native language. So, when you connect and load this driver, you'll be able to print to it directly without a sign package.

Driver or RIP?

Do I need to invest in a RIP? If the driver is a standard printer option, why would I need the RIP? To answer these questions, let's look at what it takes to get a good print from a digital printer. Overall, you want smooth transitions between the colors without obvious banding. Colors should match the screen as close as possible. Areas filled with tints should appear solid and not grainy. And, of course, you want "big" so that the image won't "fall apart" when it's scaled. You also want the controls to be easy and obvious to use. This is not all a given with a driver. Some printer manufacturers rely on third-party, software-application programs to take care of these issues - sign packages, for example.

Drivers have improved in recent years. For instance, some drivers offer color controls and a choice of dithering or screening patterns. Most, however, rely on the afore-mentioned applications for scaling. In this case, many applications do not allow for extra-large page sizes. Consequently, tiling panels to make a super-large print is virtually impossible. Fine-tuning the color controls is also either limited or non-existent. If you have embedded EPS files, you must have a PostScript RIP for them to print properly. This could either be accomplished by a sign package that handles PostScript information or a hardware controller.

Now, if you intend on driving multiple digital printers, you'll probably want to use a RIP that offers a faster throughput speed and proper printer switching. The bottom line: Unless you'll be printing just from an application like Adobe's Photoshop, you'll need some form of RIP to take care of PostScript files. Most well-known sign packages contain a RIP as an option. Plug-in modules for digital printing would certainly be available to the user. It does help to have the software package drive the vinyl cutters and digital printers.

Ready to digitally print?

You've got it all now - printer, system and software. Are you ready to digitally print? If you want exceptional prints, you should follow a few standard rules. Inkjets pose a unique problem: The heads can clog and burn out causing one or more jets to not fire. This will greatly affect the quality of your output. As a precaution, the first thing you want to do every morning is prime the printer. The printer will produce a small printout that indicates possible jets out - this is important to know before launching your print job. Fixing a non-working jet could be as easy as cleaning the head or replacing the cartridge.

Getting quality prints

The most common problem is the source image being too small. In this case, we don't mean dimensionally; rather, we're referring to file size or resolution. A 72-dpi file that looks great on your monitor will probably look grainy or pixilated when scaled to a large size. Detail will not appear because it's just not there. You need to have more pixel resolution to get a good output image.

How big is big? We prefer to have files in the 10-20 Mb size for a standard 3 x 5-in. photo. We scan at actual size (200-300 dpi) to get this file size. This will be controllable from your scanner driver. At 200 dpi, the photo will blow up properly to a 24-in. width with almost no apparent image degradation. If you are producing wider images (36-48 in.), 300-400 dpi will work just fine. Just remember, the larger the file, the more disk and processing time it will take.

A common problem with scanned images is that they appear too dark. To solve this problem, most people will use a paint program and the brightness/contrast controls to lighten the image. Usually, the result is a washed-out image with loss of detail. The best way to handle this is to use a white-point control. This feature is common in many image-editing packages and may also be found in your scanner driver. What you want to do is locate an area in the image that you know is white. The control will be an eyedropper or something to that effect. Once you click the eyedropper onto the point that should be white, the image will brighten up without losing any detail or color.

Color is the biggest headache of digital printing. Matching the colors you see on your monitor to what the printer produces is virtually impossible without investing in specialized equipment and software. In most cases, however, your customer is looking for colors that come close. Reds are red, blues are blue, and most important, flesh tones appear as they should. We could write an entire article (or book) on the art of color correction. The easiest way to achieve sufficient color is to use pre-matched links or profiles that work with your printer. Most of the RIPs and drivers will offer color/media combinations that automatically adjust the color. Use this function if it's available. You will only run into problems if you use different combinations of ink and media.

Conclusion

You now have the solutions to the most common pitfalls of digital printing. As you've read, it's not just a matter of which printer type to buy. The system and support software must be robust enough to handle the large demands of huge files. We've also explained how to correct the most common problems with the actual print process. After a while, you'll develop your own recipes for outstanding digital images.

Additive color: A color model associated with the RGB (red, green, blue) method of representing color. Equal amounts of the primaries will combine to produce the perception of white light. This is normally used in video systems/monitors.

Adobe Illustrator™: A software package for designing and illustrating. Some features include: a complete set of drawing tools, on-screen drawing and EPS-file formatting.

Airbrush printer: A large, digital-print machine (for printing billboards, etc.) that uses compressed air to drive inks through the printhead.

Aliasing: The stair-stepped (jagged) appearance in printed diagonal lines.

Anti-aliasing: A technique that smoothes the printed appearance of stair-stepped (jagged) lines. One method is to fill the edges of the line with varying shades of color (or gray). This method averages the brightness values of the edges.

Application: A computer software program that performs specific functions such as page layout, word processing, accounting, drawing and spreadsheet formation.

ASCII (American standard code for information interchange) (pronounced as-kee): ASCII is a computer code used to transfer numbers and text data between computers that run different software applications.

Banding: In digital printing, this term refers to patterns on a print caused by insufficient color or gray-scale ranges within the output device's image processor, or insufficient information contained within the original scan. Banding is most noticeable in printed areas that fade from light to dark.

Baud: A measure of speed in data transmission. Baud has the same meaning as bits per second.

Binary: A system based on the numbers 0 and 1 as on-off switches. There is no middle ground; electrical signals are represented by electrical current being positive or negative, on or off. All computer data is based on the binary system.

Bit/byte: Measurements of computer data. The bit, or binary digit (0 or 1), is the smallest unit of information a computer can work with. Because computers represent all data in numbers or digits, they are digital devices. Thus, these digits are measured in bits; each electronic signal becomes one bit. However, to represent more complex data, computers must combine these bit signals into larger groups called bytes.

Bitmap: Generally, a bitmap is associated with graphics objects. The bits are a direct representation of the picture image. In a monochrome system, one bit in the bitmap represents one pixel on screen. With color (or gray-scale) systems, several bitmaps in the bitmap represent one pixel or group of pixels.

CAD (computer-aided design): Software used to produce designs and drawings for architectural, engineering and scientific applications.

Calibration: Setting up a scanner, monitor, printer, etc., so that the system produces accurate and consistent results. Because equipment and systems vary, to calibrate is to normalize a system's internal and received information so that it presents predictable colors. If devices or consumables change, recalibration is necessary.

Card: A circuit board that performs a specific computer function (video display, sound or communication) between computers, via modem or on a network.

CAS (computer-aided sign-making): Refers to sign-related software and computer-driven, sign-making equipment.

CCD (charged coupled device): An electronic memory made of a metal-oxide semiconductor (MOS) transistor than can store patterns of charges sequentially. CCDs are used in TVs and scanning devices because they're charged by both light and electricity.

CIE (Commission Internationale de l' Eclairage): An international color standards group sometimes known as the Intl. Committee on Illumination. In 1931, using a spectrophotometer to precisely measure color, this group defined a color model where numbers describe colors along three axes. Because this system can be used to store color information, it has become a crucial part of device-independent, digital-print systems. There are newer color models in addition to the CIE.

CLUT (color look-up table): Another term for a correction table, a CLUT is a color-management software reference file that maintains the proper calibration of devices, such as monitors, printers and scanners. (See also, LUT.)

CMS (color-management system): The process of using device calibration and profiling, software-based color correction, and other utility applications to obtain predictable, quality-printed output. The output must remain within the limitations of the different devices that make up a digital-production system.

CMYK (cyan, magenta, yellow and black): The four colors in the four-color process. The primary additive colors, red, blue and green, when added together, produce white light. When overlapped, red and blue form magenta, green and red form yellow, and green and blue form cyan. These resulting colors are subtractive and when added together, they produce a dark brown. In order to create an accurate photographic reproduction, the color black must be added.

Color correction: The process of simulating the colors or original shade by using color-management software. Often, an inkjet printer serves as the CMYK output device. This process is important because spot colors cannot be acceptably reproduced with the CMYK color model without making adjustments.

Color gamut: The tonal range of colors that can be reproduced by a digital device.

Color measurement: The scientific determination of color. It uses specialized measuring machines to compare colors numerically. There is a CIE worldwide standard that helps the industry compare and match colors.

Color model: Also referred to as color space. A color model is a geometric or mathematical representation of visible colors. Well-known color models include, CMYK, RGB and HLS (hue, lightness, saturation).

Color profile: Also called device profile. This term refers to the relationship between the color models of the system devices.

Compression: The process of removing irrelevant information and reducing unneeded space from a file in order to make the file smaller.

Continuous tone: Like original photographs, drawings or paintings, continuous-tone images contain real gradients of grays or colors.

Cutting plotter: A vector-driven device (similar to CAS plotters) for cutting sign-making substrates. Recent designs include digital-print (inkjet) systems combined with cutting-plotter systems. (See also, Plotter and Printer/cutter.)

Default: An automatic decision that is made by computer software and hardware programs. The decision will automatically be carried out unless the user changes the default settings.

Densitometer: An instrument that measures transmitted or reflected light by indicating the percentage of a given area that is covered by halftone dots. This instrument is used to ensure consistency between films, proofs and printed pieces.

Desktop: In Mac and Windows, desktop simulates the top of the user's desk; the simulated environment appears on the computer monitor being used. The user's virtual desktop is organized through the tiling, cascading or overlaying of Windows.

DIC (device-independent color): The goal of DIC is to provide an independent, universal standard against which color spaces of all devices in a system can be referenced.

Digital camera: A lensed camera that uses a digital sensor for the film. Images are recorded on a disk and can be immediately output on a computer.

Digital color printing: To use multiple printheads that place specified colors of inks in predetermined places. The results are similar to photographs, but are often larger. In fact, some are billboard size.

Digital color-printing software: The computer programs that create digital color printing. The process uses mathematical algorithms to enlarge and print an image. Also, this software often includes add-on features such as color-calibration software, various pattern selections or a print-instruction screen. (See also, RIP.)

Digital imaging/digital printing: Digital imaging refers to the routines that take place before the output methods occur. These routines include: scanning, photo manipulation, color correction and RIPing. Digital printing, on the other hand, refers to a variety of computer-controlled output methods: inkjet, computer-airbrush, thermal-transfer and electrostatic printers and copiers.

Dithering: A graphics display or printing process that uses a combination of dots or textures to simulate an original image or an output device. The purpose is to create the impression of a continuous-tone gray-scale or color image.

Dot gain: A term that refers to the "weight gain" of halftone dots. During the printing process, the half-tone dots increase in size. Because this is an inherent part of the printing process, the effect of increased dot size should be anticipated ahead of time.

DPI (dots per inch): A measurement of linear resolution for a printer or scanner. For example, a resolution of 300 dpi means that there are 300 dots across and 300 dots down. A higher number of dots creates a finer resolution.

Drive: An internal or external assembly that can read and/or write electronic data using disk-storage media. For example, a disk operates much like a cassette recorder/player, with the cassette tape acting as the disk-storage media.

Driver: A small software program that links together the computer and its components and peripherals: printers, scanners and the monitor. The driver functions as a medium.

Dye sublimation: A printing method in which the color (toner or ink) is thermally converted to a gas that hardens on the special substrate used by the printer. When printers use this process, the output appears in the form of soft-edged dye spots that produce smooth, continuous tones.

Electrostatic printing: Printing large-format prints in a process similar to, but not the same as, color photocopiers. If properly done, (and laminated) the images are used for billboards, truck graphics, banners, signs or murals.

EPS (encapsulated postscript): A file type that allows the carrying of different information between software programs.

Error diffusion: In actuality, error diffusion is a random dot-placement strategy (or dithering method), spreading out the inherent failing until it is indistinguishable to the naked eye.

E-stat: A short way of saying "electrostatic."

Ethernet: A commonly used computer network for the movement of PostScript files from one computer to another.

File format: A file format is indicated by a period followed by a three- or four-letter suffix, for example, .COM. The suffix indicates what type of file it is: a document, spreadsheet, drawing, Internet web page, etc. By knowing the properties of the various types of file formats, users can determine which files to open and read, which to import into other files and which offer the best options for scanning.

FM (frequency-modulated) screening: A dithering method that uses uniform dot sizes and varies the distance between them. This method is different from conventional halftone screening, which aligns dots of varying sizes on a regular grid.

Front end: Front end refers to all the hardware and software &emdash; the scanner and computer workstation up to, but not including, the output device.

Gradation: The transition between colors or shades. Gradation occurs by mixing percentages of dominant and secondary color and then altering those colors to bring about a change.

Grand format: Super-large digital-print machines. Their printing process is usually driven by air, but recent machines may piezo print directly on a substrate.

Hard drive: The unremovable part of a computer that houses programs and data.

Hexachrome: A color-matching system that allows for the combination of six colors in order to create a larger gamut of reproducible color.

Hue: A specific shade or tint of a given color. Hue is the measurement of the wavelength of light.

Inkjet, bubblejet: Specifically, Bubblejet is a tradename for a Canon desktop inkjet printer. Bubblejet is also a name used to describe "thermal"-type inkjets.

Inkjet, phase change: This type of inkjet technology uses solid wax inserts instead of traditional inks. The wax is melted and deposited onto the substrate through the printhead.

Inkjet printer: A type of printer that sprays tiny streams of quick-drying ink onto the paper. An inkjet printer produces high-quality printing like that of a laser printer.

Interface: The communication that takes place between a system's hardware and software components.

Internet: A worldwide telephone hook-up between participating computers.

Interpolation: Interpolation is the process of injecting additional dots to digitally enlarge the original.

Large format: Large format generally refers to a manufacturer's definition of its product.

LPI (lines per inch): A traditional halftone screen measurement that refers to the number of lines of dots per inch.

LUT (look-up table): The storage space for pre-set measurements and adjustments for different media, file types, printers, etc.

Media: Another term for substrate. Common inkjet printers generally require media that have special topcoats to achieve proper adhesion and proper drying characteristics.

Modem: A device that transfers computer information across telephone lines. A modem will work with various types of communications software.

Network: A group of computers interconnected by hardware and software.

Overlaminate: A protective clear film that extends an image's outdoor life and enhances its visual quality.

Panel: Also called a tile. A division of a job based on a device's production area.

Peripheral equipment: This term refers to external input or export devices that are physically not part of a computer's housing. Examples include printers, scanners, external drives, modems, monitors, etc.

Piezo-electric: An inkjet printing technology that uses a mechanical-electric charge instead of heat to drive microdroplets through the nozzle.

Pixel: The smallest unit of data in a digital image. Together, the small discrete elements constitute an image that can be seen on a monitor or printed on a substrate. A pixel's code contains information relating to color, tone and placement within the larger image.

Plotter: A term that refers to the CAD origins of wide-format printers. A printer, so to speak, that graphs computer output.

Plug-and-play: A given computer system or peripheral device that is ready to use upon its removal from the box.

Port: An outlet or connection location on a computer which allows a peripheral device to operate. A communications port (COM port) allows the modem to operate, and a local port (LPT) enables the printer to operate.

PostScript®: An Adobe programming language that enables text and graphic images to be output from different devices with consistent and predictable results.

PPI (pixels per inch): A measurement of resolution. A pixel is a unit of data that should not be confused with dpi (dots per inch) or lpi (lines per inch). If there are more pixels per inch, the image will be sharper.

Prepress: Prepress is the process of preparing artwork, film and screens for conventional printing methods.


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