By R. Kamp for ILS 603 - Image Databases


Analog to digital to analog is the general process that a picture goes through before it is print today. First the picture is taken, generally using an analog camera, because the quality and cost of digital cameras currently cannot compare to the picture quality and equipment cost of an analog camera. Once the picture is taken, and incorporated into the catalog, or annual report or brochure, it will then be scanned and turned into digital information in order to make the different plates necessary to recreate the image using four process color. When the plates are put on the press, and the item is printed the image once again becomes an analog image, although this time the color and detail are an illusion created by tiny dots of color, unlike the original photo.


What is four color process?

Red, blue and green are the primary colors of light that the eye perceives. This is the reason that the colors that are used in televisions and color computer monitors are using red, blue and green light. When the three colors of light are mixed together, it creates white, and the absence of color is black. Unfortunately, although these colors mixed together in varying amounts on a screen translate to many colors, on paper this color combination does not work as well. The base colors for the printing process are: cyan (a light blue), magenta, yellow and black. These colors are usually referred to as CMYK.

CMYK are the subtractive colors, or secondary colors of red, blue and green light. When red and green light are combined, yellow light is created, blue and green make cyan, and red and blue make magenta. The three colors are primary colors with cyan being process blue, and magenta being process red. When combined the three colors do not make an adequate black color, so black is the fourth color. It adds depth and sharpness to printed pictures.

A picture has to be broken down into the CMYK color elements. Originally this was achieved by using a process camera and four filters. The filter had a very fine screen made up of dots. Each of these screen would filter out one of the four colors. The film was them processed and "printed" onto a special metal plate that then would be placed on the press. Currently, most printers that print four color copy digitize the images by using a scanner, and create the individual plates from the digital images. There is much more control and it is much more cost effective to digitize the image. The printer can be much more precise about dot placement once an image is digitized, and minor corrections are to make in a digital image. Making changes to photographic plates often meant shooting the picture over, which took more time and cost more for the printer and the customer.

Drawbacks to Four Color Process

There are many drawbacks to four color process printing. It is difficult to make colors look as vibrant as they do in an original photo or even on a computer screen. It is also very difficult to get the printed colors to match the original's. Certain colors are difficult to replicate successfully, particularly reds and violets. Color correction can be a very expensive process. A color problem that is "universal" such as the entire image seems too blue is much easier to correct than a particular section of an image being too dark. Image colors can look vastly different depending upon the quality of the paper used. A highly reflective white paper allows the colors to "look their best" whereas a textured paper will refract the light unevenly creating more variance in the perceived color.

Additionally, many times things that look fine in the prepress or proofing stage, do not look as good when it is printed. Most inks are mixed with water, which can affect dot size and make images not look as crisp, and making changes at the press stage that require more than simple color adjustment, can cause the plates to be pulled off of the press, which can greatly affect when a job is finished.

Improvements in Printing Technology

Many advancements in printing technology have been made in the past few years. Digital presses, stochastic screening, waterless inks, and hi-fi color have taken the printing industry by storm. These processes decrease the time it takes to prepare for printing, the color quality of the reproduction, and a versatility in printing that previously was almost unimaginable.

There are several different approaches to digital presses. Currently manufacturer are producing plastic and metal offset plates allowing the printer to expose them directly to digital data using lasers. This allows the printer not to need separate sets of film. These plates can be run on existing equipment. This advance allows the printer to take less time before running a job because the additional step of turning digital images back into analog plates is eliminated.

Another technology called computer-to-press (CTP) is more impressive in that it takes the digital image ant text straight to an image carrier on the press. For this process neither films nor plates are needed. This can dramatically increase the speed of printing process. The idea of runs of color printing "on-demand" is possible with these machines. Because the digital image must be refreshed between each print, it is possible to change the information on each printout. With CTP a catalog could change from print to print to reflect the demographics of a particular neighborhood, as Klaus Schmidt pointed out in his "Digital Printing is Here" article why should advertisers include information about lawn mowers to people who live in high-rise apartments? A bonus for printers the decreased labor costs when plates and film are eliminated. Last moment changes can easily be incorporated into the final product.

Stochastic screening, also known as Frequency-modulated (FM) is another dramatic digital improvement in printing. Stochastic screening is particularly effective at reproducing continuous tone images such as photographs. The stochastic screen is comprised of tiny (14-28 microns) dots that are spaced randomly. The randomness cuts out one of the major problems with four color process printing which is moiré. The moiré pattern shows up in printing often when printing images of things with a regular pattern like fabric, because the dots that create the image are also in a regular pattern. Instead of the eye tricking you into seeing the whole image, the pattern of dots creating the image is quite evident. The randomization of the dot pattern adds to increased sharpness in the images, and for the possibility of adding more colors to the printing process, because screen angling requirements and dot rosette structures are eliminated. Although the theory for stochastic screening has been around since the 1970's, only recently with improved digitization of images and increased computer capacity has the generation of randomized dot patterns become a reality.

One more improvement in printing technology is the advent of waterless printing. The main theory behind printing is that water and oil do not mix. The oil sticks to the part of the film or screen that attracts oil and the water attracts to rest of the image. Waterless printing has three benefits over traditional inking methods: little dot gain, more image control and less environmental impact. Dot gain is when the color spreads beyond its original boundaries, which can lead to fuzzy images, this is a particular problem with stochastic screens. Because of the lack of water, the dot precision is increased, and the clarity of the image can come closer to equaling the original image. Usually at least 500 sheets of paper are run through a water four color press before any of the images are usable. The waterless press can get by on 50 sheets, thus there is less waste. There is also less waste in the amount of ink disposed, which cuts down on disposal fees and environmental impact. Waterless printing also allows for more paper choices because the paper does not have to be able to withstand wetness and well as press pull.

Due to the advances in stochastic screening and waterless printing, hi-fi color is becoming more of a reality. Hi-fi color is usually defined as printing more color (five, six and even seven) to increase and enhance the range and depth of color that a press can print. Different vendors have had differing opinions as to the best additional colors. One manufacturer uses CMYK plus orange-red, green and violet-blue, another uses CMYK and red, green and blue. Hi-fi color is less of a reality that then other advances mentioned so far because the technological capability is viable, but the best utilization of the technology is not yet known.

Issues with the new technology

All of previously mentioned technology advancements have the potential to improve print image quality, particularly continuous tone images such as photographs, and to decrease the amount of make-ready time and press time. They do have their drawbacks, and printers (especially small printers) may want to wait a bit longer before investing in this new technology, because advancements are being made all of the time.

One problem with the digitally created plates it that it is difficult to make proofs for the consumer to examine before they go on the press. The plates have been created in a standardized way so that they can be used on retrofitted pre-existing machines. The plates are not as durable as traditional plates, so for additional runs new plates would have to be generated. Although, on the bright side, because the plates are created digitally, the new plates will duplicate the old plates.

Computer-to-plate technology is only good for relatively short runs. It is a technology that allows for runs of 50, but is not economically sound for runs over 10,000. In most printing jobs, the bigger the run, the less it cost per sheet. This is not the case with CTP. Because the image is refreshed with every rotation, new information can be added, but every image is a new one so the cost per copy stays the same. The market for on-demand printing is increasing, but unless a printer is sure of its market, it may not be wise to tie up its assets in a new digital press. A printer would have to buy the new press, because their existing presses can not be retrofitted for CTP.

Stochastic screening has many possibilities. One of its drawback once again is in creating accurate proofs for the customer, it may be difficult to replicate printed result in the proof. Another problem may be with the quality of paperstock necessary to create the best images. The combination of stochastic screening and waterless presses seems to work well, but dot gain on a regular press can easily destroy the potential imaging improvements.

Waterless presses are currently only available from one manufacturer, and the ink for the machine is more expensive that for water presses. Another drawback is that the temperature of press must be kept at a constant level or the inks will not take.

Conclusion

Within the past few years printing technology has experienced great leaps in the quality of the printed images they are able to create. Many of the advances have come about because of the improvement in computers and the ability to digitize images at higher resolutions and then output them digitally, in order to keep the image at the same level. This is only the beginning of a revolution in the printing industry.

Resources

Beach, Mark, Steve Shepro, and Ken Russon. Getting it Printed. 1986. Portland, OR: Coast to Coast Books.

Craig, James. Production for the Graphic Designer. 2d rev. ed. 1990. Oxford, England: Phaidon Press Ltd.

Cross, Lisa. "Stochastic, Waterless Prove Winning Combo." Graphics Arts Monthly, v. 67, #7 (July 1995), 74-86.

Schmidt, Klaus E. "Digital Printing is Here." Print, v. 48, #1 (Jan./Feb. 1994) p.115-116.

Schmidt, Klaus E. "'Photographic' Offset Printing," Print, v. 49, #1 (Jan./Feb. 1995) p. 114-115.

Schmidt, Klaus E. "A New Offset Offset Printing Technique," Print, v. 49, #2 (Mar./Apr. 1995) p. 242-243.

Schmidt, Klaus E. "Stochastic Printing," Print, v. 48, #3 (May./June. 1994) p. 119-120.

Sharples, Hadley. "Prepress Gets a Digital Makeover," Graphics Arts Monthly, v. 67, #2 (February 1995), 53-64.

Sharples, Hadley. "New Technologies Divide Short-Run, On-Demand," Graphics Arts Monthly, v. 67, #10 (September 1995), 40-50.

Strashun, Joann. "Hi-Fi Color: Available, but not yet Viable." Graphics Arts Monthly, v. 66, #10 (October 1994), 49-59.

Ynostroza, Roger. "Digital Presses Steal the Show." Graphics Arts Monthly, v. 67, #6 (June 1995), 66-67.

Technical Notes on Prepress Output 1995 Herzig Somerville Limited.

Electronic Prepress Glossary 1995 Herzig Somerville Limited.