Could you please explain the advantages/disadvantages of traditional, stochastic & hybrid screening

Part 2 - Answered by Don Schroeder, Group Manager, Color Products, Enovation Graphic Systems, Inc.

Note from the editor: We believe there are many experts qualified to answer this question. Enovation Graphic Systems' answer is the second of three answers that we will publish over a three week period.

Could you please explain the advantages and disadvantages of traditional screening, stochastic screening, and hybrid screening?

Advantages of FM (stochastic) Screening
FM screening can be advantageous in certain situation, but it is very image dependant. If the images are compatible with FM, the screening can produce very good results.

Disadvantages of FM (stochastic) Screening
Problems with stochastic screening occur primarily in three areas: imaging, proofing and printing.

  • Imaging issues: High-resolution levels are required in order to achieve the best possible results. But, by using such high resolution levels, the opportunities for imaging artifacts coming from imperfect drum balance or beam overlap greatly increase, which often yields slower ripping and plotting times.

  • Proofing issues: If Halftone proofing is used, the proofing media must be capable of achieving faithful reproduction of the very small FM dots, which is difficult for many media types for dots below 20 microns. Press gain must also be anticipated and be built into the proof. If this is different than the plate, it will require two separate calibrations be used. Finally, if continuous tone proofing is used, the system must be capable to simulating dot gain on press.

  • Printing issues: The problem of printing microdots has already been well-established through previous industry attempts at FM printing and is familiar to most printers. The fact that FM is now being combines with computer-to-plate technology does not change that fact. Stochastic screening can be demanding to print (a 10 micron spot = 1% dot @ 300 lpi), there is an increased tendency for ink emulsification and blanket piling, dot gain is significantly higher and tighter process controls are required. Mis-registration on press is harder to judge and correct. And, depending on the image content, the image quality is debatable and mottling and grain problems are common complaints.

    There are a number of screening options available to print buyers and specifiers, including traditional AM screening, stochastic screening, hybrid screening and an alternative (common resolution) screening.

    Fujifilm's Co-Res Screening (Common Resolution Screening) is an alternative screening. That is to say that it’s not stochastic and it’s not a hybrid (AM screening plus stochastic). Co-Res Screening takes advantage of the limitations in the human perception of color and density. At a minimum, a spot must measure at least 300 microns or else the human eye just can’t see it. Additionally, printed matter must be able to show 256 gray levels per halftone in order to avoid the appearance of tone jumps or banding to the human eye. As a result, printers have traditionally needed to bump up the resolution to 4,800 dpi to maintain 256 gray levels at 300 dpi. With these traditional screening techniques, only 64 gray levels are possible at 2,400 dpi at the same screen ruling.

    With Co-Res Screening, Fujifilm’s engineers have developed Multi-Template Technology, an innovative way of arranging halftone dots that allows us to do more with less. Rather than use monolithic dots as in AM screening, each of the 64 dots in Multi-Template Technology consists of a 3x3 matrix, effectively increasing the number of gray levels. The result is that printers can achieve 256 gray levels with 300 lpi at 2,400 dpi and better gradient capability.

    As many printers will tell you, tone jump in the midtones can be a major problem. Co-Res Screening eliminates this problem by varying the dot shape in different parts of the halftone range, yielding a smooth tonal shift, without any unpleasant jump in flesh tones, golden metals and woodwork.

    Generating 300 lpi halftone dots with lowered resolutions can be susceptible to single-color moiré and patterning artifacts, but with Fujifilm’s proprietary Moire Suppression Technology, Co-Res Screening is able to anticipate when and where single-color moiré will occur and alters the dot structure to effectively eliminate any noticeable moiré pattern.

    Advantages of Co-Res Screening
    The biggest advantage of Co-Res Screening is its flexibility and its ability to offer users both productivity and quality.

    With conventional technology, screen rulings of 300 lpi and 175 lpi required output resolutions of 4,88 dpi and 2,800 dpi respectively. This mean printers can increase throughput on their platesetters by up to 1.4 times more plates per hour, depending the CTP device, and because of the lower resolution, users will see greatly decreased ripping, plotting and processing times. Higher platemaking speeds enable printers to increase turnaround time because customer files can be RIPed faster and closer to press time.

    Additionally, Co-Res Screening brings all of the advantages of conventional screening to fine line, high-quality printing. By increasing the screen ruling and decreasing the dot size, Co-Res Screening allows users to produce high-quality 300 lpi printing with the same amount of “work” normally required for a 175 lpi print and it gives users much smoother spot colors and flesh tones, enhanced shadow detail and improved vignette transition and detail.

    Co-Res Screening is based on traditional AM screening, which press operators have been using for many years. Once our Co-Res Screening is calibrated to the proper curves, pressmen won’t see any differences from the conventional screening they’re used to running. Pressmen have a very defined set of processes and targets that they use to make a press run the way they want it to. When we were developing Co-Res Screening, Fuji’s main criterion was to allow the pressmen to continue to use the same set of tools they’ve always used and that what Co-Res allows.
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