LFP - Large-Format-Printing
PDS vs Grayscale
Tuesday 27. November 2012 - The following article explains the difference between Grayscale printing and PDS Technology in Grand Format printing.
By Erez Zimerman
The following article explains the difference between Grayscale printing and PDS Technology in Grand Format printing.
The Quality-Speed Dichotomy
High print quality is the name of the game in grand format printing today. If in the past print quality was often compromised in favor of high printing speed, this is not the case anymore. Print buyers are demanding high quality printing. Grand format signage is increasingly being used for indoor signage at Point of Sale (POS) and Point of Purchase (POP) locations. These images are viewed from a short viewing distance and are expected to be of near-photographic quality.
However, in order to remain competitive, print providers are not willing to give up the high velocity of printing they have become used to. Thus printer manufacturers are called upon to develop and manufacture printers that provide both the highest quality while maintaining the fastest speeds at the same time.
Patent-pending Parallel Drop Size technology – PDS – offers a solution that allows the desired WIN-WIN formula for printing at high velocity and achieving POP print quality.
Why is it so hard to achieve high quality printing without compromising speed?
This article will expand a bit about inkjet technology. In inkjet printing, the carriage, containing the printheads, moves back and forth across the media, while the heads inject a multitude of ink droplets onto the media. Each print head is made up of a large number of nozzles. Each nozzle ejects a single droplet of a specific size at a time. The frequency at which the nozzles are able to eject droplets is one of the key factors that determine the printing speed of an inkjet printer. Additional factors are the carriage speed and number of print heads.
Now let’s talk about the size of the droplets. In principle, the smaller the droplets are, the higher the quality of the printed output is. Small droplets enable sharper details and better color transitions. The down side of using small droplets is that they make it harder to reach high density. To reach a solid color, you would either need to print at slower speeds or print more passes over the image – both resulting in lower speeds, or else you would need to add more printheads, which adds to the printers cost.
How does Grayscale work?
Grayscale printing technology was invented some years ago in order to provide a solution to the quality/speed conflict. Printers that use Grayscale technology have small nozzles that eject small droplets. In order to obtain density, several droplets are injected at a very high frequency out of each nozzle, meeting each other in mid-air, combining into a single, larger droplet. This indeed achieves better density; however this is done at the expense of both speed and quality. The fact that each larger droplet is the result of several smaller droplets that were injected reduces the actual frequency, resulting in slower printing speeds and the larger droplets reduce the quality.
The following illustrations explains this better. Three work modes of grayscale are shown. Let’s assume that the size of the small droplets is 12 pL (picoliter) and the maximum print-head frequency is 30 kHz:
In Grayscale there are 3 possible work modes:
Small droplets
Large droplets
Full grayscale droplets
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1. Small Droplets Mode
Small 12 pL droplets are injected onto the media at 30 kHz.They meet the media at the same 30 kHz frequency.This mode provides detail, but low density. In order to gain higher density, frequency must be high, thus print speed is reduced.
SPEED IS COMPROMISED
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2. Large Droplets Mode
Three small 12 pL droplets are injected at 30 kHz and combined in mid-air, reaching the media as one, larger 36 pL droplet. Due to the fact that the 36pL droplet is made up of three 12pL droplets the frequency is divided by three, thus the 36pL droplet meets the substrate at the lower frequency of 10 kHz. This mode provides good density, but low detail. Speed is cut by three.
QUALITY AND SPEED ARE COMPROMISED
3. Full Grayscale mode
A combination of large and small droplets are injected onto the media at 30 kHz frequency. As in the case above, in order to inject a 36 pL droplet, it is necessary to use a frequency of 30Khz, but now the small droplet will need to be injected at 10Khz in order to meet the overall printing speed. Thus, the actual frequency at which they meet the media is 10 kHz. Quality is good but speed is cut by three.
SPEED IS COMPROMISED
To be honest, it is theoretically possible in grayscale to get both small and large droplets in the same run, but to date, to the best of my knowledge, there is no grand format printer that is actually doing this.
Thus, in Grayscale printing you can get either quality or speed. Not both at the same time.
Matan’s patent-pending Parallel Drop Size technology – PDS – offers a solution that allows the desired WIN-WIN solution, printing in high velocity and having POP print quality.
How does PDS work?
Matan’s R&D has invented a revolutionary technology, Parallel Drop Size – PDS, which solves the quality/speed dichotomy. Using this patent-pending technology, it is possible to achieve high definition print quality, while still maintaining the same high production printing speeds that the Barak line of super wide format UV printer is renowned for – up to 353 sqm/hr (3800 sqft/hr). The smart software algorithm instructs the printheads to simultaneously inject small 20 pL (picoliter) droplets together with larger 40 pL drops. The innovation is that you are no longer dependant on the printhead’s firing frequency. The drops that come out from the printheads of the Barak are either 20 or 40 pL in the same run. Small droplets create fine details, while the larger drops achieve ink density.
PDS – Parallel Drop Size Technology
Small and large droplets are simultaneously injected at 30 kHz frequency.
The droplets reach the media at the same frequency of 30 kHzBoth detail and density are obtained.
BOTH QUALITY AND SPEED ARE HIGH. NO COMPROMISES.
These fantastic results are now brought up to the next level in the new Barak 8Q, where PDS is combined with 8-color printing, producing stunning high-definition images for both outdoor and indoor applications.
To conclude, Grayscale printing enables either high quality or high speed. You can’t have both. PDS provides both high quality and high speed at the same time.
About the Author:
Erez Zimerman has been specializing in digital printing for over 15 years. He started his career at the Indigo R&D department. Later he joined Scitex Vision (acquired by HP) and filled several R&D roles, including as Electronics Engineer, System Engineer and Electronics Team Leader. Having gained a track record in developing wide format printers and technology, Erez joined the Marketing Department in the position of Product Manager. Next, Erez worked for 4 years at Objet Geometries, a company that develops and manufactures 3D printers based on ink jet technology, as Asia Pacific Marketing Manager and Product Manager. Erez has been with Matan since 2010 and currently serves as VP of Marketing. He holds a B.Sc in Electronics Engineering and an MBA from Bar Ilan University. Erez is a Triathlon athlete. He lives outside Tel-Aviv with his wife and two young children.