Defining Print Quality

The biggest challenge in defining print quality is that manufacturers measure the quality of print in different ways and often they may be doing it in different languages. So, how do you distinguish and compare print quality of various pieces of digital equipment? Ultimately it is defining the required output quality by evaluating the factors (and facts) of addressability, resolution and registration.

Addressability Fact

You can access the capability of a printer by evaluating a range of variables within the system. These variables include:

• The height of the print head from the substrate
• The size of the ink droplet
• How smoothly the head moves across the substrate
• The set up of the machine and the speed of printing
• The software and electronics incorporated into the RIP and printer

What is vital to achieving fast printing speeds at high quality is a press that jets small drops (less than 30 pico litres) at a high frequency, combined with the ability to handle the data and ink to get the most out of the print head.

Resolution Fact

Some manufacturers try to define quality by quoting dots per inch (dpi), but dpi is not a real measure of print quality. The printer’s dpi, while it should not be completely ignored, will not give an indication of the presses’ ability to reproduce fine detail. Fine detail is achieved by controlling all the variables of the printer including addressability and registration.

Registration Fact

All inkjet printers print better quality at lower speeds – none of them will print at top speed and top quality simultaneously. What is vital to achieving fast printing speeds at high quality is a press that jets small drops (less than 30 pico liters) at a high frequency, combined with the ability to handle the data and ink to get the most out of the print head. The placement of small drops has to be controlled accurately, so that they land where you want them to, in order to minimize shadowing caused by turbulence. The placement of drops is also controlled through the software, the pulse widths and the voltages. These factors control tails and satellites as well as place drops precisely. Without this control you won’t be able to reproduce fine text or clean lines and curves on the equipment. A small droplet size will not necessarily guarantee quality, but the accurate placement of small droplets will.

Print Quality Demonstration Proof Points

Determining the print quality of the printers you are considering is critical. It is best accomplished by printing the following during your demonstration session:

• Print a standard test file at each print mode on each printer and document the print speed (as measured by you with your stopwatch).
• Print graphics with a variety of typical files you plan to produce on the printer. This should include graphics that incorporate a range of colors you will need to provide to your key customers, large areas of heavy ink lay-down (dark colors), facial tones and tonal gradient, and text and/or bar codes.
• Fully document the print time and specific modes used to produce each graphic and anything that was done to reach the quality level you require. Examples include increasing ink saturation or the use of smoothing modes.
• Use the exact same files and materials in every print demo so you can truly make an “apples-to-apples” comparison of the presses.
• Never utilize prints for evaluation that were produced without someone from your company present to observe the entire production process.
• Always conduct an on-site demonstration of the printers you are considering prior to placing an order.