PUBLICATION CENTER

Getting the most out of your workflow by setting expectations and the proper resolution for printing.

By Justin Sherry

What resolution should I print? This question is about as simple to answer as, “How do I get my prints to match my monitor?” Within this seemingly simple inquiry, there are two distinct questions: What resolution should I prepare my file at (ppi, or pixels per inch), and what print resolution should I RIP and print the image with (dpi, or dots per inch).

The first thing to remember is that ppi and dpi are not related to one another, and while you should always try to get the image with the highest resolution (ppi) to print from, the dpi you print at can and should vary based on the job at hand and its viewing distance.

Once we receive a final file from the customer, we’re basically stuck with what they’ve given us. So if they give us an image with relatively low resolution and that’s the best they can deliver, they should be warned that their print won’t be very sharp unless they want to pay extra for us to use an upsizing software like Genuine Fractals or Alien Skin Software’s Blow Up.

DPI and Output

The most common assumption is that the more dpi I print, the more “defined” my image will look. The goal of this article is to clarify the relationship between these two elements in printing so that both the graphic designer and the print shop know how to best handle each job based on the application, ensuring a trouble-free and smooth workflow. The whole point is to save time and money in the process.

For starters, let’s get one thing straight… using a higher dpi in print doesn’t necessarily give you a sharper, more defined image. As a matter of fact, the drop size of most late-model printers is so small that it’s getting difficult to see them using a loop. Furthermore, ink drops rarely get placed on top of each other; rather, they are placed in between each other or staggered over top of one another. 

Some of the real reasons you would want to use a higher dpi print mode is to get better density (more vibrant color), or to print using a higher number of passes (to minimize horizontal banding on certain media). 

This in turn also significantly increases RIP time, print time, and ink load, which some media can’t handle anyway. To demonstrate, if you make a profile at 2,400 dpi, but have to throttle the ink limits down to 50%, technically you’re now down to 1,200 dpi since you cut the 2,400 dpi in half.

The downside is the file will still RIP just as slow and print just as slow as a 2,400 dpi mode with higher ink limits. A 1,200 dpi profile with no ink limiting would lay down the same amount of ink, but allow much faster RIP and print times.

In most cases, you would be better off printing using a lower dpi for most applications, thus saving time in both RIP time and printing, as well as saving money due to less ink consumption.

Okay, you’ve got a file that is sized appropriately, what resolution do you print it at? Depending on the make and model of your printer, you will have different options regarding available print resolutions. When you print a file at 2,400 dpi, you have the potential to lay down 2,400 drops of ink horizontally as well as 2,400 drops of ink vertically across one square inch. That is the absolute maximum amount of ink that could be laid down for that resolution, if the value of the said inch was equivalent to 400% coverage.

Since there are variables in place, such as ink limits in the RIP or driver as well as possible UCR and GCR, it is unlikely if ever that the printer’s true maximum resolution is ever truly utilized. Even if you were capable of laying down a true 2400x2400 dpi, it would be highly unlikely that the media would be capable of taking that heavy of an ink load. This would change if you switched to a lower resolution, like 600 dpi.

Printing a 24x36 backlit graphic on a premium quality backlit film, such as LexJet 7 Mil Absolute Backlit, would be a great example of when to print using a higher quality mode like 2400 dpi.  Since the two biggest hurdles to overcome when printing backlit graphics are good density, and eliminating horizontal banding, a higher dpi print mode would be optimal for this type of graphic.

PPI and Input

When preparing a file for print, the designer must decide on the resolution of the file, or the ppi. This means at 100% scale, a raster file that is 8x10 at 300 ppi will be comprised of 300 individual colored squares or pixels per inch both horizontally and vertically.

The total number of pixels for this file would be 2,400 x 3,000. Now if you take that same file and print it at 300% to scale, or 24 in. x 30 in., the file’s resolution is now reduced to 100 ppi. Because the ppi was reduced to 100, when viewed up close, the appearance of the individual pixels may be apparent to the viewer.

As a basic guideline, 300 ppi is best for work that will be viewed up close (within a foot or so), such as fine art reproductions; 150 ppi is best for work that will be viewed from at least a few feet away and more, such as posters and trade show graphics; and 100 ppi or so should be fine for graphics viewed from more than 10 feet away or so.

The Printer Variable

When comparing one model printer to another, you must remember that not all printers are created equal, and more importantly, one printer’s dpi is not necessarily the same as another printer’s dpi. Let’s take two model printers from Brand X…

Brand X had an older model printer with a 14-picoliter drop size, and had a maximum print resolution of 1,200 dpi. Their newer model printer has a reduced drop size of 4 picoliters and is capable of printing at both 1,200 dpi and 2,400 dpi.

That means that the older model printer fires a drop that is 3.5 times larger than the newer model. This also means that printing at 1,200 dpi on the older model printer will technically lay down 3.5 times more ink than printing at 1,200 dpi on the newer model printer.

If you were to compare prints from both of these printers you would notice that the newer printer, while laying down less ink, will produce a more defined image because of the smaller drop size, but also have less density because of the lighter volume of ink.

There are two different types of printheads used in inkjet printers: thermal and piezo-electric. Thermal printheads, used by HP and Canon, have a fixed drop size and use heat to jet the ink, while piezo-electric printheads use electricity to jet ink.

Some piezo-electric printheads have the capability of producing different sized ink droplets within a given print mode. This is good for a few reasons: Variable drop technology provides you with an alternative way to govern your ink by controlling the ratio of small drops to large drops And, using variable drop technology helps to mask the grain of the dots as your eyes can’t discern the individual dots at various sizes, thus making your print look more “continuous tone”.

Justin Sherry is LexJet's technical support specialist.