Printing & Design Tips: MARCH 2007, #68

Vector Drawings and Flatness

When you want to create a drawing that can be placed in a program like Quark or InDesign, you have two options. You can create a bitmapped drawing composed of printer dots, or you can create a vector drawing made up of PostScript curves, points, and lines.

A vector drawing produced in a program such as Adobe Illustrator (as opposed to a bit-mapped image produced in Photoshop) is made up of curves and control points. Essentially, it is a mathematical formula that will print a series of shapes, whereas a bit-mapped image is a checkerboard of pixels that create a pattern or shape by being either on or off (black or white). The advantage of a vector image is that it can be scaled up (enlarged) without loss of detail and will print at the highest resolution of the imagesetter, platesetter, or laser printer to which it is downloaded (unlike a raster image—bit-map—which will display an increasingly evident jagged edge as it is enlarged further and further).

The control points of such a vector image can be problematic. If your drawing has too few, it will lack detail. A complex shape will become a simple (and perhaps unusable) shape if too many control points are removed. (A rectangle, for instance, might become a triangle if one of the control points is removed. A heart shape might become an unintelligible blob if too many control points are removed.)

If, on the other hand, your drawing contains too many points, it can slow down or disable the imagesetter or platesetter by taxing the RIP (raster image processor), the software or hardware interpreting device that translates the mathematical curves and shapes of PostScript into a final bitmap of "on" or "off" spots on the imaging substrate (plate or film).

There are ways to minimize these problems. Your vector image program (Illustrator, Freehand, Corel Draw, etc.) has a “flatness” setting that allows you to adjust for this variable. Setting this variable to the optimal amount of points will allow you to print an image that has sufficient detail but that doesn't slow down or choke the RIP.

Another approach to this issue is to be aware that PostScript, the computer language that creates the shapes of the letters and images on your page, defines curves as a series of straight lines as it rasterizes the file for printing on an imagesetter or platesetter. A circle, for instance, is made up of lots and lots of adjoining straight lines. The more straight lines that make up your circle, the less evident their straightness is, and the smoother the circle appears. The smoothest circle would be composed of the largest number of short line segments (which to the naked eye would become so small as to be invisible), yet printing such a circle would slow down the RIP dramatically, particularly if the circle contains a gradient fill.

When printing curved shapes or type, increase the flatness value of your vector objects created in Illustrator by entering a number in the Output text box smaller than the existing number. To determine the flatness at which an object prints, divide the printer resolution by the object's output resolution. For example, an object with an 800 dpi output resolution prints to a 2400 dpi imagesetter with a flatness of 3 (2400/800 = 3). Since the flatness value determines how smoothly a curve will be printed, if you use a flatness level that is too high, the line segments making up the curves may be visible. Testing may be required. Also, you may want to have your print provider check a sample of your work.

It is prudent to check the output resolution setting in Illustrator. You may, in fact, need to lower this number to get a graphic to print on your laser printer. However, if you need to change the number to get the image to print, remember to reset the output resolution to 800. You may need to test the file at this point before sending it to your offset printer.

Can't Find the Right Colored Paper Stock?

You find the perfect color of paper for your job but none of the paper swatch books from the paper mills include a swatch of exactly the right color. Or, you find the perfect paper in the swatchbook, but your printer says you have to order a huge amount to meet the mill’s minimum paper order requirement. Or it might take the printer two weeks to get the paper, and you need the printed job in a week.

What do you do?

If you had planned to print your job on a small press (black text only on both sides of an 11” x 17” sheet folded to a four-page 8.5” x 11” job, for instance) on that seafoam green paper you loved and can’t get, you will probably have to move to a larger press and “paint the sheet.” That is, you can choose a PMS color that matches the paper you love but can’t get. You will cover the sheet entirely (heavy coverage with bleeds, which justifies the larger press because it will produce cleaner solids) and print the black text on the seafoam green background. No one but you will know that the sheet did not come from the paper mill in exactly that shade of green.

As with most things in printing, quantity controls the price. If you are already printing on a larger press (perhaps due to the size of your printed sheet), painting the sheet might cost 33 percent more than just printing the black text on the existing stock. This is due to your using more ink and wasting more paper in makeready. If, on the other hand, you had planned to print the job on a small press (a duplicator), but your decision to paint the sheet has necessitated your moving up to a larger press, your bill might be double what it would have been on the small press.

Finally, if you are tempted to choose a darker green and have the printer screen it back and bleed the color on all four sides, be careful. You may not like the outcome. A screened back color may look totally different than you had envisioned. It may appear to have a completely different hue and value. Only a 100 percent solid of a PMS can exactly match the swatch in your Pantone Matching System book. If you can’t find the exact color you want, check out Pantone’s pastel or metallics books, since they also contain 100 percent PMS solid colors.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]