PUB98: How to Control Lines Per Inch (LPI) From Publisher

MORE INFORMATION

What is Lines Per Inch?

The term, "lines per inch," comes from a photo-mechanical process called halftoning. Halftoning is a method of breaking up shades of gray into dots of different sizes. True halftones are created by photographing continuous tone artwork onto high-contrast film through a halftone screen. Halftone screens were originally created by etching a grid of lines onto optical glass. The number of etched lines per inch is where the term lines per inch comes from.

In a true halftone, all the dots are the same distance apart. You achieve the effect of light and dark by increasing or decreasing the size of the dots. The larger the dots, the smaller the amount of white space around them and the darker that area of the paper appears when you view it at a distance. The higher the lines per inch, the closer together the dots appear.

Electronic printers do not print true halftones. Electronic printers print dots of only a single size (measured in dots per inch or dpi); instead of changing the size of their dots they change the distance between the dots. Many electronic printers simulate true halftones by clustering their tiny fixed-size dots in such a way as to give the appearance of an array of (larger) equidistant dots of different sizes.

Setting Lines Per Inch

You can change the lines per inch setting only if you are printing to a PostScript printer. To define lines per inch, follow these steps:

Windows 95:

1. On the File menu, click Print Setup.
2. In Name box, select the PostScript printer you want to use.
3. Click Properties.
4. Click the Graphics tab.
5. In the Halftoning section, click the Use Settings Below option.
   
   The Screen Frequency box is now available and shows a recommended value.
6. In the Screen Frequency box, enter a value that represents the lines per inch you want to use.
   
   NOTE: If you type a number that is higher than the recommended value, shades of gray may not print evenly.
7. Click OK.

Windows NT:

1. Determine the Printer Resolution or dots per inch (DPI) Setting.
   
   
   1. On the Windows Start menu, point to Settings, and then click Printers.
   2. Click the PostScript printer you want to use.
   3. On the File menu, click Document Defaults.
   4. Click the Advanced Tab.
   5. Expand the Graphic section. The value assigned to Resolution is the DPI. For example, the value of Resolution may be 300 dpi.
   6. Click Cancel.
2. Select the Halftone cell size.
   
   
   1. On the Windows Start menu, point to Settings, and then click Printers.
   2. Click the PostScript printer you want to use.
   3. On the File menu, click Properties.
   4. Click the Device Settings tab.
   5. Double-click the Halftone Setup option.
   6. In the Halftone pattern box in the Device Color/Halftone Properties dialog box, select the Halftone cell size you want. For example, select the 10x10 option.
3. Calculate the Lines Per Inch
   
   Use the following formula to calculate the lines per inch:

                 Printer Resolution (dpi)
         LPI  =  ------------------------
                   Halftone cell size
   						

   For example, if you selected a halftone cell size of 10 (10x10) and the printer resolution (DPI) is 300, the lines per inch is 30:

                   300
         30 LPI =  ---
                    10