What is a line screen

A Line Screen is the measure of how many halftone lines are printed in a linear inch. The value is expressed as Lines Per Inch (LPI). This important measurement related to the way printers reproduce photographic images also defines the necessary resolution of an image. The LPI is dependent on the output device and the type of paper. Countries using the metric system may use lines per centimeter (L/cm).

To simulate shades of gray using only black ink a printer prints varying sizes and patterns of halftone spots (spots are made up of many dots of ink/toner). Small halftone spots (fewer dots) create the visual illusion of a light gray while larger halftone spots (more dots) appear darker, blacker.

The lower the LPI the more obvious the halftone dots are in the printed image. Look at these typical halftone ranges:

· A 300-600 DPI laser printer can usually only print at an LPI of 50-65, resulting in coarse images

· Because of the absorbency of newsprint, newspapers typically use 85 LPI (you can see this with your naked eye!)

· Imagesetters and platesetters print at much higher resolutions and can print up to 200 LPI (you need a magnifying glass to see these)

· Most all of magazines interiors are printed at 133 lpi (according to SWOP standards for Offset Printing)

· The main decision to use certain Line Screen versus another mostly depends on the paper being used for printing (uncoated stock generally uses a lower LPI, and coated stock generally uses a higher LPI)

The general rule of thumb is to have images with a resolution of 2 times the line screen.

One other exception to especially note is: although type should not be embedded inside non-vector graphics when this is unavoidable, the dpi should be set at or above 600 dpi.

Line art should be set at 1200 dpi.

SPI (samples per inch) is scanner and digital image resolution. To scan an image the scanner takes a sampling of portions of the image. The more samples it takes per inch, the closer the scan is to the original image. The higher the resolution, the higher the SPI.

PPI (pixels per inch) is the number of pixels displayed in an image. A digital image is composed of samples that your screen displays in pixels. The PPI is the display resolution not the image resolution. (Adobe Photoshop uses PPI and Corel Photo-Paint uses DPI for image resolution so it's no wonder everyone is confused.)

DPI (dots per inch) is a measure of the resolution of a printer. It properly refers to the dots of ink or toner used by an imagesetter, laser printer, or other printing device to print your text and graphics. In general, the more dots, the better and sharper the image. DPI is printer resolution.

LPI (lines per inch) The printer uses a halftone grid divided into cells. The cells contain the halftone spots. How close together the cells in the grid are is measured in lines per inch. This is the LPI or line screen.

The lower the LPI the more obvious the halftone dots are in the printed image. A 300-600 DPI laser printer can usually only print at an LPI of 50-65, resulting in coarser images. Higher resolution imagesetters can print a much higher LPI resulting in smoother, almost-like-continuous tone photographs.

Some types of paper can only reproduce lower LPI images because of how they absorb ink and how the dots of ink spread out on the paper. Newsprint typically uses 85 LPI. The halftone cells must be further apart because the ink spreads more (dot gain). High quality coated paper can accept more closely spaced rows of dots at 150 LPI or more because there is less dot gain.

LPI and Scanning: When scanning photographic images you need to know the final output LPI in order to insure that you scan at the proper resolution (SPI). Insufficent resolution will result in lower quality printed images. Too much resolution results in wasted information and unnecessarily large file sizes.

LPI and Digital Images: As with scans, images acquired through digital photography, from the Web, or from CD collections require the right amount of resolution for the final printed LPI.

LPI and Printing: When printing photographic images you need to know the final output LPI in order to insure that your digital images (scans, digital photos, images from CD, etc.) have sufficient resolution (SPI).

LPI and the Web: On the Web, LPI is not a factor because images display on-screen in pixels (PPI).

LPI Chart talk to your printer to find the LPI you should be using for each type of printing project
output/paper	typical LPI
screen printing	35-65
laser printer/photocopier copier or matte laser paper	50-90
laser printer/photocopier coated paper	75-110
quick printer uncoated or matte bond paper	50-90
quick printer coated paper	75-110
offset printing newsprint	60-85
offset printing uncoated paper	85-133
offset printing coated paper	120-150 +
high quality offset or gravure such as glossy color magazines	150-300

LPI Formulas LPI x 2 is most common, x 1.5 is sufficient in some cases, talk to your printer and experiment to find the best resolution for your needs
formula	example
LPI x 2 = SPI	133 x 2 = 266 required SPI typical project on uncoated paper stock
LPI x 1.5 = SPI	175 x 1.5 = 263 required SPI typical project for a glossy magazine
LPI x 2 x % (size) = SPI	85 x 2 x 150% = 255 required SPI newspaper photo to be enlarged 50% from original

file formats are PDF™ for offset printing and PostScript™. Files must be sent on Macintosh

formatted CD (650 MB), Zip (100 MB) or Jaz (1 GB). Architectural Record does not accept

files via E-mail or other electronic delivery methods. Application file and native files (QuarkXPress™, Adobe Illustrator®, Adobe Pagemaker®, Adobe Photoshop®, etc.) are not accepted.

• Include quality-control patch (color bars) within maximum dimension of ad file

• Maximum dimensions including all additional identifiers (i.e. crop marks, sign-off slugs, color bars, agency/engraver logos) are as follows: