What is the difference between LPI and DPI?
LPI is used to indicate Lines Per Inch, also known as a line screen. This is what a printing press uses to indicate the resolution of the half-tone screen used when printing (consult with the printing press to obtain this value).
DPI is used to indicate Dots Per Inch and is typically used by non-half line devices to indicate how many dots of ink are laid out in an inch (consult the printer manual to determine the DPI resolution that the printer will be using).
Some applications also use DPI to indicate the resolution of a file. This, however, is the resolution of a file, which is not made up of physical dots, but rather how many pixels high by how many pixels wide the image is. Any value that contains per inch or per centimeter is only related to an output device as it would relate to a physical representation of the image.
A more correct indication would be PPI (pixels per inch) for the resolution of a file as it relates to output. A DPI or PPI value within an image editing application will indicate how many pixels are found within the image that will be used when sent to a printer or output device to make up a single square inch. That output device will then utilize its own conversion system to convert those pixels into a physical representation.
It is important not to mix up the DPI of a printer with the DPI or PPI of an image. For example, an Inkjet printer may use 1440 horizontal dots of ink and 720 vertical dots of ink to create one square inch, but only requires between 200 and 300 pixels horizontally and vertically for that same square inch.
A typical rule of thumb is to use 300 DPI or PPI for the image’s resolution within the image editing application, regardless of the LPI or DPI settings that will be set in the printer. The exception is when displaying images on a display device (such as a monitor or projector) where a resolution of 72 DPI is the standard.
In conclusion, when determining the DPI or LPI settings for within Sharpener Pro 3.0, consult the printing company or printer manual to determine the resolution that the printer will be using (either in LPI or DPI).