Determine Image Resolution for Print in Photoshop CS5
Adobe Photoshop Creative Suite 5 provides tools to set your image resolution for print or for the web. Having the proper resolution is important to the final outcome of an image, especially if you plan to print it. Before you decide on a resolution, you should understand what some of the resolution jargon means:
dpi (dots per inch): The resolution of an image when printed.
lpi (lines per inch): The varying dot pattern that printers and presses use to create images (see Figure 6-1). This dot pattern is referred to as the lines per inch, even though it represents rows of dots. The higher the lpi, the finer the detail and the less dot pattern or line screen you see.
Dot gain: The spread of ink as it’s applied to paper. Certain types of paper spread a dot of ink farther than others. For example, newsprint has a high dot gain and typically prints at 85 lpi; a coated stock paper has a lower dot gain and can be printed at 133–150 lpi and even higher.
Human eyes typically can’t detect a dot pattern in a printed image at 133 dpi or higher.
Deciding the resolution or dpi of an image requires backward planning. If you want to create the best possible image, you should know where it’ll print before deciding its resolution. Communicate with your printer service if the image is going to press. If you’re sending an image to a high-speed copier, you can estimate that it will handle 100 lpi; a desktop printer handles 85 lpi to 100 lpi.
When creating an image for print, keep this formula in mind:
2 x lpi = dpi (dots per inch)
This formula means that if your image is going to press using 150 lpi, have your image at 300 dpi. To save space, many people in production use 1.5 x lpi because it reduces the file size significantly and you get similar results; you can decide which one works best for you.