When you work with images in a digital workspace, it is helpful to understand the concept and applications of resolution. Resolution refers to the amount of visual detail contained in an image.
A document’s resolution affects both its appearance on your computer screen and its print quality. You can specify a document’s resolution when you create a new document, save, or export a file.
Resolution and screen appearance
Most monitors have a resolution of 72 pixels-per-inch (ppi). The Corel Painter display default is 72 ppi, which means that each pixel in the Corel Painter image occupies one pixel on your monitor. The display resolution does not affect the document’s actual number of pixels-per-inch — it affects only how the image is displayed on the monitor.
For example, a 300-ppi image is displayed on-screen at approximately four times its actual size. Because each pixel in the Corel Painter image occupies one pixel on your monitor, and the monitor’s pixels are approximately four times the size of the image’s pixels (72 ppi versus 330 ppi), the image must appear four times larger on-screen in order to display all of the pixels. In other words, your 300-ppi document will be printed at approximately one-quarter of its on-screen size. To view the image at its actual size, you can set the zoom level to 25%.
If you set the dimensions in pixels and then change the number of pixels-per-inch (resolution), this change will affect the size of the printed image. If you set your document size in inches, centimeters, points, or picas and then change the resolution, the dimensions of the printed image will not be affected.
Pixels-per-inch (ppi) is equivalent to dots per inch (dpi).
An example of a high-resolution (left) and low-resolution (right) image. In printing terms, a higher dpi means that the printer will place more dots of ink for every inch of artwork.
Resolution and print quality
The resolution of output devices (printers) is measured in dots per inch, and in the case of halftones, lines per inch (lpi). Output device resolutions vary, depending on the type of press and paper used. In general, a photograph is output at a crisp 150 lpi if printed on glossy magazine stock, and at 85 lpi if printed on newspaper stock.
If you are using a personal laser or inkjet printer, set your document size in inches, centimeters, points, or picas at the dots-per-inch setting specific to your printer. For most artwork, 300 dpi is preferred. Most printers produce excellent output from images set at 300 ppi. Increasing the file’s pixels-per-inch setting does not necessarily improve the output and may create a large, unwieldy file.
You can use 150 dpi for large prints because the difference in print quality is not very noticeable on large pieces when you look at the prints from a distance.
If you are using a commercial printer or a more sophisticated output device, the dimensions of the image should always be set to the actual size that you want the image to appear in the printed piece. A good rule of thumb is to set the number of pixels-per-inch to twice the desired lines per inch. So, at 150 lpi, the setting should be twice that, or 300 ppi; at 85 lpi, the setting should be 170 ppi. If you have questions about the resolution of specific output devices, it’s a good idea to check with the print service provider.
