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» Home » Graphics Resolution:
Does It Really Matter? Screen image resolution is measured by something called PPI (pixels per inch). Printed image resolution is measured by something called DPI (dots per inch). DPI is the more common term and is often used interchangeably with PPI when referring to on-screen images. As with halftone screens, the more information that's packed into an image, the smoother its appearance. An image that has 72dpi contains less information than one that is 300dpi. There are two different levels of resolution that a designer might use; screen resolution and printing resolution. Screen resolution How an image appears on-screen is actually dependent on a couple of factors. The quality of the monitor being used plays an important role as does the actual image's quality. If an image is a 24-bit, RGB image with 16+ million colors, but a monitor is only able to display 16 colors, the image won't look too good no matter what. The common resolution for on-screen images (for electronic presentations and Web pages) is 72dpi. This is because 72dpi is what monitors can display. A higher-resolution image won't look any better on-screen but, you can be sure, the file size will be larger. Printing resolution This refers to how clearly an image will print on a printer or in professional printing uses. Laser printers, inkjet printers and imagesetters used to output film for professional printing require more information than is available in a 72dpi file to produce a smooth and clear image. How much more depends on the bit depth of the image. Typically, 1-bit bitmap images, or line art, require resolution equal to the dpi of the output device. A 600dpi device requires only 600dpi resolution for a 1-bit image. Though an imagesetter can output film and paper at resolutions of 2,400dpi and 3,600dpi, a 1-bit image requires a maximum resolution of 1,200dpi. This is because high resolution printers only use information up to 1,200dpi. Anything higher will be unused by the output device. I usually scan all my line art images at 1,200dpi for safety, no matter what the output method. Printed resolution for 8-32 bit images is a little different. This resolution is dependent on the halftone screen that will be used when the file is output. A typical halftone screen for a brochure would be 150lpi (lines per inch) The rule is to double this number for the file resolution. A designer would need 300dpi resolution for the image to be output at 150lpi. Vector images, because
they are created using PostScript
principles, are resolution independent. Like PostScript fonts, their files
are mathematical in nature and are treated as objects. A big plus for
vector images.
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