In general terms, resolution is a measure of the clarity or visual acuity by which an image can be displayed or reproduced. In computer graphics and the printing industry, resolution is a term used primarily to reference the amount of data contained in a pixel-based image such as a photograph. The amount of data contained in a pixel-based image determines whether, when printed, the image retains clarity and detail or appears unclear or distorted.
There are two common acronyms that reference this data and while conceptually similar, they are not equivalent. The first of these, Pixels Per Inch (PPI) is a measure of the amount of data an image contains. For the vast majority of print applications, an image containing 300 ppi at the size it is intended to be printed contains sufficient data. The key point here is maintaining the size of the image. The general rule of thumb is a pixel-based image can be reduced from its original size and retain the necessary data. However, enlarging a pixel-based image beyond it’s original size degrades the quality of the image.
The second common acronym, Dots Per Inch (DPI) is the measure of how many dots per inch a desktop printer (i.e., inkjets or laser printers) can produce. Inkjet printers can produce upwards of 1440 dpi, while laser printers can range as high as 2400 dpi. Commercial printing presses are not capable of printing documents beyond 300 dpi. Hence, 300 dpi is considered the standard.
It’s important to note there are instances when a lower PPI is sufficient and advisable. For example a photograph reproduced on a billboard, a large banner, or large poster are often output at resolutions below the standard 300 dpi. This is due to the relative distance from which these images are viewed. The halftone dots in the brochure you hold in your hand are not visible without the aid of magnification. The halftone dots used on a billboard might be a 1/4” to 1/2” in diameter but because they are seen from a distance, they blend into a continuous image.
Another factor in determining necessary or requisite resolution is the nature of the paper stock used in a printed piece. Coated stocks are able to hold the highest number of DPI and are used when the highest image quality is desired. Uncoated paper stocks allow ink to absorb and spread. Hence, images printed on uncoated stock do not have to hold to the 300 ppi standard.
Resolution and File Size
The greater number of pixels in an image, the larger file size. Full-color images often occupy megabytes of storage space. Web images, on the other hand, are intentionally kept to a low resolution to minimize file size, (typically 72 ppi) and enable faster transmission over the internet. Hence, images copied directly from websites are not suitable to be used in printed pieces.
If you have any questions about resolution, give us a call (330-597-8560). We’re happy to help you get the most out of your printing project.
