The Tribune

Resolution is the number of pixels (individual points of colour) contained on a computer display monitor. Sharpness of the image on a display depends on the resolution and the size of the monitor.

The term ‘resolution’ can also be used to describe the actual size of pixels, and how many pixels fit in one inch (which equals 25.4 millimeters). The abbreviation for ‘pixels per inch’ is ppi.

Before an image gets printed, its pixels do not really have any dimensions as they are just bits in an electronic file. It can be practical to define within that file how big you intend the image to be.

Resolution requirements for printing

When an image is sent to a certain output device, such as a printer or a monitor, its resolution becomes important because each device or medium needs a certain base resolution to reproduce the image with the best possible quality. Here are some typical uses of images:

Magazine printing

The general rule is that the image resolution needs to be twice the screen ruling used to print the job. Magazines are typically printed using a 150 or 175 dpi (dots per inch) screen ruling. This means images need to be 300 dpi. Note that a slightly lower resolution, such as 220 to 250 dpi, is also acceptable.

For high quality jobs such as art books, or for images containing critical patterns, a higher resolution is sometimes recommended by the printer. Typically, 400 dpi is used for such images. This rule applies to both coloor and grey scale images as well.

Cartoons and logos are examples of line art, and such images need to have a much higher resolution. Most printers recommend 800 dpi as the bare minimum, but preferably resolutions of 1200 to 2400 dpi are used.

Newspaper printing

Newspapers are printed at a higher speed on lower quality paper. This means the resolution requirements are not as high as those for magazines. Typically, a resolution of 200 to 250 dpi is considered sufficient. For line art images, 400 to 600 dpi is recommended.

Billboard printing

The larger the picture that is printed, the lower its resolution needs to be. The main reason for this is that the viewing distance also increases. For large billboards, 30 dpi is often sufficient, which means that many digital cameras are capable of generating such files.

Photo printing

Usually 250 dpi is considered the optimum resolution for printing high quality photos

Computer monitor

Most computer screens have a resolution of around 100 dpi. That is 30-inch horizontally, not diagonally. The resolution of television screens is usually even lower than that of computer screens.

If you have an image that is 640 x 480, how big a print can be made? Well, the true answer is you can make as big a print as you want, but you will very quickly start to see ‘blocks’ (pixelization) and the quality will drop off. To maximise the capability of your printer, you should print a picture to a size that the printer can handle.

For example, using a 640 x 480 image that is to be printed at 200 dpi (dots or pixels per inch). Six hundred and forty divided by 200 equals 3.2, and 480 divided by 200 equals 2.4, so if you print this picture at 3.2 inches x 2.4 inches you will get a print with 200 dots per inch. I recommend 200 dpi as a minimum for good quality prints.

Resolution and print quality

If you are unsure what resolution images are needed for a certain project, always consult your printer because if the resolution of an image is too low, this results in:

• A loss of sharpness.

• Images also get a ‘pixelated’ look.

• Straight lines will show a stair casing effect.

Finally, do not forget that resolution is only one of the parameters that determine the quality of images in a printed job. Image sharpness, noise, colour accuracy and the composition of a picture are as important as its number of pixels. Until we meet again, fill your life with memories as opposed to regrets.Enjoy life and stay on top of your game.

NB: The columnist welcomes feedback at deedee21bastian@gmail.com

ABOUT THE COLUMNIST: Deidre Marie Bastian is a professionally trained graphic designer/marketing coordinator with qualifications of M.Sc., B.Sc., A.Sc. She has trained at institutions such as: Miami Lakes Technical Centre, Success Training College, College of the Bahamas, Nova South Eastern University, Learning Tree International, Langevine International and Synergy Bahamas.