You say you want a resolution

You say you want a resolution

By Richard Heller

You say you want a resolution

A couple of weeks ago, we looked into the proper resolution to use when scanning a photo. One of the things that was mentioned was DPI, or dots per inch. What exactly does this mean?

A digital camera and a scanner have a couple of things in common; they both take “photos,” and their quality is measured in terms of resolution, or DPI. A standard camera uses film to capture an image. Film has chemicals on it that react to light in order to create a negative used to make a photo. These chemicals are spread evenly over the negative material, and the chemical molecules are bonded to each other, creating a continuous coating with no gaps between the molecules.

The scanner and digital camera use an image sensor that is sensitive to light. The difference between this and a standard camera is that the sensors are much larger than the chemical molecules in film, and they have a space between them. A 600 DPI scanner has 600 of these sensors in one square inch of space, while a 1200 DPI scanner has 1200 sensors in the same square inch. The more sensors per square inch means higher resolutions that translate into a scan or photo that is closer to film quality.

Another thing about the scanner and digital camera is that the sensor can only detect levels of white light. In order to scan color, a red, green or blue filter is used to capture the photo. The scanner does this either by making three passes over the photo using a different filter for each pass or by electronically applying the filter at high speed as it makes a single pass. This is the method the digital camera uses, which explains some of the delay a digital camera has when taking a series of photos.

When you purchase a scanner or digital camera, you should look at the resolution for the device and buy the highest “optical” resolution you can afford. By optical resolution, I mean what the sensor is actually able to capture. There is also an “interpolated” resolution, which means that the scanner or camera will add extra dots to the picture in order to make it appear as though it was taken with a higher resolution.

An inkjet or laser printer also is sold according to its resolution. Here, again, you should look at the DPI, such as 600 DPI for a laser to 1440 X 720 or greater for an inkjet. You should notice that the resolution for an inkjet has two figures for the resolution, which refer to the number of dots horizontally and vertically per square inch. The more dots the printer is capable of printing, the nicer your pictures will look. The nicer your pictures look also means the longer they will take to print. It’s not unusual for a full-page photo to take 10 minutes or more to print.

Richard Heller is an independent computer specialist who specializes in repairs, installation, upgrades, technical support, Internet sharing, data recovery and diagnostics. If you have any computer or service-related questions, please send them to The Rock River Times or e-mail

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