What is a scanner?

 Scanners can read text and images from smooth originals, e.g. B. paper, digitize. After the scanning process, the data is transferred to the computer, where it is then saved by software as an image file.

A scanner is practically part of the standard equipment of a computer in the private sector. Whether clippings from newspapers, magazines and even photos. Inexpensive entry-level devices are also available for almost all digitization processes. Only those who have special requirements should take a close look at what the scanners can do.

In order to save space, multifunction devices are often used in which a printer and a scanner are combined. This mainly results in business devices that are also suitable as copiers and/or fax machines. In the private sector, however, they are just as popular. Since you need a printer anyway, you buy a multifunction device and have the scanner integrated.

In the meantime, the scanner has become rather unusual as an additional piece of equipment for a computer. The cameras in smartphones and digicams are now so good that they can be used to make good copies of paper documents. There are apps for smartphones that crop recordings, convert them to PDF format and automatically upload them to the cloud. The quality is comparatively as good as that of a flatbed scanner.

hand scanner

The first scanners were handheld scanners that had to be moved over the template by hand. You had to move the scanner very evenly to get a usable and undistorted image on the screen. Scanning DIN A4 pages was also very complicated. The handheld scanner was not wide enough for a single scan. The scanning process had to be repeated several times until the entire page was read and could be assembled by software. The scan result depended on the skill of the operator.

At some point the flatbed scanners came onto the market, which could read a DIN A4 page in one scan pass. These devices quickly became cheaper and affordable for home users.

How a flatbed scanner works

The flatbed scanner is a box with a large flap at the top. Under this flap is a pane of glass on which the template is placed face down. The entire control electronics, the scan head and a very strong light source are located under the glass pane.

The light source shines on the paper. The printed surface of the paper reflects the light differently. Empty or white surfaces reflect the light more than colored or black surfaces. During the scanning process, a motor moves the scan head along under the glass pane. It continuously absorbs the reflected light. The scan head directs the light through a mirror system until it hits a lens. There, the light is focused and directed to light-sensitive diodes. These diodes convert the different light intensities into electrical voltage. The brighter the light, the higher the voltage. The darker the light, the lower the voltage. If a color scan is made, the light is first sent through filters with the primary colors red, green and blue. An analog-to-digital converter converts the analog voltage values ​​into digital signals. The data is then transferred to the computer.

resolution

Resolution is how much detail a scanner can capture from an original. Resolution information is given in dpi, dots per inch. However, they are only of a theoretical nature and have nothing to do with the physically achievable resolution in practice. In general, one can say that all scanners, except in the professional area, only achieve a third of what is stated. Resolutions of over 2400 dpi are pure utopia, which the average consumer doesn't even need.

So what resolution makes sense at all? It can be said that it depends on the resolution at which the template was printed and the purpose for which the scan is to be used. It brings e.g. For example, there is no point in scanning a photo at 1200 dpi if it was only printed at 300 dpi.

color depth

The most sensible color depth is 32 bits. This is the standard color depth that any screen can display. Technically, nothing more is possible. So more than 32 bits doesn't make sense. Not even if you want to print the pictures afterwards. Strictly speaking, 24 bits are already sufficient. The lower the color depth, the lower the amount of data generated.

scan quality

The scan quality cannot be recognized from technical values. But maybe other features will help. When scanning newspapers and magazines, an unwanted moiré pattern appears in the image. The scanning software should be able to remove this pattern. Ideally, the scanner has a hardware-based dust and scratch remover. In this way, you can save on subsequent image processing after the scanning process.

Color distortions can often be corrected later in image processing. Even photos that originally didn't turn out.

However, if you want the most exact color reproduction possible, you have to use a color calibration tool and also calibrate your screen.

When choosing a scanner, the question always arises as to whether slides and negatives should be scanned and whether the template should be enlarged after scanning.

For slides and negatives you absolutely need the so-called transmitted light unit. An additional light source illuminates the transmitted light template (slide or negative) from behind during scanning. The image will be brightened. And can then be scanned by the reflection original scanner. The resolution should be 1200 to 1800 dpi. The transparency unit is usually located in the cover of the scanner. The slides and negatives are placed in templates and placed under the lid.

Special slide or negative scanners are better suited for more frequent use. Not only in terms of speed, but also because of the better scan quality.