Three important features when choosing a scanner are the scan resolution, colour depth and scanning speed. We’ll run through what each of these features mean and how they may be important when deciding which device best suits your requirements.
Resolution
Image resolution is th emost important metric for a scanner. Scanner resolution is measured in the number of dots per inch (DPI) that the scanner can capture. The higher the DPI, the more detailed is the scanned image. Low resolution settings are adequate for greyscale or black and white documents. On the other side, photographs or detailed images require higher resolution.
In case you need to scan an image or a document just to share it via email, 300 DPI will be enough. If it is important for you to keep the posssibility to enlarge the image or the hoto, then you’ll want to use a higher resolution, according to the image size you would like to access.
Image resolution is based on two values: the digital value and the optical value. The optical value is the maximum number of dots per inch that a scanner can physically capture. If the scanner hardware is powerful, the optical value is higher. On the other hand, the digital resolution is based on the digital capabilities of the scanner, as it receives the image in the maximum DPI the scanner hardware has already captured, and adds artificial information to the image by digitally manipulating it.
Colour Depth
The amount of colour information -in bits per pixel- that can be captured by the scanner is called the Colour depth. The higher the colour depth, the more colour information varity and detail you will achieve. The increase in colour depth will also lead to an increase in overall file size.
Just like in the resolution, there are two colour depth factors in the world of scanners: The interal colour depth rating and the external colour depth rating. The internal colour depth is the amount of colour the scanner’s hardware can actually capture, while the external colour depth is the level of colour information the scanner can deliver to the computer.
Scanner speed
Scanner speed is an obvious factor. It's the speed that the scanner can capture an image and deliver to the computer. The speed of any scanner varies according to the quality of the image that you decide in the scan settings. A low resolution grayscale or black and white scan should be fast, but scanning an big size photo in high resolution will take longer time.
