Resolution of Scanners

02.07.2020 0 iCODIS Official

Resolution is the most important technical index of the scanner. It indicates the scanner's ability to display image details, that is, it determines the fineness of the image recorded by the scanner, and its unit is PPI(Pixels Per Inch). It is usually expressed by the number of pixel points contained in the scanned image per inch. The resolution of most scans is between 300 and 2400 PPI. The higher the PPI value is, the higher the scanning resolution is, and the higher the quality of the scanned image is, but it has limits. When the resolution exceeds a certain value, it will not significantly improve the image quality, only making the image file larger and not easy to process. No matter ocr book scanner or pdf camera scanner, scanning to 600PPI is sufficient.

There are generally two kinds of scan resolution of real resolution (also called optical resolution) and interpolation resolution.

Optical resolution is the actual resolution of the scanner, which determines the key performance index of image clarity and sharpness.

Interpolation resolution is a numerical value that improves the resolution by means of software operation, i.e. the interpolation method is used to fill in the missing information around the sampling points, so it is also called software enhanced resolution. For example, if the optical resolution of the scanner is 300PPI, the image can be increased to 600PPI by software interpolation, and the interpolation resolution can obtain less detailed information. Although the interpolation resolution is not as good as the real resolution, it can greatly reduce the price of the scanner and is very useful for some specific tasks such as scanning black and white images or enlarging small originals.

Gray scale of the scanner

Gray scale represents the range of brightness levels of an image. The higher the number of levels is, the larger the brightness range is and the richer the level of the scanner image is, and the gray scale of most scanners is 256 levels. In 256 levels of gray scale, there are actually more gray scale levels than that can be recognized by naked eyes.

Number of colors

The number of colors indicates the range of colors that the color scanner can generate. Usually, it is represented by the number of data leap, i.e. bit, representing the color of each pixel point. The so-called bit is the smallest storage unit in a computer, the value of which is expressed as 0 or 1. The more bits a scanner has, the more complex the image information can be. For example, true color image often refers to the fact that each pixel consists of three 8-bit color channels, i.e. 24-bit binary numbers. The combination of red, green and blue channels can generate a combination of 2^24=16.67M (mega) colors. The more colors a scanner can generate, the brighter and more real the scanned image is.