Medical imaging or scanners usually work on the following principle. The original image is illuminated and the reflected light is directed through a rod lens, which then focuses the reflected light and eliminates the scattered light using an optoelectronic line sensor (quick scan, fastscan). The analog light signals are converted pixel by pixel by analog-to-digital conversion to digital signals while simultaneously operating either the template or the sensor optics which is moved stepwise perpendicular to the sensor extension (slow scan). When scanning with an area sensor for X-ray measurements, the entire template or areal parts of the image can be scanned simultaneously. The repeated scanning after displacement of the sensors in the sub-pixel image resolution and possibly the photographic resolution can be increased. Certain color values are separated by sampling the primary colors (usually red, green and blue) with upstream of color filters and, if predetermined by software-based additive color mixing. This filter process is required for each primary color a scan cycle when all of the sensor elements are used for the scan and determines CT scan price.
Alternatively, Bayer sensors or other color sensors are used, in which all sensor elements are provided with a fixed color filter in a predetermined color order. This allows the scan to be performed in one pass.
CT scan light sources
The use of multi colored and switchable light sources in only one scan pass is needed because the color separation is given by the light sources themselves. The sensors measure during the scanning, for example, with lighting through LEDs on the basis of a certain wavelength. Alternatively, colored light sources with a continuous light spectrum can be used. In the prism method, the original is illuminated with white light. The reflected light is passed through a prism which splits the color components. These are covered by adjacent optical sensors. With this technology, only one scan is required, which influences the CT scan price. The quality of a scanner depends on sampling resolution and sampling frequency or spatial frequency, screen frequency, output frequency (output resolution), density range (dynamics), tonal (shades of gray), color depth and scan speed. Simple scanner with an ADF process about ten pages per minute. High-performance scanner with a mechanism for turning 40 pages of a book per minute.
The quality of scanners can often be estimated by means of cavity effect. This dice are made of black cardboard scanned with about ten centimeters on a side and a hole of about five millimeters in diameter on the side of the hole.