An image sensor is a device for receiving optical image to an electric signal. In most cases, semiconductor-based image sensors are used which can detect light up to the middle infrared. However, there also exist two-dimensional solid-state detectors for recording high-energy ionizing radiation types such as X-ray and gamma radiation.
Technical solutions for recording an image in the visible range to the infrared are often based on two-dimensional arrays ( " array " ), the signals are read out electronically. Especially with infrared is called this as a Focal Plane Array (FPA ).
- 2.1 Sensor sizes and formats 2.1.1 Selection of some popular formats
Examples of image sensors in the visible and near- infrared:
- Silicon sensors have relatively low image noise, what could possibly be reduced in the future by the use of black silicon on. CCD sensor (CCD) image sensors with color filter wheel or sensitive sensors (single filter per pixel, see Bayer sensor) for color images
- CMOS sensor ( correct term Active Pixel Sensor ), lying based on CMOS technology, with side by side or one above the other ( Foveon X3) color- sensitive sensors for color images
Examples of image sensors for other spectral ranges:
- Nipkow disk ( historically used for lighting, but also for other types of radiation )
- Microbolometer (medium to far infrared, in astronomy, thermal imagers and target detection systems )
- Pyroelectric array (medium to far infrared)
- Focal plane arrays based on photodiodes from mercury - cadmium-telluride (MCT ) for thermal imagers and target detection systems in the mid-infrared range (wavelength: 3.5-5 microns )
Image intensifier tubes and image intensifiers, the microchannel plate (MCP) are used to amplify an image signal and converting it into visible light; they are not referred to as image sensor, even though they often have the essential characteristics of such.
It is special, very small sensors to scan small images with high resolution, as with electronic light microscopes or Refraktiometern. Features:
- Very small pixel size
- High optical resolution
- Low sensitivity
- Low dynamics
It is provided with a radiation sensitive layer for digital X-ray detectors (TFA ) sensor. Features:
- High pixel size
- Low optical resolution
- High sensitivity
- Mean dynamics
Sensor sizes and formats
In the adjacent diagram common sensor sizes are shown, which are used in digital video and photo cameras. Leaving the medium format sensors disregarded, a 56 -fold difference in size (relative to the sensor surface ) between the smallest and the largest sensor that are used in compact and SLR cameras, recognizable. This difference is one of several factors that affect the image quality. The price of the sensor chip increases with the sensor surface.
Selection of some popular formats
Image resolution and pixel arrangement
In digital photography, the rounded total number of pixels is measured in megapixels ( MP) as a clue to the theoretically achievable resolution. However, the actual resolution depends on many factors - the number of pixels alone does not allow quality statement. Was there first almost only the aspect ratio of 4:3, it is now increasingly the 3:2 format of the classic small picture and camera models with 16:9 format.