An image sensor is a device for recording two-dimensional images from light by electrical or mechanical means. In most cases, semiconductor-based image sensors are used that can pick up light up to the mid- infrared . But there are also two-dimensional semiconductor detectors for recording high-energy ionizing types of radiation such as X-rays and gamma rays .
Technical solutions for recording an image in the visible range up to infrared are often based on two-dimensional arrangements (arrays), the signals of which are read out electronically. In the case of infrared in particular, this is also known as a focal plane array (FPA).
Examples of image sensors in the visible range and in the near infrared:
- Silicon sensors have relatively little image noise , which could possibly be further reduced by using black silicon .
- CCD sensor (CCD) image sensors, with filter wheel or color-sensitive sensors (individual filters per pixel , see Bayer sensor ) also for color images
- CMOS sensor (correct name Active Pixel Sensor ), based on CMOS technology, with color-sensitive sensors lying next to or on top of each other ( Foveon X3 ), also for color images
- Vidicon tube
Examples of image sensors for other spectral ranges :
- Nipkow disk (historically for light, but can also be used for other types of radiation)
- Microbolometer array (mid to far infrared , in astronomy , in thermal imaging cameras and homing systems )
- Pyroelectric array (mid to far infrared)
- Focal plane arrays based on photodiodes made of mercury-cadmium-telluride (MCT), for thermal imaging cameras and target finding systems in the mid-infrared range ( wavelength : 3.5–5 µm)
Image converter tubes and residual light intensifiers , including the microchannel plate (MCP), serve to amplify an image signal or convert it into visible light; they are not referred to as an image sensor, although they often have essential features of one.
These are special, very small sensors to scan small images with high resolution, such as in electronic light microscopes or refractiometers. Properties:
- Very small pixel size
- High optical resolution
- Low sensitivity
- Low dynamic
These are detectors for digital X-ray ( TFA sensor ) provided with a radiation-sensitive layer . Properties:
- High pixel size
- Low optical resolution
- High sensitivity
- Medium dynamic
Sensor sizes and formats
The graphic on the right shows common sensor sizes that are used in digital video and photo cameras . If the medium format sensors are disregarded, a 56-fold difference in size (based on the sensor surface) can be seen between the smallest and largest sensors used in compact and single-lens reflex cameras. This difference is one of several factors that affect image quality and sensitivity. The largest image sensor built in 2018 has an effective size of 205 mm × 202 mm. The price for the sensor chips usually increases with the sensor area.
Choice of some popular formats
|Micro-Four-Thirds and Four-Thirds||21.633 mm|
|APS-C and DX||27-28 mm|
|FX (full format)||43.267 mm|
The inch designations in the adjacent graphic are no longer directly related to the inch dimension. The dimensions are based on the properties of the vidicon tube .
Image resolution and pixel arrangement
In digital photography , the rounded total number of pixels is given in megapixels (MP) as a guide for the theoretically achievable resolution. The actual resolution, however, depends on many factors - the number of pixels alone does not allow a quality statement. In the beginning there was almost only an aspect ratio of 4: 3, but now there is an increasing number of the 3: 2 format of the classic small picture as well as camera models with 16: 9 format .
- Canon succeeds in developing world's largest CMOS image sensor, with ultra-high sensitivity. Retrieved June 25, 2018