Scanner camera
A scanner camera is a digital camera with a line sensor . There are two basic designs; a combination of an analog camera with a digital camera back (called a scanback ) or as a unit.
Due to the scanning principle, the scanner camera is only suitable for still motifs in photography. Today, the main application for the scanner camera is digital reproduction, for which very large resolutions are required depending on the size of the original (e.g. approx. 425 megapixels are required to reproduce a DIN A0 original with 300 dpi). At the same time, the scanner camera offers very good detail and color reproduction, since no interpolation of the color channels is required , as is the case with a digital camera with a Bayer sensor .
functionality
Scanner cameras work on the scanner principle , i. that is, they work similarly to a flatbed scanner . The image is scanned line by line while the line sensor is mechanically guided over the image area by a stepping motor .
Each line is exposed and read out individually. There are 3 lines available for the basic colors red, green and blue. Therefore there is the complete color information for each pixel. Stable continuous light is required for exposure (e.g. modern LED video lights). Line-by-line exposure means that long exposure times are not possible with a scanner camera, since the scan would then take a very long time. Modern scanner cameras work with exposure times of 1/500 s to about 1/20 s, so that, depending on the desired resolution, the scan times range from a few seconds to about 10 minutes. In this respect, a scan with a resolution that is comparable with a digital camera with a Bayer sensor only takes a few seconds. If the scanner camera is used with moving subjects, this does not result in blurring, but rather a distortion of the moving object in the subject. In this respect, landscapes or architecture can also be photographed with very high resolution.
A further development, which was brought to market maturity by the Seitz company in 2007 with the cooperation of the sensor manufacturer DALSA , allows shorter scanning times (from around one second). This also makes it possible to record moving scenes. The underlying principle is the use of several scan lines arranged directly next to each other on a chip. While the sensor mechanically scans the image, the content of one scan line is electronically shifted to the next, synchronized with the image, so that overall more light can be captured and the exposure time can be shortened. However, with this principle, color interpolation is again required, since a column-wise RGB color filter is used. The image quality achieved is therefore significantly lower than that of a trilinear line sensor.
Use and special features
The scanner camera is only rarely used in professional photography, as modern 35mm or medium format systems usually provide sufficient resolution for this application.
The main area of application of the scanner camera is the digital reproduction of archival documents, paintings, large templates (e.g. maps and plans), transmitted light materials (e.g. glass plates), etc. The focus here is on the high resolution and image quality that can be achieved.
In particular, the digitization of national cultural assets (cultural heritage) should be mentioned here. Here, high quality requirements are set and formulated in corresponding standards (e.g. Metamorfoze in the Netherlands, FADGI in the USA, DFG rules of practice "Digitization" in Germany).
Since scanner cameras record all colors (RGB 3-line scanner) for each pixel and not a large part of blue and red ( there are 50 on a "one shot" image sensor, like digital cameras with one-shot sensors and Bayer mosaic color filters) % green-sensitive, 25% red-sensitive and 25% blue-sensitive pixels), the data quality is significantly higher than with corresponding digital cameras.
Manufacturers are
- Rencay (model 24k³) with uninterpolated 24,000 × 39,000 pixels as the highest resolution and 48 bit color depth (Photokina 2016),
- Betterlight (S10K-HS) with 10,200 element Kodak line and a resolution of 10,200 × 13,800 pixels,
Are no longer represented on the market
- Anagram company (picture gate 8000 david²) with uninterpolated 16,000 × 26,000 pixels image resolution and 48 bit color depth,
- Pentacon (Scan 7000) with 20,000 × 20,000 pixels and 48-bit color depth with SilverFast Archive Suite (novelty at photokina 2010).
These resolutions are well above those of available image sensors and even above the number of sensors in the human eye. In the area of the reproduction of art and scientific photography (example: Herbar Digital ) there is therefore no alternative to scanner cameras.
In contrast, the space probe's grayscale scanner camera , which took the first image of the surface of an alien planet in 1975 and transmitted it to Earth at 256 bit / s , had a line width of just 128 pixels .
Also interesting is the fact that it is often unavoidable in other areas where exact color reproduction at high resolution is important: Because scanner cameras “see” all colors (RGB 3-line scanner) and not like cameras with One -Shot sensor and Bayer mosaic color filter have to be content with interpolating a large part of blue and red (on a "one shot" image sensor there are 50% green-sensitive, 25% red-sensitive and 25% blue-sensitive pixels), the data quality is around many times higher than is the case with their non-scanning competition.
There are also panorama cameras z. B. for the FBI for crime scene recordings ( forensic evidence ) and the military for field recordings for high-resolution combat simulators.
Individual evidence
- ↑ Bernd Leitenberger: The Venera 9-16 space probes. Retrieved March 8, 2019 .
