Siemens star
Encyclopedia
A Siemens star is a device used to test the resolution
of optical instrument
s, printer
s and display
s. It consists of a pattern of bright "spokes" on a dark background, which radiate from a common centre and become wider as they get further from it. Theoretically the spokes only meet at the exact centre of the star; the spokes and the gaps between them become narrower the closer to the centre one looks, but they never touch except at the centre. When printed or displayed on a device with limited resolution, however, the spokes appear to touch at some distance from the centre. The smallest gap visible is limited by the smallest dot of ink the printer can produce, making the Siemens star a useful tool for comparing two printers' resolutions (DPI
). Similarly, it can be applied to a camera
's optical resolution by taking photographs of a Siemens star printed at high resolution and comparing photographs from different cameras to see which retained the centre detail the closest.
In the field of video production
, where it is often called a "back focus chart", the Siemens star is widely used to adjust the back focus of removable lenses. It also used during film or video shoots to help setting the focus
in special situations.
Siemens stars are similar to the sunburst pattern
used as a background in graphic design, as in the Japanese Naval Ensign. They are useful in drawing the eye to a point on the page.
Optical resolution
Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged.An imaging system may have many individual components including a lens and recording and display components...
of optical instrument
Optical instrument
An optical instrument either processes light waves to enhance an image for viewing, or analyzes light waves to determine one of a number of characteristic properties.-Image enhancement:...
s, printer
Computer printer
In computing, a printer is a peripheral which produces a text or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most new printers, a...
s and display
Display device
A display device is an output device for presentation of information in visual or tactile form...
s. It consists of a pattern of bright "spokes" on a dark background, which radiate from a common centre and become wider as they get further from it. Theoretically the spokes only meet at the exact centre of the star; the spokes and the gaps between them become narrower the closer to the centre one looks, but they never touch except at the centre. When printed or displayed on a device with limited resolution, however, the spokes appear to touch at some distance from the centre. The smallest gap visible is limited by the smallest dot of ink the printer can produce, making the Siemens star a useful tool for comparing two printers' resolutions (DPI
Dots per inch
Dots per inch is a measure of spatial printing or video dot density, in particular the number of individual dots that can be placed in a line within the span of 1 inch . The DPI value tends to correlate with image resolution, but is related only indirectly.- DPI measurement in monitor...
). Similarly, it can be applied to a camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
's optical resolution by taking photographs of a Siemens star printed at high resolution and comparing photographs from different cameras to see which retained the centre detail the closest.
In the field of video production
Video production
Video production is videography, the process of capturing moving images on electronic media even streaming media. The term includes methods of production and post-production...
, where it is often called a "back focus chart", the Siemens star is widely used to adjust the back focus of removable lenses. It also used during film or video shoots to help setting the focus
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
in special situations.
Siemens stars are similar to the sunburst pattern
Sunburst (design)
A Sunburst is a design or figure commonly used in architectural ornaments and design patterns. It consists of rays or "beams" radiating out from a central disk in the manner of sunbeams. Sometimes part of a sunburst, a semicircular or semi-elliptical shape, is used...
used as a background in graphic design, as in the Japanese Naval Ensign. They are useful in drawing the eye to a point on the page.
External links
- ISO 15775 chart (pdf) resolution test chart featuring a vectorVector graphicsVector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...
siemens star