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Instead of single lines, line pairs are often used, composed of a dark line and an adjacent light line; for example, a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens are most often quoted in line pairs per millimeter.
These 54 elements are provided in a standardized series of logarithmic steps in the spatial frequency range from 0.250 to 912.3 line pairs per millimeter (lp/mm). The series of elements spans the range of resolution of the unaided eye, down to the diffraction limits of conventional light microscopy .
Often found covering a range of 0.25 to 228 cycles/mm. Each group consists of six elements. The group is designated by a group number (-2, -1, 0, 1, 2, etc.) which is the power to which 2 should be raised to obtain the spatial frequency of the first element (e.g., group -2 is 0.25 line pairs per millimeter). Each element is the 6th root of 2 ...
Johnson's criteria. Johnson's criteria, or the Johnson criteria, created by John Johnson, describe both spatial domain and frequency domain approaches to analyze the ability of observers to perform visual tasks using image intensifier technology. [1] It was an important breakthrough in evaluating the performance of visual devices and guided the ...
The SI unit of spatial frequency is the reciprocal metre (m −1), [1] although cycles per meter (c/m) is also common. In image-processing applications, spatial frequency is often expressed in units of cycles per millimeter (c/mm) or also line pairs per millimeter (LP/mm). In wave propagation, the spatial frequency is also known as wavenumber.
More accurately known as limiting resolution, tube resolution is measured in line pairs per millimeter or lp/mm. This is a measure of how many lines of varying intensity (light to dark) can be resolved within a millimeter of screen area. However the limiting resolution itself is a measure of the Modulation Transfer Function.
At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image. Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate.
It is calculated using the number of line pairs per millimeter that a user can detect multiplied by the image intensifier's signal-to-noise (SNR) ratio. [ 39 ] [ 40 ] [ 33 ] [ 41 ] In the late 1990s, innovations in photocathode technology significantly increased the SNR, with new tubes surpassing Gen 3 performance.