Convert Dots per point to Lines per millimetre

Convert Dots per point (dot/pt) to Lines per millimetre (lp/mm) instantly and accurately.

Conversion Formula

lp/mm = dot/pt × 2.834645669

About Dots per point

The dot per point (dot/pt) expresses output resolution relative to the PostScript point - exactly 1/72 inch, codified by Adobe in the PostScript Language Reference (1985). The Apple Macintosh 128K (1984) ran its built-in CRT at exactly 72 DPI, placing 1 dot per point - an intentional WYSIWYG design: a 12-point character on screen measured 12 pixels tall and printed at 12 points on the Apple LaserWriter. Device resolution milestones: Apple LaserWriter (1985) 300 DPI = 300/72 ≈ 4.17 dot/pt; HP LaserJet 4 (1992) 600 DPI ≈ 8.33 dot/pt; Linotronic 300 imagesetter (1985) 1270 DPI ≈ 17.64 dot/pt; Agfa Selectset 5000 at 2400 DPI = 33.33 dot/pt. TrueType and OpenType font hinting instructions align outline points to raster device pixels at the current dot/pt ratio. The CSS pt unit equals the PostScript point: 1 CSS pt = 1/72 CSS in = 4/3 CSS px at 1 dppx. 1 dot/pt = 72 DPI = 72 PPI.

About Lines per millimetre

The line pair per millimetre (lp/mm) is the fundamental unit of spatial resolution in classical optics, characterising the resolving power of a lens, film emulsion, sensor, or microscope objective. A resolving power of N lp/mm means adjacent line pairs separated by 1/(2N) mm can be distinguished - derived from the Abbe diffraction limit (Ernst Abbe, 1873) and Rayleigh criterion (Lord Rayleigh, 1879). Film benchmarks at MTF50: Kodak Tri-X 400: 63 lp/mm; Fujifilm Velvia 50: 160 lp/mm; Kodak Technical Pan: 320 lp/mm. Lens benchmarks: Leica APO-Summicron-M 50 mm f/2 ASPH: ≈ 75 lp/mm at centre. CMOS sensor Nyquist frequency: for pixel pitch p mm, f_Nyquist = 1/(2p) lp/mm - a 4.63 µm pixel limits at ≈ 108 lp/mm. As a dimensional unit, 1 lp/mm = 25.4 LPI = 25.4 PPI exactly. 1 lp/mm = 25.4 PPI.

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