Editing Pixel (section)

===Logical pixel<span class="anchor" id="Logical"></span>===
In graphic, web design, and user interfaces, a "pixel" may refer to a fixed length rather than a true pixel on the screen to accommodate different [[pixel densities]]. A typical definition, such as in [[CSS]], is that a "physical" pixel is {{convert|1/96|in|mm}}. Doing so makes sure a given element will display as the same size no matter what screen resolution views it.<ref>{{cite web|url=https://www.w3.org/Style/Examples/007/units.en.html|publisher=w3.org|title=CSS: em, px, pt, cm, in...|date=8 November 2017|access-date=21 December 2017|url-status=live|archive-url=https://web.archive.org/web/20171106223130/http://www.w3.org/Style/Examples/007/units.en.html|archive-date=6 November 2017}}</ref>

There may, however, be some further adjustments between a "physical" pixel and an on-screen logical pixel. As screens are viewed at difference distances (consider a phone, a computer display, and a TV), the desired length (a "reference pixel") is scaled relative to a reference viewing distance ({{convert|28|in|cm}} in CSS). In addition, as true screen pixel densities are rarely multiples of 96 dpi, some rounding is often applied so that a logical pixel is an integer amount of actual pixels. Doing so avoids render artifacts. The final "pixel" obtained after these two steps becomes the "anchor" to which all other absolute measurements (e.g. the "centimeter") are based on.<ref>{{cite web |title=CSS Values and Units Module Level 3 |url=https://www.w3.org/TR/css-values-3/#ref-for-px② |website=www.w3.org}}</ref>

Worked example, with a {{convert|30|in|cm|adj=on}} 2160p TV placed {{convert|56|in|cm}} away from the viewer:
* Calculate the scaled pixel size as {{math|1={{frac|1|96}} in × (56/28) = {{convert|1/48|in|mm}}}}.
* Calculate the DPI of the TV as {{math|1=2160 / (30 in / {{sqrt|9^2 + 16^2}} × 16) ≈ 82.61 dpi}}.
* Calculate the real-pixel count per logical-pixel as {{math|1={{frac|1|48}} in × 82.61 dpi ≈ 1.721 pixels}}.
A browser will then choose to use the 1.721× pixel size, or round to a 2× ratio.