Explanation of PX PT-lb EM and PS-Pitch VA units



PT (Point, LB): is a unit of physical length that refers to an inch of 72 points.

px (pixel, pixels): is a virtual length unit, is the digital image length unit of the computer system, if PX to be converted to physical length, you need to specify the accuracy dpi (Dots per inch, pixels per inch), when scanning printing generally have dpi optional. Windows system By default is 96dpi,apple system default is 72dpi.

em (relative length units, relative to the font size of the text within the current object): is a unit of relative length, originally referred to as the width of the letter m, hence the name EM. Now refers to a multiple of the width of the character, using a similar percentage, such as: 0.8em, 1.2em,2em and so on. Usually 1em=16px.

Font Size: is a unique unit in the Chinese font, in Chinese code to denote a specific point of Point pt, easy to remember, Express.

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The conversion formula for PT and PX can be derived according to the PT definition:

PT = 1/72 (inch), px = 1/dpi (inch) point = 1/72 (inch) pt = lb

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The pound is a rather odd unit, and it has historical reasons:

Pound as weight everyone knows, that is, 1 lbs = 0.4535 9,237 kilograms. But as font size is often only published by workers in the industry to know. Now the computer industry is using this word as well. You choose the font size for each software, measured in pounds. PT is the abbreviation for point, We usually use Word to type fonts on our computers, and the display is mostly 12pt.
The source is the number of feet that the print workers used to determine the size of the font, using their own feet. The United States also has a number of different PT sizes, which are not unified until 1886.

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So pt = px * 72/dpi

Calculated as 96dpi under Windows, 1 pt = px * 72/96= px * 3/4

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PS Font has a variety of units, PT/PX, etc., set in place in edit-preferences-units with ruler

If you want to view the DPI of the current document

Select Image-Image size

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Finally, the word spacing VA

The unit of VA is em*1000

Why is *1000, because the value of EM is generally relatively small, not easy to see, so it is shown in the form of *1000

Layout apps such as Adobe ' s Photoshop, Illustrator and InDesign use Em's in their tracking but manipulate the unit so it ' s An easier number for designers to play with. To make it easier they times it by 1000.

Reference website: https://stackoverflow.com/questions/2760784/how-to-calculate-css-letter-spacing-v-s-tracking-in-typography

To prevent URL links from invalidating, the screenshot is as follows

Specific:

When the font is 22 pixels, the VA value is 55, and the pixel value of the space is calculated

22 * (55/1000) = 1.21 pixels

Some people's fonts are PT units, for example, 16pt

Then one more step. PT to Pixel conversion

16/3 * 4 = 21px

Then 21 * (55/1000) = 1.15 pixels

Above, I understand now, through practice, feel almost. If there is an error, please correct it.