Pixels, Resolution, DPI, PPI
foreword
At present, most displays are based on dot matrix. A series of small dots are arranged to form a large rectangle, and each small dot displays a different color to form an image. We call each small dot a pixel (pixel) .
concept point
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Dot: A point of physical properties, through which the printer or screen prints the picture. The dot point of a screen is fixed. For a specific display, after multiple dots are arranged, the width and height of a whole are called the "physical size" of the display, and the unit is "width x height", for example 12"x7.5".
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Pixel: A pixel is a colored square, and a Pixel may consist of many physical Dots. Under specific settings, how many rows and columns of pixels the display has is called the "resolution (geometry)" of the display, and the expression method is "the number of width pixels x the number of height pixels", such as 1440x900. Under the same resolution, each The size of dots can still be large or small. Also 900 points, if each point is 1 mm, it is 90 cm, if each point is 1 cm, it is 9 meters.
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DPI: dots per inch, called resolution, the number of Dots that can be contained in one inch, this pixel refers to the physical pixel, which actually exists.
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PPI: pixels per inch, how many pixels per inch. PPI=number of pixels (√(x²+y²))/physical size (inches), x is the number of pixels on the x-axis, y is the number of pixels on the y-axis, and the diagonal is used to calculate because the screen is opposite The corner length (screen size, physical size) is an exact value determined by the manufacturer when it is manufactured.
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DP: The abbreviation of Device independent Pixel (device independent pixel), also called DiP, 1dp means the length of 1px when the screen pixel density is 160ppi, which is the concept of andriod.
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PT: point is a unit of length. The general standard is 1 pt = 1/72 inch (1 inch = 2.54 cm). This standard is also called PostScript point. There is no essential difference between Point and centimeter, millimeter or other units, but the length is different. pt has nothing to do with the screen, it only has something to do with the document resolution, which is Apple's concept.
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DP and PT are standard units used to define applications on different devices and under different DPIs.
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Px: css pixels logical pixels, the abstract unit used by browsers
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DPR: device pixel ratio, device pixel scaling ratio, plane: 1px = (dpr)^2 * dp, latitude: 1px = dpr * 2
Example: iphone5: resolution 640px * 1136px, PPI: 326PPI, the dpr chart shows that the dpr of iphone5 is 2, according to the latitude: 1px = dpr * px, the screen of iphone5 is 320px * 568px.
- Screen resolution
Resolution is the number of pixels on the screen, for example, a 2560×1440px screen has 2560 pixels horizontally and 1440 pixels vertically. The 27" display has a point-to-point resolution of 2560×1440px, 109PPI. If you lower the screen resolution, you will find that the windows and icons on the screen become larger, because the pixels on the 27" are reduced. In fact, there are still so many pixels, and the PPI is still the same PPI. The reason for the fewer pixels is that when you lower the screen resolution, the operating system will stretch to fill the screen. At this time, the CPU/GPU will use point-to-point pixels to calculate a Set of new resolutions.
Screen:
HD: 1280*720px resolution
full HD: 1920 * 1080px resolution
4K: QHD or UHD (Ultra High Definition), the minimum resolution is 3840×2160px, another common resolution is 4096×2160px
Retina screen: Retina is a specification that greatly increases the ppi value of the screen by reducing the volume of pixels and the spacing between pixels. Retina screen dpr is greater than or equal to 2.