Frame, physical screen size and picture resolution developed by iOS

Model	Screen size (inch)	Logical Resolution (POINT)	Scaling factor (scale factor)	Physical resolution (pixel)	Pixel Density (PPI)
Iphone3gs	3.5	320 * 480	@1x	320 * 480	163
Iphone4/4s	3.5	320 * 480	@2x	640 * 960	326
Iphone5/5s	4	320 * 568	@2x	640 * 1136	326
iphone6/6s	4.7	375 * 667	@2x	750 * 1334	326
iphone6plus/6s Plus	5.5	414 * 736	@3x	1242 * 2208	401

Figure 1

Physical screen Size: it is generally measured by the length of the diagonal (inches), which is the actual size you see.

The logical resolution is corresponding to the physical screen size, just for the programmer to better control the position of the control, its reaction to the program is our usual frame. As you can see from Figure 1, the physical screen sizes of IPHONE3GS and iphone4/4s are the same, their frame (logical resolution) also corresponds, and the iphone4/4s and iphone5/5s have different screen sizes, and their logical resolution is different.

Physical resolution: The maximum number of pixels that can be displayed on the LCD screen, that is, how many light emitting elements are contained in a screen. A screen of the same size, the number of light emitting units is determined at the time of manufacture. For example iphone4/4s relative to IPHONE3GS, its screen size has not changed but its physical resolution is improved, the visual effect is clear, that is, the granularity has become smaller.

For a uiimage element, if the frame is not set, its size in the screen is determined by the resolution of the picture and the logical resolution of the device, such as a picture with a 320*480 resolution,    The logical resolution size is 320*480 and 160*240, respectively, on the iphone3gs and iphone4/4s of uiimage that do not have a frame set. The actual development of the UI gives the picture is based on the physical resolution to give, if the iphone6/6s as a design template, then you get the high-fidelity picture should be 750 * 1334 pixels, when the control frame, you should set the high-fidelity image size (based on the image of the pixel)/2.

Frame, physical screen size and picture resolution developed by iOS