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Points
Point
At the beginning, coordinates of all drawings are specified in points.
At the beginning, all positions of the image are specified by coordinate points.
Points are abstract units, they only make sense in this mathematical coordinate space.
Vertices are abstract units that are meaningful only in the logical coordinate system.
Rendered pixels
Pixel rendering
Point-based drawings are rendered into pixels. This process is known as Rasterization
Point-based images are rendered as pixels. This process is called Rasterization.
Point Coordinates are multiplied by scale factor to get pixel coordinates. Higher scale factors result in higher level of detail.
Obtain the pixel coordinates by multiplying the coordinate points and the proportional coefficient. A higher proportional factor will show more details.
Physical pixels
Physical Pixel
The device screen may have lower pixel resolution than the image rendered in previous step.
The resolution displayed on the device screen may be lower than that shown in the previous step.
Before the image can be displayed, it must be downsampled (resized) to lower pixel resolution.
To display the previous image, you must re-sample (resize) at a lower pixel resolution ).
Physical Device
Physical Device
Finally, computed pixels are displayed on the physical screen.
Finally, the calculated pixels are displayed on the physical screen.
The PPI number tells you how to adjust pixels fit into one inch and thus how large the pixels appear in the real world.
The number of PPI determines how many pixels are loaded by 1 inch, so that large physical pixels are displayed on the real screen.
IPhone resolution Ultimate Guide (including iPhone 6/6 +)