Sometimes, when you consider the characteristics of a smartphone or tablet, you can find such a parameter as PPI, next to which one or another figure is indicated. For example, PPI 401. The question arises – what does this parameter mean??
PPI (from English pixels per inch – pixels per inch) – a unit of resolution for the screen. Measured in the number of pixels that fall on one inch of the screen surface. For example, let’s take a resolution of 254 PPI. This means that one inch of the surface (2.54 cm) contains 254 points. Accordingly, each pixel in the image in this case is 0.1 × 0.1 mm.
Why do manufacturers indicate this value? In fact, the answer is simple: the higher the number of pixels per inch (PPI), the smaller the dimension of the pixel itself, which means that on the device’s screen you will not see graininess.
It is believed that the human eye is able to see the pixels on the screen, where the PPI is 330-350. If the number is higher, it is almost impossible or difficult to see the pixels. It turns out that the higher the PPI, the better, although, it should be noted, the PPI 350 is enough to not see the grain on the screen. If the PPI is, for example, 250, then you can see the pixels on the screen. Someone does not pay attention to this, for someone this is a real problem.
PPI increases with screen resolution. So, for example, PPI for a 5-inch smartphone screen with a resolution of 1280 × 720 pixels is 294, and with a resolution of 1920 × 1080 pixels, this figure increases to PPI 441. Agree, the difference is large. But you need to remember that high resolution can negatively affect the autonomy of the device.
Here is an example of an image from the iPhone screen, where on the left side we see a significantly lower number of PPI, and on the right, respectively, a larger:
As you can replace, the difference is visible to the naked eye.