Should we say definition or screen resolution? If the two elements are very strongly linked, they are not quite alike. We show you how to tell the difference.
When announcing a television, smartphone, tablet or PC, manufacturers often communicate data relating to the screen: diagonal, definition, or even colorimetric spectrum covered and refresh rate. Sometimes manufacturers also talk about resolution. It often happens that the marks tangle the brushes and mix resolution and definition.
I have to say that English does not make things easier since resolutionin the language of Shakespeare, translates into French by definition. English speakers are therefore forced to go through expressions like display resolution for the definition or pixel density for the resolution in order to clearly differentiate the two.
Let’s go together to discover these two terms which are ultimately easy to understand and which have all their importance on a technical sheet.
Definition: the number of pixels
The definition is the number of pixels present on the slab. It is calculated in pixels, by multiplying the number of points on a horizontal line by that of a vertical line. For example, the QHD definition corresponds to 2560 pixels in width by 1440 pixels in height (or the reverse for a smartphone held in portrait mode), i.e. a total of 3,686,400 pixels. A 4K/UHD panel has a total of 8,294,400 pixels since its definition is 3840 x 2160 pixels.
As a reminder, the higher the definition of the display, the more power the GPU (the graphics chip of the SoC) will need to maintain display of images at native rendering. To maintain a speed of 60 frames per second with a QHD definition, you need about 1.5 times more power than with a Full HD definition.
This is where a technique called upscale or scaling of the screen definition: the device calculates an image in Full HD for example, then displays it in 4K by calculating the missing pixels by interpolation. This is how a service can sell a 4K UHD display, for example, without the images being natively offered in 3840 x 2160 pixels.
Resolution: pixel density and Retina
The resolution is the ratio between the definition of the panel (expressed in pixels) and its display surface (whose diagonal is expressed in inches). We therefore speak of Pixel Per Inch (PPP) for the resolution, or in English Pixel Per Inch (PPI), or Dot Per Inch (DPI). The higher this number, the higher the pixel density will be..
Let’s take a concrete example: a smartphone with a 5.5-inch screen and a 4K UHD definition of 3840 x 2160 pixels on one side, and a 55-inch television with the same 4K UHD definition of 3840 x 2160 pixels. In the first case, the resolution is approximately 800 dpi, while in the second case we have a resolution, or pixel density, of only 80 dpi, or 10 times less. Here this example was trivial, but we can sometimes encounter larger screens, with better definition, but still with a lower resolution.
The calculation being a little more complex than the definition (you have to divide the total number of pixels by the surface of the slab), you can use the PPI Calculator tool, available online.
The resolution is an extremely important element to take into account for reading comfort.. The lower the resolution, the more the pixels will be visible and will appear “larger”. 220 DPI is a pretty low resolution, and website reading won’t be very pleasant since the characters won’t be well defined. It all depends of course on the distance from which you look at the screen. A television is designed to be watched from several meters away, whereas a smartphone is used more like 25 cm from the face.
let’s remember that the term Retina was invented by Apple and refers to a smartphone with a resolution greater than 300 DPI, deemed the most suitable density for reading on a smartphone-sized screen (3.5 inches at the time of the creation of this term) and used at a distance of about 25 cm.
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LCD, OLED, PenTile or RGB: reduced resolution
Regarding resolution and definition, another variable must be taken into account: the type of panel. Most LCD screens use three subpixels to form a pixel: a red subpixel, a green subpixel, and a blue (RGB) subpixel. This is not the case with Samsung’s AMOLED panels, which use PenTile RGBG technology. It makes it possible to produce panels with higher definition at a lower cost and more easily. But on a PenTile panel, a pixel is made up of two sub-pixels: either red and green, or blue and green.
Thereby, the definition announced by Samsung is only achieved by the green sub-pixels while the blue and red sub-pixels are half as numerous. If this was a problem when the first generations of AMOLED smartphones arrived, such as the Galaxy Nexus, this is no longer the case today where the quality of the panels and the increase in definitions have largely compensated for the lack of PenTile technology.
Pay attention to the display format
The standard definitions on our smartphones have been widely revised with the adoption of generally longer edge-to-edge screens. We have thus swapped the traditional 16:9 for formats 18:9, 19:9, 20:9 or even 21:9. Manufacturers then speak of “Full HD+” or “QHD+” definitions, which generally mean that pixels have been added in length to adapt to the format, Full HD and QHD being definitions in the 16:9 format.
This is also the case for 4K which corresponds to a cinema format of 4096 x 2160 pixels in 17:9. On our TV screens in 16:9 format, we are therefore talking about 4K UHD, or 3840 x 2160 pixels.
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