LCD screens in a nutshell (page 8: Understanding 16.7 or 16.2 millions colors?)

Understanding 16.7 or 16.2 millions colors

All screens pretend to display 16 millions of colours. Still, after the comma, the figure changes: 2 or sometime it is better: 7.

On the paper, screens are able to display 256 shades of red, 256 shades of blue, and 256 shades of green. The combination of all three provides 16.7 millions of different shade. This is what VA or IPS screen does.

TN screens are more economical. In fact, they only display 64 red, 64 blue and 64 green. The maximum amount of colours is 262 144. In order to reach 16 millions of colours, the manufacturers are using the dithering process. The process is to display two close colours so quickly that only one is seen.

So instead of recognising all 0,1,2,3,4 shades and so on until 255, TN screens only knows the shades 0,4 ,8 ,12 ,16 ,20 … until 252.

Displaying shade 2

Manufacturers have several possibilities:

If the manufacturer wants to work on one pixel only: at T0 the pixel is white, at T1 the pixel has the shade 4, then the pixel comes back to shade 0 at T2, then shade 4 at T3, etc. The eye mixes the two shades and only sees the colour 2.


T0	T1	T2	T3

The necessity of using two periods to get the right shade is the inconvenience of this process. It is also possible to use the four next pixels (in a square shape). Two of them will have the shade 0 and the two others the shade 4. So from your point of view the colour will be 2.

Displaying shade 1

The first approach is to display shade 0 for T0, T1, T2 and shade 4 for T3. So you will see (0+0+0+4) / 4= shade 1. But three periods will be necessary to get shade 1. There again this process is too long.


T0	T1	T2	T3

The other possibility is using one pixel with the shade 4 and three pixels with the shade 0.

This method is very efficient. But it still has two main issues: the screen flickering is perceptible and the shade 253, 254 and 255 can’t be displayed. With the dithering, all colours are displayed from 0 to 252, so the result is 253 red x 253 blue x 253 green = 16.2 millions of colours.