What is the difference between e-book displays and smartphones and tablets?

On the Internet, many copies are already broken about whether, from the user's point of view, e-book screens (made with E Ink technology) differ from the screens of tablets and smartphones (using LCD and OLED technologies), or is there no significant difference? Light - is it light in Africa ?!

The time has come for many years of these disputes to sort out this issue and draw a thick line.

First, the decoding of LCD, OLED and E Ink.
The LCD is a Liquid Crystal Display, a liquid crystal display. They have variations: TN, IPS, VA, and others.

OLED is a display based on light-emitting organic diodes, Organic Light-Emitting Diode. They also have varieties: AMOLED and Super AMOLED.

E Ink (Electronic Ink) is a display based on "electronic ink" ("electronic paper"), where the image is formed by microscopic pigment particles. Actually, it is also formed on “real” paper, but then it cannot change.

Their varieties mainly denote the change of their generations (VizPlex, Pearl, Carta).

First - briefly a few words about the technological features of the construction of the image on the screens of these types, which leads to the difference for the user.

LCD and OLED screens are light-emitting, although they do it in different ways.

According to LCD technology, an image (in the form of pixels) is formed in a layer of liquid crystals, the transparency of which changes under the influence of an electric field (due to the rotation of the polarization axis of liquid crystals, to put it simply). But this layer of liquid crystals itself does not emit light; light is emitted by a backlight lamp located behind this layer.

In OLED screens, on the contrary, each pixel emits light, since each pixel is a radiating LED.

According to the E Ink technology, the screen does not contain light-emitting elements (the backlight, when it is, is organized in a special way, this will be discussed later); and the image is formed by the physical movement of pigment particles.

The principle of operation of the E Ink screens is schematically presented in the following figure:


What is interesting, after removing the voltage applied to the electrodes, all particles remain in their places and the image does not disappear anywhere. This is a characteristic feature of E Ink displays - the lack of energy consumption when displaying static images. But when you change the image energy is still necessary to move the particles.

Now consider micrographs of these types of screens (made using an entry-level digital microscope, so that “what happened - it happened”).

Micrograph of the screen on the "electronic ink" E Ink:

Some of the "roughness" of the image is associated with a rough (matte) surface of the screen.

Micrograph of the LCD screen type TN + Film:


The structure of subpixels - uniform.

Micrograph of the IPS LCD screen: The


presence of the internal structure of subpixels and their “shaggy” borders are noticeable.

Micrograph of the AMOLED screen:


A different form of subpixels of different colors is noticeable (one of the options).

What else should I pay attention to?

On LCD and OLED screens, luminous pixels do not occupy the wholethe surface of the screen (between them - black gaps); and on the E Ink screen, the pixels forming the image occupy the entire surface of the screen. And this is another similarity with the image on paper.

Moreover, if on the LCD or OLED screens only one color of the three colors of subpixels is active, the “dark” area of ​​the screen will be even more times than with a white screen.

If at the same time to watch the image from such a distance at which the pixels are guaranteed to "merge" for the observer, then this value will not be. But for those who like to watch from a close distance, the situation will be different - part of the cones on the retina will be lit too much, and the other part - too weak.

But, as you know, "you have to pay for everything." A more uniform brightness on the screen with “electronic paper” is achieved by a high price: all of them are monochrome (black and white, and not even with “50 shades of gray”, but only with 16). True, attempts have been made recently to release E Ink color screens, but it is still far from mass production.

It also brings together E Ink in physical properties with paper and the matte surface of the screens (“real” paper is also matte). And it is matte - for all E Ink screens produced now.

LCD and OLED screens are also matte, but only on the most expensive tablets. Smartphones, according to tradition, are made of glossy screens, in which external sources of light are well reflected.

Now to the question of how good is the similarity of E Ink screens to paper?

When we read a paper document, although we are not aware of this, the instant “automatic dimming” of the media works. As soon as we bring a paper document into a lighter place, it immediately becomes lighter. And this is quite natural, because the paper “works” in reflected light.

Similarly, the screen works on "electronic paper" - in reflected light.

Thus, in both cases, the brightness and contrast parameters of the carriers instantly and optimally adjust to the external light environment. This is another of their usefulness for vision. Recall that physicians do not recommend watching TV in complete darkness: high contrast changes in light surroundings irritate eyesight.

LCD and OLED screens also have an automatic brightness control (hardware, not natural), but it works “not immediately.”

The similarity of the E Ink screens with paper results in one more unique advantage: the higher the brightness of the external light, the better you can see the image on them; while for LCD / OLED screens the situation is diametrically opposite. In addition, in order to see something on the LCD / OLED screens in direct sunlight, you have to turn on the brightness to a maximum, which quickly discharges the batteries of mobile devices.

Another positive factor of the screens on the "electronic ink" - the "absolute" viewing angles (also like paper).

On LCD screens, the brightness drops quite a bit when the viewing angle deviates from the vertical (especially on screens of the TN + Film type). True, OLED screens largely managed to solve this problem.

Another problem LCD and OLED screens - flickering lights. Its existence is due to the fact that the brightness adjustment in them is carried out using PWM (pulse-width modulation) with a frequency of 60-200 Hz (more - better).

It has a different visibility at different levels of brightness; Maximum-noticeable is usually at a brightness of about 50%.

To detect this type of illumination can be long known "pencil-stroboscopic method"; that is, waving a fan in front of the screen with a pencil between two fingers. For flickering screens, the pencil forms a whole range of silhouettes; in the "flicker-free" they are visible only in the extreme positions of the pencil (at the moments when the direction of movement changes).

E Ink screens have no backlighting - no problem!

But, interestingly, although the E Ink screens with illuminations have already appeared, they still do not have such a problem. It is solved due to a significant increase in the frequency of PWM.

The technical organization of the backlight of the E Ink screens is completely different than that of the LCD screens (while the OLED does not have the backlight as a separate functional part of the screens).

On LCD screens, the backlight is provided by the lamp behind the layer in which the image is formed. But for E Ink screens, such a backlight does not fit: it’s like reading the pages of a book "on the open".

In this regard, the backlight for E Ink screens works in the outer layer of the screen. The light propagating in this narrow layer illuminates the formed image with a “sliding” light from above; whereby this backlight works in the same way as if it were an external light.

And now, dear readers, allow me to put a cunning and villainous stab in the back with such good screens on “electronic ink”.

Due to the fact that the formation of the image on them is carried out by mechanical movement of particles, the speed of such screens is low. For most E Ink screens, the full screen refresh time is about 0.45 seconds (from technical data, up to 0.2 seconds in real conditions). Cinema on such screens can not be seen in principle, even black and white.

Another problem, but less significant, is the so-called “image artifacts”, which represent pale traces on the screen from the previous image. True, this problem was solved for the texts (Snow Field technology); but for “large-sized” images (drawings and other graphics), the problem is “stuck”.

In order to combat artifacts, a full screen reset is usually carried out periodically, i.e. it is completely blackened, and only then a new image is drawn on it. The frequency of “reset” is usually recommended - once for 5-10 pages.

At this point, it’s time to take stock (“pluses” and “minuses” of E Ink) and determine the possible area of ​​application of E Ink screens.

The advantages of E Ink screens compared to LCD / OLED screens:

  • work in reflected light, no loss of image quality in high ambient light (up to direct sunlight);
  • "Absolute" viewing angles;
  • low energy consumption (with dropping to zero when transmitting static images);
  • image pixels cover the entire area of ​​the screen without gaps;
  • matte screen coating, "blurring" reflections from light sources;
  • no screen flicker due to PWM backlight;
  • similarity in optical properties with the “real” paper at the physical level.

"Cons" screens E Ink compared with LCD / OLED screens:

  • the inability (at the moment) to transfer the image in color (not counting the experimental samples);
  • the ability to transmit only 16 gradations of gray brightness;
  • the presence of artifacts in the image (traces of the previous image);
  • low screen performance.

It is the last flaw that will be decisive for the range of possible applications for E Ink screens. They can be used only where no quick change of the image on the screen is required (and a black and white image is permissible, of course):

  • eBooks;
  • Digital Watch;
  • electronic price tags;
  • electronic bulletin boards and information signs.

There was also an attempt to integrate the E Ink screen into the phone (the sensational YotaPhone), but such use was not widespread.

Thank you all for your attention!

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