Important characteristics of smartphone displays

In this year came the Google Pixel 2 and Pixel 2 XL. Many have probably heard about the screen issues in the older model. Display in smartphones is probably one of the most important parts. Because all interactions with the device occur through the display. In this article we will talk about the characteristics of the screen and not the brightness or the latest technology, namely technical characteristics. Some of them are really important and which, in fact, just a marketing ploy.

Contrast ratio

The contrast ratio is checked is very simple: measure the luminance of the display white and black area, and the contrast ratio is simply the ratio of these two numbers. Obviously, the higher the number, the better it will look in the display. Very high brightness contributes to white color. But let’s face it: no real display is designed for bright lighting.

Thus, the display contrast is almost always determined by how deep black color. With the advent of OLED, the black depth was very good. OLED panels emit light depending on the amount of energy passing through it. And if power off, the display does not emit light.

Zero or near zero emission in the dark will generate a high value of contrast ratio. Some smartphones with OLED panels specifications require contrast ratio from hundreds of thousands to one or even a million to one. Some producers even stated “infinite” contrast in their OLED screens.

The problem is that these indicators is what you will get if you independently measured the black level in total darkness (assuming you can actually get this rate). In practice, this requires quite complex equipment . Under normal lighting conditions or in dark rooms, the actual contrast of most displays is limited to the amount of ambient light that is reflected on the display.

Most screens give an effective contrast in the range from 50:1 to 100:1 under normal viewing conditions with normal ambient light levels. If the figure is closer to the result of 200:1, it’s just an incredible screen.

Colors

Another important specification in which the statement “bigger is better” leads us astray is the range of colors that represents the range of colors displayed on the screen. Usually, the color scheme is denoted in percentage of the specific reference space or gamut. The traditional color scheme used in cable TV USA called “NTSC gamut”.

Some displays give a “105% NTSC” and many immediately think they are excellent. In fact, over a wide range does nothing for the quality or accuracy of the image. Photos and videos are produced with a specific set of characteristics of color space including the display gamma. If the display does not meet these specifications (or the software for color management), then the resulting image will not be accurate.

If you open the picture on the screen with increased color gamut, all colors are very saturated

Ideally I want to have a display with a high percentage of colors, but rather a range that would fit the image. Today, almost all television programs and images of digital cameras are created to sRGB or “Rec. 709”, which themselves make up only about 72% of the standard field rate of NTSC. Newer standards, such as DCI-P3 or “Rec. 2020” is good, but not perfect.

Color depth

There is a very important parameter, which many do not pay attention or do not understand the “color depth”, or as it is sometimes called the “number of colors”. It is easy to understand. If your display can handle, say, eight bits of data for each red, green and blue primary colors, you can get out of them 256 different “levels of gray” (since 28=256). If so, then:

256(RED) x 256(GREEN) x 256(BLUE) = 16,78 million different colors.

That’s a good thing? It is obvious that a wide variety of colors is always better. Why not try to reach 10 bits for each primary color? So it is possible to billion within. But not so simple. “Color” is merely a perception; it is something constructed by our own visual systems and has no real physical existence or meaning.

How many different colors our eyes can distinguish? It is about a few million. Any changes different colors, shades, etc., from the point of view of perception to the human eye, is simply meaningless. The greater the number of bits per color (within reason) can be used in many situations.

Don’t worry too much if:

  • The absolute contrast in dim lighting 2000-3000:1.
  • A high percentage of color.
  • A large “number of colors”.

But it’s better if records of display will be as follows:

  • The right contrast in low light conditions with low reflection rate of the screen itself.
  • The right color scheme that most closely matches with the real image.
  • A good indicator of color accuracy and gamma.
  • Response time “Moving picture” (MPRT) and similar response characteristics (moving blur on the edges, etc.).

Insights

What we get in the end? And the fact that our knowledge of the good and the bad the display is often not correct. This article demonstrated only a few examples of how you can look at the performance specs, but not understand what they mean. But this may lead to confusion in assessing the quality of the display.

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