Why is the pixel density is not as important as it may seem

Long ago I worked in the production of LCD-monitors and televisions. And once I participated in a conversation with the engineers of the leading companies developing a display control circuit. They accused all of us who design and create screens in "nosodispleynoy engineering» ( «nose on glass engineering» - N.O.G.E.).

According to them, we have focused on improvements that can be seen, only his nose buried in the screen. We are increasing indicators that in everyday use do not play a role. And they were absolutely right.

Today, the mobile industry is doing the same. Pay attention to what is called the main characteristics of the screen in the tablet and smartphone. By and large, this is only the number of pixels and even, perhaps, a certain display technology (IPS, OLED or other). But is it really the only parts that need to pay attention? And in general, whether they are the most important?

Let's go back to seven years ago, at the time when he was presented with the iPhone 4 RetinaLCD monitor. Apple chose the name because this screen has a density of 326 pixels per inch, which corresponds to the resolution of the human eye (retina - retina).

Most likely, you do not need a higher density because can not tell the difference.

Some experts, including Dr. Ray Soneyru (Ray Soneira) from the company DisplayMate Technologies, disputed this claim. But even critics agree that this figure crept very close to the limit, which makes sense for practical use. 300 dpi - density pictures in glossy magazines. And their quality no one has ever complained.

And now this. Maximum density of the screen accessible on the smartphone market is 806 pixels per inch. It is about Sony Xperia Z5 Premium, 5,5-inch display which accommodates full 4K-image (2 160 to 3 840 pixels). There are several phone with a resolution of about 1440 to 2960 pixels and screen sizes of 5.5 to 6 inches with a density greater than 550 dpi.

Even Apple, which first assured us that 326 pixels per inch will be enough, this figure increased to 458 units in the display Super Retina for iPhone X.

The technical term for this all - madness.

Without a doubt, you may notice tiny differences down to the level of density of 500 pixels per inch. Provided that you have perfect vision, and you keep the phone more than 30 cm from the eye. But still, if today there is the possibility of creating such products, it does not mean that they have to create. It also does not mean that these displays generally work better than others.

To ensure the operation of all of these pixels require more computing power and energy battery. The more pixels on the screen, the less remains room for an "open field" - the part that emits light - in each of them. Therefore, suffer the brightness and energy efficiency lighting - or a combination of both.

On what are the parameters necessary to pay attention to?

Today, the displays are no longer suffer from problems such as distortion and violation of the image linearity. We are not faced with them as long as the manufacturers have stopped using CRT screens for more than ten years ago. So is our modern displays are not perfect? The answer - of course not. I can list at least three display properties that need to be improved much more than the number of pixels.

The image quality in bright light

The first - is the picture quality at the sunlight. It can improve by increasing the brightness and contrast discernible by the user. To make it comfortable to look at emission display (emitting light), it should display a white color as bright as those around him.

In addition to the brightness (which uses energy), the screen must provide contrast sufficient for use in good light. The characteristics of the OLED-displays usually indicate contrast ratio of 100 000: 1 or even 1 million: 1. But this is also nonsense. Such figures you get only in a completely dark room between the black and white display color.

In real operating conditions, the contrast is reduced under the influence of ambient light. And this is a problem for modern displays. Rare display screen is capable of providing in excess of 50: 1 in a typical room, and in a bright lighting conditions, this value is even lower. We would like to see a full-color reflective display technology, but there is nothing in the market.

color accuracy

The following property, which should interest us - is the color accuracy. But do not confuse it with the performance palette. The value of the latter determines the spectrum of colors that the display is capable of displaying. The OLED display, and now QLED impose a wide palette of colors, but they do not provide high color fidelity.

The wide color palette would be ideal if there is a raw material whose potential she could uncover. But with the wide color palette of a typical display only makes the image too bright and cartoonish.

Instead, we need screens that accurately convey the colors from the palette content creator (sRGB or Rec. 709). The accuracy of the transfer expressed in metric ΔE *, which indicates the difference between the two colors. If its value reaches 1, the error becomes noticeable. Show me Display option, which ensures a low difference in calculating the ΔE * on the basis of a few tests, and then we will have at least something.

Playing pitch

Color accuracy and overall image quality is largely dependent on the tone reproduction - properties, better known as the correct range. Most errors in the display of colors on the LCD- and OLED-displays are associated with the incorrect reproduction of colors within the three primary colors.

conclusion

Enough considered pixels. Instead, let's demand the improvement of those characteristics that can really improve the quality of images. There are still many ways to make a good screen, in addition to simply measure the amount of points.