Defective pixels. How to check

Do you turn on the monitor (or TV) and see a dot out of the right colors in the picture? It can be permanently black or permanently white, less often blue, red or green. But whatever the broken pixel, there is little pleasant in this: even one problem point will be an eyesore and spoil the impression of a high-quality, in general, screen.

Why this happens, where the dead pixels come from and what to do with them – we will tell below.

Briefly about the monitor device and the cause of pixel problems

In LCD screens, the image is created from a “grid” of several million (or even tens of millions if it’s a 4K monitor) pixels. Each pixel consists of 3 sub-pixels: red, green and blue. Each subpixel is controlled by a transistor that turns it on or off.

If the transistor fails, the sub-pixel it controls will remain on or off. On the screen, we will see this as a dot that stands out in color.

What dead pixels look like:

  • white (“dead” pixel) – means that the transistor is always off;
  • black (“hot” pixel) – the transistor is always on;
  • red, blue or green that do not change color (“hung” pixel, if the transistor of an individual subpixel works, but is frozen in some position).

And it is also possible that a group of pixels is damaged at once. Visually, this can be shown as a larger dot, as well as a spot of different sizes, or even a whole line.

DPI, Pixels, Retina: How Device Screens Work

DPI or Dots Per Inch (dots per inch) is a measure of dot density originally used in printing. This is the number of ink dots the printer can fit in one inch.

The lower the DPI, the less detailed the print. This concept is also used for computer screens called PPI or Pixels Per Inch (pixels per inch). It’s the same principle here: the value counts the number of pixels that your screen can display on 1 inch. The term DPI is also used to describe screen performance.

Windows computers default to a PPI of 96. Macs use a PPI of 72. These values ​​were due to screens being manufactured at the time displaying 72 “dots” or pixels per inch. This was the case in the 80s, and now devices on Windows, Mac and other platforms have many variations of PPI screen resolution.

Resolution, pixel and physical size

Asking someone what the pixel size is is a great way to confuse a person with a tricky question. A pixel has no size, no physical meaning or meaning outside of its mathematical representation. It is part of the relationship between the physical screen size expressed in inches and the screen resolution expressed in pixels per inch and the screen pixel size expressed in pixels.

Regular non-Retina desktop screens (including Macs) will have a PPI between 72 and 120. Designing with a PPI between 72 and 120 ensures that your work will be roughly the same proportions in size everywhere.

Here is an example. The Mac Cinema Display 27″ screen has a PPI of 109, which means it displays 109 pixels per inch of screen real estate. The beveled width is 25.7 inches (65 cm). The width of the screen itself is approximately 23.5 inches, so 23. 5 * 109 ~ 2560, which forms the native screen resolution of 2560 * 1440 px.

Influence on design

Let’s say you draw a 109 * 109 px blue square on the screen we just talked about.

This square will have a physical size of 1*1 inch. But if the user’s screen has a PPI of 72, your blue square will be larger in physical size. Since the PPI is 72, it would take about an inch and a half of screen real estate to display a 109 pixel square.

Regardless of the difference in color and resolution, remember that everyone will see your design differently. Your goal should be to find the best compromise that covers the largest percentage of users.

How to remove a dead pixel

The method that is the most popular in solving our problem, as it helps in 80% of cases.

The principle of its use is that during the operation of a special program with a fast frequency, the colors of the pixels next to the broken one change.

As a result, more current is supplied to the problem area, as a result, the defective pixel is gradually resuscitated.

In each case, the recovery time of a broken pixel may be different, it all depends on the complexity of the situation and on the program settings.

In the utility settings, you can change the frequency of color changes and the period of its operation. In some cases, it will take from 20 minutes to 5-6 hours to solve the problem.

What is 4K Resolution

To understand what it is, let’s first understand what “HD” means. Remember that this is a super-simplified version of the explanation. I’ll just explain with an example of the most common permissions. There are different categories of HD.

The term HD applies to any resolution starting at 1280 * 720 px or 720p by 720 horizontal lines. Some may call this resolution SD, by the standard definition.

The term full HD applies to 1920 * 1080 px screens. Most TVs use this resolution, as do a growing number of advanced high-end phones (Galaxy SIV, HTC one, Sony Xperia Z, Nexus5).

4K resolution starts from 3840*2160 pixels. It is also called Quad HD, UHD from Ultra HD. Roughly speaking, you can fit 4 at 1080p into a 4K display by the number of pixels.

The second resolution of 4K is 4096 * 2160. It is slightly larger, used for projectors and professional cameras.