Pixel errors

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Subpixel defect

A pixel error is a defective pixel , usually on an LC screen . In LCDs, pixel defects are usually caused by manufacturing defects. Such errors are also possible with CRT screens, for example due to errors in the shadow mask . A pixel error is expressed e.g. B. by a continuously lit pixel or a continuously black pixel. In the case of LCDs, individual subpixels can also be affected by an error. While manufacturers and retailers are mostly of the opinion that pixel errors are tolerable, consumers and ergonomists are mostly of the opinion that pixel errors are a major problem. Even if the user does not recognize the pixel error, they can still subconsciously disturb. They therefore represent an ergonomics problem.

Pixel defect classes

Maximum permissible errors per 1 million pixels according to ISO 9241-307
Error class
error class
ISO 13406-2
Error type 1
continuously lit pixel
Error type 2
constantly black pixel
Error type 3
a defective subpixel ,
constantly lit.
Error type 3
a defective subpixel ,
constantly black
0 I. 0 0 0 0
I. 1 1
2-n 2 * n + 1
II II 2 2
5-n 2 * n
III III 5 15th up to 50
IV IV 50 150 up to 500
constantly lit subpixel (mouse pointer for comparison)

The manufacturers defined pixel error class II as “common” in the sense of ISO 13406-2 and thus elevated it to the basic standard . According to this, for example, in a TFT display with a resolution of 1920 × 1080 pixels (= 2.073 million pixels), four pixels may be permanently lit, four pixels may be black and up to ten sub-pixels may be defective. The ISO 13406 series of standards was withdrawn in 2009 and replaced by the ISO 9241 series . According to this, in error class II, a maximum of two pixels may be permanently lit or continuously black and a maximum of ten defective subpixels may be found.

Software-related pixel errors

Display errors in the form of constantly lit or dark pixels can also arise on the software side due to incorrect device drivers or incorrect program code, especially in 3D games. Since this is not a matter of hardware damage, but rather errors in the calculation of the screen content (in 3D games, for example, two adjacent textures without edge smoothing), the problem can be solved by correcting the software.

Thermal problems

Overheating of the image-generating hardware (graphics card etc.), for example due to excessive overclocking or poor ventilation, can cause display errors, which then usually appear in the form of much more pronounced artifacts than just a single incorrectly displayed pixel.

Pixel defects in the digital camera

If the pixel errors occur in the image sensor of a digital camera , one speaks of “dead pixels” in the case of always dark pixels. If, on the other hand, the pixel is always bright, there is still no common German name; the English term is “stuck pixel” (meaning “stuck pixel”). Pixels represent an intermediate form, which only show an anomalous behavior in certain cases, mostly with high ISO values ​​or long exposure times. If these pixels are then too bright, they are called " hot pixel " , also in the absence of a common German term . A suitable German term would be "oversensitive pixel". There is still no technical term for the theoretically occurring case that a pixel is under-sensitive. The effect of over-sensitive pixels can sometimes be reduced by actively cooling the image sensor.

In the case of digital cameras, pixel errors are best "repaired" by the camera's firmware. The defective pixel is then simply ignored and an average value is calculated from the neighboring pixels instead. Since these are actually subpixels, namely of a certain color, it should be noted that a green pixel, for example, must be calculated from the neighboring green pixels so that there are no color falsifications. The prerequisite for this process is that the firmware knows the defective subpixels, i. H. a corresponding list is available. In general, this is determined during the manufacturing process of the camera and permanently programmed. However, aging and environmental influences often lead to further defects, for example one to three more “hot pixels” every year, the position of which the firmware has to learn. Depending on the camera manufacturer and price range, this happens either automatically, manually or not at all. With the latter “procedure”, manufacturers can more or less deliberately, because it is a simple software-technical procedure, differentiate more expensive from cheaper cameras. If "hot pixels" or "stuck pixels" then appear, there are glowing dots in the same place on every photo, with red or blue dots appearing twice as large as green ones because of the Bayer pattern that is commonly used . Such errors can also be removed later with image processing programs.

Web links

Wiktionary: Pixel errors  - explanations of meanings, word origins, synonyms, translations