bad pixel

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bad pixel

A defective pixel on an LCD screen. Bad pixels are often transistors that are permanently dead and appear as black dots or permanently energized and show up as white or colored dots ("hot pixels"). These pixel defects usually occur at the time of manufacture. However, if a bad pixel appears after the screen has been in use for some time, it may also be due to a dented or scratched polarizer (see LCD).

Sometimes, it is possible to repair a bad pixel by gently rubbing the screen with a cloth or running a pixel repair over the area for several hours, the latter repetitively flashing colors on and off to attempt to dislodge a stuck pixel.

Does It Matter?
It depends. On an LCD TV, which is displaying motion and is situated several feet from the viewer, dead or lit pixels may not matter. On a computer monitor only two feet away, they may be very annoying, especially if located in the center of the screen. Equipment manufacturers have different policies regarding defective pixels. They typically state that if a certain number of bad pixels exist when the display was purchased, the unit may be returned.


Polarizer Damage
This red pixel is due to damage on the polarizer, which is the screen layer in front of the user (see LCD).







It Can Be Annoying
One bad pixel can be very glaring, depending on where it shows up; witness the single, green pixel on this man's black coat.







Test for Yourself
Dead pixel testers such as Dead Pixel Locator from Astris.com let the user find bad spots by displaying different colors across the entire screen.







Repair Stuck Pixels
Pixel repair programs cycle rapidly through all the colors to possibly dislodge a stuck pixel. There is no guarantee, but if a stuck pixel is annoying, it is worth a try. When this animated GIF is retrieved from Killdeadpixel.com, it is placed over the stuck pixel and left alone for an hour or more.
References in periodicals archive ?
The OV9715 incorporates image processing functions, including exposure control, gain control, white balance, lens correction and defective pixel correction.
They also feature all standard image quality controls such as color saturation, hue, gamma, sharpness (edge enhancement), lens correction, defective pixel canceling and noise canceling.
All required image processing functions, including defective pixel and noise canceling, RAW scaling, image size, frame rate, exposure, gain, cropping and orientation are programmable through the serial camera control bus (SCCB) interface.
All required image processing functions, including exposure control and defective pixel cancelling are programmable through the serial camera control bus (SCCB) interface.
d) Automatic exposure adjustment (Auto Exposure) Automatic white balance adjustment (Auto White Balance) Output picture size adjustment (Output image size adjustment) Color interpolation, level correction 9 Main functions (Color/contour adjustment) Color difference matrix conversion (Color difference matrix transformation) The degree of picture clearness (Image sharpness adjustment) Defective pixel compensation (Pixel Correction) Auto focus JPEG compression (d) Targeted values, subject to change
42mm Power consumption 290mW Lens composition Three pieces Frame rate 20 fps Major functions - automatic exposure - automatic white balance adjustment - output picture size adjustment - color interpolation, gray level correction - color difference matrix conversion - degree compensation of image quality - defective pixel compensation Additional features - macro function - single module contains an electric wave and signal processing LSI
All required image processing functions, including exposure control, white balance, and defective pixel detection and correction are programmable through the SCCB interface.
On-the-fly defective pixel correction ensures that each picture captured is of the highest quality.
It also offers color saturation, hue, gamma, sharpness (edge enhancement), lens correction, defective pixel canceling, and noise canceling to improve image quality.
Exposure control, white balance and defective pixel canceling are programmable through the serial camera control bus interface.
It also offers all required automatic image control functions, including automatic exposure control, automatic white balance, automatic black level calibration, as well as defective pixel correction, gamma correction and lens shading correction.