A hot pixel is a pixel that reads bright on longer exposures due to charge leakage, the longer the exposure and higher the gain the more visible the hot pixels. This is due to the fact that the natural variance in charge leakage between pixels is intensified by the increased amount of light or gain. Given a sufficiently long exposure time, you will see pixels respond noticeably brighter than others on any digital camera regardless of make or model. Sensor manufacturers provide a tolerance for each of their sensors as well as defining what intensity is considered a hot pixel. Generally, tolerances for CMOS sensors are higher than those for CCD sensors. All sensors shipped are verified to be within these tolerances.
If you suspect that your camera has a hot pixel, please contact Pixelink support at [email protected].
CMOS sensors almost always have some pixels that don’t have the full dynamic range that they should. Most of these pixels can be corrected with the flat field correction parameters, also implemented in the camera. However, the pixels that cannot be properly corrected with flat field correction are considered defective pixels. These dead or hot pixels, usually stuck dark or bright, are corrected with the defective pixel correction routine. This routine corrects the defective pixel with interpolated values based on neighboring pixels.
Typical correction methods include averaging with immediate same-colour neighbors, or even going out to the second set of neighbors. Correction can span multiple pixels if by some chance many consecutive pixels in a row are defective. Boundary conditions also exist to handle defective pixels at the edges of the image array.
When This is Used
To replace dead or hot pixels with interpolated neighbours.
When the camera is factory calibrated or field calibrated, the FFC Wizard calibration utility will test each pixel and mark it as defective if needed. This is performed after the flat field correction, i.e., only pixels that look defective after flat field correction will be flagged. In most cases increasing exposure time or camera gain before running the FFC Wizard will yield more defective pixels flagged, and therefore more corrected.
The defective pixel correction routine is always on, and cannot be turned off by a user.
How This is Done
All pixels that are flagged as defective will be corrected on the fly as video is streaming.
There are no settings that the user can adjust.
The SDPC Wizard and FFC Wizard are installed when installing Pixelink Capture or the SDK, and can also be used to correct hot pixels.
For information on the FFC Wizard (for PL-A and PL-B cameras), see Flat Field Correction.
For information on the SDPC Wizard (for PL-C and PL-D cameras), see Static Defective Pixel Correction Wizard Guide and Static Defective Pixel Correction Wizard Manual.