Defective Pixel Correction; Figure 24: Defective Pixel Map - Teledyne FLIR A68 Series User Manual

Defective Pixel Correction

The FLIR A68/A38 series camera uses a defective pixel map to identify bad pixels in
the sensor. These bad pixels are replaced by the average value of neighboring valid
pixels. The defective pixel map is an 8-bit bitmap file (.bmp) that uses two pixel
values; 0 (black) indicates a good pixel, non-zero values indicates a bad pixel.

Figure 24: Defective Pixel Map

Two defective pixel maps are available: a factory calibrated set and a user-defined
map. The factory calibrated defective pixel map identifies defective pixels across the
full range of ambient operating temperatures. The user-defined map adds pixels to the
list of defective pixels if additional pixels become defective during the camera's life
after factory initialization.
The user-defined map can be updated manually or using automatic defective pixel
detection. Automatic pixel detection updates the user-defined map by launching a
sequence that compares each pixel value with the average value of its neighbors.
To generate valid results, a uniform scene should be presented to the camera; the
internal mechanical shutter can be used, or alternatively a uniform scene can be
presented in front of the lens (for example, a sheet of paper, or a cardboard box;
additionally, it can help to adjust the lens completely out of focus).
Configurable parameters include the size of the neighborhood window and the
threshold used to identify bad pixels (the number of standard deviations from the
average value).
The Defective Pixel Detection Window Size (defectivePixelDetectionWindowSize) and
Defective Pixel Threshold features (defectivePixelDetectionResponseThreshold)
determines the algorithm behavior. In general, for very uniform images, a larger
window size provides more statistics; for less uniform images, a smaller window is
recommended (a smaller window also results in faster execution time). The threshold
sets the number of standard deviations from the normal pixel response beyond which a
pixel is considered defective.
64 • Features and Configuration Options FLIR A68/A38 Series IR Camera User's Manual