BOBCAT Hardware User’s Manual
Imperx, Inc.
Rev. 2.0.2
6421 Congress Ave.
11/20/2012
Boca Raton, FL 33487
+1 (561) 989-0006
136 of 265
2.16 DEFECTIVE PIXEL CORRECTION
A CCD imager is composed of a two-dimensional array of light sensitive pixels. In
general, the majority of the pixels have similar sensitivity. Unfortunately, there are some
pixels which sensitivity deviates from the average pixel sensitivity. A defective pixel is
defined as a pixel whose response deviates by more than 15% from the average response.
In extreme cases these pixels can be stuck „black‟ or stuck „white‟ and are non-responsive
to light. There are two major types of pixel defects – “Defective” and “Hot”.
1.
”
Defective
” – these are pixels which sensitivity deviates more than 15% due to
fluctuations in the CCD manufacturing process. Two type of defective pixels are
possible:
a.
“
DARK
” is defined as a pixel, whose sensitivity is lower than the sensitivity of
the adjacent pixels. In some cases this pixel will have no response (completely
dark).
b.
“
BRIGHT
” is defined as a pixel, whose sensitivity is higher than the sensitivity
of the adjacent pixels. In some cases this pixel will have full response (completely
bright).
2.
“
Hot
” – these are pixel, which in normal camera operation behaves as normal pixel
(the sensitivity is equal to the one of the adjacent pixels), but during long time
integration behaves as a high intensity bright pixel. In some cases this pixel will have
full response (completely bright).
2.16.1 Static Pixel Correction
Static Defective and Hot pixel correction works with predetermined and
preloaded Defective and Hot pixel maps. During factory final testing, our
manufacturing engineers run a program specially designed to identify these
„defective‟ and “hot” pixels. The program creates a map file which lists the
coordinates (i.e. row and column) of every defective pixel. This file, called the
Defect Pixel Map, is then downloaded into the camera‟s non-volatile memory.
Users may wish, however, to create and to upload their own DPM file because of the
uniqueness of their operating environment or camera use.
When „Defective Pixel
Correction‟ is enabled, the camera will compare each pixel‟s coordinates with
entries in the „defect‟ map. If a match is found, then the camera will „correct‟ the
defective pixel. When „Hot Pixel Correction‟ is enabled, the camera will compare
each pixel‟s coordinates with entries in the „defect‟ map. If a match is found, then
the camera will „correct‟ the hot pixel. The "Defective/Hot Pixel Map" can be
displayed upon user request.