CHEETAH Hardware User’s Manual
Imperx, Inc.
Rev. 0.3
6421 Congress Ave.
8/26/2016
Boca Raton, FL 33487
+1 (561) 989-0006
52 of 121
2.14
DEFECTIVE PIXEL CORRECTION
A CMOS 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. 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 due to fluctuations in the
CMOS manufacturing process. During final camera testing at the factory up to
1024 defective pixels are identified and will be automatically corrected if
defective pixel correction is enabled. 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 pixels, 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). During final camera testing at the
factory, up to 8192 hot pixels will be identified and will be automatically
corrected, if hot pixel correction is enabled.
2.14.1 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.
