Cheetah Pregius Camera with 10 GigE Vision Interface – User Manual
October 8, 2020
Page
141
of
170
Rev 1.0
Hot and Defective Pixel Correction
A CMOS imager is composed of a two-dimensional array of light sensitive pixels. In general, most
of the pixels have similar sensitivity. However, some pixels deviate from the average pixel
sensitivity and are called
defective pixels
and
hot pixels
.
Defective pixels
(also known as
dead pixels
)—these are pixels whose sensitivity deviates due to
fluctuations in the CMOS manufacturing process and materials. Two types of defective pixels are
possible:
•
Dark
– a pixel whose sensitivity is lower than the sensitivity of the adjacent pixels. In some
cases, this pixel will have no response (completely dark).
•
Bright
– a pixel whose sensitivity is higher than the sensitivity of the adjacent pixels. In some
cases, this pixel will have full response (completely bright).
Hot pixels
– these are pixels that in normal camera operation behave as normal pixels (sensitivity
equal to one of the adjacent pixels). But during long exposures or at elevated temperatures, the
pixel becomes far brighter than the average of the pixels surrounding it. In some cases, the pixel
becomes so bright that it saturates.
At the factory, final testing identifies and stores maps of both hot and defective pixels. Enabling
DefectPixelCorrection
and
BadPixelCorrection
using the Factory option, corrects hot and
defective pixels using the Factory map.
The camera employs
static
pixel maps to correct up hot and defective pixels. During factory
testing, engineers identify the coordinates of hot and defective pixels. They create a map file
listing the pixel coordinates of these pixels by row and column, and the camera corrects the hot
and defective pixels found at these coordinates. The map file downloads into the camera's non-
volatile memory.
When Factory or User correction is enabled, the camera compares each pixel’s coordinates with
entries in the pixel map. If a match is found, the camera corrects the defective pixel.
You can create your own Hot Pixel Map (HPM) or Defective Pixel Map (DPM) file and upload it
using the Imperx Upload Utility application (refer to the
for more information).
Flat Field Correction
The camera uses a factory installed flat field correction (located in FFC0) algorithm to correct
some of the image sensor’s non-uniformity. You can upload your own FFC table to one of the
FFC1 – FFC8 tables using Imperx Upload Utility. While not recommended, you can disable the
FFC.
